BRAFV600E dictates cell survival via c-Myc-dependent induction of Skp2 in human melanoma

Abstract

BRAFV600E mutation is frequently observed in melanoma, and contributes to tumor malignancy. Despite inhibition of BRAF causes a profound cell growth inhibition and a strong clinical benefit in BRAFV600E melanoma, acquired drug resistance is still the major hurdle. In this study, we demonstrate that BRAFV600E drives cell growth and glycolysis in melanoma cells but does so by a previously unappreciated mechanism that involves direct induction of Skp2. Skp2 is highly expressed in melanoma tissues and particularly in tissues with BRAFV600E mutation. The inhibition of BRAFV600E by either siRNA or inhibitor vemurafenib suppressed Skp2 expression and cell growth. Mechanistic study shows that BRAFV600E suppression of Skp2 is dependent on c-Myc transcription factor via specifically bounding to the E-box region on SKP2 promoter. Further, the overexpression of Skp2 resulted in a markedly increase in cell growth, cell cycle progression and glycolysis which were repressed by BRAFV600E inhibition. Supporting the biological significance, Skp2 is specifically correlated with poor patient outcome in BRAFV600E but did not in BRAFWT melanomas. Thus, as a downstream target of BRAFV600E, Skp2 is critical for responses to BRAF inhibition, indicating targeting Skp2 might be a promising strategy for the treatment of BRAFi resistant melanomas.