The sMAF transcription factor MAFG is a potent driver of melanoma
While common mutations in potent proto-oncogenes and tumor suppressors induce melanoma formation, no recurrent mutations associated with the late stages of melanomagenesis have been identified. Instead, non-mutational mechanisms such as the deregulation of transcriptiona or epigenetic programs typically promote the malignang progression and metastasis of melanoma. We have previously identified the small MAFG transcription factor MAFG as a critical target of the melanoma suppressor miRNA miRN-29, prompting an in-depth evaluation of the role of MAFG in melanoma. MAFG expression is elevated in melanoma compared to melanocytes and increases with tumor stage. Ectopic expression of MAFG in human melanocytes and melanoma cells enhances proliferation in virto and promotes melanoma growth in vivo. Moreover, MAFG overexpression in BRAFV600E; PTEN+/- mice accelerated melanomagenesis, significantly shortening overall survival. Despite being a critical NRF2 dimerization partner, NRF2 was dispensable for the effects of MAFG. Moreover, MAFG overexpression in melanoma had no effect on the activity of NRF2 transcriptional reporters, nor did it induce transcriptional programs associated with NRF2. RNA sequencing and pathway analysis revealed MAFG-mediated effects on melanoma-associated processes such as pigmentation. Indeed, MAFG downregulated MITF and its target genes in the pigmentation pathway in melanoma cells. We next analyzed the connection between MAFG and MITF and found that MAFG binds to MITF to impede its binding to melanocytic differentiation genes, thus promoting a less differentiated and more aggressive phenotype. Our study establishes MAFG as a potent driver of melanoma development through the relocation of MITF. Overall design: RNA was isolated from WM164, A375 and SKMEL28 cells overexpressing either GFP or MAFG using Qiagen miRNease kit