Oncogenic BRAF signalling increases Mcl-1 expression in cutaneous metastatic melanoma

The Bcl-2 family member Mcl-1 is essential for melanoma survival; however, the influence of oncogenic BRAF signalling remains elusive. In this study, Mcl-1 splice variant expression was determined in a panel of melanoma cell lines in relation to BRAF mutational status. Mcl-1L mRNA expression was increased in melanoma cells compared with primary melanocytes with significantly increased mRNA and protein expression observed in BRAF(V600E) mutant melanoma cells. Although no change in Mcl-1S mRNA was observed, Mcl-1S protein expression also increased in BRAF mutant melanoma cells. Additionally, while over-expression of mutant BRAF(V600E) increased both Mcl-1L and Mcl-1S expression, inhibition of hyperactive BRAF signalling resulted in decreased Mcl-1L expression. These studies suggest that the regulation of Mcl-1 expression by BRAF signalling is increased by oncogenic activation of BRAF, revealing a mechanism of apoptotic resistance which may be overcome by the use of more specifically targeted Mcl-1 inhibitors.