Background
PRAK (p38-regulated /activated kinase), also referred to as mitogen-activated protein kinase (MAPK)-activated protein kinase (MAPKAPK)-5, is an ubiquitously expressed serine/threonine kinase regulated by p38α and p38β MAP kinases. Activated JNK, p38γ or p38δ are unable to induce phosphorylation of PRAK in vitro. Phosphorylation of PRAK occurs in vivo in response to p38 activation by stress-related extracellular stimuli including UV light, oxidation and proinflammatory cytokines. Two other substrates for p38, MAPKAPK-2 and MAPKAPK-3/3pK, share approximately 45% sequence homology with PRAK including the phosphorylation motif recognized by p38, Lys-X-Thr-Pro. Activated PRAK has been shown to specifically phosphorylate HSP 27 in vitro, suggesting that the protein may play a role in stress-induced small heat shock protein phosphorylation in vivo.