c-Kit mutants require hypoxia-inducible factor 1α to transform melanocytes

Abstract

Many studies have highlighted the critical role of c-Kit in normal melanocyte development but its role in melanoma development remains unclear. Although c-Kit expression is often lost during melanoma progression, a subset of melanoma has been found to overexpress c-Kit and mutations activating c-Kit have recently been identified in some acral and mucosal melanoma. To address the role of these c-Kit mutants in the transformation of melanocytes, we characterized the physiological responses of melanocytes expressing the most frequent c-Kit mutants found in melanoma (K642E and L576P) and a novel mutant we identified in an acral melanoma. We analysed signaling pathways activated downstream of c-Kit and showed that all three mutants led to a strong activation of the phosphatidyl-inositol-3 kinase (PI3K) pathway but only weak activation of the Ras/Raf/Mek/Erk pathway, which was not sufficient to promote uncontrolled melanocyte proliferation and transformation. However, in hypoxic conditions or coexpressed with a constitutively active form of hypoxia-inducible factor 1a (HIF-1a), c-Kit mutants activate the Ras/Raf/Mek/Erk pathway, stimulate proliferation and transform melanocytes. Proliferation of melanocytes transformed by these mutants was specifically inhibited by imatinib. These results show for the first time that melanocytes require a specific epigenetic environment to be transformed by c-Kit mutants and highlight a distinct molecular mechanism of melanocyte transformation.

KIT Pathway Alterations in Mucosal Melanomas of the Vulva and Other Sites

“…Of 12 tumors with KIT mutations, 5 (42%) were positive for p-ERK and 8 (67%) showed positivity for p-AKT. Similar results have been observed in KIT-mutated GISTs (36) and a KIT-mutated acral melanoma (37). Importantly, treatment of KIT-mutant mucosal melanoma cells in vitro with imatinib results in decreased levels of ERK and AKT phosphorylation (32).…”

A novel oncogenic role for the miRNA-506-514 cluster in initiating melanocyte transformation and promoting melanoma growth

“…Moreover, many previous publications have utilized the soft agar assay to demonstrate the transformation capacity of oncogenes (Rasmussen et al, 2001;Lu et al, 2008;Syed et al, 2008;Monsel et al, 2010), as this assay is well documented to be predictive of in vivo tumorigenicity (Rhim, 1983;Trainer et al, 1988), malignant potential (Montesano et al, 1977) and drug response (Zirvi et al, 1983;Scholz et al, 1990). Taken together, these observations increase confidence in the oncogenic potential of the miR-506-514 cluster.…”

Genetic, Epigenetic and Molecular Changes in Melanoma: A New Paradigm for Biological Classification

“…KIT is expressed at maximum level at the invading edge of tumors, this suggesting a role for dynamic RTK activation in metastasis (Handolias et al, 2010). Monsel et al (Monsel et al, 2010) demonstrated that c-Kit mutated melanocytes require a specific epigenetic environment to be transformed in melanoma cells. c-Kit mutants cause in fact a strong activation of the phosphatidyl-inositol-3 kinase (PI3K) pathway, which, per se, is not sufficient to promote transformation of melanocytes.…”

“…A critical role for c-Kit for normal neural crest and normal www.intechopen.com Genetic, Epigenetic and Molecular Changes in Melanoma: A New Paradigm for Biological Classification 41 melanocyte development, (Rother &Jones, 2009) differentiation, proliferation, survival andmigration (Wehrle-Haller, 2003) has been recognized, but its function in melanoma remains somewhat unclear. As a rule, c-Kit expression is lost during melanoma progression, but a subset of melanomas has been found to overexpress it and mutations activating c-Kit, mostly constituted by L576P (up to 50% of mutations), have recently been identified in some mucosal and AL melanoma subtypes (5-20% of cases), but not in cases arising from chronic sun-damaged skin (Rother & Jones, 2009;Monsel et al, 2010). KIT is expressed at maximum level at the invading edge of tumors, this suggesting a role for dynamic RTK activation in metastasis (Handolias et al, 2010).…”

“…c-Kit mutants cause in fact a strong activation of the phosphatidyl-inositol-3 kinase (PI3K) pathway, which, per se, is not sufficient to promote transformation of melanocytes. However, in the chronic hypoxic skin microenvironment, and/or when a constitutively active form of hypoxia-inducible factor 1alpha (HIF-1alpha) is coexpressed, cKit mutants activate also the Ras/Raf/Mek/Erk pathway, transforming the melanocytes, (Monsel et al, 2010). This scenario is extremely interesting, considering that KIT mutations are mutually exclusive with BRAF and NRAS, to identify a subset of melanomas arising from a distinct molecular mechanism of transformation, which may be specifically targeted by KIT inhibitors, such as imatinib or sorafenib (Monsel et al, 2010).…”