MAPK

Mitogen-activated protein kinases are the terminal modules of three-tier cascades, switched on by dual phosphorylation of a Thr-X-Tyr motif by MAP2Ks. The human family comprises the classical ERK1/2 (MAPK3 and MAPK1) proliferation module downstream of RAS-RAF-MEK, the stress-activated JNK1-3 and p38 alpha through delta branches that relay inflammatory and genotoxic signals, ERK5, and the atypical ERK3, ERK4 and ERK7/MAPK15 enzymes whose regulation departs from the classical modules. NLK, an evolutionarily divergent relative, modulates Wnt and Notch transcription. Substrate selectivity is enforced by docking grooves that bind D-motifs. Pharmacology is mature, with MEK inhibitors approved in oncology and p38 inhibitors extensively tested in inflammatory disease.