MAP2K1 and cancer: Thus, both basal and stimulated phosphorylation of MEK1 were significantly increased in the cancer–related mutations Q56P-MEK1 and K57N-MEK1, while there was no change or even a small decrease in the phosphorylation of Y130C-MEK1 as compared to WT control in both COS7 and HeLa cells (Fig. 4A,C).