MITF/miR-579-3p novel regulatory axis controls BRAF-mutated melanoma decision between cell senescence or progression upon exposure to MAPK inhibitors.

Abstract Therapy of metastatic melanoma has improved dramatically over the last years thanks to the development of targeted therapies (MAPK inhibitors) and immunotherapies. However, drug resistance continues to be a major limitation to the efficacy of these therapies. Our research group has provided robust evidence as to the involvement of a set of microRNAs in the development of resistance to target therapy in BRAF-mutated melanoma cell lines. Among them, a pivotal role is played by miR-579-3p, whose role as oncosuppressor was discovered by our group some years ago. Here we show that miR-579-3p and the microphthalmia-associated transcription factor (MITF) influence reciprocally their expression through positive feedback regulatory loops. In particular we show that miR-579-3p is specifically deregulated in BRAF-mutant melanomas and that its expression levels mirror those of MITF. Luciferase and ChIP studies show that MITF is a positive regulator of miR-579-3p, which is located in the intron 11 of the human gene ZFR (Zink-finger recombinase) and is co-transcribed with its host gene. Moreover, miR-579-3p, by targeting BRAF is able to stabilize MITF protein thus inducing its own transcription. As a consequence, upon exposure to MAPK inhibitors or, alternatively upon miR-579-3p transfection, the activation of this newly uncovered miR-579-3p/MITF axis induces a potent block of proliferation and senescence of BRAF-mutant melanoma cells. Moreover, the long term development of resistance to MAPKi is able to select cells characterized by the loss of both miR-579-3p and MITF and the same down-regulation is also present in patients relapsing after targeted therapies treatments. Altogether these findings suggest that miR-579-3p/MITF interplay potentially governs the balance between proliferation, senescence and resistance to target therapies in BRAF-mutant melanomas. KEYWORDS: Acknowledgements This study was supported by Italian Association for Cancer Research (AIRC) grants IG19865 to G. Ciliberto and IG24451 to R. Mancini and by the Lazio Innova grants 2018 n. 85-2017-13750 and 2020 n. A0375-2020-36657 to R. Mancini and by Italian Minister of Health grant PRIN 2017 (Prot. 2017HWTP2K) to G. Ciliberto and R. Mancini, by Italian Minister of Health through “Ricerca Corrente” grant L2/1 to P.A. Ascierto. The study was also supported by Lega Italiana per la Lotta ai Tumori (LILT) grant n. 2021U0001637 to L. Fattore. We thank all patients who donated samples for this research