MAPK1 and cancer: Of these, ERK2 (encoded by the gene MAPK1) was reported to increase the activity and phosphorylation of the oncoprotein RPS6KA1 (ribosomal protein S6 kinase, 90 kDa, polypeptide A1), leading to cancer cell proliferation (Kyriakis and Avruch, 2001; Zhao et al., 1995).