YABBI 6743

No. of Pages 6, Model 5G

15 July 2014 Archives of Biochemistry and Biophysics xxx (2014) xxx–xxx 1

Contents lists available at ScienceDirect

Archives of Biochemistry and Biophysics journal homepage: www.elsevier.com/locate/yabbi

2

Review

5 4 6

Cyclic AMP (cAMP) signaling in melanocytes and melanoma

7

Q1

Carlos Iván Rodríguez, Vijayasaradhi Setaluri ⇑

8

Q2

Molecular and Environmental Toxicology Center, Department of Dermatology, University of Wisconsin, School of Medicine and Public Health, Madison, WI 53706, United States

9 10

a r t i c l e

1 3 2 0 13 14 15 16 17 18 19 20 21 22 23 24

25 26 27 28 29

i n f o

Article history: Received 20 May 2014 and in revised form 30 June 2014 Available online xxxx

Q3

Keywords: Melanocytes Melanoma cAMP signaling PKA PDE CREB MC1R aMSH MAPK BRAFV600E NRASQ61R

a b s t r a c t G-protein coupled receptors (GPCRs), which include melanocortin-1 receptor (MC1R), play a crucial role in melanocytes development, proliferation and differentiation. Activation of the MC1R by the a-melanocyte stimulating hormone (a-MSH) leads to the activation of the cAMP signaling pathway that is mainly associated with differentiation and pigment production. Some MC1R polymorphisms produce cAMP signaling impairment and pigmentary phenotypes such as the red head color and fair skin phenotype (RHC) that is usually associated with higher risk for melanoma development. Despite its importance in melanocyte biology, the role of cAMP signaling cutaneous melanoma is not well understood. Melanoma is primarily driven by mutations in the components of mitogen-activated protein kinases (MAPK) pathway. Increasing evidence, however, now suggests that cAMP signaling also plays an important role in melanoma even though genetic alterations in components of this pathway are note commonly found in melanoma. Here we review these new roles for cAMP in melanoma including its contribution to the notorious treatment resistance of melanoma. Ó 2014 Published by Elsevier Inc.

31 32 33 34 35 36 37 38 39 40 41 42 43 44

45 46 47

Introduction

48

Cutaneous melanoma, which develops from melanocytes in the skin, makes up about 4% of all skin cancers and is the most aggressive among them. Melanoma incidence has been increasing in the last 30 years and currently it is estimated that >60,000 individuals will be diagnosed with this deadly cancer in the United States [1,2]. Long-time survival rates (5 years) for patients with stage III (regional) and stage IV (distant metastatic) melanoma are 62.4% and 16.0% respectively [3] due its resistance to most chemical agents for therapy [4]. Moreover, melanoma survivors are about nine times more susceptible to develop additional melanomas compared to the general population [5]. Genetic alterations that cause dysregulation of mitogen-activated protein kinases (MAPK)1 pathway contribute to the development of about 78% of all melanomas [6,7]. Development, differentiation and functions of normal human melanocytes, on the other hand, are orchestrated in large part by the 30 -50 -cyclic adenosine

49 50 51 52 53 54 55 56 57 58 59 60 61 62

⇑ Corresponding author. Address: Department of Dermatology, School of Medicine and Public Health, University of Wisconsin-Madison, 1300 University Avenue, B-25, Madison, WI 53706, United States. Fax: +1 (608) 263 5223. E-mail address: [email protected] (V. Setaluri). 1 Abbreviations used: GPCRs, G-protein coupled receptors; MC1R, melanocortin-1 receptor; a-MSH, a-melanocyte stimulating hormone; MAPK, mitogen-activated protein kinases; MITF, microphthalmia-associated transcription factor; CREB, cAMP responsive element binding protein; PKA, protein kinase A; MMP2, matrix metalloproteinase 2.

monophosphate (cAMP) signaling. The cAMP pathway is less mitogenic in melanocytes in cell culture [8]; and it is primarily associated with differentiation because it stimulates melanin synthesis [9,10]. However, the role of cAMP in melanoma is not well understood. Some recent studies have described new and important roles for cAMP signaling in melanoma treatment resistance, but its role in the natural history of melanoma remain to be understood. The importance of understanding cAMP signaling in melanoma is highlighted by the observation that there is crosstalk between cAMP signaling and the mitogen-activated protein kinase (MAPK) pathway that transduces growth-stimulating signals from the cell surface receptor tyrosine kinases (RTKs). Here, we review the current knowledge on the role of cAMP signaling in melanocyte biology and its relevance to the better understanding of various aspects of melanoma, from genetic predisposition and malignant transformation of melanocytes to progression and treatment resistance.

63

Components and regulation of melanocytic cAMP signaling

79

Melanocytes, the melanin pigment producing cells in the skin, hair and eyes [11], arise from the neural crest. The Wingless-type (Wnt) signaling pathway plays an important and critical role in melanocyte development by activating a sequence of molecular events that lead to the expression of the microphthalmia-associated transcription factor (MITF), the master regulator of melanocytes [12]. The Wnt signaling pathway, acting through the

80

http://dx.doi.org/10.1016/j.abb.2014.07.003 0003-9861/Ó 2014 Published by Elsevier Inc.

Please cite this article in press as: C.I. Rodríguez, V. Setaluri, Arch. Biochem. Biophys. (2014), http://dx.doi.org/10.1016/j.abb.2014.07.003

64 65 66 67 68 69 70 71 72 73 74 75 76 77 78

81 82 83 84 85 86

YABBI 6743

No. of Pages 6, Model 5G

15 July 2014 2

C.I. Rodríguez, V. Setaluri / Archives of Biochemistry and Biophysics xxx (2014) xxx–xxx

143

Frizzled receptors, cell surface proteins that are members of the large G-protein coupled receptors (GPCRs), causes stabilization of b-catenin, which in turn activates transcription of the melanocyte-lineage specific isoform MITF-M [13–15]. MITF regulates survival and proliferation of melanocytes precursors and pigment production by melanocytes [16,17]. GPCRs, the seven-transmembrane receptors, regulate many physiological processes such as vision, smell, and cell biological processes such as cell growth and adhesion [18,19]. Dysregulation of GPCR signaling causes a variety of inherited and acquired diseases, such as thyroid disorders, congenital night blindness and retinitis pigmentosa [20]. GPCR signaling plays a central role in the biology of melanocytes. Specifically, melanin pigment synthesis is regulated by the activation of the GPCR melanocortin-1 receptor (MC1R) by a-melanocyte stimulating hormone (a-MSH) [21,22]. MC1R signaling activates cAMP signaling cascade leading to expression of genes, including MITF, that contain cAMP responsive element (CRE) in their regulatory region. Single nucleotide polymorphisms in MC1R that affect the receptor activity and impair cAMP signaling produce the red hair color (RHC) and fair skin phenotype [23–25]. These MC1R variant melanocytes are highly sensitive to ultraviolet light (UV) exposure that produces cytotoxic effects compared to wild type MC1R melanocytes [26]. Consequently, these MC1R variants are associated with susceptibility for developing skin cancer, such as squamous cell carcinoma [27] and melanoma [28,29]. The strength of cAMP signaling is determined by the cellular levels of this second messenger that is generated from ATP by the activity of adenylate cyclases (ADCYs) and converted to AMP by phosphodiesterases (PDEs). Therefore, cellular levels of cAMP are determined by the relative activity of ADCYs and PDEs. Upon activation of MC1R by a-MSH, the Gas subunit activates ADCYs, increasing the cAMP levels. The increased cAMP signals the activation of protein kinase A (PKA) which phosphorylates cAMP responsive element binding protein (CREB). CREB is a transcription factor that regulates the expression of MITF by biding to the MITF-M promoter [30]. Intracellular cAMP levels are also regulated by the PDEs, which hydrolyze cAMP and, therefore, lower its concentration [31]. The MAPK pathway regulates many important cellular functions such as proliferation, migration, and differentiation [32]. In melanocytes, c-Kit is an important RTK involved in development [33]. MITF expression is activated also through the c-Kit/MAPK signaling [34]. Binding of mast/stem cell growth factor (SCF/kit ligand) to c-Kit receptor leads to the activation of the small GTPase Rat sarcoma (RAS), which in turn activates the rapid accelerated fibrosarcoma (RAF/MAP3K) kinases family. There are three types of RAF kinases, ARAF, BRAF, and CRAF. BRAF activates (via phosphorylation) the MAPK kinase (MEK/MAP2K), which then activates the MAPK extracellular signal regulated kinases (ERKs) [35]. The RAF kinase CRAF is inhibited by PKA, linking the cAMP signaling with the MAPK in melanocytes [10]. Interestingly, it has been shown that the a-MSH/ MC1R signaling can also trigger the activation of MAPK pathway in a cAMP-independent manner [17], although this is not nearly as robust as that induced by RTK signaling or signaling through the Gq-coupled endothelin B receptor [36]. Fig. 1 summarizes interactions between cAMP signaling and MAPK pathway.

144

Adenylate cyclases (ADCYs)

145

In mammals, there are ten different isoforms of ADCYs (ADCY1– ADCY10). Except for ADCY10 (also known as sAC), which is a soluble isoform, ADCYs consist of an amino-terminus, two repeats of six transmembrane spans (M1 and M2) and two cytoplasmic domains (C1 and C2) that form the catalytic domain. Upon activation of the appropriate GPCR, the Gas subunit binds to the C2

87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142

146 147 148 149 150

domain of the ADCY and induces a conformational change allowing ATP to bind at the catalytic domain for its conversion to cAMP. This catalytic activity is negatively regulated by the Gai subunit, which binds to the C1 domain and interferes with the active conformation and inhibits ADCY activity [37,38]. ADYCs also contain an internal site which mediates inhibition by adenosine and other adenosine derivatives and requires an intact adenine (purine) ring for binding. Because of this, this site has been designated as the ‘‘P-site’’ [39–41]. ADCYs can be activated or inactivated pharmacologically. The most commonly used chemical activator of the ADCY is forskolin (FSK), which binds to a site in the cytosolic domains. One of the most potent inhibitor of ADCYs is 20 ,50 -dideoxyadenosine (DDA), which is a P-site inhibitor. Very little is known is about the expression of various ADCY enzyme isoforms in melanocytes and melanoma [42]. By using semi-quantitative RT-PCR, expressions of different ADCYs was analyzed in B16 mouse melanoma cell line after treatment with FSK for 6 days. It was found that expression of ADCY1, 3, 4, 6, 7 and 9 increased by up to 4-fold compared to control. In contrast, ADCY2 expression decreased by 30% [42]. Recently, using a strategy to screen genes that confer resistance to MAPK inhibition in BRAFV600E mutant melanoma cells, Johannessen et al. have found that ADCY9 could contribute to acquiring resistance to MAPK inhibitors [43]. In this screen, which included over 16,000 human open reading frames (ORF), it was found that a cAMP-dependent melanocytic differentiation-related signaling could confer resistance to MAPK inhibition [43]. In vitro studies showed that this resistance was mediated by MITF upregulation, which was achieved by increased ADCY9 expression [43]. Additionally, pharmacological activation of ADCY by forskolin was able to confer resistance to MAPK inhibition in BRAFV600E melanoma cells [43]. Overall, this report uncovers new roles for cAMP signaling in melanoma. Profiling cAMP levels and ADCY expression in melanoma harboring different mutations (BRAFV600E vs. NRASQ61R) could provide new insights into the role of this pathway in the context of different melanoma oncogenic pathways. Similarly, assessing ADCY expression levels in tumor could serve as a biomarker providing insights about the tumor aggressiveness including intrinsic resistance to MAPK inhibitors. There are limited reports on sAC isoform in melanocyte and melanoma biology. Unlike the transmembrane ADCYs, sAC activity is not triggered by GPCR activation. It is regulated by bicarbonate ions [44]. To date, studies on sAC have focused mainly on its value as a tissue biomarker for pigmented lesions, such as benign nevi, lentigo maligna, and melanoma [45,46]. It is still unknown if sAC activity is involved in melanoma development and progression. Contribution of sAC in regulating cAMP levels in melanoma is a fertile area of research including the possibility that it could be involved in melanoma chemoresistance. Although ADCYs are ubiquitously expressed, their differential tissue expression might allow for their exploitation as therapeutic targets. However, additional research to establish their role in melanoma is clearly warranted. For example, different viable ADCY isoform knockout mice are available and could be employed in this direction [37]. Interestingly, most of the phenotypic defects present in these mice are associated with changes in behavioral responses, but no defects in coat color are described. Crossing these ADCY knockout mice, especially the ADCY9 knockout mice [37], with the available genetic mouse melanoma models will be a direct way to test the role of ADCYs melanoma development and progression.

151

Phosphodiesterases (PDEs)

212

PDEs negatively regulate cyclic nucleotide (both cAMP and cGMP) signaling by lowering their intracellular levels by hydrolysis

213

Please cite this article in press as: C.I. Rodríguez, V. Setaluri, Arch. Biochem. Biophys. (2014), http://dx.doi.org/10.1016/j.abb.2014.07.003

152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211

214

YABBI 6743

No. of Pages 6, Model 5G

15 July 2014 C.I. Rodríguez, V. Setaluri / Archives of Biochemistry and Biophysics xxx (2014) xxx–xxx

3

Fig. 1. Crosstalk between cAMP and MAPK signaling. Melanocyte development, differentiation and melanin production is highly regulated by different signaling pathways that ultimately lead to MITF expression and activation. Figure shows a simplified schematic of MITF regulation by three different pathways: Wnt signaling (melanocytes development); MC1R – cAMP signaling and the cKIT – MAPK signaling (differentiation and proliferation). Additionally, aMSH/MC1R signaling can trigger the activation of MAPK pathway in a cAMP-independent manner (solid red arrow). Interaction between cAMP pathway and MAPK pathway occurs through PKA, which inhibits CRAF activity. However, when oncogenic RAS is present, there is a switch of downstream effector of RAS from BRAF to CRAF. This is due to downregulation of cAMP activity by hyperactivity of PDE4. Recent reports about cAMP signaling roles in resistance to MAPK pathway inhibition suggests an indirect regulation of CREB by ERK in BRAFV600E melanoma cells (dashed red arrow). MC1R – Melanocortin Receptor 1; a-MSH – alpha melanocyte stimulating hormone; G-proteins a, b, c; ADCY – adenylate cyclase, cAMP – cyclic AMP; PDE – phosphodiesterase; CREB – cAMP Responsive Element Binding Protein; CRE – cAMP Resposive Element; MITF – microphthalmia associated transcription factor; Wnt – Wingless-type ligand; cKIT – stem cell factor receptor.

215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237

[31]. In mammals, there are eleven (PDE1–PDE11) different PDEs that hydrolyze cyclic nucleotides. PDEs share common structural features that include a catalytic domain of about 270 amino acids, a regulatory domain (regulatory proteins that bind to this domain vary by PDE family type, for example calmodulin for PDE1), a dimerization motifs, and a domain that can be prenylated or phosphorylated [47]. Among PDEs, PDE4 has been shown to play an important role in melanocyte biology and melanoma [48,49]. Increasing cAMP concentration by inhibition of PDE4, by a specific inhibitor rolipram, promotes melanoma cell proliferation [48]. A recent study showed that PDE4D3 transcription can be regulated by MITF creating a feedback loop between cAMP–MITF–PDE4D3. This homeostatic circuit negatively regulates cAMP signaling by increasing PDE4D3 expression by MITF [49]. Recently, it has been reported that PDE4D is important in different types of cancer, including melanoma, breast cancer, and lung cancer [50]. Homozygous microdeletions in the human PDE4 gene were shown to be present in different cancer types such as breast cancer and melanoma [50]. These microdeletions were found to be associated with an elevated protein expression. PDE4D inhibition in melanoma caused decreased proliferation and apoptosis [50]. Ectopic expression of PDE4D2 in melanoma cells enhanced their

proliferation and produced larger xenograft tumors in nude mice [50]. Overall, PDE4 appears to have tumor-promoting properties highlighting the importance of cAMP signaling in melanoma. PDE2 can hydrolyze both cAMP and cGMP, preferring the latter. In PMP oral melanoma cell line, it has been reported that the only PDE2 variant present is the PDE2A2 that harbors a point mutation. Inhibition of PDE2A2 decreased cell proliferation and increased the number of cells arrested in G2/M [51]. Recently, it was shown that inhibition of PDE2A by siRNA or a dominant negative PDE2A decreased growth and invasion of oral melanoma cells. In contrast, PDE4 inhibition with rolipram did not produce the negative effect on growth and invasion in these oral melanoma cells [52]. Since cAMP hydrolysis by PDE2 is greatly increased by allosteric regulation by cGMP, it would be interesting to evaluate cGMP signaling components and how cGMP levels affect cAMP signaling in melanoma. Different viable PDE knockout mice are available [53,54]. PDE4D knockout mice exhibit decreased viability (increased death rate within 4 weeks after birth) and growth retardation [54]. Interestingly, even though it was not pointed out, data presented in this paper show that the knockout mice have darker color and darkly pigmented tail [54]. However, no pigmentation disorder have been reported in other PDE knockout mice [53]. It will be worthwhile to

Please cite this article in press as: C.I. Rodríguez, V. Setaluri, Arch. Biochem. Biophys. (2014), http://dx.doi.org/10.1016/j.abb.2014.07.003

238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260

YABBI 6743

No. of Pages 6, Model 5G

15 July 2014 4

C.I. Rodríguez, V. Setaluri / Archives of Biochemistry and Biophysics xxx (2014) xxx–xxx

268

test how this increased pigmentation in the PDE4D-deficient mice affects melanoma tumor formation using the available genetic mouse models. As discussed so far, cAMP activity is dependent on its production by ADCYs and its degradation by PDEs. The equilibrium between the activity of these two enzymatic components leads to the activation of the downstream effectors protein kinase A (PKA) and the cAMP responsive element binding protein CREB.

269

Protein kinase A (PKA)

270

Protein kinase A is a member of family of cAMP-dependent kinases. PKA holoenzyme is a tetramer composed of two monomeric catalytic (C) subunits and two regulatory (R) subunits. The two main PKA isotypes (type I and II) are distinguished by their regulatory subunits (RI and RII). There are 4 different regulatory subunits, RI-a, RI-b and RII-a and RII-b. Similarly, there are 3 catalytic subunits, Ca, Cb, and Cc, which can bind to different regulatory subunits to form up to 12 different holoenzymes [55]. As previously mentioned, by its inhibitory action on CRAF, PKA mediates the crosstalk between cAMP and MAPK. Therefore, in cells with high cAMP levels and activated PKA, RAS activates BRAF but not CRAF. BRAF activity is regulated by ERK in a negative feedback regulatory loop. When RAS is mutated, the negative regulation of the MAPK pathway through the inactivation of BRAF by ERK is bypassed via CRAF activation. This is achieved by elevated activity of PDE4, which degrades cAMP and prevents activity of PKA. Consequently, inhibition of CRAF is relieved allowing it to be activated by RAS, thus leading to the activation of downstream MEK/ERK [56]. These findings provide novel insight into cAMP and MAPK pathway signaling interaction in melanoma [57]. The existence of such crosstalk between two important signaling pathways was also demonstrated in other types of cancers such as human non-small cell lung carcinoma and colorectal carcinoma [58]. More importantly, it was shown that PKA can phosphorylate BRAF disrupting the oncogenic RAS binding for its activation [58]. The implication of such interaction between PKA and BRAF in melanoma remains to be investigated. It has been reported that the catalytic subunit of PKA is expressed at significantly higher levels in human metastatic melanoma compared to primary melanoma and melanocytes [55]. PKA has also been shown to have a negative effect in melanoma by inducing cell cycle delay [59]. In vitro kinase assay showed PKA can phosphorylate the phosphatase cdc25B. This phosphorylation inhibits cdc25B phosphatase activity that dephosphorylates cyclin B/cyclin dependent kinase 1 (CDK1) complexes leading to delayed progression from G2 to mitosis in melanoma cells [59]. Intriguingly, it has been reported that catalytic subunit PKAa can confer resistance to MAPK pathway inhibition in BRAFV600E melanoma after overexpression and inhibition of PKA by H89, a PKA inhibitor, can block this resistance [43]. There are specific human diseases associated with PKA abnormalities [60–62]. It is well documented that the inherited multiple endocrine neoplasia syndrome Carney Complex (CNC) is due to inactivating mutations in the PRKAR1A (PKA subunit RI-a) gene. A small subset of patients with CNC develops schwannomas that are known as psammomatous melanotic schwannomas due to the presence of high degree of pigmentation. This phenotype has been also reported in a mouse knockout model. Genetically engineered mice deficient for different PKA subunits have been described [60]. Deficiency of different PKA subunits causes defects ranging from embryonic lethality to defects in learning. However, no pigmentary defects have been described. As previously mentioned for ADCY and PDE knockout mouse models, generating melanocyte specific conditional knockout mice to cross with the

261 262 263 264 265 266 267

271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324

genetic models of melanoma will provide definitive information about the roles of PKA in melanoma. In addition, mutations in the PRKAR1A gene are also associated with pigmented skin lesions in acrodysostosis patients [62]. This gain of function mutation in PRKAR1A leads to constitutive inhibition of PKA activity (catalytic subunits) by the inability of the regulatory domain to dissociate from the catalytic domain of PKA [61]. Taken together, these observations show other mechanisms for cAMP activity in pigmentation due to PKA inactivation in these patients. Alternatively, other signaling pathways might be compensating for this deficiency by activating PKA effector, CREB.

325

Cyclic AMP responsive element binding protein (CREB)

336

CREB is an important and ubiquitously expressed transcription factor of the leucine zipper protein family. CREB binds to cAMP responsive element (CRE) in the regulatory regions of its target genes. As principal effector of cAMP signaling, CREB is crucial for activation of MTIF expression and hence melanocyte development and differentiation. CREB is activated by Ser133 phosphorylation by cAMP-dependent PKA [63]. Although CREB is known to be highly expressed in majority of melanomas (based on immunohistochemical analysis of CREB1, Protein Human Atlas – http:// www.proteinatlas.org/), there are limited studies on its role in melanoma. CREB has been implicated in melanoma tumor growth and metastasis [64]. Expression of a dominant-negative CREB has been shown to decrease the number of lung tumors formed in nude mice injected with BRAF and NRAS wild type MeWo melanoma cells [64]. Several genes regulated by CREB have been identified to contribute to melanoma [43,64–68]. One of these genes is the matrix metalloproteinase 2 (MMP2), which is regulated by CREB [65]. CREB has been also shown to regulate the transcription of the cysteine-rich protein 61 (CCN1/CYR61), which negatively regulates angiogenesis and induces apoptosis.66 CREB also transcriptionally regulates Activator Protein-2a (AP-2a), a transcription factor known to act as a tumor suppressor [67]. In melanoma, CREB also regulates expression of the adipocyte enhancer-binding protein 1 (AEBP1), which is upregulated by treatment of PLX4032 and in post-treatment tumors with acquired resistance [68]. Overall, this study showed that AEBP1, which plays an important role in BRAFV600E tumors with acquired resistance, is positively regulated by PI3K/Akt–CREB–AEBP1–NF-kB signaling Q4 pathway [68]. Recently, it was shown that CREB induction, by treatment with forskolin or dibutyryl cAMP, conferred resistance to MAPK pathway inhibition in BRAFV600E melanoma. Moreover, examination of pCREB levels in biopsies of patients before or during treatment with RAF or RAF + MEK inhibitors showed decreased expression. In addition, pCREB levels in tumor relapse reached similar levels to pre-treatment tumors [43]. Taken together, this suggests an indirect regulation of CREB by ERK in BRAFV600E melanoma (Fig. 1). This possibility of altered CREB/pCREB ratio in melanoma could serve as a useful prognostic biomarker. Understanding the correlation between pCREB levels and melanoma aggressiveness (primary vs. metastatic) could greatly improve melanoma prognosis and treatment.

337

MAPK and cAMP signaling in melanoma

380

Mutations in the components of the MAPK pathway are present in majority of cutaneous melanoma tumors: BRAF (>50% of melanomas), NRAS (20–25% of melanomas) [69]. BRAFV600E bypasses regulation by RAS, leading to a constitutive activation of MEK/ ERK [17]. Recent studies have shown significant tumor regression using BRAFV600E specific inhibitors [4,69–71]. In 2011, the drug

381

Please cite this article in press as: C.I. Rodríguez, V. Setaluri, Arch. Biochem. Biophys. (2014), http://dx.doi.org/10.1016/j.abb.2014.07.003

326 327 328 329 330 331 332 333 334 335

338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379

382 383 384 385 386

YABBI 6743

No. of Pages 6, Model 5G

15 July 2014 C.I. Rodríguez, V. Setaluri / Archives of Biochemistry and Biophysics xxx (2014) xxx–xxx 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452

vemurafenib (also known as PLX4032) was approved by the US Food and Drug Administration (FDA) for treatment to metastatic melanoma [72]. Although impressive favorable disease outcomes are being reported, unfortunately, it has also become clear that months after such treatment, tumors often reappear showing resistance to chemotherapy. In contrast to MAPK pathway genes, to date, there are no reports of mutations in the cAMP signaling components in melanoma. However, cAMP signaling components have been implicated in acquired drug resistance. As previously mentioned, by expressing over 16,000 ORF’s, Johannessen et al. have identified that GPCR protein class conferred the highest resistance activity to MAPK inhibition in BRAFV600E melanoma cells [43]. Further analysis showed that cAMP signaling (ADCY–PKA–CREB), which is activated by many GPCRs, can also confer resistance to MAPK inhibition in BRAFV600E melanoma. Both overexpression and pharmacological activation of ADCYs by FSK conferred resistance to MAPK inhibition of BRAFV600E melanoma cells and increased phosphorylation of CREB [43]. This cAMP signaling-mediated resistance produced minimal ERK phosphorylation restoration [43], suggesting a MAPK-independent pathway(s) mediating cell survival. Moreover, these studies showed that this resistance involves transcription factors downstream of cAMP signaling, including MITF, FOS, NRA4A and NR41 [43]. Additionally, expression of either ADCY9 or catalytic subunit PKAa not only conferred resistance to MAPK inhibition but increased expression and maintenance of MITF. Furthermore, analysis of biopsies from BRAFV600E melanoma patients showed pCREB downregulation by inhibition of RAF and MEK but restored in relapsed tumors [43]. Intriguingly, among the GPCR genes conferring resistance, MC1R is not present among them which suggests an MC1R-independent cAMP signaling activation in BRAFV600E melanoma. Overall, these findings further expand the roles of cAMP signaling in melanoma by bringing it to the field of drug resistance. As previously discussed, the presence of oncogenic RAS in melanoma leads to downregulation of cAMP. This causes RAS effector switch from BRAF to CRAF due to downregulation of PKA activity that inhibits CRAF [56]. Additionally, Krayem et al. recently showed that in BRAFwt and NRASwt melanoma cells sensitive to vemurafenib, cAMP levels were higher and pCRAF levels were lower than in treatment-resistant cells [73]. Treatment by either forskolin or 3isobutyl-1-methylxanthine (IBMX, a non-selective PDE inhibitor) sensitized these cells to treatment with vemurafenib [73]. Taken together, these data suggest that even though mutations in cAMP signaling components are not present in melanoma, modulation of cAMP levels can be a useful strategy for treatment a subset of melanomas that do not harbor the signature mutations in BRAF and NRAS. Much of the data discussed so far suggest that increased cAMP signaling promotes melanoma tumor progression [43,51,52,64– 68,74]. Interestingly, in vivo studies with non-functional MCIR mice (RHC) have shown a different perspective. Upregulation of cAMP signaling (by topical application of ADCY activator – forskolin) rescued pigmentation and this chemically induced pigmentation was able to protect mice from UV-light induced DNA damage and reduce tumor formation [75]. In addition, Lyons et al. recently showed that cAMP signaling, upon activation of the MC1R, delays cell cycle progression by inhibition of cdc25B (a CDK1 phosphatase) and that MC1R overexpression or its activation by a-MSH or other small molecules that activate adenylate cyclase (such as forskolin) decreases proliferation of melanoma by causing G2 cell cycle arrest [59]. The inhibitory role of MC1R on proliferation of these melanoma cell lines shows the potential of MC1R for therapeutic intervention once again. Previous studies have proposed the usage of a-MSH analogs as a strategy for melanoma prevention [76]. MIC1R agonists induce a tanning response

5

that could reduce the skin UV damage to DNA; and consequently could decrease the risk of malignant transformation of melanocytes [76,77]. Considering Lyons report about the negative role of MC1R, these analogs could potentially be used as therapeutic and chemo-preventive agent. In contrast, it has been proposed, based on case reports, that patients that are predisposed to develop melanoma (i.e., patients with history of melanoma) could develop neoplastic melanocytic lesions upon treatment with synthetic a-MSH analogs [78]. Additionally, few other cases have been reported increased risk of melanoma associated with usage of synthetic aMSH [79–81], albeit based on anecdotal data. Therefore, MC1R modulation should be considered with caution, especially with predisposed patients. Nevertheless, this apparent problem could be solved through better understanding of MC1R activation and cAMP signaling roles in melanoma.

453

Conclusion

468

Thus, while the role of cAMP signaling in melanocytes and its mechanism of action primarily through activation of MITF expression is firmly established, the role of cAMP signaling in melanocyte transformation, melanoma development and progression, and melanoma resistance (both intrinsic and acquired) to treatment remain to be fully understood. Ongoing studies in our laboratory and that of others indicate that cAMP signaling play different roles in melanoma cell growth based on the oncogenic mutation. Clearly, additional studies are warranted to better define the complex role of this important second messenger. More research investigating cAMP modulation as a therapeutic strategy in melanoma is clearly warranted. In a broader context, GPCRs, which are the targets of approximately 30% of all pharmaceuticals in the market [82], have also emerged as therapeutic targets in different types of cancer [83]. A concerted effort to screen this large collection of GPCR targeting agents, especially those that modulate cellular cAMP levels, might yield novel anti-melanoma agents that could be effective alone or in combination with the current modalities of targeted therapies. Additionally, retrospective epidemiological studies and prospective monitoring of individuals on GPCR/cAMP modulating drugs for melanoma incidence, progression and drug resistance may also provide important biological insights for prevention and treatment of melanoma.

469

Funding source

493

Science and Medicine Graduate Research Scholars (SciMed GRS).

494

References

496

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]

A. Vultur, M. Herlyn, Cancer Cell 23 (2013) 706. e1. R. Siegel, J. Ma, Z. Zou, A. Jemal, CA Cancer J. Clin. 64 (2014) 9–29. C.E. DeSantis, C.C. Lin, A.B. Mariotto, et al., CA Cancer J. Clin. (2014). A.K. Salama, K.T. Flaherty, Clin. Cancer Res. 19 (2013) 4326–4334. R. Siegel, C. Desantis, K. Virgo, et al., CA Cancer J. Clin. 62 (2012) 220–241. E. Hodis, I.R. Watson, G.V. Kryukov, et al., Cell 150 (2012) 251–263. M. Krauthammer, Y. Kong, B.H. Ha, et al., Nat. Genet. 44 (2012) 1006–1014. R. Halaban, Pigment Cell Res. 13 (2000) 4–14. Z. Abdel-Malek, V.B. Swope, I. Suzuki, et al., Proc. Natl. Acad. Sci. U.S.A. 92 (1995) 1789–1793. N. Dumaz, R. Hayward, J. Martin, et al., Cancer Res. 66 (2006) 9483–9491. A. Uong, L.I. Zon, J. Cell. Physiol. 222 (2010) 38–41. R.I. Dorsky, R.T. Moon, D.W. Raible, Nature 396 (1998) 370–373. H.R. Widlund, D.E. Fisher, Oncogene 22 (2003) 3035–3041. A.T. Weeraratna, Cancer Metastasis Rev. 24 (2005) 237–250. J.A. Carlson, G.P. Linette, A. Aplin, B. Ng, A. Slominski, Dermatol. Clin. 25 (2007) 541–557. viii-ix. A.A. Rosenkranz, T.A. Slastnikova, M.O. Durymanov, A.S. Sobolev, Biochemistry (Mosc) 78 (2013) 1228–1237.

Please cite this article in press as: C.I. Rodríguez, V. Setaluri, Arch. Biochem. Biophys. (2014), http://dx.doi.org/10.1016/j.abb.2014.07.003

454 455 456 457 458 459 460 461 462 463 464 465 466 467

470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492

495

497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515

YABBI 6743

No. of Pages 6, Model 5G

15 July 2014 6 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565

C.I. Rodríguez, V. Setaluri / Archives of Biochemistry and Biophysics xxx (2014) xxx–xxx

[17] C. Herraiz, F. Journé, Z. Abdel-Malek, G. Ghanem, C. Jiménez-Cervantes, J.C. García-Borrón, Mol. Endocrinol. 25 (2011) 138–156. [18] K.L. Pierce, R.T. Premont, R.J. Lefkowitz, Nat. Rev. Mol. Cell Biol. 3 (2002) 639– 650. [19] H.H. Lin, Chang Gung Med. J. 35 (2012) 15–27. [20] A.M. Spiegel, L.S. Weinstein, Annu. Rev. Med. 55 (2004) 27–39. [21] A. Slominski, D.J. Tobin, S. Shibahara, J. Wortsman, Physiol. Rev. 84 (2004) 1155–1228. [22] A.L. Kadekaro, S. Leachman, R.J. Kavanagh, et al., FASEB J. 24 (2010) 3850– 3860. [23] P. Valverde, E. Healy, I. Jackson, J.L. Rees, A.J. Thody, Nat. Genet. 11 (1995) 328– 330. [24] N.F. Box, J.R. Wyeth, L.E. O’Gorman, N.G. Martin, R.A. Sturm, Hum. Mol. Genet. 6 (1997) 1891–1897. [25] H.B. Schiöth, S.R. Phillips, R. Rudzish, M.A. Birch-Machin, J.E. Wikberg, J.L. Rees, Biochem. Biophys. Res. Commun. 260 (1999) 488–491. [26] M.C. Scott, K. Wakamatsu, S. Ito, et al., J. Cell Sci. 115 (2002) 2349–2355. [27] N.F. Box, D.L. Duffy, R.E. Irving, et al., J. Invest. Dermatol. 116 (2001) 224–229. [28] J.S. Palmer, D.L. Duffy, N.F. Box, et al., Am. J. Hum. Genet. 66 (2000) 176–186. [29] C. Kennedy, J. ter Huurne, M. Berkhout, et al., J. Invest. Dermatol. 117 (2001) 294–300. [30] C. Levy, M. Khaled, D.E. Fisher, Trends Mol. Med. 12 (2006) 406–414. [31] J.A. Beavo, Physiol. Rev. 75 (1995) 725–748. [32] M. Katz, I. Amit, Y. Yarden, Biochim. Biophys. Acta 1773 (2007) 1161–1176. [33] B. Wehrle-Haller, Pigment Cell Res. 16 (2003) 287–296. [34] T.J. Hemesath, E.R. Price, C. Takemoto, T. Badalian, D.E. Fisher, Nature 391 (1998) 298–301. [35] C. Wellbrock, M. Karasarides, R. Marais, Nat. Rev. Mol. Cell Biol. 5 (2004) 875– 885. [36] A. Tada, E. Pereira, D. Beitner-Johnson, R. Kavanagh, Z.A. Abdel-Malek, J. Invest. Dermatol. 118 (2002) 316–322. [37] S. Pierre, T. Eschenhagen, G. Geisslinger, K. Scholich, Nat. Rev. Drug Discov. 8 (2009) 321–335. [38] C.W. Dessauer, T.T. Scully, A.G. Gilman, J. Biol. Chem. 272 (1997) 22272– 22277. [39] J.J. Tesmer, C.W. Dessauer, R.K. Sunahara, et al., Biochemistry 39 (2000) 14464–14471. [40] R.A. Johnson, S.M. Yeung, D. Stübner, M. Bushfield, I. Shoshani, Mol. Pharmacol. 35 (1989) 681–688. [41] J. Wolff, C. Londos, D.M. Cooper, Adv. Cyclic Nucleotide Res. 14 (1981) 199–214. [42] D.H. Cho, C.D. Bae, Y.S. Juhnn, Exp. Mol. Med. 32 (2000) 235–242. [43] C.M. Johannessen, L.A. Johnson, F. Piccioni, et al., Nature 504 (2013) 138–142. [44] M. Tresguerres, L.R. Levin, J. Buck, Kidney Int. 79 (2011) 1277–1288. [45] C.M. Magro, S.E. Yang, J.H. Zippin, A. Zembowicz, Arch. Pathol. Lab. Med. 136 (2012) 1558–1564. [46] C.M. Magro, A.N. Crowson, G. Desman, J.H. Zippin, Arch. Dermatol. 148 (2012) 335–344. [47] C. Lugnier, Pharmacol. Ther. 109 (2006) 366–398. [48] M. Narita, T. Murata, K. Shimizu, et al., Oncol. Rep. 17 (2007) 1133–1139. [49] M. Khaled, C. Levy, D.E. Fisher, Genes Dev. 24 (2010) 2276–2281.

[50] D.C. Lin, L. Xu, L.W. Ding, et al., Proc. Natl. Acad. Sci. U.S.A. 110 (2013) 6109– 6114. [51] H. Morita, T. Murata, K. Shimizu, K. Okumura, M. Inui, T. Tagawa, Oncol. Rep. 29 (2013) 1275–1284. [52] K. Hiramoto, T. Murata, K. Shimizu, et al., Cell. Signal. (2014). [53] D.H. Maurice, H. Ke, F. Ahmad, Y. Wang, J. Chung, V.C. Manganiello, Nat. Rev. Drug Discov. 13 (2014) 290–314. [54] S.L. Jin, F.J. Richard, W.P. Kuo, A.J. D’Ercole, M. Conti, Proc. Natl. Acad. Sci. U.S.A. 96 (1999) 11998–12003. [55] S.J. Beebe, P. Salomonsky, C. Holroyd, D. Becker, Cell Growth Differ. 4 (1993) 1005–1012. [56] A. Marquette, J. André, M. Bagot, A. Bensussan, N. Dumaz, Nat. Struct. Mol. Biol. 18 (2011) 584–591. [57] N. Dumaz, Small GTPases 2 (2011) 289–292. [58] Y. Li, M. Takahashi, P.J. Stork, J. Biol. Chem. (2013). [59] J. Lyons, B.C. Bastian, F. McCormick, Proc. Natl. Acad. Sci. U.S.A. 110 (2013) 13845–13850. [60] L.S. Kirschner, Z. Yin, G.N. Jones, E. Mahoney, Endocr. Relat. Cancer 16 (2009) 773–793. [61] A. Linglart, C. Menguy, A. Couvineau, et al., N. Engl. J. Med. 364 (2011) 2218– 2226. [62] A. Linglart, H. Fryssira, O. Hiort, et al., J. Clin. Endocrinol. Metab. 97 (2012) E2328–E2338. [63] G.A. Gonzalez, M.R. Montminy, Cell 59 (1989) 675–680. [64] S. Xie, J.E. Price, M. Luca, D. Jean, Z. Ronai, M. Bar-Eli, Oncogene 15 (1997) 2069–2075. [65] V.O. Melnikova, A.A. Mourad-Zeidan, D.C. Lev, M. Bar-Eli, J. Biol. Chem. 281 (2006) 2911–2922. [66] A.S. Dobroff, H. Wang, V.O. Melnikova, et al., J. Biol. Chem. 284 (2009) 26194– 26206. [67] V.O. Melnikova, A.S. Dobroff, M. Zigler, et al., PLoS One 5 (2010) e12452. [68] W. Hu, L. Jin, C.C. Jiang, et al., Cell Death Dis. 4 (2013) e914. [69] K.T. Flaherty, Annu. Rev. Med. 63 (2012) 171–183. [70] H. Tsao, L. Chin, L.A. Garraway, D.E. Fisher, Genes Dev. 26 (2012) 1131–1155. [71] F. Su, W.D. Bradley, Q. Wang, et al., Cancer Res. 72 (2012) 969–978. [72] S. Jang, M.B. Atkins, Clin. Pharmacol. Ther. (2013). [73] M. Krayem, F. Journe, M. Wiedig, et al., Eur. J. Cancer 50 (2014) 1310–1320. [74] J.H. Zippin, J. Farrell, D. Huron, et al., J. Cell Biol. 164 (2004) 527–534. [75] J.A. D’Orazio, T. Nobuhisa, R. Cui, et al., Nature 443 (2006) 340–344. [76] Z.A. Abdel-Malek, A.L. Kadekaro, R.J. Kavanagh, et al., FASEB J. 20 (2006) 1561– 1563. [77] Z.A. Abdel-Malek, Adv. Exp. Med. Biol. 681 (2010) 126–132. [78] A.R. Cardones, J.M. Grichnik, Arch. Dermatol. 145 (2009) 441–444. [79] D. Paurobally, F. Jason, B. Dezfoulian, A.F. Nikkels, Br. J. Dermatol. 164 (2011) 1403–1405. [80] S. Ong, J. Bowling, Australas. J. Dermatol. 53 (2012) 301–302. [81] C. Reid, T. Fitzgerald, A. Fabre, B. Kirby, Ir. Med. J. 106 (2013) 148–149. [82] A.J. Kimple, D.E. Bosch, P.M. Giguère, D.P. Siderovski, Pharmacol. Rev. 63 (2011) 728–749. [83] R.T. Dorsam, J.S. Gutkind, Nat. Rev. Cancer 7 (2007) 79–94.

566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616

Please cite this article in press as: C.I. Rodríguez, V. Setaluri, Arch. Biochem. Biophys. (2014), http://dx.doi.org/10.1016/j.abb.2014.07.003