MEK1

MEK1 is a MAP kinase or ERK kinase that phosphorylates the ERK gene product and acts as an immediate upstream activator of ERK signaling[1][2]. Mechanistically, MEK1 and MEK2 phosphorylate and activate ERK1/ERK2, positioning MEK proteins as pathway gatekeepers in the RAS-RAF-MEK-ERK cascade[3][4]. This cascade regulates cell proliferation, differentiation, survival, invasion, and other ERK-dependent cellular responses[3][5]. In disease models, ERK pathway activation is prominent in cancers driven by receptor tyrosine kinase, RAS, BRAF, CRAF, MEK1, or MEK2 alterations, which promote growth factor-independent ERK1/2 activation[5]. Compared with MEK2, MEK1 shares the same ERK substrates, but Mek1- embryos die from placental defects whereas Mek2- mice survive, indicating isoform-related developmental differences and functional redundancy controlled by total MEK protein level[4]. Structurally, MEK1 and MEK2 are closely related dual-specificity tyrosine/threonine kinases with a hydrophobic allosteric pocket adjacent to the ATP-binding site[6][5]. For experimental applications, PD098059 selectively inhibited MEK without significant inhibition of MAPK itself, and allosteric MEK blockade suppressed colon tumor growth in vivo[7][8].