We sequenced 8 melanoma exomes to identify novel somatic mutations in metastatic melanoma.,Focusing on the MAP3K family, we found that 24% of melanoma cell lines have mutations in the protein-coding regions of either MAP3K5 or MAP3K9.,Structural modelling predicts that mutations in the kinase domain may affect the activity and regulation of MAP3K5/9 protein kinases.,The position of the mutations and loss of heterozygosity of MAP3K5 and MAP3K9 in 85% and 67% of melanoma samples, respectively, together suggest that the mutations are likely inactivating.,In vitro kinase assay shows reduction in kinase activity in MAP3K5 I780F and MAP3K9 W333X mutants.,Overexpression of MAP3K5 or MAP3K9 mutant in HEK293T cells reduces phosphorylation of downstream MAP kinases.,Attenuation of MAP3K9 function in melanoma cells using siRNA leads to increased cell viability after temozolomide treatment, suggesting that decreased MAP3K pathway activity can lead to chemoresistance in melanoma.
Cutaneous malignant melanoma is a highly aggressive and frequently chemoresistant cancer, whose incidence continues to rise.,Epidemiological studies reveal that the major etiological melanoma risk factor is ultraviolet (UV) solar radiation, with the highest risk associated with intermittent burning doses, especially during childhood1,2.,We have experimentally validated these epidemiological findings using the hepatocyte growth factor/scatter factor (HGF/SF) transgenic mouse model, which develops lesions in stages highly reminiscent of human melanoma with respect to biological, genetic and etiologic criteria, but only when irradiated as neonatal pups with UVB, not UVA3,4.,However, mechanisms underlying UVB-initiated, neonatal-specific melanomagenesis remain largely unknown.,Here we introduce a mouse model permitting fluorescence-aided melanocyte imaging and isolation following in vivo UV irradiation.,We use expression profiling to show that activated neonatal skin melanocytes isolated following a melanomagenic UVB dose bear a distinct, persistent interferon response signature, including genes associated with immunoevasion.,UVB-induced melanocyte activation, characterized by aberrant growth and migration, was abolished by antibody-mediated systemic blockade of interferon-γ (IFN-γ), but not type-I interferons.,IFN-γ was produced by macrophages recruited to neonatal skin by UVB-induced ligands to the chemokine receptor Ccr2.,Admixed recruited skin macrophages enhanced transplanted melanoma growth by inhibiting apoptosis; notably, IFN-γ blockade abolished macrophage-enhanced melanoma growth and survival.,IFN-γ-producing macrophages were also identified in 70% of human melanomas examined.,Our data reveal an unanticipated role for IFN-γ in promoting melanocytic cell survival/immunoevasion, and suggest that IFN-γ-R signaling represents a novel therapeutic melanoma target.