BRAF and cancer: To test this, we stably expressed disease-representative MEK mutants (cancer-derived Q56P, K57N, and C121S; RASopathy-derived F53S and Y130C) in A375 melanoma cells harboring BRafV600E (Supplementary Fig. 2b), and assessed their effects on the sensitivity of the tumor cells to BRaf- or MEK-inhibitors.