Note that in the time course experiment using four breast cancer cell lines, the MEK inhibitor sensitivity of the two MAP2K4 mutant breast cancer cell lines was also not very apparent during the first 72 h of culture (Fig. 1c) and similar result was seen in the isogenic MAP3K1 and MAP2K4 knockout cells (Fig. 3b, c). Here, MAP2K4 is linked to breast carcinoma.