Abstract 3041: The small MAF transcription factor MAFG is a potent driver of melanoma

Abstract

Abstract 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 transcriptional or epigenetic programs typically promote the malignant progression and metastasis of melanoma. We have previously identified the small MAF transcription factor MAFG as a critical target of the melanoma suppressor miRNA miR-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 vitro and promotes melanoma growth in vivo. Moreover, MAFG overexpression in BrafV600E; PtenFL/+ 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 cells 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 hypoxia, the PI3K/AKT pathway, and pigmentation. Indeed, MAFG induced HIF1a under normoxic conditions, enhanced AKT phosphorylation, and downregulated MITF and its target genes in the pigmentation pathway in melanoma cells. Interestingly, MAFG also potently enhanced AXL expression, suggesting that MAFG may promote melanoma, at least in part, by affecting the MITF/AXL balance that is associated with melanoma phenotype switching. We next analyzed whether MAFG is required for melanoma. Interestingly, silencing MAFG in human melanoma cells robustly inhibited growth in vitro. Moreover, the CRISPR/Cas9-mediated knockout of MAFG in an aggressive BrafV600E; PtenFL/FL model potently prevented melanoma formation. Given the mild phenotype of MAFG whole-body knockout mice, our results suggest targeting of MAFG or its downstream pathways as a viable therapeutic approach in melanoma. In conclusion, our study establishes MAFG as a potent driver of melanoma development and nominates it as a therapeutic target. Citation Format: Olga Vera, Michael Martinez, Zulaida Soto-Vargas, Xiaonan Xu, Florian Karreth. The small MAF transcription factor MAFG is a potent driver of melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3041.