MAPK1 and cancer: Notably, both total and the phosphorylated endogenous EGFR, but not its downstream p-AKT and p-ERK, were slightly increased by ectopic RAB31 in various cancer cell lines (Supplementary information, Fig. S10e), indicating that EGFR signaling from plasma membrane to endosomal surface20 is not affected by RAB31, but the activated EGFR is retained in the MVEs by RAB31.