MAP kinase (MAPK, mitogen-activated protein kinase) is also termed as extracellular regulated protein kinase (ERK). It consists of a family of protein kinases. MAP kinase isoforms are widely expressed in the central nervous system, thymus, spleen, heart, lung, kidney, and in high levels in PC12 cells and in fibroblasts.
Mitogen-activated protein kinase (MAPK) superfamily of enzymes is involved in widespread signalling pathways. Members of this family include the ERK1/2 (extracellular signal-regulated protein kinase, also termed p42/p44 MAPK), JNK and p38 MAPK subfamilies. These are the terminal enzymes in a signalling cascade where each kinase phosphorylates and activates the next member in the sequence. Phosphorylation of both tyrosine and threonine is essential for the full activation of all MAPKs. Several kinases participate in activation of the ERK cascade. This cascade is initiated by the small G protein Ras, which upon stimulation causes activation Raf1 kinase. Raf1 continues the transmission by activating MEK. Activated MEK appears to be the only kinase capable of specifically phosphorylating and activating ERK. ERK appears to be an important regulatory molecule, which by can phosphorylate regulatory targets in the cytosol (phospholipase A2, PLA2), translocated into and phosphorylate substrates in the nucleus (ELK1). The activation of ERK cascade mediates and regulates the signal transduction pathways in response to stress, mitogenic signals and is important in development and differentiation, learning, memory and survival. MAPK plays a crucial role in various signal transduction pathways, leading signals of growth factor and G protein coupled receptors to their intracellular targets. MAP kinase regulates several cellular processes including proliferation, differentiatio, cellular morphology and oncogenesis.
