Cancer Letters xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Cancer Letters journal homepage: www.elsevier.com/locate/canlet

Mini-review

Mitochondrial dysfunctions in cancer: Genetic defects and oncogenic signaling impinging on TCA cycle activity Enrico Desideri a, Rolando Vegliante a, Maria Rosa Ciriolo a,b,⇑ a b

Department of Biology, University of Rome ‘‘Tor Vergata’’, Via della Ricerca Scientifica, 00133 Rome, Italy IRCCS San Raffaele Pisana, Via di Val Cannuta, 00166 Rome, Italy

a r t i c l e

i n f o

Article history: Received 20 December 2013 Received in revised form 12 February 2014 Accepted 18 February 2014 Available online xxxx Keywords: Isocitrate dehydrogenase Fumarate hydratase Succinate dehydrogenase HIF p53 Aconitase

a b s t r a c t The tricarboxylic acid (TCA) cycle is a central route for oxidative metabolism. Besides being responsible for the production of NADH and FADH2, which fuel the mitochondrial electron transport chain to generate ATP, the TCA cycle is also a robust source of metabolic intermediates required for anabolic reactions. This is particularly important for highly proliferating cells, like tumour cells, which require a continuous supply of precursors for the synthesis of lipids, proteins and nucleic acids. A number of mutations among the TCA cycle enzymes have been discovered and their association with some tumour types has been established. In this review we summarise the current knowledge regarding alterations of the TCA cycle in tumours, with particular attention to the three germline mutations of the enzymes succinate dehydrogenase, fumarate hydratase and isocitrate dehydrogenase, which are involved in the pathogenesis of tumours, and to the aberrant regulation of TCA cycle components that are under the control of oncogenes and tumour suppressors. Ó 2014 Elsevier Ireland Ltd. All rights reserved.

1. Introduction Although mitochondria are often presented as power plants producing ATP by means of the oxidative phosphorylation (OXPHOS), this limited view does not reflect the importance of these organelles for cellular viability. Indeed, ATP production is only one of the innumerable functions in which mitochondria are involved. For instance, they are responsible for the activation of programmed mechanisms of cell death through the release of pro-apoptotic molecules (e.g. cytochrome c and apoptosis-inducing factor) [1]. Mitochondria are also the organelles where the enzymes involved in the tricarboxylic acid (TCA) cycle reside. The TCA cycle is pivotal for the entire cellular metabolism. Besides providing NADH and FADH2 required for the function of the electron transport chain (ETC), many TCA cycle intermediates can be converted and channeled towards anabolic pathways producing lipids, nucleic acids and proteins [2]. In the light of the essential role of mitochondria, it is not surprising that defects in mitochondria components have been found to be involved in the most diverse human diseases, ranging from neurodegeneration and

⇑ Corresponding author at: Department of Biology, University of Rome ‘‘Tor Vergata’’, Via della Ricerca Scientifica, 00133 Rome, Italy. Tel.: +39 06 7259 4369; fax: +39 06 7259 4311. E-mail address: [email protected] (M.R. Ciriolo).

cardiovascular diseases to obesity and cancer [3–5]. In this review, we aim at summarising the current knowledge concerning the relationship linking defects and aberrant regulation of TCA cycle components to tumour formation and progression. 2. Overview on the TCA cycle In its most simplistic conception (Fig. 1), the TCA cycle (also known as Kreb’s cycle or citric acid cycle) is a cyclic metabolic pathway consisting in the oxidation of acetyl-CoA, deriving from glycolysis through pyruvate dehydrogenase and from lipid b-oxidation, to CO2, with the concomitant production of NADH and FADH2, which feed the ETC, and GTP/ATP. Namely, the net production is 3 NADH, 1 FADH2 and 1 GTP/ATP for each molecule of acetyl-CoA consumed. The TCA cycle begins with the condensation of the acetyl moiety of acetyl-CoA with oxaloacetate by citrate synthase to form citrate. Citrate is reversibly isomerised to isocitrate by mitochondrial aconitase (ACO2) and then decarboxylated to a-ketoglutarate (a-KG) by mitochondrial isocitrate dehydrogenase (IDH). In this reaction, one molecule of CO2 is released and one molecule of NAD+ is reduced to NADH. In the next step, a-KG is further decarboxylated to succinyl-CoA by a-KG dehydrogenase (a-KGDH) complex, with the release of a second molecule of CO2 and the production of a further molecule of NADH. The second part of the TCA cycle consists of a set of reactions aimed at oxidising

http://dx.doi.org/10.1016/j.canlet.2014.02.023 0304-3835/Ó 2014 Elsevier Ireland Ltd. All rights reserved.

Please cite this article in press as: E. Desideri et al., Mitochondrial dysfunctions in cancer: Genetic defects and oncogenic signaling impinging on TCA cycle activity, Cancer Lett. (2014), http://dx.doi.org/10.1016/j.canlet.2014.02.023

2

E. Desideri et al. / Cancer Letters xxx (2014) xxx–xxx

Fig. 1. Oncogenes and tumour suppressors tune the TCA cycle. TCA cycle alterations induced by oncogenes and tumour suppressors are shown. The tumour suppressor p53 represses ACO2 expression and the TCA cycle-related enzyme ME1. HIF1-a upregulates PDK1 expression and indirectly downregulates ACO2. Myc upregulation replenishes TCA cycle by increasing GLS expression.

succinyl-CoA to restore oxaloacetate. Succinyl-CoA is transformed to succinate by succinate-CoA ligase (SUCL), also known as succinate-CoA synthetase. SUCL is a dimeric protein consisting of one a subunit (SUCL1) and one of b subunits, that can be either the ADP-forming (SUCLA2) or the GDP-forming (SUCLG2); the nucleotide, ATP or GTP, generated in the reaction, depends on the type of the b subunit present. Succinate is then oxidised to fumarate by succinate dehydrogenase (SDH), which also represents the complex II of the ETC. In this step, a molecule of FADH2 is produced. Then fumarate is hydrated to malate by fumarate hydratase (FH) and finally malate is oxidised by malate dehydrogenase to restore oxaloacetate. Besides being a central pathway for energetic metabolism, the TCA cycle provides metabolic intermediates for biosynthetic reactions (cataplerosis) leading to the de novo synthesis of proteins, lipids and nucleic acids. This property is particularly exploited by fast-proliferating cells, such as tumour cells, which require a continuous production of biomass to sustain their accelerated growth rate. Citrate can be exported to the cytosol where it is cleaved by ATP-citrate lyase (ACLY) to acetyl-CoA and oxaloacetate. While acetyl-CoA is essential to sustain the de novo fatty acid synthesis, oxaloacetate can be converted to malate and then to pyruvate, with the concomitant production of NAD+ and NADPH, two essential cofactors for glycolysis and for the antioxidant defense, respectively [6]. a-KG and oxaloacetate can be converted into their related aminoacids, glutamate and aspartate, by glutamate dehydrogenase and aspartate aminotransferase, and these amino acids can act as precursors for the synthesis of other amino acids and for the de novo synthesis of purines. Finally, succinyl-CoA is an intermediate in porphyrin and heme synthesis [7], whose increase is a hallmark of some tumour types, such as human breast carcinoma and non-small-cell lung cancer [8,9].

Although many cancer cells rely primarily on glycolysis, rather than on OXPHOS to produce ATP [10–12], on the basis of what is mentioned above the TCA cycle must be preserved to avoid the depletion of its intermediates. In particular, different reactions (anaplerosis) which refill and maintain the TCA cycle are induced to comply with this condition. Two of the most important anaplerotic reactions are the ATP-dependent carboxylation of pyruvate to oxaloacetate by pyruvate carboxylase, and the conversion of glutamate, mainly deriving from the deamination of glutamine by glutaminase 1, to a-KG by glutamate dehydrogenase [2,13].

3. Genetic defects in the TCA cycle are linked to cancer occurrence Genetic defects have been found to affect TCA cycle components and to be responsible for the onset of a number of diseases, mainly the neurodegenerative ones. Fumarate hydratase autosomic recessive mutations cause severe and early encephalopathy [14]. Patients with an inherited deficiency of a-KGDH present a progressive, severe encephalopathy with axial hypotonia and psychotic behaviour [15], while mutations in the gene encoding for SUCLA2, have been found in patients affected by encephalomyopathy and mitochondrial DNA (mtDNA) depletion [16]. Despite the strong connection between TCA cycle alterations and pathological conditions, the connection between tumourigenesis and cancer progression remained elusive for long time. Indeed, only recently the development of some tumour types has been linked to dominant mutations of genes encoding for three TCA cycle enzymes, IDH, SDH and FH, paving the way for investigations about metabolic enzymes-mediated oncogenesis [17–19].

Please cite this article in press as: E. Desideri et al., Mitochondrial dysfunctions in cancer: Genetic defects and oncogenic signaling impinging on TCA cycle activity, Cancer Lett. (2014), http://dx.doi.org/10.1016/j.canlet.2014.02.023

E. Desideri et al. / Cancer Letters xxx (2014) xxx–xxx

3.1. Isocitrate dehydrogenase There are three isoforms of IDH encoded by the nuclear genome: IDH1 and IDH2 are NADP+-dependent homodimeric enzymes located in the cytosol and the mitochondria, respectively, whereas the NAD+-dependent IDH3 is a mitochondrial heterotetrameric enzyme and the most active in the TCA cycle under physiological conditions [20]. While no correlation between IDH3 mutations and cancer promotion has been documented so far [21], mutations in IDH1 and IDH2 were found in 70% of grade II– III gliomas and secondary glioblastomas [19,22], as well as in a small fraction (about 16–17%) of acute myeloid leukemia patients [23]. Moreover, mutations in IDH1 and IDH2 are associated with tumours of other tissues such as thyroid and prostate, even if at lower frequencies [24,25]. The main IDH mutations identified in some of the described tumours are changes of the amino acid residues R132 in IDH1 and R172 or R140 in IDH2 [26]. These mutations confer a neomorphic catalytic activity to the enzyme, consisting in the capability to convert a-KG into (R)-2-hydroxyglutaric acid ((R)-2HG), which has been demonstrated to be an oncometabolite that drives the transformation of human astrocytes and the acquisition of a cancerous phenotype [26,27]. 3.2. Succinate dehydrogenase SDH is a nuclear genome–encoded enzyme made of four subunits (named A–D) [28]. This is one of the few TCA cycle enzymes which does not have a cytosolic counterpart. The first evidence of a connection between SDH mutations and cancer development emerged ten years ago when dominant mutations in subunits SDHB, SDHC and SDHD were found in hereditary paragangliomas and adrenal gland pheochromocytomas [29–31]. More recently, also mutations in SDHA have been associated with these tumour types [32], and a link between mutations in SHDB and renal cell carcinoma or T cell acute leukemia also exists [28,33,34]. Moreover, mutations in SDH genes correlate with the development of tumours of gastrointestinal, testicular and renal tissues [28]. Defects in the SDHB gene are mainly missense and nonsense mutations, while only nonsense mutations have been found in the SDHD gene [35]. 3.3. Fumarate hydratase The two FH isoforms encoded by the FH gene present a distinct sub-cellular localisation (i.e. cytosolic and mitochondrial) and both function as homotetramers [36]. Dominant mutations in the FH gene, the majority of which are missense mutations, predispose to tumour formation, whereas recessive mutations cause early death and acute encephalopathies [18,37]. FH mutations are associated with predisposition to multiple cutaneous and uterine leiomyomas, hereditary leiomyomatosis and renal cell cancer, with the latter being particularly aggressive [18,38,39]. Other tumours associated with FH defects include Leydig cell tumours, ovary cystadenomas, cerebral cavernomas, uterine leiomyosarcomas and breast cancer [40]. Patients with FH mutations show reduced mitochondrial FH activity, and no detectable cytosolic enzyme suggesting that the tumour suppressor role of FH is associated with the cytoplasmic isoform [41]. 4. Mechanisms linking TCA cycle genetic alterations and cancer It is well established that mutations in the three TCA cycle enzymes described above cause several intracellular alterations, such as the accumulation of TCA cycle metabolites, which can favour cancer occurrence. The most validated lines of evidence

3

show a direct link between TCA cycle defects, prolyl hydroxylases (PHDs) and cancer. Moreover, TCA cycle defects indirectly modulate the intracellular redox state, which in turn may provide the optimal environment for the formation and progression of tumours. 4.1. Prolyl hydroxylases, HIF1-a and the hypoxic response Paragangliomas, developing in patients showing SDH defects, are frequent clinical presentations of people living at high altitude who are exposed to a chronic hypoxic environment. This evidence suggested a possible link between SDH mutations and the cellular pathways of hypoxic response [20]. Selak and colleagues were the first to demonstrate that SDH-deficient cells accumulate the hypoxic inducible factor 1 (HIF1, the main transcription factor regulating the hypoxic response [42]. It is well-known that the hypoxic response is a common hallmark of tumours since it promotes, for instance, metabolic adaptations (i.e. aerobic glycolysis) and angiogenesis [43]. These and other observations highlighted the evidence that defects of TCA cycle enzymes are correlated to cancer by a mechanism that takes advantage of the hypoxic response. Under normoxia two proline residues in the a subunit of HIF1 are hydroxylated by PHDs, a family of enzymes catalysing the hydroxylation of a large class of substrates with the concomitant oxidation of a-KG to succinate. Once hydroxylated, HIF1-a is degraded via the proteasome through a mechanism driven by the E3-ubiquitin ligase pVHL (encoded by the von Hippel-Lindau gene). Under hypoxic conditions or decreased a-KG levels, HIF1a is no longer degraded, thereby accumulating in the nucleus where it can manage the hypoxic response via the transcription of a specific set of genes [44]. Pseudohypoxia is a very frequent condition in tumour tissues, since cells adopt a hypoxic phenotype even in presence of normal oxygen tension. The notion that a-KG and succinate are involved in the reaction catalysed by PHDs clearly shows that the TCA cycle is strictly connected to the regulation of the hypoxic response. This evidence has been strengthened by the demonstration that succinate, fumarate and oxalacetate can inhibit PHDs, resulting in the stabilisation of HIF1-a and the activation of the downstream hypoxic pathways [45–48]. As a consequence, succinate and fumarate accumulation, due to SDH and FH deficiencies respectively, as well as decreased a-KG availability resulting from the neomorphic activity of mutated IDH1 and IDH2, can all promote pseudohypoxia and support tumour development and/or growth. So far, it is not yet clear whether the pseudohypoxia response caused by TCA cycle defects is sufficient to promote tumourigenesis or to support tumour progression. However, some recent results are raising the question whether HIF1-a stabilisation can really represent a common feature of all tumour types deriving from TCA cycle defects. Indeed, Koivunen and coworkers demonstrated that HIF1-a acts as suppressor in tumours carrying IDH1/2 mutations as the oncometabolite (R)-2HG also promotes HIF1-a degradation by stabilising PHDs activity [49]. Coherently, they also demonstrated that HIF1a downregulation promoted the transformation and proliferation of astrocytes, thereby confirming a tumour suppressor role of HIF1-a [49]. 4.2. Prolyl hydroxylases and epigenetic regulation PHDs are a large family of hydroxylases with broad-spectrum substrates. Therefore it is plausible that their reduced activity is associated with tumourigenesis in a way independent of HIF1-a and pseudohypoxic phenotype [50]. For instance, in SDH mutants, succinate accumulation inhibits the activity of EglN3, a prolyl hydroxylase necessary for the apoptotic cell death of some neuronal precursor cells occurring during development, thus potentially

Please cite this article in press as: E. Desideri et al., Mitochondrial dysfunctions in cancer: Genetic defects and oncogenic signaling impinging on TCA cycle activity, Cancer Lett. (2014), http://dx.doi.org/10.1016/j.canlet.2014.02.023

4

E. Desideri et al. / Cancer Letters xxx (2014) xxx–xxx

facilitating carcinogenesis in these cells [51]. Another pseudohypoxia-independent mechanism linking the TCA cycle to tumours involves epigenetic regulation that controls gene transcriptional activities through chemical modifications of DNA or histones. For instance, in IDH1/2-deficient models, increased levels of (R)-2HG inhibit the Ten-Eleven Translocation (TET) family of 5-methylcytosine (5mC) hydroxylases, which catalyse the a-KG-dependent removal of methyl groups on DNA [52]. Interestingly, the accumulation of both fumarate and succinate can modulate gene expression by inhibiting the activity of TETs, as well as that of the histone demethylases Jumonji C-terminal domain, which demethylate substrates after having operated an a-KG-dependent hydroxylation [53–55]. 4.3. Intracellular redox state It has been known for many years that pro-oxidant conditions, in particular induced by mitochondria-deriving reactive oxygen species (ROS), can contribute to tumourigenesis or sustain tumour progression. In fact, many tumour tissues show higher ROS levels, when compared to their normal counterparts [56]. A possible correlation between defects in the TCA cycle and pro-oxidant cellular environment can therefore be envisaged. It has been demonstrated that IDH1/2-mutated cells are characterised by lower levels of glutamate with respect to normal cells, and this amino acid is required for the biosynthesis of glutathione, the most abundant cellular antioxidant [57] that is involved in the regulation of many cellular processes [58,59]. Moreover, mutated IDHs not only have the enzyme’s ability to produce NADPH impaired, but also contribute to NADPH consumption to generate (R)-2-HG [26,27]. Since NADPH is the main upstream electron donor for the maintenance of the whole cellular antioxidant machinery, it is clear how IDH1/2 mutations can modulate the intracellular redox state towards a more oxidising environment [60]. Oxidising conditions can trigger the activation of autophagy [61], a tumour suppressor mechanism that could provide a possible link between (R)-2HG accumulation and tumourigenesis. Indeed, it has recently been demonstrated that glioma cell lines expressing the R132H mutant of IDH1 show an accumulation of the autophagic marker p62 [62], which is a hallmark of defective autophagy and known to drive tumourigenesis [63]. Early studies in Caenorhabditis elegans show that SDHC mutant mev-1 generated superoxide O2 [64,65] thereby indicating that ROS production can be also induced by SDH mutations. Further studies performed in mouse fibroblasts transfected with a murine equivalent of the mev-1 mutant confirmed that it induces increased ROS production and DNA mutation frequency [66]. Conflicting data are, instead, available about the role of FH mutation-dependent fumarate accumulation in modulating the cellular redox state. The strongest evidence came from two separate studies demonstrating that FH defects are associated with a reduced intracellular environment due to the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2), the main transcription factor regulating the antioxidant defense [67,68]. Fumarate accumulation results in succinylation of several cysteine residues of Keap1, the inhibitory partner that physiologically prevents Nrf2 nuclear translocation and activity, thereby resulting in the stabilization of Nrf2 [67,68]. The antioxidant response induced upon FH mutation does not seem to reconcile with the assumption that pro-oxidant conditions favour tumours development. However, it is worthwhile to remind that a highly reducing environment also stimulates cell proliferation and prevents differentiation [69]. This aspect is particularly evident in cancer stem cells, in which the enhanced antioxidant defense and the reduced ROS levels with respect to their normal counterparts, increase the proliferation rate and likely promote the initial events underlying cancer formation [70,71].

5. Beyond genetic defects: oncogenes and tumour suppressors control TCA cycle activity Genetic defects are not the sole alteration resulting in a dysregulated TCA cycle. An aberrant expression of TCA cycle components may represent either a direct or indirect consequence of oncogene activation or mutation of tumour suppressors (Fig. 1). HIF1-a and p53, two master regulators of cell metabolism that are often altered in tumours, are good examples of proteins which have a profound influence on TCA cycle functions. 5.1. Malic enzymes The tumour suppressor p53 is mutated in a great number of tumour types [72,73]. It virtually influences all metabolic pathways, including the TCA cycle. For instance, p53 can suppress the expression of the TCA-related malic enzymes 1 (ME1) and 2 (ME2), which convert malate into pyruvate and represent an important source of NADPH [74]. The expression of MEs is augmented in some tumours, and their overexpression has been shown to accelerate tumour growth in xenograft models [75,76]. On the contrary, the downregulation of MEs reduces tumour cell growth through multiple mechanisms which include the stabilization of p53 and the induction of senescence [74]. The discovery of the mutual regulation of p53 and MEs provides the link between metabolism and senescence and identifies MEs as new potential targets for the development of anticancer strategies. 5.2. Mitochondrial aconitase A recently identified target of p53 in prostate cancer cells is ACO2. Prostate cells produce and secrete great amounts of citrate. This is possible through a limiting ACO2 activity, which results in a reduced conversion of citrate to isocitrate. The crucial role of ACO2 in cancer is revealed by the evidence that an abnormal expression of ACO2 is implicated in the tumourigenesis of prostate [77]. In 2011, Tsui and colleagues revealed a possible rationale for the increased expression of ACO2 mRNA in metastatic prostate cancer cells. They discovered an inverse correlation between p53 expression and ACO2 mRNA levels in human prostate carcinoma cells [78], albeit the molecular mechanism still remains unknown. Multiple cancer-associated alterations that affect ACO2 expression or activity are now emerging. In a very recent paper, Ternette et al. showed that FH-deficient cells present a decrease in ACO2 activity, resulting from the succination of three cysteine residues that are crucial for the iron-sulphur cluster binding [79]. The repression of ACO2 activity may contribute to the metabolic rearrangement observed in many cancer cells and favour cancer development. The evidence that a decreased expression of ACO2 is associated with a poor prognosis in gastric cancer patients [80] is in agreement with this hypothesis. Further evidence supporting the involvement of ACO2 in tumours derives from the discovery that hypoxic conditions upregulate the HIF1-a target miR-210, both in normal and transformed cells, and that miR-210 in turn represses the expression of iron-sulphur cluster assembly proteins. These proteins facilitate the assembly of iron-sulphur clusters incorporated into enzymes involved in mitochondrial metabolism, and their repression interferes with the enzymatic activity of many mitochondrial proteins, including ACO2 [81]. High expression levels of miR-210 are also associated with tumour proliferation and invasion, and with a poor outcome in breast cancer patients [82]. Decreased ACO2 expression results in higher levels of citrate, which can be redirected to the cytosol, thus contributing to restore acetyl-CoA and oxaloacetate pools. Acetyl-CoA generated from citrate is required for the de novo synthesis of fatty acids, which

Please cite this article in press as: E. Desideri et al., Mitochondrial dysfunctions in cancer: Genetic defects and oncogenic signaling impinging on TCA cycle activity, Cancer Lett. (2014), http://dx.doi.org/10.1016/j.canlet.2014.02.023

E. Desideri et al. / Cancer Letters xxx (2014) xxx–xxx

is elevated in many cancer cells to meet the high demand for substrates required for the production of biomass. The occurrence of a lipogenic phenotype is increasingly considered as a new hallmark of many cancer cells and is an appealing target for the development of novel anticancer therapies [83]. In this context, targeting citrate metabolism has already revealed promising results in both in vitro and in vivo studies. For instance, the inhibition of the citrate carrier restrains tumour proliferation in vitro and, similarly, the inhibition of ACLY, which converts citrate to acetyl-CoA and oxaloacetate, impairs the growth and induces the differentiation of many glycolytic tumours [84,85]. Interestingly, a very recent finding revealed that ACLY inhibition reduced the population of cancer stem cells in many cell lines with a broad range of genetic backgrounds [86]. Although this work has been performed exclusively in vitro, the widespread applicability, together with the intriguing possibility to target cancer stem cells, which are an underlying cause of chemotherapy resistance and cancer recurrence [87], may provide new opportunities for the development of a highly effective therapy. 5.3. Pyruvate dehydrogenase kinase 1 The activation of HIF1-a is critical for the metabolic reprogramming of cancer cells, and usually results in the upregulation of many glycolytic enzymes and the repression of the activity of the TCA cycle [88]. One of the well documented effects of HIF1-a upregulation is the transactivation of the gene encoding for pyruvate dehydrogenase kinase 1 (PDK1), which phosphorylates a serine residue on pyruvate dehydrogenase, thereby repressing its activity [89]. The overexpression of PDK1 is widespread in a large number of tumour types and is a key regulatory switch contributing to the well-known glycolytic phenotype characteristic of many cancer and proliferating cells (the Warburg’s effect) [90,91]. Indeed, PDK1 overexpression attenuates the flux of pyruvate through the TCA cycle and favours pyruvate conversion to lactate by lactate dehydrogenase to restore NAD+ required for glycolysis. Although the enhancement of glycolysis confers several metabolic advantages to cancer cells, the reduction of pyruvate entry into the TCA cycle causes a depletion of TCA cycle intermediates, thus limiting the availability of precursors for lipid, protein and nucleic acid synthesis. Therefore the TCA cycle must be maintained fully functional and constantly replenished with its intermediates. In this context, the role of the oncogene Myc is crucial. Indeed, Myc regulates the expression of the enzyme glutaminase, which catalyses the first step of glutamine entry into the TCA cycle in the form of a-KG [92]. This key role of glutamine in maintaining a fully functional TCA cycle, in addition to its role as substrate for nucleic acid, glutathione and hexosamine synthesis, explains the extreme addiction to glutamine exhibited by many cancer cells [93]. 6. Concluding remarks The TCA cycle represents the core of oxidative metabolism. Indeed, it is at the crossroads of two of the main metabolic routes, glycolysis and lipid b-oxidation. Alterations of TCA cycle components have long been known to correlate with the most diverse pathologies, including neurodegeneration and cancer. Three germline dominant mutations of TCA cycle components (SDH, FH and IDH) have been discovered and associated with the pathogenesis of some tumours. Mutations of these enzymes result in the accumulation of metabolites that activate HIF1-a (SDH and FH) or that are not present in normal conditions (IDH). Besides being involved in tumourigenesis, alterations of TCA cycle components can be the result of oncogene activation (e.g. HIF1-a, Myc) or mutation of tumour suppressors (e.g. p53). In this scenario, ACO2

5

is a good example of an enzyme dysregulated in some types of cancer and whose regulation is under the control of oncogenes and tumour suppressors, HIF1-a and p53, respectively. The advantage of ACO2 upregulation in cancer might be found in the accumulation of citrate, which can be exported to the cytosol and used as precursor for lipid and NADPH biosynthesis, molecules that are required for tumour proliferation. Citrate export to the cytosol reveals a critical role of the TCA cycle in sustaining tumour growth. Indeed, despite many tumour cells preferentially use glycolysis instead of OXPHOS for the production of ATP, the TCA cycle provides many intermediates which are constantly drained by anabolic reactions. The impoverishment of the TCA cycle must therefore be compensated by the continuous refill of its intermediates through anaplerotic reactions. In the absence of sufficient replenishments, the TCA cycle would not work properly, resulting in the inadequate supply of biomass for cancer cell growth. This aspect paves the way for therapeutic strategies targeting enzymes involved in anaplerotic reactions, which could exploit the extreme addiction of cancer cells to biosynthetic precursors, in the absence of which the proliferation rate and the viability will be strongly compromised. Acknowledgments This work was partially supported by Grants from Associazione Italiana per la Ricerca sul Cancro (AIRC, IG 10636) and Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR). References [1] C. Wang, R.J. Youle, The role of mitochondria in apoptosis*, Annu. Rev. Genet. 43 (2009) 95–118. [2] O.E. Owen, S.C. Kalhan, R.W. Hanson, The key role of anaplerosis and cataplerosis for citric acid cycle function, J. Biol. Chem. 277 (2002) 30409– 30412. [3] J. Nunnari, A. Suomalainen, Mitochondria: in sickness and in health, Cell 148 (2012) 1145–1159. [4] M. Brandon, P. Baldi, D.C. Wallace, Mitochondrial mutations in cancer, Oncogene 25 (2006) 4647–4662. [5] J.C. Bournat, C.W. Brown, Mitochondrial dysfunction in obesity, Curr. Opin. Endocrinol. Diabetes Obesity 17 (2010) 446–452. [6] D.C. Wallace, W. Fan, V. Procaccio, Mitochondrial energetics and therapeutics, Annu. Rev. Pathol. 5 (2010) 297–348. [7] R.F. Labbe, T. Kurumada, J. Onisawa, The role of succinyl-CoA synthetase in the control of heme biosynthesis, Biochim. Biophys. Acta 111 (1965) 403–415. [8] J. Hooda, D. Cadinu, M.M. Alam, A. Shah, T.M. Cao, L.A. Sullivan, R. Brekken, L. Zhang, Enhanced heme function and mitochondrial respiration promote the progression of lung cancer cells, PLoS ONE 8 (2013) e63402. [9] N.M. Navone, C.F. Polo, A.L. Frisardi, N.E. Andrade, A.M. Battle, Heme biosynthesis in human breast cancer–mimetic ‘‘in vitro’’ studies and some heme enzymic activity levels, Int. J. Biochem. 22 (1990) 1407–1411. [10] J. Zheng, Energy metabolism of cancer: glycolysis versus oxidative phosphorylation (review), Oncol. Lett. 4 (2012) 1151–1157. [11] D.A. Scott, A.D. Richardson, F.V. Filipp, C.A. Knutzen, G.G. Chiang, Z.A. Ronai, A.L. Osterman, J.W. Smith, Comparative metabolic flux profiling of melanoma cell lines: beyond the Warburg effect, J. Biol. Chem. 286 (2011) 42626–42634. [12] D. Hanahan, R.A. Weinberg, Hallmarks of cancer: the next generation, Cell 144 (2011) 646–674. [13] S. Jitrapakdee, A. Vidal-Puig, J.C. Wallace, Anaplerotic roles of pyruvate carboxylase in mammalian tissues, Cell. Mol. Life Sci. 63 (2006) 843–854. [14] A.G. Saini, P. Singhi, Infantile metabolic encephalopathy due to fumarase deficiency, J. Child Neurol. 28 (2013) 535–537. [15] N. Guffon, C. Lopez-Mediavilla, R. Dumoulin, B. Mousson, C. Godinot, H. Carrier, J.M. Collombet, P. Divry, M. Mathieu, P. Guibaud, 2-Ketoglutarate dehydrogenase deficiency, a rare cause of primary hyperlactataemia: report of a new case, J. Inherit. Metab. Dis. 16 (1993) 821–830. [16] R. Carrozzo, C. Dionisi-Vici, U. Steuerwald, S. Lucioli, F. Deodato, S. Di Giandomenico, E. Bertini, B. Franke, L.A. Kluijtmans, M.C. Meschini, C. Rizzo, F. Piemonte, R. Rodenburg, R. Santer, F.M. Santorelli, A. van Rooij, D. Vermuntde Koning, E. Morava, R.A. Wevers, SUCLA2 mutations are associated with mild methylmalonic aciduria, Leigh-like encephalomyopathy, dystonia and deafness, Brain 130 (2007) 862–874. [17] B.E. Baysal, R.E. Ferrell, J.E. Willett-Brozick, E.C. Lawrence, D. Myssiorek, A. Bosch, A. van der Mey, P.E. Taschner, W.S. Rubinstein, E.N. Myers, C.W. Richard 3rd, C.J. Cornelisse, P. Devilee, B. Devlin, Mutations in SDHD, a mitochondrial complex II gene, in hereditary paraganglioma, Science 287 (2000) 848–851.

Please cite this article in press as: E. Desideri et al., Mitochondrial dysfunctions in cancer: Genetic defects and oncogenic signaling impinging on TCA cycle activity, Cancer Lett. (2014), http://dx.doi.org/10.1016/j.canlet.2014.02.023

6

E. Desideri et al. / Cancer Letters xxx (2014) xxx–xxx

[18] I.P. Tomlinson, N.A. Alam, A.J. Rowan, E. Barclay, E.E. Jaeger, D. Kelsell, I. Leigh, P. Gorman, H. Lamlum, S. Rahman, R.R. Roylance, S. Olpin, S. Bevan, K. Barker, N. Hearle, R.S. Houlston, M. Kiuru, R. Lehtonen, A. Karhu, S. Vilkki, P. Laiho, C. Eklund, O. Vierimaa, K. Aittomaki, M. Hietala, P. Sistonen, A. Paetau, R. Salovaara, R. Herva, V. Launonen, L.A. Aaltonen, Germline mutations in FH predispose to dominantly inherited uterine fibroids, skin leiomyomata and papillary renal cell cancer, Nat. Genet. 30 (2002) 406–410. [19] H. Yan, D.W. Parsons, G. Jin, R. McLendon, B.A. Rasheed, W. Yuan, I. Kos, I. Batinic-Haberle, S. Jones, G.J. Riggins, H. Friedman, A. Friedman, D. Reardon, J. Herndon, K.W. Kinzler, V.E. Velculescu, B. Vogelstein, D.D. Bigner, IDH1 and IDH2 mutations in gliomas, N. Engl. J. Med. 360 (2009) 765–773. [20] N. Raimundo, B.E. Baysal, G.S. Shadel, Revisiting the TCA cycle: signaling to tumor formation, Trends Mol. Med. 17 (2011) 641–649. [21] D. Krell, M. Assoku, M. Galloway, P. Mulholland, I. Tomlinson, C. Bardella, Screen for IDH1, IDH2, IDH3, D2HGDH and L2HGDH mutations in glioblastoma, PLoS ONE 6 (2011) e19868. [22] D.W. Parsons, S. Jones, X. Zhang, J.C. Lin, R.J. Leary, P. Angenendt, P. Mankoo, H. Carter, I.M. Siu, G.L. Gallia, A. Olivi, R. McLendon, B.A. Rasheed, S. Keir, T. Nikolskaya, Y. Nikolsky, D.A. Busam, H. Tekleab, L.A. Diaz Jr., J. Hartigan, D.R. Smith, R.L. Strausberg, S.K. Marie, S.M. Shinjo, H. Yan, G.J. Riggins, D.D. Bigner, R. Karchin, N. Papadopoulos, G. Parmigiani, B. Vogelstein, V.E. Velculescu, K.W. Kinzler, An integrated genomic analysis of human glioblastoma multiforme, Science 321 (2008) 1807–1812. [23] L. Dang, S. Jin, S.M. Su, IDH mutations in glioma and acute myeloid leukemia, Trends Mol. Med. 16 (2010) 387–397. [24] M.R. Kang, M.S. Kim, J.E. Oh, Y.R. Kim, S.Y. Song, S.I. Seo, J.Y. Lee, N.J. Yoo, S.H. Lee, Mutational analysis of IDH1 codon 132 in glioblastomas and other common cancers, Int. J. Cancer 125 (2009) 353–355. [25] K.E. Yen, M.A. Bittinger, S.M. Su, V.R. Fantin, Cancer-associated IDH mutations: biomarker and therapeutic opportunities, Oncogene 29 (2010) 6409–6417. [26] L. Dang, D.W. White, S. Gross, B.D. Bennett, M.A. Bittinger, E.M. Driggers, V.R. Fantin, H.G. Jang, S. Jin, M.C. Keenan, K.M. Marks, R.M. Prins, P.S. Ward, K.E. Yen, L.M. Liau, J.D. Rabinowitz, L.C. Cantley, C.B. Thompson, M.G. Vander Heiden, S.M. Su, Cancer-associated IDH1 mutations produce 2hydroxyglutarate, Nature 462 (2009) 739–744. [27] P.S. Ward, J. Patel, D.R. Wise, O. Abdel-Wahab, B.D. Bennett, H.A. Coller, J.R. Cross, V.R. Fantin, C.V. Hedvat, A.E. Perl, J.D. Rabinowitz, M. Carroll, S.M. Su, K.A. Sharp, R.L. Levine, C.B. Thompson, The common feature of leukemiaassociated IDH1 and IDH2 mutations is a neomorphic enzyme activity converting alpha-ketoglutarate to 2-hydroxyglutarate, Cancer Cell 17 (2010) 225–234. [28] C. Bardella, P.J. Pollard, I. Tomlinson, SDH mutations in cancer, Biochim. Biophys. Acta 2011 (1807) 1432–1443. [29] S. Niemann, U. Muller, Mutations in SDHC cause autosomal dominant paraganglioma, type 3, Nat. Genet. 26 (2000) 268–270. [30] D. Astuti, F. Douglas, T.W. Lennard, I.A. Aligianis, E.R. Woodward, D.G. Evans, C. Eng, F. Latif, E.R. Maher, Germline SDHD mutation in familial phaeochromocytoma, Lancet 357 (2001) 1181–1182. [31] B.E. Baysal, J.E. Willett-Brozick, E.C. Lawrence, C.M. Drovdlic, S.A. Savul, D.R. McLeod, H.A. Yee, D.E. Brackmann, W.H. Slattery 3rd, E.N. Myers, R.E. Ferrell, W.S. Rubinstein, Prevalence of SDHB, SDHC, and SDHD germline mutations in clinic patients with head and neck paragangliomas, J. Med. Genet. 39 (2002) 178–183. [32] N. Burnichon, J.J. Briere, R. Libe, L. Vescovo, J. Riviere, F. Tissier, E. Jouanno, X. Jeunemaitre, P. Benit, A. Tzagoloff, P. Rustin, J. Bertherat, J. Favier, A.P. Gimenez-Roqueplo, SDHA is a tumor suppressor gene causing paraganglioma, Hum. Mol. Genet. 19 (2010) 3011–3020. [33] S. Vanharanta, M. Buchta, S.R. McWhinney, S.K. Virta, M. Peczkowska, C.D. Morrison, R. Lehtonen, A. Januszewicz, H. Jarvinen, M. Juhola, J.P. Mecklin, E. Pukkala, R. Herva, M. Kiuru, N.N. Nupponen, L.A. Aaltonen, H.P. Neumann, C. Eng, Early-onset renal cell carcinoma as a novel extraparaganglial component of SDHB-associated heritable paraganglioma, Am. J. Hum. Genet. 74 (2004) 153–159. [34] B.E. Baysal, A recurrent stop-codon mutation in succinate dehydrogenase subunit B gene in normal peripheral blood and childhood T-cell acute leukemia, PLoS ONE 2 (2007) e436. [35] E. Gottlieb, I.P. Tomlinson, Mitochondrial tumour suppressors: a genetic and biochemical update, Nat. Rev. Cancer 5 (2005) 857–866. [36] I.E. Scheffler, Mitochondria, second ed., J. Wiley and Sons Inc, Hoboken, New Jersey, 2008. [37] J.P. Bayley, V. Launonen, I.P. Tomlinson, The FH mutation database: an online database of fumarate hydratase mutations involved in the MCUL (HLRCC) tumor syndrome and congenital fumarase deficiency, BMC Med. Genet. 9 (2008) 20. [38] V. Launonen, O. Vierimaa, M. Kiuru, J. Isola, S. Roth, E. Pukkala, P. Sistonen, R. Herva, L.A. Aaltonen, Inherited susceptibility to uterine leiomyomas and renal cell cancer, Proc. Natl. Acad. Sci. U. S. A. 98 (2001) 3387–3392. [39] M.A. Refae, N. Wong, F. Patenaude, L.R. Begin, W.D. Foulkes, Hereditary leiomyomatosis and renal cell cancer: an unusual and aggressive form of hereditary renal carcinoma, Nat. Clin. Pract. Oncol. 4 (2007) 256–261. [40] H.J. Lehtonen, Hereditary leiomyomatosis and renal cell cancer: update on clinical and molecular characteristics, Familial Cancer 10 (2011) 397–411. [41] N. Raimundo, J. Ahtinen, K. Fumic, I. Baric, A.M. Remes, R. Renkonen, R. Lapatto, A. Suomalainen, Differential metabolic consequences of fumarate hydratase and respiratory chain defects, Biochim. Biophys. Acta 1782 (2008) 287–294.

[42] M.A. Selak, S.M. Armour, E.D. MacKenzie, H. Boulahbel, D.G. Watson, K.D. Mansfield, Y. Pan, M.C. Simon, C.B. Thompson, E. Gottlieb, Succinate links TCA cycle dysfunction to oncogenesis by inhibiting HIF-alpha prolyl hydroxylase, Cancer Cell 7 (2005) 77–85. [43] A.J. Majmundar, W.J. Wong, M.C. Simon, Hypoxia-inducible factors and the response to hypoxic stress, Mol. Cell 40 (2010) 294–309. [44] K. Tanimoto, Y. Makino, T. Pereira, L. Poellinger, Mechanism of regulation of the hypoxia-inducible factor-1 alpha by the von Hippel–Lindau tumor suppressor protein, EMBO J. 19 (2000) 4298–4309. [45] L. O’Flaherty, J. Adam, L.C. Heather, A.V. Zhdanov, Y.L. Chung, M.X. Miranda, J. Croft, S. Olpin, K. Clarke, C.W. Pugh, J. Griffiths, D. Papkovsky, H. Ashrafian, P.J. Ratcliffe, P.J. Pollard, Dysregulation of hypoxia pathways in fumarate hydratase-deficient cells is independent of defective mitochondrial metabolism, Hum. Mol. Genet. 19 (2010) 3844–3851. [46] O. Yogev, E. Singer, E. Shaulian, M. Goldberg, T.D. Fox, O. Pines, Fumarase: a mitochondrial metabolic enzyme and a cytosolic/nuclear component of the DNA damage response, PLoS Biol. 8 (2010) e1000328. [47] J.S. Isaacs, Y.J. Jung, D.R. Mole, S. Lee, C. Torres-Cabala, Y.L. Chung, M. Merino, J. Trepel, B. Zbar, J. Toro, P.J. Ratcliffe, W.M. Linehan, L. Neckers, HIF overexpression correlates with biallelic loss of fumarate hydratase in renal cancer: novel role of fumarate in regulation of HIF stability, Cancer Cell 8 (2005) 143–153. [48] P. Koivunen, M. Hirsila, A.M. Remes, I.E. Hassinen, K.I. Kivirikko, J. Myllyharju, Inhibition of hypoxia-inducible factor (HIF) hydroxylases by citric acid cycle intermediates: possible links between cell metabolism and stabilization of HIF, J. Biol. Chem. 282 (2007) 4524–4532. [49] P. Koivunen, S. Lee, C.G. Duncan, G. Lopez, G. Lu, S. Ramkissoon, J.A. Losman, P. Joensuu, U. Bergmann, S. Gross, J. Travins, S. Weiss, R. Looper, K.L. Ligon, R.G. Verhaak, H. Yan, W.G. Kaelin Jr., Transformation by the (R)-enantiomer of 2hydroxyglutarate linked to EGLN activation, Nature 483 (2012) 484–488. [50] A. Ozer, R.K. Bruick, Non-heme dioxygenases: cellular sensors and regulators jelly rolled into one?, Nat Chem. Biol. 3 (2007) 144–153. [51] S. Lee, E. Nakamura, H. Yang, W. Wei, M.S. Linggi, M.P. Sajan, R.V. Farese, R.S. Freeman, B.D. Carter, W.G. Kaelin Jr., S. Schlisio, Neuronal apoptosis linked to EglN3 prolyl hydroxylase and familial pheochromocytoma genes: developmental culling and cancer, Cancer Cell 8 (2005) 155–167. [52] M.E. Figueroa, O. Abdel-Wahab, C. Lu, P.S. Ward, J. Patel, A. Shih, Y. Li, N. Bhagwat, A. Vasanthakumar, H.F. Fernandez, M.S. Tallman, Z. Sun, K. Wolniak, J.K. Peeters, W. Liu, S.E. Choe, V.R. Fantin, E. Paietta, B. Lowenberg, J.D. Licht, L.A. Godley, R. Delwel, P.J. Valk, C.B. Thompson, R.L. Levine, A. Melnick, Leukemic IDH1 and IDH2 mutations result in a hypermethylation phenotype, disrupt TET2 function, and impair hematopoietic differentiation, Cancer Cell 18 (2010) 553–567. [53] A.M. Cervera, J.P. Bayley, P. Devilee, K.J. McCreath, Inhibition of succinate dehydrogenase dysregulates histone modification in mammalian cells, Mol. Cancer 8 (2009) 89. [54] E.H. Smith, R. Janknecht, L.J. Maher 3rd, Succinate inhibition of alphaketoglutarate-dependent enzymes in a yeast model of paraganglioma, Hum. Mol. Genet. 16 (2007) 3136–3148. [55] M. Xiao, H. Yang, W. Xu, S. Ma, H. Lin, H. Zhu, L. Liu, Y. Liu, C. Yang, Y. Xu, S. Zhao, D. Ye, Y. Xiong, K.L. Guan, Inhibition of alpha-KG-dependent histone and DNA demethylases by fumarate and succinate that are accumulated in mutations of FH and SDH tumor suppressors, Genes Dev. 26 (2012) 1326– 1338. [56] S. Toyokuni, K. Okamoto, J. Yodoi, H. Hiai, Persistent oxidative stress in cancer, FEBS Lett. 358 (1995) 1–3. [57] Z.J. Reitman, G. Jin, E.D. Karoly, I. Spasojevic, J. Yang, K.W. Kinzler, Y. He, D.D. Bigner, B. Vogelstein, H. Yan, Profiling the effects of isocitrate dehydrogenase 1 and 2 mutations on the cellular metabolome, Proc. Natl. Acad. Sci. U. S. A. 108 (2011) 3270–3275. [58] R. Franco, J.A. Cidlowski, Apoptosis and glutathione: beyond an antioxidant, Cell Death Differ. 16 (2009) 1303–1314. [59] E. Desideri, G. Filomeni, M.R. Ciriolo, Glutathione participates in the modulation of starvation-induced autophagy in carcinoma cells, Autophagy 8 (2012) 1769–1781. [60] G. Filomeni, G. Rotilio, M.R. Ciriolo, Disulfide relays and phosphorylative cascades: partners in redox-mediated signaling pathways, Cell Death Differ. 12 (2005) 1555–1563. [61] G. Filomeni, E. Desideri, S. Cardaci, G. Rotilio, M.R. Ciriolo, Under the ROS...thiol network is the principal suspect for autophagy commitment, Autophagy 6 (2010) 999–1005. [62] M.R. Gilbert, Y. Liu, J. Neltner, H. Pu, A. Morris, M. Sunkara, T. Pittman, N. Kyprianou, C. Horbinski, Autophagy and oxidative stress in gliomas with IDH1 mutations, Acta Neuropathol. (Berl.) (2013). [63] R. Mathew, C.M. Karp, B. Beaudoin, N. Vuong, G. Chen, H.Y. Chen, K. Bray, A. Reddy, G. Bhanot, C. Gelinas, R.S. Dipaola, V. Karantza-Wadsworth, E. White, Autophagy suppresses tumorigenesis through elimination of p62, Cell 137 (2009) 1062–1075. [64] N. Ishii, M. Fujii, P.S. Hartman, M. Tsuda, K. Yasuda, N. Senoo-Matsuda, S. Yanase, D. Ayusawa, K. Suzuki, A mutation in succinate dehydrogenase cytochrome b causes oxidative stress and ageing in nematodes, Nature 394 (1998) 694–697. [65] N. Senoo-Matsuda, K. Yasuda, M. Tsuda, T. Ohkubo, S. Yoshimura, H. Nakazawa, P.S. Hartman, N. Ishii, A defect in the cytochrome b large subunit in complex II causes both superoxide anion overproduction and abnormal

Please cite this article in press as: E. Desideri et al., Mitochondrial dysfunctions in cancer: Genetic defects and oncogenic signaling impinging on TCA cycle activity, Cancer Lett. (2014), http://dx.doi.org/10.1016/j.canlet.2014.02.023

E. Desideri et al. / Cancer Letters xxx (2014) xxx–xxx

[66]

[67]

[68]

[69]

[70]

[71]

[72]

[73] [74]

[75]

[76]

[77]

[78]

energy metabolism in caenorhabditis elegans, J. Biol. Chem. 276 (2001) 41553–41558. T. Ishii, K. Yasuda, A. Akatsuka, O. Hino, P.S. Hartman, N. Ishii, A mutation in the SDHC gene of complex II increases oxidative stress, resulting in apoptosis and tumorigenesis, Cancer Res. 65 (2005) 203–209. J. Adam, E. Hatipoglu, L. O’Flaherty, N. Ternette, N. Sahgal, H. Lockstone, D. Baban, E. Nye, G.W. Stamp, K. Wolhuter, M. Stevens, R. Fischer, P. Carmeliet, P.H. Maxwell, C.W. Pugh, N. Frizzell, T. Soga, B.M. Kessler, M. El-Bahrawy, P.J. Ratcliffe, P.J. Pollard, Renal cyst formation in Fh1-deficient mice is independent of the Hif/Phd pathway: roles for fumarate in KEAP1 succination and Nrf2 signaling, Cancer Cell 20 (2011) 524–537. A. Ooi, J.C. Wong, D. Petillo, D. Roossien, V. Perrier-Trudova, D. Whitten, B.W. Min, M.H. Tan, Z. Zhang, X.J. Yang, M. Zhou, B. Gardie, V. Molinie, S. Richard, P.H. Tan, B.T. Teh, K.A. Furge, An antioxidant response phenotype shared between hereditary and sporadic type 2 papillary renal cell carcinoma, Cancer Cell 20 (2011) 511–523. F.Q. Schafer, G.R. Buettner, Redox environment of the cell as viewed through the redox state of the glutathione disulfide/glutathione couple, Free Radical Biol. Med. 30 (2001) 1191–1212. M. Diehn, R.W. Cho, N.A. Lobo, T. Kalisky, M.J. Dorie, A.N. Kulp, D. Qian, J.S. Lam, L.E. Ailles, M. Wong, B. Joshua, M.J. Kaplan, I. Wapnir, F.M. Dirbas, G. Somlo, C. Garberoglio, B. Paz, J. Shen, S.K. Lau, S.R. Quake, J.M. Brown, I.L. Weissman, M.F. Clarke, Association of reactive oxygen species levels and radioresistance in cancer stem cells, Nature 458 (2009) 780–783. T. Ishimoto, O. Nagano, T. Yae, M. Tamada, T. Motohara, H. Oshima, M. Oshima, T. Ikeda, R. Asaba, H. Yagi, T. Masuko, T. Shimizu, T. Ishikawa, K. Kai, E. Takahashi, Y. Imamura, Y. Baba, M. Ohmura, M. Suematsu, H. Baba, H. Saya, CD44 variant regulates redox status in cancer cells by stabilizing the xCT subunit of system xc(-) and thereby promotes tumor growth, Cancer cell 19 (2011) 387–400. M. Olivier, M. Hollstein, P. Hainaut, TP53 mutations in human cancers: origins, consequences, and clinical use, Cold Spring Harb. Perspect. Biol. 2 (2010) a001008. P.A. Muller, K.H. Vousden, P53 mutations in cancer, Nat. Cell Biol. 15 (2013) 2– 8. P. Jiang, W. Du, A. Mancuso, K.E. Wellen, X. Yang, Reciprocal regulation of p53 and malic enzymes modulates metabolism and senescence, Nature 493 (2013) 689–693. W.J. Wasilenko, A.C. Marchok, Malic enzyme and malate dehydrogenase activities in rat tracheal epithelial cells during the progression of neoplasia, Cancer Lett. 28 (1985) 35–42. L.A. Sauer, R.T. Dauchy, W.O. Nagel, H.P. Morris, Mitochondrial malic enzymes. Mitochondrial NAD(P)+-dependent malic enzyme activity and malatedependent pyruvate formation are progression-linked in Morris hepatomas, J. Biol. Chem. 255 (1980) 3844–3848. K.K. Singh, M.M. Desouki, R.B. Franklin, L.C. Costello, Mitochondrial aconitase and citrate metabolism in malignant and nonmalignant human prostate tissues, Mol. Cancer 5 (2006) 14. K.H. Tsui, T.H. Feng, Y.F. Lin, P.L. Chang, H.H. Juang, P53 downregulates the gene expression of mitochondrial aconitase in human prostate carcinoma cells, Prostate 71 (2011) 62–70.

7

[79] N. Ternette, M. Yang, M. Laroyia, M. Kitagawa, L. O’Flaherty, K. Wolhulter, K. Igarashi, K. Saito, K. Kato, R. Fischer, A. Berquand, B.M. Kessler, T. Lappin, N. Frizzell, T. Soga, J. Adam, P.J. Pollard, Inhibition of mitochondrial aconitase by succination in fumarate hydratase deficiency, Cell Rep. 3 (2013) 689–700. [80] P. Wang, C. Mai, Y.L. Wei, J.J. Zhao, Y.M. Hu, Z.L. Zeng, J. Yang, W.H. Lu, R.H. Xu, P. Huang, Decreased expression of the mitochondrial metabolic enzyme aconitase (ACO2) is associated with poor prognosis in gastric cancer, Med. Oncol. 30 (2013) 552. [81] S.Y. Chan, Y.Y. Zhang, C. Hemann, C.E. Mahoney, J.L. Zweier, J. Loscalzo, MicroRNA-210 controls mitochondrial metabolism during hypoxia by repressing the iron–sulfur cluster assembly proteins ISCU1/2, Cell Metab. 10 (2009) 273–284. [82] F. Rothe, M. Ignatiadis, C. Chaboteaux, B. Haibe-Kains, N. Kheddoumi, S. Majjaj, B. Badran, H. Fayyad-Kazan, C. Desmedt, A.L. Harris, M. Piccart, C. Sotiriou, Global microRNA expression profiling identifies MiR-210 associated with tumor proliferation, invasion and poor clinical outcome in breast cancer, PLoS ONE 6 (2011) e20980. [83] C.R. Santos, A. Schulze, Lipid metabolism in cancer, FEBS J. 279 (2012) 2610– 2623. [84] G. Hatzivassiliou, F. Zhao, D.E. Bauer, C. Andreadis, A.N. Shaw, D. Dhanak, S.R. Hingorani, D.A. Tuveson, C.B. Thompson, ATP citrate lyase inhibition can suppress tumor cell growth, Cancer Cell 8 (2005) 311–321. [85] O. Catalina-Rodriguez, V.K. Kolukula, Y. Tomita, A. Preet, F. Palmieri, A. Wellstein, S. Byers, A.J. Giaccia, E. Glasgow, C. Albanese, M.L. Avantaggiati, The mitochondrial citrate transporter, CIC, is essential for mitochondrial homeostasis, Oncotarget 3 (2012) 1220–1235. [86] J.I. Hanai, N. Doro, P. Seth, V.P. Sukhatme, ATP citrate lyase knockdown impacts cancer stem cells in vitro, Cell Death Dis. 4 (2013) e696. [87] X. Ning, J. Shu, Y. Du, Q. Ben, Z. Li, Therapeutic strategies targeting cancer stem cells, Cancer Biol. Ther. 14 (2013) 295–303. [88] J. Pouyssegur, F. Dayan, N.M. Mazure, Hypoxia signalling in cancer and approaches to enforce tumour regression, Nature 441 (2006) 437–443. [89] J.W. Kim, I. Tchernyshyov, G.L. Semenza, C.V. Dang, HIF-1-mediated expression of pyruvate dehydrogenase kinase: a metabolic switch required for cellular adaptation to hypoxia, Cell Metab. 3 (2006) 177–185. [90] S. Fujiwara, Y. Kawano, H. Yuki, Y. Okuno, K. Nosaka, H. Mitsuya, H. Hata, PDK1 inhibition is a novel therapeutic target in multiple myeloma, Br. J. Cancer 108 (2013) 170–178. [91] R.A. Cairns, I.S. Harris, T.W. Mak, Regulation of cancer cell metabolism, Nat. Rev. Cancer 11 (2011) 85–95. [92] P. Gao, I. Tchernyshyov, T.C. Chang, Y.S. Lee, K. Kita, T. Ochi, K.I. Zeller, A.M. De Marzo, J.E. Van Eyk, J.T. Mendell, C.V. Dang, c-Myc suppression of miR-23a/b enhances mitochondrial glutaminase expression and glutamine metabolism, Nature 458 (2009) 762–765. [93] D.R. Wise, C.B. Thompson, Glutamine addiction: a new therapeutic target in cancer, Trends Biochem. Sci. 35 (2010) 427–433.

Please cite this article in press as: E. Desideri et al., Mitochondrial dysfunctions in cancer: Genetic defects and oncogenic signaling impinging on TCA cycle activity, Cancer Lett. (2014), http://dx.doi.org/10.1016/j.canlet.2014.02.023