Mitogen activated protein kinases (MAP kinases) act as switch kinases that transmits information of increased intracellular tyrosine phosphorylation to that of serine/threonine phosporylation. MAPK-activated protein kinases (or MKs; formerly MAPKAP kinases) respond to mitogenic and stress stimuli through proline-directed phosphorylation and activation of the kinase domain by extracellular signal-regulated kinases 1 and 2 and p38 MAPKs.(ffta)
The signaling cascade is:
mitogen → MAPKK kinase (MAPKKK) → MAPK kinase (MAPKK) → MAP kinase (MAPK) → signaling
Among the substrates of ERK are the members of the p90 ribosomal S6 kinase (RSK) family of serine/threonine kinases (10). RSK plays an active role in nuclear signaling by phosphorylating the cyclic AMP response element binding protein (CRE-binding protein, CREB) (33), c-Fos (5), and IB (27). Phosphorylation of Bad (3, 29) and C/EBPß (4) by RSK can protect cells from apoptosis. RSK has also been implicated in cell cycle regulation. RSK phosphorylates histone H3 (25), suggesting that RSK may regulate chromatin remodeling.[s-fft]
MAP kinases are also called ERKs for extracellular-signal regulated kinases, microtubule associated protein-2 kinase (MAP-2 kinase), myelin basic protein kinase (MBP kinase), ribosomal S6 protein kinase (RSK-kinase) and EGF receptor threonine kinase (ERT kinase). Maximal MAP kinase activity requires phosphorylation of both tyrosine and threonine residues. Activators of the extracellular-signal regulated kinase family (ERKs) of MAPKs include the mitogens, Ras [fft], polypeptide growth factors PDGF, CSF-1, IGF-1, EGF insulin, PMA.
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