MEK

MEK (Mitogen-activated protein kinase kinase, MAPKK) is a kinase enzyme which phosphorylates mitogen-activated protein kinases (MAPKs). The activated MAPK leads to the phosphorylation of downstream transcription factors that regulate various responses such as stress signaling, pathogen response, and hormone signaling.

In general, the MAPKKK phosphorylates a serine or threonine residue on a MAPKK, which sequentially activates a MAPK (ERK, p38 or JNK), the last protein in the cascade. Activation of the p38 MAPK occurs mainly through mitogen-activated protein kinase kinase 3 (MKK3) and MKK6 (sometimes MKK4). The JNK is regulated by two upstream MAP2Ks: MKK4 and MKK7. The highly homologous kinases, MEK1 and MEK2, act downstream of Ras and Raf to activate ERK mitogen-activated protein kinases.