MAPK1 and cancer: As reported before, the RAF inhibitor vemurafenib activated RAF–MEK–ERK signaling in a paradoxical manner in the Ras-mutated cancer cell lines H1299 (NrasQ61K) and Sk-mel-2 (NrasQ61R) but not in the Ras-WT cancer cell line H522 (Fig. 4, A–F).