MAPK3 and cancer: As the phosphorylation status of RKIP in the heart is different than in epithelial or cancer cells, RKIP does not inhibit ERK1/2 in cardiomyocytes, which is of particular relevance since ERK1/2 signaling in the heart is responsible for cardiomyocyte survival and protection from stress-induced cardiomyocyte death ([26,27]; also see Section 3.2 “ERK1/2 in the heart”).