Response to targeted therapies varies significantly despite shared oncogenic mutations. Nowhere is this more apparent than in BRAF(V600E)-mutated melanomas where initial drug response can be striking and yet relapse is commonplace. Resistance to BRAF inhibitors have been attributed to the activation of various receptor tyrosine kinases (RTKs) though the underlying mechanisms have been largely uncharacterized. Here, we found that EGFR induced vemurafenib resistance is ligand dependent. We then employed whole-genome expression analysis and discovererd that vemurafenib resistance correlated with the loss of MITF, along with its melanocyte lineage program, and with the activation of EGFR signaling. An inverse relationship between MITF, vemurafenib resistance and EGFR was then observed in patient samples of recurrent melanoma and was conserved across melanoma cell lines and patients’ tumor specimens. Functional studies revealed that MITF depletion activated EGFR signaling and consequently recapitulated the resistance phenotype. In contrast, forced expression of MITF in melanoma and colon cancer cells inhibited EGFR and conferred sensitivity to BRAF/MEK inhibitors. These findings indicate that an “autocrine drug resistance loop” is suppressed by melanocyte lineage signal(s), such as MITF. This resistance loop modulates drug response and could explain the unique sensitivity of melanomas to BRAF inhibition.

EphA2 is a member of the Eph family of receptor tyrosine kinases and is highly expressed in many aggressive cancer types, including melanoma. We recently showed that EphA2 is also upregulated by ultraviolet radiation and is able to induce apoptosis. These findings suggest that EphA2 may have different, even paradoxical, effects on viability depending on the cellular context and that EphA2 mediates a delicate balance between life and death of the cell. To functionally clarify EphA2’s role in melanoma, we analyzed a panel of melanoma cell lines and found that EphA2 levels are elevated in a significant fraction of the samples. Specific depletion of EphA2 in high-expressing melanoma cells using shRNA led to profound reductions in cellular viability, colony formation and migration in vitro and a dramatic loss of tumorigenic potential in vivo. Stable introduction of EphA2 into low-expressing lines enhanced proliferation, colony formation and migration further supporting its pro-malignant phenotype. Interestingly, transient expression of EphA2 and/or BrafV600E in non-transformed melanocytes led to significant and additive apoptosis. These results verify that EphA2 is an important oncogene and potentially a common source of “addiction” for many melanoma cells. Moreover, acute induction of EphA2 may purge genetically-susceptible cells thereby uncovering a more aggressive population that is in fact dependent on the oncogene.

One of the physiologic consequences of excessive UV radiation (UVR) exposure is apoptosis. This critical response serves to eliminate genetically injured cells and arises, in part, from activation of DNA damage and p53 signaling. Other contributory pathways, however, likely exist but have not been fully characterized. In a recent global screen of UVR response genes in melanocytes, we identified the receptor tyrosine kinase EPHA2. Using a combination of genetic and pharmacologic approaches, we set out to investigate the upstream regulation of EphA2 by UVR and the functional consequences of this effect. We found that the UVR-associated increase in EphA2 occurs in melanocytes, keratinocytes, and fibroblasts from both human and murine sources. More specifically, UVR effectively up-regulated EphA2 individually in p53-null, p63-null, and p73-null murine embryonic fibroblasts (MEF), suggesting that the p53 family of transcription factors is not essential for the observed effect. However, inhibition of mitogen-activated protein kinase (MAPK) signaling by U0126 and PD98059 significantly reduced the UVR response whereas overexpression of oncogenic NRAS led to an increase in EphA2. These results confirm that UVR induces EphA2 by a p53-independent, but MAPK-dependent, mechanism. In response to UV irradiation, Epha2

Background For patients with advanced melanoma, primary and secondary resistance to selective BRAF inhibition remains one of the most critically compelling challenges. One rationale argues that novel biologically-informed strategies are needed to maximally cripple melanoma cells up front before compensatory mechanisms emerge. Since p53 is uncommonly mutated in melanoma, restoration of its function represents an attractive adjunct to selective BRAF inhibition. Experimental Design Thirty-seven BRAF(V600E)-mutated melanoma lines were subjected to synergy studies in vitro using a combination of vemurafenib and nutlin-3 (Nt-3). In addition, cellular responses and in vivo efficacy were also determined. We also analyzed changes in the levels of canonical apoptotic/survival factors in response to vemurafenib. Results Dual targeting of BRAF(V600E) and HDM2 with vemurafenib and Nt-3, respectively, synergistically induced apoptosis and suppressed melanoma viability in vitro and tumor growth in vivo. Suppression of p53 in melanoma cells abrogated Nt-3′s effects fully and vemurafenib’s effects partially. A survey of canonical survival factors revealed that both vemurafenib and Nt-3 independently attenuated levels of the anti-apoptotic protein, survivin. Genetic depletion of survivin reproduces the cytotoxic effects of the combination strategy. Conclusion These results demonstrate preclinical feasibility for overcoming primary vemurafenib resistance by restoring p53 function. Moreover, it identifies survivin as one downstream mediator of the observed synergism and a potential secondary target.

Although TERT promoter mutations have been associated with a worsened prognosis in melanoma, the relationship between mutation status and downstream telomerase activity and telomere length remains convoluted. Using Sanger sequencing and techniques based on quantitative reverse transcriptase in real time, we evaluated 60 melanoma cell lines for TERT promoter mutational status, copy number, gene expression, and telomere length to provide a comprehensive analysis of the TERT/telomere pathway and establish a classification system whereby the associations between TERT mutations and their downstream molecular manifestations can more easily be ascertained. Mutations at positions -124/125 and -146 were associated with the highest levels of TERT gene expression but had no appreciable impact on absolute telomere length. In contrast, the common variant rs2853669 (at position -245) was significantly associated with longer telomere length via a recessive model in our cohort (P ¼ 0.003). Our results, which are from assays performed on purified melanoma cell lines, suggest that the TERT promoter harbors a more complex mutational landscape than previously thought. Furthermore, the failure of TERT promoter mutations to consistently correlate with TERT expression and telomere length suggests an alternative method whereby tumor cells escape the critical shortening of telomeres.

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Background The penetrance of CDKN2A mutations is subject to geographic and latitudinal variation and is presumably dictated by UVR exposure and possibly other co-inherited genetic factors. The frequency of mutations increases with the number of family members affected and the number of primary tumors and also fluctuates with geography. Up to date, little is known about the prevalence of CDKN2A mutations in melanoma patients from Greece. Objective To characterize the frequency of CDKN2A and CDK4 mutations in a hospital-based population of Greek patients with melanoma. Methods Three-hundred and four consecutive single primary melanoma (SPM), 9 familial melanomas (FM) and 7 multiple primary melanoma cases (MPM) were assessed for sequence variants in exons 1α, 1β and 2 of CDKN2A and exon 2 of CDK4. Results Germline CDKN2A mutations were detected in 10 of 304 SPM (3.29%), in 4 of 7 MPM (57.0%) and in 2 of 9 FM (22.2%) cases. The most common mutation was a Northern European allele (p16 p.R24P) detected in 8 individuals. Five previously unreported CDKN2A variants were also identified: −34G>C, c.41_43delins20bp, c.301G>C(p.G101R), c.301G>A(p.G101E) and c.296_297insGACC. We also describe the first report of a Cdk4 p.R24H substitution in a Greek family. Conclusions The Greek population appears to harbor a higher prevalence of CDKN2A mutation than other reported cohorts. This supports the notion that genetic susceptibility may play a stronger influence in a country with a relatively low incidence of melanoma. Furthermore, the identification of Northern European alleles suggests that gene migration may be responsible, in part, for the observed cases in Greece.

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