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Catalytic domain of the Serine/Threonine Kinase, Extracellular signal-Regulated Kinase 5 STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. ERK5 (also called Big MAPK1 (BMK1) or MAPK7) has a unique C-terminal extension, making it approximately twice as big as other MAPKs. This extension contains transcriptional activation capability which is inhibited by the N-terminal half. ERK5 is activated in response to growth factors and stress by a cascade that leads to its phosphorylation by the MAP2K MEK5, which in turn is regulated by the MAP3Ks MEKK2 and MEKK3. Activated ERK5 phosphorylates its targets including myocyte enhancer factor 2 (MEF2), Sap1a, c-Myc, and RSK. It plays a role in EGF-induced cell proliferation during the G1/S phase transition. Studies on knockout mice revealed that ERK5 is essential for cardiovascular development and plays an important role in angiogenesis. It is also critical for neural differentiation and survival. The ERK5 pathway has been implicated in the pathogenesis of many diseases including cancer, cardiac hypertrophy, and atherosclerosis. MAPKs are important mediators of cellular responses to extracellular signals. The ERK5 subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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