The serine/threonine kinase PRAK is activated in response to cellular stress and proinflammatory cytokines, through its phosphorylation by MAP kinases including MAPK1/ERK, MAPK14/p38 alpha, and MAPK11/p38 beta. PRAK has been reported to have a putative tumor suppressor function by mediating senescence upon activation by p38 in response to oncogenic ras. It is thought that phosphorylation of p53 by PRAK following activation of p38 MAPK by ras plays an important role in ras induced senescence ａ