Available online at www.sciencedirect.com
ScienceDirect TERT promoter mutations in cancer development Barbara Heidenreich1, P Sivaramakrishna Rachakonda1, Kari Hemminki1,2 and Rajiv Kumar1 Human telomerase reverse transcriptase (TERT) encodes a rate-limiting catalytic subunit of telomerase that maintains genomic integrity. TERT expression is mostly repressed in somatic cells with exception of proliferative cells in selfrenewing tissues and cancer. Immortality associated with cancer cells has been attributed to telomerase overexpression. The precise mechanism behind the TERT activation in cancers has mostly remained unknown. The newly described germline and recurrent somatic mutations in melanoma and other cancers in the TERT promoter that create de novo E-twenty six/ternary complex factors (Ets/TCF) binding sites, provide an insight into the possible cause of tumorspecific increased TERT expression. In this review we discuss the discovery and possible implications of the TERT promoter mutations in melanoma and other cancers. Addresses 1 Division of Molecular Genetic Epidemiology, German Cancer Research Center, Im Neuenheimer Feld 580, 69120 Heidelberg, Germany 2 Center for Primary Health Care Research, Lund University, Malmo¨, Sweden Corresponding author: Kumar, Rajiv ([email protected])
Current Opinion in Genetics & Development 2014, 24:30–37 This review comes from a themed issue on Cancer genomics Edited by David J Adams and Ultan McDermott For a complete overview see the Issue and the Editorial Available online 20th December 2013 0959-437X/$ – see front matter, # 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gde.2013.11.005
expression of telomerase or in its absence by an alternative lengthening of telomeres (ALT) mechanism [10– 14,15]. Human telomerase reverse transcriptase (TERT) gene encodes the catalytic subunit of telomerase that together with a RNA component, TERC, maintains genomic integrity by telomere elongation [16]. Though TERT and TERC are sufficient for in vitro telomerase activity, the in vivo telomerase functioning requires additional components that associate with TERT and TERC, to form the holoenzyme [17,18]. Those include dyskerin (DKC), NOP10 ribonucleoprotein (NOP10), GAR1 ribonucleoprotein homolog (yeast) (GAR1), NHP2 ribonucleoprotein (NHP2), reptin and pontin [11,19–22]. Deregulation of telomerase has been shown to be a ubiquitous feature in human cancers with over 90% of cancers showing an upregulation of the enzyme [11,23,24]. The telomerase activity is dependent on a number of factors, regulated at various stages, which include gene transcription, mRNA splicing, maturation and modifications of TERT and TERC, transport and localization of those components and assembly of active ribonucleoprotein to telomeres telomerase [4,5,16,20,21,25–27]. The catalytic component TERT acts as a determinant of telomerase activity and its transcription is repressed in most of the somatic cells with the exception of proliferative cells of self-renewing tissues [28–30]. An increased expression of TERT has been consistently demonstrated to be a fundamental requirement for cellular transformation [4,31–33,34,35].
Introduction The telomere sequences at the chromosomal ends, composed of tandem repeats of TTAGGG, are protected by a number of molecules that constitute the capping Shelterin complex [1,2]. The incomplete replication due to limitations of the process, called ‘endreplication problem’, results in shortening of telomeres in each successive mitotic cell division that eventually leads to replicative senescence referred to as the ‘Hayflick limit’ [3–5]. Maintenance of telomere repeat length is dependent on sustained expression of telomerase holoenzyme that adds de novo repeat units at the end of each replication cycle [6,7]. Progressive attrition of telomeres is also defined as one of the hallmarks of aging of organisms [8,9]. Cancer cells, characteristically, acquire infinite capability to divide through maintenance of telomeres by sustained Current Opinion in Genetics & Development 2014, 24:30–37
The mechanism of TERT upregulation in cancers had been attributed to several mechanisms including epigenetic deregulation as well as genetic amplification of the locus containing TERT gene [36,37]. In the absence of any evidence of a definite mechanism, the telomerase activity in tumor cells has been attributed to the assumption of stem cells being the progenitors in all cancers [38]. The normal stem cells in self-renewing tissues retain telomerase throughout lifetime replication thus abrogating a requirement for a positive selection [6]. The recently discovered TERT promoter mutations add a new dimension to the acquisition of telomerase activity in human cancers. In this review we provide an overview and possible implications of the newly discovered mutations in the promoter of the TERT gene in a wide range of cancers. www.sciencedirect.com
TERT promoter mutations Heidenreich et al. 31
Structure and regulation of the TERT promoter The human TERT gene is located on chromosome 5p15.33 and the promoter region of the gene is considered to be the most important regulatory element for telomerase expression. The TERT promoter contains binding motifs for several factors that regulate the gene transcription and distinctly lacks a TATA box or a similar sequence [39–43]. The core promoter region consists of 260 base pairs with several transcription-factor binding sites that include E-boxes where c-Myc has been confirmed to bind and activate the transcription [44–48]. BRCA1 in conjunction with N-Myc interacting protein (Nmi) forms a complex with c-Myc and inhibits TERT promoter activity, that property is lost in some mutant forms of BRCA1 [49]. Other sequence elements in TERT promoter include GC-boxes, which are binding sites for zinc finger transcription factor, Sp1 [4,45]. Transcription of the TERT gene is also regulated by various hormones, cytokines and oncogenes [45]. Several repressors of the TERT transcription are also known. p53 has been shown to downregulate TERT transcription in a Sp1-dependent manner [50]. Ets transcription factors that comprise over 30 members are prominently associated with telomerase activation [42,51]. Ets2 has been shown to form a complex with c-Myc in a breast cancer cell line [44,51]. Ets transcription factors are also shown to be stimulated by oncogenes EGF, Her2/Nez, Ras and Raf [52,53]. The activation of oncogenes and inactivation of tumor suppressors are known to account for cellular immortalization through induction of TERT transcription [54]. The high GC content around the transcription start site of the TERT promoter confers epigenetic regulation through methylation and chromatin remodeling [37,55].
TERT promoter mutations in human cancers A discovery of a high-penetrant disease-segregating causal germline mutation in a melanoma family and highly specific and recurrent somatic mutations in tumors from unrelated patients in the TERT promoter has likely provided a definite mechanism for cancer-specific TERT activation [56,57]. Two independent studies using diverse approaches discovered non-coding mutations, mainly at two residues, within the core promoter region of the TERT gene. One study was based on the identification of a causal gene mutation in a large melanoma pedigree where affected individuals presented a severe form of the disease with an early age of onset. The linkage analysis identified a 2.2 megabase telomeric region on chromosome 5p that included TERT along with more than 80 other genes [56]. Sequencing of the entire stretch of DNA region in the family resulted in identification of a disease segregating A > C (T > G) single base change at 57 bp (Chr 5: 1,295,161 hg19 coordinate) from ATG start site. The germline mutation was present in affected and absent in unaffected individuals in the family with the exception of one. Subsequent screening www.sciencedirect.com
of cell lines derived from melanoma metastases from unrelated patients led to the detection of recurrent and mutually exclusive somatic mutations at two residues 124 and 146 from the ATG start site in the TERT promoter [56]. Serendipitously, an independent study using a whole genome sequencing approach also reported the recurrent somatic TERT promoter mutations at the same positions [57]. Other mutations detected in TERT promoter included the CC > TT tandem mutations at 124/ 125 and 138/ 139 bp from ATG start site. The germline and somatic mutations in the non-coding part of the TERT gene were defined by common salient features. One of the underlying features included a de novo creation of CCGGAA/T general binding motifs for E-twenty six/ ternary complex factors (Ets/TCF) transcription factors, which differed from pre-existing GGAA/T Ets binding sites within the TERT promoter (Figure 1). The somatic mutations at both positions being C > T and the additional detection of CC > TT tandem mutations in a proportion of tumors augmented the evidence for the UV-origin of tumor specific nucleotide changes in melanoma as shown previously in studies based on whole genome sequencing [58]. Interestingly, the mutations detected in the TERT promoter in melanoma were more frequent than those in the BRAF gene. It was also observed that the TERT promoter mutations tend to occur more often than expected by chance in tumors with either BRAF mutations (odds ratio [OR] 3.2, 95% confidence interval [CI] 1.3–8.2) or with concomitant alterations in both BRAF and CDKN2A (OR 5.6, 95% CI 2.4–13.8) [56]. BRAF mutations, due to occurrence and role in development of melanocytic nevi, are considered as the driver genetic lesions in melanoma [56,59,60]. The loss of CDKN2A has been suggested to play a role in the escape of melanocytes from BRAF induced senescence [61]. The acquisition of TERT promoter mutations can be hypothesized to facilitate stabilization of the transformed genome through reversal of telomeric loss. Most melanocytic nevi carry BRAF mutations, whereas TERT promoter mutations and CDKN2A alterations are detected only in primary melanoma and beyond [56,62]. Bonafide of newly discovered non-coding mutations in the TERT promoter was established by the detection in cancers other than melanoma [63]. The frequency of the mutations seems to vary between cancer types (Table 1). The highest frequencies of the TERT promoter mutations have so far been reported, besides melanoma, in pleomorphic dermal sarcoma, myxoid liposarcoma, glioma, urothelial cell carcinoma of bladder, basal and squamous cell carcinoma of skin, liver cancer and others [63,64–76]. The mutations occur in other cancer types as well, albeit, at low frequencies [63,67]. Based on the prevalence in different cancer types it has been hypothesized that the TERT promoter mutations mainly occur in tumors that are derived from tissues with low rates of Current Opinion in Genetics & Development 2014, 24:30–37
32 Cancer genomics
Figure 1
Transcription start site Sp1
Sp1
Ets 2 Ets 2
E-box
–100
–150
–150
Sp1
–140
ATG
–50
–130
–120
–1
–60
–50
Wild type
Mutant Ets/TCF
Ets/TCF
Ets/TCF
Ets/TCF Increased transcription Current Opinion in Genetics & Development
Schematic representation of a part of the TERT promoter that contains residues, which are affected by a germline mutation in a melanoma family at the position 57 bp and recurrent somatic mutations at the positions 124 and 146 bp from the ATG start site. The mutations create CCGGAA/T binding motif for Ets/TCF transcription factors that results in an increased TERT expression. Pre-existing binding sites for other transcriptions factors are shown above the sequence.
self-renewal [63,77]. Unlike melanoma and other skin related malignancies, no tumor from the cancers affecting internal organs carried CC > TT tandem mutations in the TERT promoter with the exception of that at the positions 138/ 139 bp from ATG start site in bladder cancer. The tandem mutation reported so far in 4 of the 1231 bladder tumors could also be generated by a singlebase mutation at 138 bp as the base change at 139 bp has been reported as a rare polymorphism represented by rs35550267 [56,65,66]. The differences in mutational pattern in cancer types are known to reflect etiological divergences and the C > T base change in tumors can also be attributed to APOBEC cytidine deaminase expression in cancer development [78,79].
Functional aspects of TERT promoter mutations
from thyroid cancers, primary glioma, malignant pleural mesothelioma and liver cancers with TERT promoter mutations were associated with higher gene expression than those without mutations [67,69,72,74]. Though limited at the moment, the available data do indicate a tendency of the TERT promoter mutations being present in specific clinical and phenotypic subtypes and appear to be associated with adversarial forms of the disease. While in medulloblastomas the TERT promoter mutations were inversely associated with increased OTX2 expression; in primary adult glioma, the mutations occurred mainly in conjunction with EGFR amplification [69]. Glioma patients with TERT promoter mutations showed an association with poorer survival than patients without mutations; in thyroid cancer, mutations are reportedly more frequent in advanced thyroid cancers than in papillary thyroid cancers [63,70,71].
The high recurrence, specificity and gain of function support that the non-coding TERT promoter mutations are driver rather than passenger events in cancer development. The functional relevance of the mutations was indicated by the basic reporter assays that showed 2–4fold increased promoter activity [56,57,80]. Tumors
The studies on bladder cancer consistently showed that TERT promoter mutations are the most frequent lesions with even distribution across all stages and grades [65,66,80]. Intriguingly, an observed interaction has raised a possibility of eventual use of the TERT promoter
Current Opinion in Genetics & Development 2014, 24:30–37
www.sciencedirect.com
TERT promoter mutations Heidenreich et al. 33
Table 1 TERT promoter mutations in cancers Cancer type
Mutation frequency (%) a
Ref.
Bladder cancer Glioma Ependymomas Astrocytomas Mixed gliomas Oligodendrogliomas Melanoma Cutaneous melanoma Ocular melanoma (not specified) Uveal melanoma Conjunctival melanoma Squamous cell carcinoma (SCC) SCC of head and neck SCC of esophagus SCC of the cervix SCC of the skin Bowen’s disease Basal cell carcinoma of skin Thyroid b ATC + PDTC DTC FTC HCC PTC Atypical fibroxanthoma Myxoid liposarcoma Pleomorphic dermal sarcomas Liver c Fibrosarcoma Dysembryoplastic neuroepithelial tumor Medulloblastoma Solitary fibrous tumor (SFT) Ovarian, clear cell carcinoma Ovarian, low grade serous Malignant pleural mesothelioma Endometrial cancer Myxofibrosarcoma Neuroblastoma Osteosarcoma
887/1231 (72.1)
[63,64–67,80]
1/36 (2.7) 574/1059 (54.2) 102/188 (54.3) 46/72 (63.9)
[63] [63,64,67,69,73] [63,69] [63,67]
136/256 (53) 0/25 0/47 12/38 (32)
[56,57,67] [67] [68] [68]
12/70 (17.1) 5/313 (1.6) 1/22 (4.5) 14/31 (45.2) 1/11 (9.1) 31/42 (73.8)
[63] [77] [63] [63,76] [76] [76]
73/170 (42.9) 41/336 (12.2) 20/143 (14.0) 4/25 (16.0) 61/506 (12.1) 25/27 (92.6) 19/24 (79.1) 26/34 (76.5) 218/531 (41.1) 1/3 (33.3) 1/3 (33.3) 19/91 (20.8%) 2/10 (20.0%) 2/12 (16.6%) 1/8 (12.5%) 8/71 (11.3%) 2/19 (10.5%) 1/10 (10.0%) 2/22 (9.1%) 1/23 (4.3%)
[67,70,71] [70] [67,70] [71] [67,70,71] [75] [63] [75] [63,74] [63] [63] [63] [63] [63] [63] [72] [63] [63] [63] [63]
Ref [63]: no mutations were found in acute myeloid leukemia (n = 48), alveolar rhabdomyosarcoma (n = 7), atypical lipomatous tumor (n = 10), breast carcinoma (n = 88), cholangiosarcoma (n = 28), central/conventional chondrosarcoma (n = 9), chronic lymphoid leukemia (n = 15), chronic myeloid leukemia (n = 6), colorectal adenocarcinoma (n = 22), embryonal rhabdomyosarcoma (n = 8), esthesioneuroblastoma (n = 11), extraskeletal myxoid chondrosarcoma (n = 3), fibrolammellar carcinoma of the liver (n = 12), gall bladder carcinoma (n = 10), hepatoblastoma (n = 3), leiomyosarcoma (n = 3), conventional lipoma (n = 8), low grade fibromyxoid sarcoma (n = 9), malignant peripheral nerve sheath tumor (n = 3), medullary thyroid carcinoma (n = 24), meningioma (n = 20), mesothelioma (n = 4), pancreatic acinar carcinoma (n = 25), pancreatic ductal adenocarcinoma (n = 24), pancreatic neuroendocrine tumor (n = 68), prostate carcinoma (n = 34), spinal ependymoma (n = 9), synovial sarcoma (n = 16), or undifferentiated pleomorphic soft tissue sarcoma (n = 10) samples. Ref [67]: no mutations were found in Phaeochromocytoma (n = 17); CCRCC, CromRCC and PRCC of the kidney (n = 26). Refs [63,67]: No mutations were found in gastrointestinal stromal tumors (n = 45). Refs [56,67]: No mutations were found in melanocytic nevi (n = 34). Refs [67,70]: No mutations were found in benign thyroid tumors (n = 166) or medullary thyroid carcinoma (n = 44). a Includes all reported TERT promoter mutations; most common mutations are 124C > T (Chr 5:1,295,228 hg19 coordinate) and 146C > T (1,295,250). In melanoma 146C > T mutation is more frequent than the 124C > T; in cancers, especially in gliomas, thyroid cancers and bladder cancers the latter is the most common mutation. Additionally, in melanoma two CC > TT tandem mutations affecting 124/ 125 and 138/ 139 residues were also detected with a combined frequency of 9%[56]. b ATC, anaplastic thyroid carcinoma; FTC, follicular thyroid carcinoma; PDTC, poorly differentiated thyroid carcinoma; PTC, papillary thyroid carcinoma; HCC, Hurthle cell cancers; DTC, differentiated thyroid cancer. c Includes Hepatocellular carcinoma, Cirrhotic tissue, Cirrhotic macronodules, Hepatocellular adenomas, HCA with HCC foci.
mutations in conjunction with a common polymorphism within the sequence as biomarkers in bladder cancer. The data from bladder cancer showed that the variant allele of a common polymorphism at 245 bp from ATG start site www.sciencedirect.com
in the TERT promoter acts as a modifier of the effect of TERT promoter mutations on patient survival and disease recurrence [80]. Bladder cancer patients with TERT promoter mutations in tumors showed almost two-fold Current Opinion in Genetics & Development 2014, 24:30–37
34 Cancer genomics
decreased survival and increased disease recurrence in the absence but not in the presence of the variant allele for the rs2853669 polymorphism [80]. Mechanistic support for the observation was provided by the fact that mutations result in de novo creation of Ets/TCF binding motifs; the variant allele of the rs2853669 polymorphism, on the contrary, disrupts a preexisting non-canonical Ets2 binding site in the proximal region of the TERT promoter, adjacent to an E-box [44]. The occurrence of highly specific TERT promoter mutations indicates a strong selection pressure for the gene over-expression on path to cellular transformation. Increased telomerase production has been demonstrated to promote cancer progression in an animal model [81]. The effect of the promoter mutations on TERT expression can be tenable only in the presence of Ets/TCF transcription factors that can specifically bind to the de novo sites created by the mutations. Some of the Ets/TCF transcription factors are downstream targets of MAPK pathway, where BRAF is a prominent intermediate [82–84]. Whether in melanoma activated BRAF is a driving force in selection of TERT promoter mutations remains to be determined. Nevertheless, expression of Ets transcription factors is ubiquitous in melanoma and other cancers [85,86]. Many studies have stressed the function of the TERT gene beyond its role in maintenance of the telomere; therefore the mutations in the TERT promoter can affect non-canonical processes associated with TERT [87–91]. TERT acts as a modulator of Wnt-b-catenin signaling pathway and induces stem cell characteristics in glioma; TERT also regulates expression of NF-kB, a master regulator of inflammation [92,93,94]. TERT was shown to be important for proliferation of p53-negative cells through ATR mediated stabilization of ETV1, which binds downstream of the transcriptional start site [95]. Other non-canonical functions of TERT include enhanced cell proliferation, decreased apoptosis, regulation of DNA damage responses, chromatin state and increased cellular proliferation life span [96–98]. The effect of the mutations beyond transcription also remains a probability. The human TERT promoter contains Grich sequence and has potential for G-quadruplex formation that can potentially be targeted to regulate gene transcription [99]. G-quadruplexes have been also implicated in inhibition of telomerase and control of gene expression [100].
Conceptual advancement and therapeutic possibilities The TERT promoter mutations are thought to represent a conceptual advancement in the sense that those instead of altering an encoded protein modulate transcriptional regulation and represent first evidence of driver alterations in so called ‘dark matter’ of the Current Opinion in Genetics & Development 2014, 24:30–37
human genome [101,102]. A host of germline variants discovered through genome wide association studies contribute to the susceptibility of various diseases through transcriptional deregulation [103]. While TERT promoter mutations represent novel findings in human cancer, alterations in components associated with telomerase assembly, telomere protection or telomere recruitment are known to impact stem cell function and lifespan in mammals through various disorders [104,105]. Several strategies of therapeutic telomerase inhibition including small molecular inhibitors, immunotherapy, gene therapy, telomere and telomerase-proteins in different cancers have entered clinical trial [106]. It will be interesting to see if the TERT promoter mutations, that increase gene expression, influence the current on-going research on targeted therapeutics or if the use of telomerase inhibitors in conjunction with kinase inhibitors like vemurafenib or similar small molecules in melanoma can alleviate recurrent resistance [107].
References and recommended reading Papers of particular interest, published within the period of review have been highlighted as: of special interest of outstanding interest 1.
Lu Y, Wei B, Zhang T, Chen Z, Ye J: How will telomeric complex be further contributed to our longevity? The potential novel biomarkers of telomere complex counteracting both aging and cancer. Protein Cell 2013, 4:573-581.
2.
de Lange T: How telomeres solve the end-protection problem. Science 2009, 326:948-952.
3.
Hayflick L: The limited in vitro lifetime of human diploid cell strains. Exp Cell Res 1965, 37:614-636.
4.
Cong YS, Wright WE, Shay JW: Human telomerase and its regulation. Microbiol Mol Biol Rev 2002, 66:407-425.
5.
Nandakumar J, Cech TR: Finding the end: recruitment of telomerase to telomeres. Nat Rev Mol Cell Biol 2013, 14:69-82.
6.
Masutomi K, Yu EY, Khurts S, Ben-Porath I, Currier JL, Metz GB, Brooks MW, Kaneko S, Murakami S, DeCaprio JA et al.: Telomerase maintains telomere structure in normal human cells. Cell 2003, 114:241-253.
7.
Marion RM, Blasco MA: Telomere rejuvenation during nuclear reprogramming. Curr Opin Genet Dev 2010, 20:190-196.
8.
Lopez-Otin C, Blasco MA, Partridge L, Serrano M, Kroemer G: The hallmarks of aging. Cell 2013, 153:1194-1217.
9.
Bernardes de Jesus B, Blasco MA: Telomerase at the intersection of cancer and aging. Trends Genet 2013, 29:513520.
10. Hanahan D, Weinberg RA: Hallmarks of cancer: the next generation. Cell 2011, 144:646-674. 11. Low KC, Tergaonkar V: Telomerase: central regulator of all of the hallmarks of cancer. Trends Biochem Sci 2013, 38:426-434. 12. Heaphy CM, Subhawong AP, Hong SM, Goggins MG, Montgomery EA, Gabrielson E, Netto GJ, Epstein JI, Lotan TL, Westra WH et al.: Prevalence of the alternative lengthening of telomeres telomere maintenance mechanism in human cancer subtypes. Am J Pathol 2011, 179:1608-1615. www.sciencedirect.com
TERT promoter mutations Heidenreich et al. 35
13. Lovejoy CA, Li W, Reisenweber S, Thongthip S, Bruno J, de Lange T, De S, Petrini JH, Sung PA, Jasin M et al.: Loss of ATRX, genome instability, and an altered DNA damage response are hallmarks of the alternative lengthening of telomeres pathway. PLoS Genet 2012, 8:e1002772. 14. Cesare AJ, Reddel RR: Alternative lengthening of telomeres: models, mechanisms and implications. Nat Rev Genet 2010, 11:319-330. 15. Heaphy CM, de Wilde RF, Jiao Y, Klein AP, Edil BH, Shi C, Bettegowda C, Rodriguez FJ, Eberhart CG, Hebbar S et al.: Altered telomeres in tumors with ATRX and DAXX mutations. Science 2011, 333:425. This study showed an association of mutations in ATRX/DAXX genes with abnormal telomere due to alternative lengthening of telomeres.
of telomerase limits the growth of human cancer cells. Nat Med 1999, 5:1164-1170. 34. Hahn WC, Counter CM, Lundberg AS, Beijersbergen RL, Brooks MW, Weinberg RA: Creation of human tumour cells with defined genetic elements. Nature 1999, 400:464-468. First study that demonstrated in vitro conversion of normal human cells into tumor cells. 35. Kiyono T, Foster SA, Koop JI, McDougall JK, Galloway DA, Klingelhutz AJ: Both Rb/p16INK4a inactivation and telomerase activity are required to immortalize human epithelial cells. Nature 1998, 396:84-88. 36. Hahn WC, Meyerson M: Telomerase activation, cellular immortalization and cancer. Ann Med 2001, 33:123-129.
16. Podlevsky JD, Chen JJ: It all comes together at the ends: telomerase structure, function, and biogenesis. Mutat Res 2012, 730:3-11.
37. Zhu J, Zhao Y, Wang S: Chromatin and epigenetic regulation of the telomerase reverse transcriptase gene. Protein Cell 2010, 1:22-32.
17. Weinrich SL, Pruzan R, Ma L, Ouellette M, Tesmer VM, Holt SE, Bodnar AG, Lichtsteiner S, Kim NW, Trager JB et al.: Reconstitution of human telomerase with the template RNA component hTR and the catalytic protein subunit hTRT. Nat Genet 1997, 17:498-502.
38. Armanios M, Greider CW: Telomerase and cancer stem cells. Cold Spring Harb Symp Quant Biol 2005, 70:205-208.
18. Masutomi K, Kaneko S, Hayashi N, Yamashita T, Shirota Y, Kobayashi K, Murakami S: Telomerase activity reconstituted in vitro with purified human telomerase reverse transcriptase and human telomerase RNA component. J Biol Chem 2000, 275:22568-22573. 19. Lewis KA, Wuttke DS: Telomerase and telomere-associated proteins: structural insights into mechanism and evolution. Structure 2012, 20:28-39. 20. Venteicher AS, Abreu EB, Meng Z, McCann KE, Terns RM, Veenstra TD, Terns MP, Artandi SE: A human telomerase holoenzyme protein required for Cajal body localization and telomere synthesis. Science 2009, 323: 644-648. 21. Egan ED, Collins K: Specificity and stoichiometry of subunit interactions in the human telomerase holoenzyme assembled in vivo. Mol Cell Biol 2010, 30:2775-2786. 22. Collins K: The biogenesis and regulation of telomerase holoenzymes. Nat Rev Mol Cell Biol 2006, 7:484-494. 23. Shay JW, Bacchetti S: A survey of telomerase activity in human cancer. Eur J Cancer 1997, 33:787-791. 24. Shay JW, Zou Y, Hiyama E, Wright WE: Telomerase and cancer. Hum Mol Genet 2001, 10:677-685. 25. Venteicher AS, Artandi SE: TCAB1: driving telomerase to Cajal bodies. Cell Cycle 2009, 8:1329-1331. 26. Fu D, Collins K: Distinct biogenesis pathways for human telomerase RNA and H/ACA small nucleolar RNAs. Mol Cell 2003, 11:1361-1372. 27. Cristofari G, Sikora K, Lingner J: Telomerase unplugged. ACS Chem Biol 2007, 2:155-158. 28. Shay JW, Wright WE: Telomerase therapeutics for cancer: challenges and new directions. Nat Rev Drug Discov 2006, 5:577-584. 29. Hiyama E, Hiyama K: Telomere and telomerase in stem cells. Br J Cancer 2007, 96:1020-1024. 30. Wright WE, Piatyszek MA, Rainey WE, Byrd W, Shay JW: Telomerase activity in human germline and embryonic tissues and cells. Dev Genet 1996, 18:173-179. 31. Xu L, Li S, Stohr BA: The role of telomere biology in cancer. Annu Rev Pathol 2013, 8:49-78. 32. Kolquist KA, Ellisen LW, Counter CM, Meyerson M, Tan LK, Weinberg RA, Haber DA, Gerald WL: Expression of TERT in early premalignant lesions and a subset of cells in normal tissues. Nat Genet 1998, 19:182-186. 33. Hahn WC, Stewart SA, Brooks MW, York SG, Eaton E, Kurachi A, Beijersbergen RL, Knoll JH, Meyerson M, Weinberg RA: Inhibition www.sciencedirect.com
39. Cong YS, Wen J, Bacchetti S: The human telomerase catalytic subunit hTERT: organization of the gene and characterization of the promoter. Hum Mol Genet 1999, 8:137-142. 40. Poole JC, Andrews LG, Tollefsbol TO: Activity, function, and gene regulation of the catalytic subunit of telomerase (hTERT). Gene 2001, 269:1-12. 41. Horikawa I, Cable PL, Afshari C, Barrett JC: Cloning and characterization of the promoter region of human telomerase reverse transcriptase gene. Cancer Res 1999, 59:826-830. 42. Gladych M, Wojtyla A, Rubis B: Human telomerase expression regulation. Biochem Cell Biol 2011, 89:359-376. 43. Wojtyla A, Gladych M, Rubis B: Human telomerase activity regulation. Mol Biol Rep 2011, 38:3339-3349. 44. Xu D, Dwyer J, Li H, Duan W, Liu JP: Ets2 maintains hTERT gene expression and breast cancer cell proliferation by interacting with c-Myc. J Biol Chem 2008, 283:23567-23580. 45. Kyo S, Takakura M, Fujiwara T, Inoue M: Understanding and exploiting hTERT promoter regulation for diagnosis and treatment of human cancers. Cancer Sci 2008, 99:1528-1538. 46. Hashimoto M, Kyo S, Hua X, Tahara H, Nakajima M, Takakura M, Sakaguchi J, Maida Y, Nakamura M, Ikoma T et al.: Role of menin in the regulation of telomerase activity in normal and cancer cells. Int J Oncol 2008, 33:333-340. 47. Akutagawa O, Nishi H, Kyo S, Terauchi F, Yamazawa K, Higuma C, Inoue M, Isaka K: Early growth response-1 mediates downregulation of telomerase in cervical cancer. Cancer Sci 2008, 99:1401-1406. 48. Cerezo A, Kalthoff H, Schuermann M, Schafer B, Boukamp P: Dual regulation of telomerase activity through c-Myc-dependent inhibition and alternative splicing of hTERT. J Cell Sci 2002, 115:1305-1312. 49. Li H, Lee TH, Avraham H: A novel tricomplex of BRCA1, Nmi, and c-Myc inhibits c-Myc-induced human telomerase reverse transcriptase gene (hTERT) promoter activity in breast cancer. J Biol Chem 2002, 277:20965-20973. 50. Kanaya T, Kyo S, Hamada K, Takakura M, Kitagawa Y, Harada H, Inoue M: Adenoviral expression of p53 represses telomerase activity through down-regulation of human telomerase reverse transcriptase transcription. Clin Cancer Res 2000, 6:1239-1247. 51. Dwyer JM, Liu JP: Ets2 transcription factor, telomerase activity and breast cancer. Clin Exp Pharmacol Physiol 2010, 37:83-87. 52. Goueli BS, Janknecht R: Upregulation of the catalytic telomerase subunit by the transcription factor ER81 and oncogenic HER2/Neu, Ras, or Raf. Mol Cell Biol 2004, 24:25-35. 53. Maida Y, Kyo S, Kanaya T, Wang Z, Yatabe N, Tanaka M, Nakamura M, Ohmichi M, Gotoh N, Murakami S et al.: Direct activation of telomerase by EGF through Ets-mediated Current Opinion in Genetics & Development 2014, 24:30–37
36 Cancer genomics
transactivation of TERT via MAP kinase signaling pathway. Oncogene 2002, 21:4071-4079. 54. Lin SY, Elledge SJ: Multiple tumor suppressor pathways negatively regulate telomerase. Cell 2003, 113:881-889. 55. Li AY, Lin HH, Kuo CY, Shih HM, Wang CC, Yen Y, Ann DK: High-mobility group A2 protein modulates hTERT transcription to promote tumorigenesis. Mol Cell Biol 2011, 31:2605-2617. 56. Horn S, Figl A, Rachakonda PS, Fischer C, Sucker A, Gast A, Kadel S, Moll I, Nagore E, Hemminki K et al.: TERT promoter mutations in familial and sporadic melanoma. Science 2013, 339:959-961. First study to report a causal mutation in a large melanoma family and recurrent somatic mutations in tumors from unrelated melanoma patients in the TERT promoter that result in creation of de novo Ets/TCF transcription factor binding motifs. 57. Huang FW, Hodis E, Xu MJ, Kryukov GV, Chin L, Garraway LA: Highly recurrent TERT promoter mutations in human melanoma. Science 2013, 339:957-959. First study to show recurrent somatic mutations in the TERT promoter in melanoma. This study also showed same mutations in cell lines from tumors other than melanoma. 58. Hodis E, Watson IR, Kryukov GV, Arold ST, Imielinski M, Theurillat JP, Nickerson E, Auclair D, Li L, Place C et al.: A landscape of driver mutations in melanoma. Cell 2012, 150:251-263. This study presented a mutational landscape in melanoma and showed a distinction between driver and passenger mutations. 59. Dhomen N, Reis-Filho JS, da Rocha Dias S, Hayward R, Savage K, Delmas V, Larue L, Pritchard C, Marais R: Oncogenic Braf induces melanocyte senescence and melanoma in mice. Cancer Cell 2009, 15:294-303. This study demonstrated V600E BRAF as a founder mutation in melanoma development. 60. Michaloglou C, Vredeveld LC, Mooi WJ, Peeper DS: BRAF(E600) in benign and malignant human tumours. Oncogene 2008, 27:877-895. 61. Michaloglou C, Vredeveld LC, Soengas MS, Denoyelle C, Kuilman T, van der Horst CM, Majoor DM, Shay JW, Mooi WJ, Peeper DS: BRAFE600-associated senescence-like cell cycle arrest of human naevi. Nature 2005, 436:720-724. 62. Kumar R, Angelini S, Snellman E, Hemminki K: BRAF mutations are common somatic events in melanocytic nevi. J Invest Dermatol 2004, 122:342-348. 63. Killela PJ, Reitman ZJ, Jiao Y, Bettegowda C, Agrawal N, Diaz LA Jr, Friedman AH, Friedman H, Gallia GL, Giovanella BC et al.: TERT promoter mutations occur frequently in gliomas and a subset of tumors derived from cells with low rates of selfrenewal. Proc Natl Acad Sci U S A 2013, 110:6021-6026. First study to show TERT promoter mutations in a large number of tumors from different cancer types and presented a hypothesis for the observed distribution of the mutations. 64. Liu X, Wu G, Shan Y, Hartmann C, von Deimling A, Xing M: Highly prevalent TERT promoter mutations in bladder cancer and glioblastoma. Cell Cycle 2013, 12:1637-1638. 65. Hurst CD, Platt FM, Knowles MA: Comprehensive mutation analysis of the TERT promoter in bladder cancer and detection of mutations in voided urine. Eur Urol 2013 http://dx.doi.org/ 10.1016/j.eururo.2013.08.057. 66. Allory Y, Beukers W, Sagrera A, Flandez M, Marques M, Marquez M, van der Keur KA, Dyrskjot L, Lurkin I, Vermeij M et al.: Telomerase reverse transcriptase promoter mutations in bladder cancer: high frequency across stages, detection in urine, and lack of association with outcome. Eur Urol 2013 http://dx.doi.org/10.1016/j.eururo.2013.08.052.
mutations in ocular melanoma distinguish between conjunctival and uveal tumours. Br J Cancer 2013, 109:497-501. 69. Arita H, Narita Y, Fukushima S, Tateishi K, Matsushita Y, Yoshida A, Miyakita Y, Ohno M, Collins VP, Kawahara N et al.: Upregulating mutations in the TERT promoter commonly occur in adult malignant gliomas and are strongly associated with total 1p19q loss. Acta Neuropathol 2013, 126:267-276. 70. Liu X, Bishop J, Shan Y, Pai S, Liu D, Murugan AK, Sun H, ElNaggar AK, Xing M: Highly prevalent TERT promoter mutations in aggressive thyroid cancers. Endocr Relat Cancer 2013, 20:603-610. 71. Landa I, Ganly I, Chan TA, Mitsutake N, Matsuse M, Ibrahimpasic T, Ghossein RA, Fagin JA: Frequent somatic TERT promoter mutations in thyroid cancer: higher prevalence in advanced forms of the disease. J Clin Endocrinol Metab 2013, 98:E1562-E1566. 72. Tallet A, Nault JC, Renier A, Hysi I, Galateau-Salle F, Cazes A, Copin MC, Hofman P, Andujar P, Le Pimpec-Barthes F et al.: Overexpression and promoter mutation of the TERT gene in malignant pleural mesothelioma. Oncogene 2013 http:// dx.doi.org/10.1038/onc.2013.351. 73. Nonoguchi N, Ohta T, Oh JE, Kim YH, Kleihues P, Ohgaki H: TERT promoter mutations in primary and secondary glioblastomas. Acta Neuropathol 2013, 126:931-937. 74. Nault JC, Mallet M, Pilati C, Calderaro J, Bioulac-Sage P, Laurent C, Laurent A, Cherqui D, Balabaud C, Rossi JZ: High frequency of telomerase reverse-transcriptase promoter somatic mutations in hepatocellular carcinoma and preneoplastic lesions. Nat Commun 2013, 4:2218. 75. Griewank KG, Schilling B, Murali R, Bielefeld N, Schwamborn M, Sucker A, Zimmer L, Hillen U, Schaller J, Brenn T et al.: TERT promoter mutations are frequent in atypical fibroxanthomas and pleomorphic dermal sarcomas. Mod Pathol 2013 http:// dx.doi.org/10.1038/modpathol.2013.168. 76. Scott GA, Laughlin TS, Rothberg PG: Mutations of the TERT promoter are common in basal cell carcinoma and squamous cell carcinoma. Mod Pathol 2013 http://dx.doi.org/10.1038/ modpathol.2013.167. 77. Zhao Y, Gao Y, Chen Z, Hu X, Zhou F, He J: Low frequency of TERT promoter somatic mutation in 313 sporadic esophageal squamous cell carcinomas. Int J Cancer 2013, 134:493-494. 78. Roberts SA, Lawrence MS, Klimczak LJ, Grimm SA, Fargo D, Stojanov P, Kiezun A, Kryukov GV, Carter SL, Saksena G et al.: An APOBEC cytidine deaminase mutagenesis pattern is widespread in human cancers. Nat Genet 2013, 45:970-976. This study provides a clue about the origin of most prevalent somatic mutation in human cancers. 79. Alexandrov LB, Nik-Zainal S, Wedge DC, Aparicio SA, Behjati S, Biankin AV, Bignell GR, Bolli N, Borg A, Borresen-Dale AL et al.: Signatures of mutational processes in human cancer. Nature 2013, 500:415-421. This unique study has identified the distinct mutational signatures that define somatic mutations in human cancers. 80. Rachakonda PS, Hosen I, de Verdier PJ, Fallah M, Heidenreich B, Ryk C, Wiklund NP, Steineck G, Schadendorf D, Hemminki K et al.: TERT promoter mutations in bladder cancer affect patient survival and disease recurrence through modification by a common polymorphism. Proc Natl Acad Sci U S A 2013, 110:17426-17431. This study showed the possibility of eventual use of TERT promoter mutations in conjunction with a common polymorphism within the sequence.
67. Vinagre J, Almeida A, Populo H, Batista R, Lyra J, Pinto V, Coelho R, Celestino R, Prazeres H, Lima L et al.: Frequency of TERT promoter mutations in human cancers. Nat Commun 2013, 4:2185.
81. Ding Z, Wu CJ, Jaskelioff M, Ivanova E, Kost-Alimova M, Protopopov A, Chu GC, Wang G, Lu X, Labrot ES et al.: Telomerase reactivation following telomere dysfunction yields murine prostate tumors with bone metastases. Cell 2012, 148:896-907. This study showed restoration of telomerase in tumor cells with telomere dysfunction enables complete malignant progression of murine prostate cancer.
68. Griewank KG, Murali R, Schilling B, Scholz S, Sucker A, Song M, Susskind D, Grabellus F, Zimmer L, Hillen U et al.: TERT promoter
82. Rao VN, Reddy ES: elk-1 proteins interact with MAP kinases. Oncogene 1994, 9:1855-1860.
Current Opinion in Genetics & Development 2014, 24:30–37
www.sciencedirect.com
TERT promoter mutations Heidenreich et al. 37
83. Kar A, Gutierrez-Hartmann A: Molecular mechanisms of ETS transcription factor-mediated tumorigenesis. Crit Rev Biochem Mol Biol 2013, 48:522-543. 84. Buchwalter G, Gross C, Wasylyk B: Ets ternary complex transcription factors. Gene 2004, 324:1-14. 85. Uhlen M, Oksvold P, Fagerberg L, Lundberg E, Jonasson K, Forsberg M, Zwahlen M, Kampf C, Wester K, Hober S et al.: Towards a knowledge-based Human Protein Atlas. Nat Biotechnol 2010, 28:1248-1250. 86. Jane-Valbuena J, Widlund HR, Perner S, Johnson LA, Dibner AC, Lin WM, Baker AC, Nazarian RM, Vijayendran KG, Sellers WR et al.: An oncogenic role for ETV1 in melanoma. Cancer Res 2010, 70:2075-2084. 87. Stewart SA, Hahn WC, O’Connor BF, Banner EN, Lundberg AS, Modha P, Mizuno H, Brooks MW, Fleming M, Zimonjic DB et al.: Telomerase contributes to tumorigenesis by a telomere length-independent mechanism. Proc Natl Acad Sci U S A 2002, 99:12606-12611. 88. Blasco MA: Telomerase beyond telomeres. Nat Rev Cancer 2002, 2:627-633. 89. Calado RT, Chen J: Telomerase: not just for the elongation of telomeres. Bioessays 2006, 28:109-112. 90. Parkinson EK, Fitchett C, Cereser B: Dissecting the noncanonical functions of telomerase. Cytogenet Genome Res 2008, 122:273-280. 91. Martinez P, Blasco MA: Telomeric and extra-telomeric roles for telomerase and the telomere-binding proteins. Nat Rev Cancer 2011, 11:161-176. 92. Mukherjee S, Firpo EJ, Wang Y, Roberts JM: Separation of telomerase functions by reverse genetics. Proc Natl Acad Sci U S A 2011, 108:E1363-E1371. This study descibed in detail non-canonical functions of the TERT gene. 93. Ghosh A, Saginc G, Leow SC, Khattar E, Shin EM, Yan TD, Wong M, Zhang Z, Li G, Sung WK et al.: Telomerase directly regulates NF-kappaB-dependent transcription. Nat Cell Biol 2012, 14:1270-1281. 94. Beck S, Jin X, Sohn YW, Kim JK, Kim SH, Yin J, Pian X, Kim SC, Nam DH, Choi YJ et al.: Telomerase activity-independent function of TERT allows glioma cells to attain cancer stem cell characteristics by inducing EGFR expression. Mol Cells 2011, 31:9-15. 95. Xie L, Gazin C, Park SM, Zhu LJ, Debily MA, Kittler EL, Zapp ML, Lapointe D, Gobeil S, Virbasius CM et al.: A synthetic interaction
www.sciencedirect.com
screen identifies factors selectively required for proliferation and TERT transcription in p53-deficient human cancer cells. PLoS Genet 2012, 8:e1003151. 96. Del Bufalo D, Rizzo A, Trisciuoglio D, Cardinali G, Torrisi MR, Zangemeister-Wittke U, Zupi G, Biroccio A: Involvement of hTERT in apoptosis induced by interference with Bcl-2 expression and function. Cell Death Differ 2005, 12:1429-1438. 97. Rahman R, Latonen L, Wiman KG: hTERT antagonizes p53induced apoptosis independently of telomerase activity. Oncogene 2005, 24:1320-1327. 98. Masutomi K, Possemato R, Wong JM, Currier JL, Tothova Z, Manola JB, Ganesan S, Lansdorp PM, Collins K, Hahn WC: The telomerase reverse transcriptase regulates chromatin state and DNA damage responses. Proc Natl Acad Sci U S A 2005, 102:8222-8227. 99. Lim KW, Lacroix L, Yue DJ, Lim JK, Lim JM, Phan AT: Coexistence of two distinct G-quadruplex conformations in the hTERT promoter. J Am Chem Soc 2010, 132:1233112342. 100. Grand CL, Han H, Munoz RM, Weitman S, Von Hoff DD, Hurley LH, Bearss DJ: The cationic porphyrin TMPyP4 down-regulates cMYC and human telomerase reverse transcriptase expression and inhibits tumor growth in vivo. Mol Cancer Ther 2002, 1:565573. 101 Vogelstein B, Papadopoulos N, Velculescu VE, Zhou S, Diaz LA Jr, Kinzler KW: Cancer genome landscapes. Science 2013, 339:1546-1558. This review provided an overview of cancer genome landscape and future perspectives. 102. Patton EE, Harrington L: Cancer: trouble upstream. Nature 2013, 495:320-321. 103. Lee TI, Young RA: Transcriptional regulation and its misregulation in disease. Cell 2013, 152:1237-1251. 104. Armanios M, Price C: Telomeres and disease: an overview. Mutat Res 2012, 730:1-2. 105. Armanios M: Telomeres and age-related disease: how telomere biology informs clinical paradigms. J Clin Invest 2013, 123:996-1002. 106. Ruden M, Puri N: Novel anticancer therapeutics targeting telomerase. Cancer Treat Rev 2013, 39:444-456. 107. Sullivan RJ, Flaherty KT: Resistance to BRAF-targeted therapy in melanoma. Eur J Cancer 2013, 49:1297-1304.
Current Opinion in Genetics & Development 2014, 24:30–37
ScienceDirect TERT promoter mutations in cancer development Barbara Heidenreich1, P Sivaramakrishna Rachakonda1, Kari Hemminki1,2 and Rajiv Kumar1 Human telomerase reverse transcriptase (TERT) encodes a rate-limiting catalytic subunit of telomerase that maintains genomic integrity. TERT expression is mostly repressed in somatic cells with exception of proliferative cells in selfrenewing tissues and cancer. Immortality associated with cancer cells has been attributed to telomerase overexpression. The precise mechanism behind the TERT activation in cancers has mostly remained unknown. The newly described germline and recurrent somatic mutations in melanoma and other cancers in the TERT promoter that create de novo E-twenty six/ternary complex factors (Ets/TCF) binding sites, provide an insight into the possible cause of tumorspecific increased TERT expression. In this review we discuss the discovery and possible implications of the TERT promoter mutations in melanoma and other cancers. Addresses 1 Division of Molecular Genetic Epidemiology, German Cancer Research Center, Im Neuenheimer Feld 580, 69120 Heidelberg, Germany 2 Center for Primary Health Care Research, Lund University, Malmo¨, Sweden Corresponding author: Kumar, Rajiv ([email protected])
Current Opinion in Genetics & Development 2014, 24:30–37 This review comes from a themed issue on Cancer genomics Edited by David J Adams and Ultan McDermott For a complete overview see the Issue and the Editorial Available online 20th December 2013 0959-437X/$ – see front matter, # 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gde.2013.11.005
expression of telomerase or in its absence by an alternative lengthening of telomeres (ALT) mechanism [10– 14,15]. Human telomerase reverse transcriptase (TERT) gene encodes the catalytic subunit of telomerase that together with a RNA component, TERC, maintains genomic integrity by telomere elongation [16]. Though TERT and TERC are sufficient for in vitro telomerase activity, the in vivo telomerase functioning requires additional components that associate with TERT and TERC, to form the holoenzyme [17,18]. Those include dyskerin (DKC), NOP10 ribonucleoprotein (NOP10), GAR1 ribonucleoprotein homolog (yeast) (GAR1), NHP2 ribonucleoprotein (NHP2), reptin and pontin [11,19–22]. Deregulation of telomerase has been shown to be a ubiquitous feature in human cancers with over 90% of cancers showing an upregulation of the enzyme [11,23,24]. The telomerase activity is dependent on a number of factors, regulated at various stages, which include gene transcription, mRNA splicing, maturation and modifications of TERT and TERC, transport and localization of those components and assembly of active ribonucleoprotein to telomeres telomerase [4,5,16,20,21,25–27]. The catalytic component TERT acts as a determinant of telomerase activity and its transcription is repressed in most of the somatic cells with the exception of proliferative cells of self-renewing tissues [28–30]. An increased expression of TERT has been consistently demonstrated to be a fundamental requirement for cellular transformation [4,31–33,34,35].
Introduction The telomere sequences at the chromosomal ends, composed of tandem repeats of TTAGGG, are protected by a number of molecules that constitute the capping Shelterin complex [1,2]. The incomplete replication due to limitations of the process, called ‘endreplication problem’, results in shortening of telomeres in each successive mitotic cell division that eventually leads to replicative senescence referred to as the ‘Hayflick limit’ [3–5]. Maintenance of telomere repeat length is dependent on sustained expression of telomerase holoenzyme that adds de novo repeat units at the end of each replication cycle [6,7]. Progressive attrition of telomeres is also defined as one of the hallmarks of aging of organisms [8,9]. Cancer cells, characteristically, acquire infinite capability to divide through maintenance of telomeres by sustained Current Opinion in Genetics & Development 2014, 24:30–37
The mechanism of TERT upregulation in cancers had been attributed to several mechanisms including epigenetic deregulation as well as genetic amplification of the locus containing TERT gene [36,37]. In the absence of any evidence of a definite mechanism, the telomerase activity in tumor cells has been attributed to the assumption of stem cells being the progenitors in all cancers [38]. The normal stem cells in self-renewing tissues retain telomerase throughout lifetime replication thus abrogating a requirement for a positive selection [6]. The recently discovered TERT promoter mutations add a new dimension to the acquisition of telomerase activity in human cancers. In this review we provide an overview and possible implications of the newly discovered mutations in the promoter of the TERT gene in a wide range of cancers. www.sciencedirect.com
TERT promoter mutations Heidenreich et al. 31
Structure and regulation of the TERT promoter The human TERT gene is located on chromosome 5p15.33 and the promoter region of the gene is considered to be the most important regulatory element for telomerase expression. The TERT promoter contains binding motifs for several factors that regulate the gene transcription and distinctly lacks a TATA box or a similar sequence [39–43]. The core promoter region consists of 260 base pairs with several transcription-factor binding sites that include E-boxes where c-Myc has been confirmed to bind and activate the transcription [44–48]. BRCA1 in conjunction with N-Myc interacting protein (Nmi) forms a complex with c-Myc and inhibits TERT promoter activity, that property is lost in some mutant forms of BRCA1 [49]. Other sequence elements in TERT promoter include GC-boxes, which are binding sites for zinc finger transcription factor, Sp1 [4,45]. Transcription of the TERT gene is also regulated by various hormones, cytokines and oncogenes [45]. Several repressors of the TERT transcription are also known. p53 has been shown to downregulate TERT transcription in a Sp1-dependent manner [50]. Ets transcription factors that comprise over 30 members are prominently associated with telomerase activation [42,51]. Ets2 has been shown to form a complex with c-Myc in a breast cancer cell line [44,51]. Ets transcription factors are also shown to be stimulated by oncogenes EGF, Her2/Nez, Ras and Raf [52,53]. The activation of oncogenes and inactivation of tumor suppressors are known to account for cellular immortalization through induction of TERT transcription [54]. The high GC content around the transcription start site of the TERT promoter confers epigenetic regulation through methylation and chromatin remodeling [37,55].
TERT promoter mutations in human cancers A discovery of a high-penetrant disease-segregating causal germline mutation in a melanoma family and highly specific and recurrent somatic mutations in tumors from unrelated patients in the TERT promoter has likely provided a definite mechanism for cancer-specific TERT activation [56,57]. Two independent studies using diverse approaches discovered non-coding mutations, mainly at two residues, within the core promoter region of the TERT gene. One study was based on the identification of a causal gene mutation in a large melanoma pedigree where affected individuals presented a severe form of the disease with an early age of onset. The linkage analysis identified a 2.2 megabase telomeric region on chromosome 5p that included TERT along with more than 80 other genes [56]. Sequencing of the entire stretch of DNA region in the family resulted in identification of a disease segregating A > C (T > G) single base change at 57 bp (Chr 5: 1,295,161 hg19 coordinate) from ATG start site. The germline mutation was present in affected and absent in unaffected individuals in the family with the exception of one. Subsequent screening www.sciencedirect.com
of cell lines derived from melanoma metastases from unrelated patients led to the detection of recurrent and mutually exclusive somatic mutations at two residues 124 and 146 from the ATG start site in the TERT promoter [56]. Serendipitously, an independent study using a whole genome sequencing approach also reported the recurrent somatic TERT promoter mutations at the same positions [57]. Other mutations detected in TERT promoter included the CC > TT tandem mutations at 124/ 125 and 138/ 139 bp from ATG start site. The germline and somatic mutations in the non-coding part of the TERT gene were defined by common salient features. One of the underlying features included a de novo creation of CCGGAA/T general binding motifs for E-twenty six/ ternary complex factors (Ets/TCF) transcription factors, which differed from pre-existing GGAA/T Ets binding sites within the TERT promoter (Figure 1). The somatic mutations at both positions being C > T and the additional detection of CC > TT tandem mutations in a proportion of tumors augmented the evidence for the UV-origin of tumor specific nucleotide changes in melanoma as shown previously in studies based on whole genome sequencing [58]. Interestingly, the mutations detected in the TERT promoter in melanoma were more frequent than those in the BRAF gene. It was also observed that the TERT promoter mutations tend to occur more often than expected by chance in tumors with either BRAF mutations (odds ratio [OR] 3.2, 95% confidence interval [CI] 1.3–8.2) or with concomitant alterations in both BRAF and CDKN2A (OR 5.6, 95% CI 2.4–13.8) [56]. BRAF mutations, due to occurrence and role in development of melanocytic nevi, are considered as the driver genetic lesions in melanoma [56,59,60]. The loss of CDKN2A has been suggested to play a role in the escape of melanocytes from BRAF induced senescence [61]. The acquisition of TERT promoter mutations can be hypothesized to facilitate stabilization of the transformed genome through reversal of telomeric loss. Most melanocytic nevi carry BRAF mutations, whereas TERT promoter mutations and CDKN2A alterations are detected only in primary melanoma and beyond [56,62]. Bonafide of newly discovered non-coding mutations in the TERT promoter was established by the detection in cancers other than melanoma [63]. The frequency of the mutations seems to vary between cancer types (Table 1). The highest frequencies of the TERT promoter mutations have so far been reported, besides melanoma, in pleomorphic dermal sarcoma, myxoid liposarcoma, glioma, urothelial cell carcinoma of bladder, basal and squamous cell carcinoma of skin, liver cancer and others [63,64–76]. The mutations occur in other cancer types as well, albeit, at low frequencies [63,67]. Based on the prevalence in different cancer types it has been hypothesized that the TERT promoter mutations mainly occur in tumors that are derived from tissues with low rates of Current Opinion in Genetics & Development 2014, 24:30–37
32 Cancer genomics
Figure 1
Transcription start site Sp1
Sp1
Ets 2 Ets 2
E-box
–100
–150
–150
Sp1
–140
ATG
–50
–130
–120
–1
–60
–50
Wild type
Mutant Ets/TCF
Ets/TCF
Ets/TCF
Ets/TCF Increased transcription Current Opinion in Genetics & Development
Schematic representation of a part of the TERT promoter that contains residues, which are affected by a germline mutation in a melanoma family at the position 57 bp and recurrent somatic mutations at the positions 124 and 146 bp from the ATG start site. The mutations create CCGGAA/T binding motif for Ets/TCF transcription factors that results in an increased TERT expression. Pre-existing binding sites for other transcriptions factors are shown above the sequence.
self-renewal [63,77]. Unlike melanoma and other skin related malignancies, no tumor from the cancers affecting internal organs carried CC > TT tandem mutations in the TERT promoter with the exception of that at the positions 138/ 139 bp from ATG start site in bladder cancer. The tandem mutation reported so far in 4 of the 1231 bladder tumors could also be generated by a singlebase mutation at 138 bp as the base change at 139 bp has been reported as a rare polymorphism represented by rs35550267 [56,65,66]. The differences in mutational pattern in cancer types are known to reflect etiological divergences and the C > T base change in tumors can also be attributed to APOBEC cytidine deaminase expression in cancer development [78,79].
Functional aspects of TERT promoter mutations
from thyroid cancers, primary glioma, malignant pleural mesothelioma and liver cancers with TERT promoter mutations were associated with higher gene expression than those without mutations [67,69,72,74]. Though limited at the moment, the available data do indicate a tendency of the TERT promoter mutations being present in specific clinical and phenotypic subtypes and appear to be associated with adversarial forms of the disease. While in medulloblastomas the TERT promoter mutations were inversely associated with increased OTX2 expression; in primary adult glioma, the mutations occurred mainly in conjunction with EGFR amplification [69]. Glioma patients with TERT promoter mutations showed an association with poorer survival than patients without mutations; in thyroid cancer, mutations are reportedly more frequent in advanced thyroid cancers than in papillary thyroid cancers [63,70,71].
The high recurrence, specificity and gain of function support that the non-coding TERT promoter mutations are driver rather than passenger events in cancer development. The functional relevance of the mutations was indicated by the basic reporter assays that showed 2–4fold increased promoter activity [56,57,80]. Tumors
The studies on bladder cancer consistently showed that TERT promoter mutations are the most frequent lesions with even distribution across all stages and grades [65,66,80]. Intriguingly, an observed interaction has raised a possibility of eventual use of the TERT promoter
Current Opinion in Genetics & Development 2014, 24:30–37
www.sciencedirect.com
TERT promoter mutations Heidenreich et al. 33
Table 1 TERT promoter mutations in cancers Cancer type
Mutation frequency (%) a
Ref.
Bladder cancer Glioma Ependymomas Astrocytomas Mixed gliomas Oligodendrogliomas Melanoma Cutaneous melanoma Ocular melanoma (not specified) Uveal melanoma Conjunctival melanoma Squamous cell carcinoma (SCC) SCC of head and neck SCC of esophagus SCC of the cervix SCC of the skin Bowen’s disease Basal cell carcinoma of skin Thyroid b ATC + PDTC DTC FTC HCC PTC Atypical fibroxanthoma Myxoid liposarcoma Pleomorphic dermal sarcomas Liver c Fibrosarcoma Dysembryoplastic neuroepithelial tumor Medulloblastoma Solitary fibrous tumor (SFT) Ovarian, clear cell carcinoma Ovarian, low grade serous Malignant pleural mesothelioma Endometrial cancer Myxofibrosarcoma Neuroblastoma Osteosarcoma
887/1231 (72.1)
[63,64–67,80]
1/36 (2.7) 574/1059 (54.2) 102/188 (54.3) 46/72 (63.9)
[63] [63,64,67,69,73] [63,69] [63,67]
136/256 (53) 0/25 0/47 12/38 (32)
[56,57,67] [67] [68] [68]
12/70 (17.1) 5/313 (1.6) 1/22 (4.5) 14/31 (45.2) 1/11 (9.1) 31/42 (73.8)
[63] [77] [63] [63,76] [76] [76]
73/170 (42.9) 41/336 (12.2) 20/143 (14.0) 4/25 (16.0) 61/506 (12.1) 25/27 (92.6) 19/24 (79.1) 26/34 (76.5) 218/531 (41.1) 1/3 (33.3) 1/3 (33.3) 19/91 (20.8%) 2/10 (20.0%) 2/12 (16.6%) 1/8 (12.5%) 8/71 (11.3%) 2/19 (10.5%) 1/10 (10.0%) 2/22 (9.1%) 1/23 (4.3%)
[67,70,71] [70] [67,70] [71] [67,70,71] [75] [63] [75] [63,74] [63] [63] [63] [63] [63] [63] [72] [63] [63] [63] [63]
Ref [63]: no mutations were found in acute myeloid leukemia (n = 48), alveolar rhabdomyosarcoma (n = 7), atypical lipomatous tumor (n = 10), breast carcinoma (n = 88), cholangiosarcoma (n = 28), central/conventional chondrosarcoma (n = 9), chronic lymphoid leukemia (n = 15), chronic myeloid leukemia (n = 6), colorectal adenocarcinoma (n = 22), embryonal rhabdomyosarcoma (n = 8), esthesioneuroblastoma (n = 11), extraskeletal myxoid chondrosarcoma (n = 3), fibrolammellar carcinoma of the liver (n = 12), gall bladder carcinoma (n = 10), hepatoblastoma (n = 3), leiomyosarcoma (n = 3), conventional lipoma (n = 8), low grade fibromyxoid sarcoma (n = 9), malignant peripheral nerve sheath tumor (n = 3), medullary thyroid carcinoma (n = 24), meningioma (n = 20), mesothelioma (n = 4), pancreatic acinar carcinoma (n = 25), pancreatic ductal adenocarcinoma (n = 24), pancreatic neuroendocrine tumor (n = 68), prostate carcinoma (n = 34), spinal ependymoma (n = 9), synovial sarcoma (n = 16), or undifferentiated pleomorphic soft tissue sarcoma (n = 10) samples. Ref [67]: no mutations were found in Phaeochromocytoma (n = 17); CCRCC, CromRCC and PRCC of the kidney (n = 26). Refs [63,67]: No mutations were found in gastrointestinal stromal tumors (n = 45). Refs [56,67]: No mutations were found in melanocytic nevi (n = 34). Refs [67,70]: No mutations were found in benign thyroid tumors (n = 166) or medullary thyroid carcinoma (n = 44). a Includes all reported TERT promoter mutations; most common mutations are 124C > T (Chr 5:1,295,228 hg19 coordinate) and 146C > T (1,295,250). In melanoma 146C > T mutation is more frequent than the 124C > T; in cancers, especially in gliomas, thyroid cancers and bladder cancers the latter is the most common mutation. Additionally, in melanoma two CC > TT tandem mutations affecting 124/ 125 and 138/ 139 residues were also detected with a combined frequency of 9%[56]. b ATC, anaplastic thyroid carcinoma; FTC, follicular thyroid carcinoma; PDTC, poorly differentiated thyroid carcinoma; PTC, papillary thyroid carcinoma; HCC, Hurthle cell cancers; DTC, differentiated thyroid cancer. c Includes Hepatocellular carcinoma, Cirrhotic tissue, Cirrhotic macronodules, Hepatocellular adenomas, HCA with HCC foci.
mutations in conjunction with a common polymorphism within the sequence as biomarkers in bladder cancer. The data from bladder cancer showed that the variant allele of a common polymorphism at 245 bp from ATG start site www.sciencedirect.com
in the TERT promoter acts as a modifier of the effect of TERT promoter mutations on patient survival and disease recurrence [80]. Bladder cancer patients with TERT promoter mutations in tumors showed almost two-fold Current Opinion in Genetics & Development 2014, 24:30–37
34 Cancer genomics
decreased survival and increased disease recurrence in the absence but not in the presence of the variant allele for the rs2853669 polymorphism [80]. Mechanistic support for the observation was provided by the fact that mutations result in de novo creation of Ets/TCF binding motifs; the variant allele of the rs2853669 polymorphism, on the contrary, disrupts a preexisting non-canonical Ets2 binding site in the proximal region of the TERT promoter, adjacent to an E-box [44]. The occurrence of highly specific TERT promoter mutations indicates a strong selection pressure for the gene over-expression on path to cellular transformation. Increased telomerase production has been demonstrated to promote cancer progression in an animal model [81]. The effect of the promoter mutations on TERT expression can be tenable only in the presence of Ets/TCF transcription factors that can specifically bind to the de novo sites created by the mutations. Some of the Ets/TCF transcription factors are downstream targets of MAPK pathway, where BRAF is a prominent intermediate [82–84]. Whether in melanoma activated BRAF is a driving force in selection of TERT promoter mutations remains to be determined. Nevertheless, expression of Ets transcription factors is ubiquitous in melanoma and other cancers [85,86]. Many studies have stressed the function of the TERT gene beyond its role in maintenance of the telomere; therefore the mutations in the TERT promoter can affect non-canonical processes associated with TERT [87–91]. TERT acts as a modulator of Wnt-b-catenin signaling pathway and induces stem cell characteristics in glioma; TERT also regulates expression of NF-kB, a master regulator of inflammation [92,93,94]. TERT was shown to be important for proliferation of p53-negative cells through ATR mediated stabilization of ETV1, which binds downstream of the transcriptional start site [95]. Other non-canonical functions of TERT include enhanced cell proliferation, decreased apoptosis, regulation of DNA damage responses, chromatin state and increased cellular proliferation life span [96–98]. The effect of the mutations beyond transcription also remains a probability. The human TERT promoter contains Grich sequence and has potential for G-quadruplex formation that can potentially be targeted to regulate gene transcription [99]. G-quadruplexes have been also implicated in inhibition of telomerase and control of gene expression [100].
Conceptual advancement and therapeutic possibilities The TERT promoter mutations are thought to represent a conceptual advancement in the sense that those instead of altering an encoded protein modulate transcriptional regulation and represent first evidence of driver alterations in so called ‘dark matter’ of the Current Opinion in Genetics & Development 2014, 24:30–37
human genome [101,102]. A host of germline variants discovered through genome wide association studies contribute to the susceptibility of various diseases through transcriptional deregulation [103]. While TERT promoter mutations represent novel findings in human cancer, alterations in components associated with telomerase assembly, telomere protection or telomere recruitment are known to impact stem cell function and lifespan in mammals through various disorders [104,105]. Several strategies of therapeutic telomerase inhibition including small molecular inhibitors, immunotherapy, gene therapy, telomere and telomerase-proteins in different cancers have entered clinical trial [106]. It will be interesting to see if the TERT promoter mutations, that increase gene expression, influence the current on-going research on targeted therapeutics or if the use of telomerase inhibitors in conjunction with kinase inhibitors like vemurafenib or similar small molecules in melanoma can alleviate recurrent resistance [107].
References and recommended reading Papers of particular interest, published within the period of review have been highlighted as: of special interest of outstanding interest 1.
Lu Y, Wei B, Zhang T, Chen Z, Ye J: How will telomeric complex be further contributed to our longevity? The potential novel biomarkers of telomere complex counteracting both aging and cancer. Protein Cell 2013, 4:573-581.
2.
de Lange T: How telomeres solve the end-protection problem. Science 2009, 326:948-952.
3.
Hayflick L: The limited in vitro lifetime of human diploid cell strains. Exp Cell Res 1965, 37:614-636.
4.
Cong YS, Wright WE, Shay JW: Human telomerase and its regulation. Microbiol Mol Biol Rev 2002, 66:407-425.
5.
Nandakumar J, Cech TR: Finding the end: recruitment of telomerase to telomeres. Nat Rev Mol Cell Biol 2013, 14:69-82.
6.
Masutomi K, Yu EY, Khurts S, Ben-Porath I, Currier JL, Metz GB, Brooks MW, Kaneko S, Murakami S, DeCaprio JA et al.: Telomerase maintains telomere structure in normal human cells. Cell 2003, 114:241-253.
7.
Marion RM, Blasco MA: Telomere rejuvenation during nuclear reprogramming. Curr Opin Genet Dev 2010, 20:190-196.
8.
Lopez-Otin C, Blasco MA, Partridge L, Serrano M, Kroemer G: The hallmarks of aging. Cell 2013, 153:1194-1217.
9.
Bernardes de Jesus B, Blasco MA: Telomerase at the intersection of cancer and aging. Trends Genet 2013, 29:513520.
10. Hanahan D, Weinberg RA: Hallmarks of cancer: the next generation. Cell 2011, 144:646-674. 11. Low KC, Tergaonkar V: Telomerase: central regulator of all of the hallmarks of cancer. Trends Biochem Sci 2013, 38:426-434. 12. Heaphy CM, Subhawong AP, Hong SM, Goggins MG, Montgomery EA, Gabrielson E, Netto GJ, Epstein JI, Lotan TL, Westra WH et al.: Prevalence of the alternative lengthening of telomeres telomere maintenance mechanism in human cancer subtypes. Am J Pathol 2011, 179:1608-1615. www.sciencedirect.com
TERT promoter mutations Heidenreich et al. 35
13. Lovejoy CA, Li W, Reisenweber S, Thongthip S, Bruno J, de Lange T, De S, Petrini JH, Sung PA, Jasin M et al.: Loss of ATRX, genome instability, and an altered DNA damage response are hallmarks of the alternative lengthening of telomeres pathway. PLoS Genet 2012, 8:e1002772. 14. Cesare AJ, Reddel RR: Alternative lengthening of telomeres: models, mechanisms and implications. Nat Rev Genet 2010, 11:319-330. 15. Heaphy CM, de Wilde RF, Jiao Y, Klein AP, Edil BH, Shi C, Bettegowda C, Rodriguez FJ, Eberhart CG, Hebbar S et al.: Altered telomeres in tumors with ATRX and DAXX mutations. Science 2011, 333:425. This study showed an association of mutations in ATRX/DAXX genes with abnormal telomere due to alternative lengthening of telomeres.
of telomerase limits the growth of human cancer cells. Nat Med 1999, 5:1164-1170. 34. Hahn WC, Counter CM, Lundberg AS, Beijersbergen RL, Brooks MW, Weinberg RA: Creation of human tumour cells with defined genetic elements. Nature 1999, 400:464-468. First study that demonstrated in vitro conversion of normal human cells into tumor cells. 35. Kiyono T, Foster SA, Koop JI, McDougall JK, Galloway DA, Klingelhutz AJ: Both Rb/p16INK4a inactivation and telomerase activity are required to immortalize human epithelial cells. Nature 1998, 396:84-88. 36. Hahn WC, Meyerson M: Telomerase activation, cellular immortalization and cancer. Ann Med 2001, 33:123-129.
16. Podlevsky JD, Chen JJ: It all comes together at the ends: telomerase structure, function, and biogenesis. Mutat Res 2012, 730:3-11.
37. Zhu J, Zhao Y, Wang S: Chromatin and epigenetic regulation of the telomerase reverse transcriptase gene. Protein Cell 2010, 1:22-32.
17. Weinrich SL, Pruzan R, Ma L, Ouellette M, Tesmer VM, Holt SE, Bodnar AG, Lichtsteiner S, Kim NW, Trager JB et al.: Reconstitution of human telomerase with the template RNA component hTR and the catalytic protein subunit hTRT. Nat Genet 1997, 17:498-502.
38. Armanios M, Greider CW: Telomerase and cancer stem cells. Cold Spring Harb Symp Quant Biol 2005, 70:205-208.
18. Masutomi K, Kaneko S, Hayashi N, Yamashita T, Shirota Y, Kobayashi K, Murakami S: Telomerase activity reconstituted in vitro with purified human telomerase reverse transcriptase and human telomerase RNA component. J Biol Chem 2000, 275:22568-22573. 19. Lewis KA, Wuttke DS: Telomerase and telomere-associated proteins: structural insights into mechanism and evolution. Structure 2012, 20:28-39. 20. Venteicher AS, Abreu EB, Meng Z, McCann KE, Terns RM, Veenstra TD, Terns MP, Artandi SE: A human telomerase holoenzyme protein required for Cajal body localization and telomere synthesis. Science 2009, 323: 644-648. 21. Egan ED, Collins K: Specificity and stoichiometry of subunit interactions in the human telomerase holoenzyme assembled in vivo. Mol Cell Biol 2010, 30:2775-2786. 22. Collins K: The biogenesis and regulation of telomerase holoenzymes. Nat Rev Mol Cell Biol 2006, 7:484-494. 23. Shay JW, Bacchetti S: A survey of telomerase activity in human cancer. Eur J Cancer 1997, 33:787-791. 24. Shay JW, Zou Y, Hiyama E, Wright WE: Telomerase and cancer. Hum Mol Genet 2001, 10:677-685. 25. Venteicher AS, Artandi SE: TCAB1: driving telomerase to Cajal bodies. Cell Cycle 2009, 8:1329-1331. 26. Fu D, Collins K: Distinct biogenesis pathways for human telomerase RNA and H/ACA small nucleolar RNAs. Mol Cell 2003, 11:1361-1372. 27. Cristofari G, Sikora K, Lingner J: Telomerase unplugged. ACS Chem Biol 2007, 2:155-158. 28. Shay JW, Wright WE: Telomerase therapeutics for cancer: challenges and new directions. Nat Rev Drug Discov 2006, 5:577-584. 29. Hiyama E, Hiyama K: Telomere and telomerase in stem cells. Br J Cancer 2007, 96:1020-1024. 30. Wright WE, Piatyszek MA, Rainey WE, Byrd W, Shay JW: Telomerase activity in human germline and embryonic tissues and cells. Dev Genet 1996, 18:173-179. 31. Xu L, Li S, Stohr BA: The role of telomere biology in cancer. Annu Rev Pathol 2013, 8:49-78. 32. Kolquist KA, Ellisen LW, Counter CM, Meyerson M, Tan LK, Weinberg RA, Haber DA, Gerald WL: Expression of TERT in early premalignant lesions and a subset of cells in normal tissues. Nat Genet 1998, 19:182-186. 33. Hahn WC, Stewart SA, Brooks MW, York SG, Eaton E, Kurachi A, Beijersbergen RL, Knoll JH, Meyerson M, Weinberg RA: Inhibition www.sciencedirect.com
39. Cong YS, Wen J, Bacchetti S: The human telomerase catalytic subunit hTERT: organization of the gene and characterization of the promoter. Hum Mol Genet 1999, 8:137-142. 40. Poole JC, Andrews LG, Tollefsbol TO: Activity, function, and gene regulation of the catalytic subunit of telomerase (hTERT). Gene 2001, 269:1-12. 41. Horikawa I, Cable PL, Afshari C, Barrett JC: Cloning and characterization of the promoter region of human telomerase reverse transcriptase gene. Cancer Res 1999, 59:826-830. 42. Gladych M, Wojtyla A, Rubis B: Human telomerase expression regulation. Biochem Cell Biol 2011, 89:359-376. 43. Wojtyla A, Gladych M, Rubis B: Human telomerase activity regulation. Mol Biol Rep 2011, 38:3339-3349. 44. Xu D, Dwyer J, Li H, Duan W, Liu JP: Ets2 maintains hTERT gene expression and breast cancer cell proliferation by interacting with c-Myc. J Biol Chem 2008, 283:23567-23580. 45. Kyo S, Takakura M, Fujiwara T, Inoue M: Understanding and exploiting hTERT promoter regulation for diagnosis and treatment of human cancers. Cancer Sci 2008, 99:1528-1538. 46. Hashimoto M, Kyo S, Hua X, Tahara H, Nakajima M, Takakura M, Sakaguchi J, Maida Y, Nakamura M, Ikoma T et al.: Role of menin in the regulation of telomerase activity in normal and cancer cells. Int J Oncol 2008, 33:333-340. 47. Akutagawa O, Nishi H, Kyo S, Terauchi F, Yamazawa K, Higuma C, Inoue M, Isaka K: Early growth response-1 mediates downregulation of telomerase in cervical cancer. Cancer Sci 2008, 99:1401-1406. 48. Cerezo A, Kalthoff H, Schuermann M, Schafer B, Boukamp P: Dual regulation of telomerase activity through c-Myc-dependent inhibition and alternative splicing of hTERT. J Cell Sci 2002, 115:1305-1312. 49. Li H, Lee TH, Avraham H: A novel tricomplex of BRCA1, Nmi, and c-Myc inhibits c-Myc-induced human telomerase reverse transcriptase gene (hTERT) promoter activity in breast cancer. J Biol Chem 2002, 277:20965-20973. 50. Kanaya T, Kyo S, Hamada K, Takakura M, Kitagawa Y, Harada H, Inoue M: Adenoviral expression of p53 represses telomerase activity through down-regulation of human telomerase reverse transcriptase transcription. Clin Cancer Res 2000, 6:1239-1247. 51. Dwyer JM, Liu JP: Ets2 transcription factor, telomerase activity and breast cancer. Clin Exp Pharmacol Physiol 2010, 37:83-87. 52. Goueli BS, Janknecht R: Upregulation of the catalytic telomerase subunit by the transcription factor ER81 and oncogenic HER2/Neu, Ras, or Raf. Mol Cell Biol 2004, 24:25-35. 53. Maida Y, Kyo S, Kanaya T, Wang Z, Yatabe N, Tanaka M, Nakamura M, Ohmichi M, Gotoh N, Murakami S et al.: Direct activation of telomerase by EGF through Ets-mediated Current Opinion in Genetics & Development 2014, 24:30–37
36 Cancer genomics
transactivation of TERT via MAP kinase signaling pathway. Oncogene 2002, 21:4071-4079. 54. Lin SY, Elledge SJ: Multiple tumor suppressor pathways negatively regulate telomerase. Cell 2003, 113:881-889. 55. Li AY, Lin HH, Kuo CY, Shih HM, Wang CC, Yen Y, Ann DK: High-mobility group A2 protein modulates hTERT transcription to promote tumorigenesis. Mol Cell Biol 2011, 31:2605-2617. 56. Horn S, Figl A, Rachakonda PS, Fischer C, Sucker A, Gast A, Kadel S, Moll I, Nagore E, Hemminki K et al.: TERT promoter mutations in familial and sporadic melanoma. Science 2013, 339:959-961. First study to report a causal mutation in a large melanoma family and recurrent somatic mutations in tumors from unrelated melanoma patients in the TERT promoter that result in creation of de novo Ets/TCF transcription factor binding motifs. 57. Huang FW, Hodis E, Xu MJ, Kryukov GV, Chin L, Garraway LA: Highly recurrent TERT promoter mutations in human melanoma. Science 2013, 339:957-959. First study to show recurrent somatic mutations in the TERT promoter in melanoma. This study also showed same mutations in cell lines from tumors other than melanoma. 58. Hodis E, Watson IR, Kryukov GV, Arold ST, Imielinski M, Theurillat JP, Nickerson E, Auclair D, Li L, Place C et al.: A landscape of driver mutations in melanoma. Cell 2012, 150:251-263. This study presented a mutational landscape in melanoma and showed a distinction between driver and passenger mutations. 59. Dhomen N, Reis-Filho JS, da Rocha Dias S, Hayward R, Savage K, Delmas V, Larue L, Pritchard C, Marais R: Oncogenic Braf induces melanocyte senescence and melanoma in mice. Cancer Cell 2009, 15:294-303. This study demonstrated V600E BRAF as a founder mutation in melanoma development. 60. Michaloglou C, Vredeveld LC, Mooi WJ, Peeper DS: BRAF(E600) in benign and malignant human tumours. Oncogene 2008, 27:877-895. 61. Michaloglou C, Vredeveld LC, Soengas MS, Denoyelle C, Kuilman T, van der Horst CM, Majoor DM, Shay JW, Mooi WJ, Peeper DS: BRAFE600-associated senescence-like cell cycle arrest of human naevi. Nature 2005, 436:720-724. 62. Kumar R, Angelini S, Snellman E, Hemminki K: BRAF mutations are common somatic events in melanocytic nevi. J Invest Dermatol 2004, 122:342-348. 63. Killela PJ, Reitman ZJ, Jiao Y, Bettegowda C, Agrawal N, Diaz LA Jr, Friedman AH, Friedman H, Gallia GL, Giovanella BC et al.: TERT promoter mutations occur frequently in gliomas and a subset of tumors derived from cells with low rates of selfrenewal. Proc Natl Acad Sci U S A 2013, 110:6021-6026. First study to show TERT promoter mutations in a large number of tumors from different cancer types and presented a hypothesis for the observed distribution of the mutations. 64. Liu X, Wu G, Shan Y, Hartmann C, von Deimling A, Xing M: Highly prevalent TERT promoter mutations in bladder cancer and glioblastoma. Cell Cycle 2013, 12:1637-1638. 65. Hurst CD, Platt FM, Knowles MA: Comprehensive mutation analysis of the TERT promoter in bladder cancer and detection of mutations in voided urine. Eur Urol 2013 http://dx.doi.org/ 10.1016/j.eururo.2013.08.057. 66. Allory Y, Beukers W, Sagrera A, Flandez M, Marques M, Marquez M, van der Keur KA, Dyrskjot L, Lurkin I, Vermeij M et al.: Telomerase reverse transcriptase promoter mutations in bladder cancer: high frequency across stages, detection in urine, and lack of association with outcome. Eur Urol 2013 http://dx.doi.org/10.1016/j.eururo.2013.08.052.
mutations in ocular melanoma distinguish between conjunctival and uveal tumours. Br J Cancer 2013, 109:497-501. 69. Arita H, Narita Y, Fukushima S, Tateishi K, Matsushita Y, Yoshida A, Miyakita Y, Ohno M, Collins VP, Kawahara N et al.: Upregulating mutations in the TERT promoter commonly occur in adult malignant gliomas and are strongly associated with total 1p19q loss. Acta Neuropathol 2013, 126:267-276. 70. Liu X, Bishop J, Shan Y, Pai S, Liu D, Murugan AK, Sun H, ElNaggar AK, Xing M: Highly prevalent TERT promoter mutations in aggressive thyroid cancers. Endocr Relat Cancer 2013, 20:603-610. 71. Landa I, Ganly I, Chan TA, Mitsutake N, Matsuse M, Ibrahimpasic T, Ghossein RA, Fagin JA: Frequent somatic TERT promoter mutations in thyroid cancer: higher prevalence in advanced forms of the disease. J Clin Endocrinol Metab 2013, 98:E1562-E1566. 72. Tallet A, Nault JC, Renier A, Hysi I, Galateau-Salle F, Cazes A, Copin MC, Hofman P, Andujar P, Le Pimpec-Barthes F et al.: Overexpression and promoter mutation of the TERT gene in malignant pleural mesothelioma. Oncogene 2013 http:// dx.doi.org/10.1038/onc.2013.351. 73. Nonoguchi N, Ohta T, Oh JE, Kim YH, Kleihues P, Ohgaki H: TERT promoter mutations in primary and secondary glioblastomas. Acta Neuropathol 2013, 126:931-937. 74. Nault JC, Mallet M, Pilati C, Calderaro J, Bioulac-Sage P, Laurent C, Laurent A, Cherqui D, Balabaud C, Rossi JZ: High frequency of telomerase reverse-transcriptase promoter somatic mutations in hepatocellular carcinoma and preneoplastic lesions. Nat Commun 2013, 4:2218. 75. Griewank KG, Schilling B, Murali R, Bielefeld N, Schwamborn M, Sucker A, Zimmer L, Hillen U, Schaller J, Brenn T et al.: TERT promoter mutations are frequent in atypical fibroxanthomas and pleomorphic dermal sarcomas. Mod Pathol 2013 http:// dx.doi.org/10.1038/modpathol.2013.168. 76. Scott GA, Laughlin TS, Rothberg PG: Mutations of the TERT promoter are common in basal cell carcinoma and squamous cell carcinoma. Mod Pathol 2013 http://dx.doi.org/10.1038/ modpathol.2013.167. 77. Zhao Y, Gao Y, Chen Z, Hu X, Zhou F, He J: Low frequency of TERT promoter somatic mutation in 313 sporadic esophageal squamous cell carcinomas. Int J Cancer 2013, 134:493-494. 78. Roberts SA, Lawrence MS, Klimczak LJ, Grimm SA, Fargo D, Stojanov P, Kiezun A, Kryukov GV, Carter SL, Saksena G et al.: An APOBEC cytidine deaminase mutagenesis pattern is widespread in human cancers. Nat Genet 2013, 45:970-976. This study provides a clue about the origin of most prevalent somatic mutation in human cancers. 79. Alexandrov LB, Nik-Zainal S, Wedge DC, Aparicio SA, Behjati S, Biankin AV, Bignell GR, Bolli N, Borg A, Borresen-Dale AL et al.: Signatures of mutational processes in human cancer. Nature 2013, 500:415-421. This unique study has identified the distinct mutational signatures that define somatic mutations in human cancers. 80. Rachakonda PS, Hosen I, de Verdier PJ, Fallah M, Heidenreich B, Ryk C, Wiklund NP, Steineck G, Schadendorf D, Hemminki K et al.: TERT promoter mutations in bladder cancer affect patient survival and disease recurrence through modification by a common polymorphism. Proc Natl Acad Sci U S A 2013, 110:17426-17431. This study showed the possibility of eventual use of TERT promoter mutations in conjunction with a common polymorphism within the sequence.
67. Vinagre J, Almeida A, Populo H, Batista R, Lyra J, Pinto V, Coelho R, Celestino R, Prazeres H, Lima L et al.: Frequency of TERT promoter mutations in human cancers. Nat Commun 2013, 4:2185.
81. Ding Z, Wu CJ, Jaskelioff M, Ivanova E, Kost-Alimova M, Protopopov A, Chu GC, Wang G, Lu X, Labrot ES et al.: Telomerase reactivation following telomere dysfunction yields murine prostate tumors with bone metastases. Cell 2012, 148:896-907. This study showed restoration of telomerase in tumor cells with telomere dysfunction enables complete malignant progression of murine prostate cancer.
68. Griewank KG, Murali R, Schilling B, Scholz S, Sucker A, Song M, Susskind D, Grabellus F, Zimmer L, Hillen U et al.: TERT promoter
82. Rao VN, Reddy ES: elk-1 proteins interact with MAP kinases. Oncogene 1994, 9:1855-1860.
Current Opinion in Genetics & Development 2014, 24:30–37
www.sciencedirect.com
TERT promoter mutations Heidenreich et al. 37
83. Kar A, Gutierrez-Hartmann A: Molecular mechanisms of ETS transcription factor-mediated tumorigenesis. Crit Rev Biochem Mol Biol 2013, 48:522-543. 84. Buchwalter G, Gross C, Wasylyk B: Ets ternary complex transcription factors. Gene 2004, 324:1-14. 85. Uhlen M, Oksvold P, Fagerberg L, Lundberg E, Jonasson K, Forsberg M, Zwahlen M, Kampf C, Wester K, Hober S et al.: Towards a knowledge-based Human Protein Atlas. Nat Biotechnol 2010, 28:1248-1250. 86. Jane-Valbuena J, Widlund HR, Perner S, Johnson LA, Dibner AC, Lin WM, Baker AC, Nazarian RM, Vijayendran KG, Sellers WR et al.: An oncogenic role for ETV1 in melanoma. Cancer Res 2010, 70:2075-2084. 87. Stewart SA, Hahn WC, O’Connor BF, Banner EN, Lundberg AS, Modha P, Mizuno H, Brooks MW, Fleming M, Zimonjic DB et al.: Telomerase contributes to tumorigenesis by a telomere length-independent mechanism. Proc Natl Acad Sci U S A 2002, 99:12606-12611. 88. Blasco MA: Telomerase beyond telomeres. Nat Rev Cancer 2002, 2:627-633. 89. Calado RT, Chen J: Telomerase: not just for the elongation of telomeres. Bioessays 2006, 28:109-112. 90. Parkinson EK, Fitchett C, Cereser B: Dissecting the noncanonical functions of telomerase. Cytogenet Genome Res 2008, 122:273-280. 91. Martinez P, Blasco MA: Telomeric and extra-telomeric roles for telomerase and the telomere-binding proteins. Nat Rev Cancer 2011, 11:161-176. 92. Mukherjee S, Firpo EJ, Wang Y, Roberts JM: Separation of telomerase functions by reverse genetics. Proc Natl Acad Sci U S A 2011, 108:E1363-E1371. This study descibed in detail non-canonical functions of the TERT gene. 93. Ghosh A, Saginc G, Leow SC, Khattar E, Shin EM, Yan TD, Wong M, Zhang Z, Li G, Sung WK et al.: Telomerase directly regulates NF-kappaB-dependent transcription. Nat Cell Biol 2012, 14:1270-1281. 94. Beck S, Jin X, Sohn YW, Kim JK, Kim SH, Yin J, Pian X, Kim SC, Nam DH, Choi YJ et al.: Telomerase activity-independent function of TERT allows glioma cells to attain cancer stem cell characteristics by inducing EGFR expression. Mol Cells 2011, 31:9-15. 95. Xie L, Gazin C, Park SM, Zhu LJ, Debily MA, Kittler EL, Zapp ML, Lapointe D, Gobeil S, Virbasius CM et al.: A synthetic interaction
www.sciencedirect.com
screen identifies factors selectively required for proliferation and TERT transcription in p53-deficient human cancer cells. PLoS Genet 2012, 8:e1003151. 96. Del Bufalo D, Rizzo A, Trisciuoglio D, Cardinali G, Torrisi MR, Zangemeister-Wittke U, Zupi G, Biroccio A: Involvement of hTERT in apoptosis induced by interference with Bcl-2 expression and function. Cell Death Differ 2005, 12:1429-1438. 97. Rahman R, Latonen L, Wiman KG: hTERT antagonizes p53induced apoptosis independently of telomerase activity. Oncogene 2005, 24:1320-1327. 98. Masutomi K, Possemato R, Wong JM, Currier JL, Tothova Z, Manola JB, Ganesan S, Lansdorp PM, Collins K, Hahn WC: The telomerase reverse transcriptase regulates chromatin state and DNA damage responses. Proc Natl Acad Sci U S A 2005, 102:8222-8227. 99. Lim KW, Lacroix L, Yue DJ, Lim JK, Lim JM, Phan AT: Coexistence of two distinct G-quadruplex conformations in the hTERT promoter. J Am Chem Soc 2010, 132:1233112342. 100. Grand CL, Han H, Munoz RM, Weitman S, Von Hoff DD, Hurley LH, Bearss DJ: The cationic porphyrin TMPyP4 down-regulates cMYC and human telomerase reverse transcriptase expression and inhibits tumor growth in vivo. Mol Cancer Ther 2002, 1:565573. 101 Vogelstein B, Papadopoulos N, Velculescu VE, Zhou S, Diaz LA Jr, Kinzler KW: Cancer genome landscapes. Science 2013, 339:1546-1558. This review provided an overview of cancer genome landscape and future perspectives. 102. Patton EE, Harrington L: Cancer: trouble upstream. Nature 2013, 495:320-321. 103. Lee TI, Young RA: Transcriptional regulation and its misregulation in disease. Cell 2013, 152:1237-1251. 104. Armanios M, Price C: Telomeres and disease: an overview. Mutat Res 2012, 730:1-2. 105. Armanios M: Telomeres and age-related disease: how telomere biology informs clinical paradigms. J Clin Invest 2013, 123:996-1002. 106. Ruden M, Puri N: Novel anticancer therapeutics targeting telomerase. Cancer Treat Rev 2013, 39:444-456. 107. Sullivan RJ, Flaherty KT: Resistance to BRAF-targeted therapy in melanoma. Eur J Cancer 2013, 49:1297-1304.
Current Opinion in Genetics & Development 2014, 24:30–37
