MAPK3 and cancer: However, like most protein kinases it also has other domains that are sites for further regulation by other pathways that are known to play a role in cancer, such as phosphorylation by ERK1/2 and CDK1 (Tusa et al., 2018), or possess non-catalytic functions that are not well targeted by small molecules such as the NLS and the TAD (Lochhead et al., 2020).