MAP kinase activated protein kinase 2 (MAPKAP Kinase 2), also known as p45 hsp27 kinase, is a 45-54 kDa serine/threonine protein kinase that contains a proline rich sequence and two putative SH3 binding sites. MAPKAP Kinase 2 is activated in response to stress, IL1 and TNF, possibly catalyzed by p38/Hog dependent phosphorylation. One of the major substrates of MAPKAP Kinase 2 is hsp27, which stimulates actin polymerization in order to facilitate recovery from destruction of cytoskeleton during cellular stresses. MAPKAP2 is implicated in several disorders including ischemic brain injury and heart failure and has been shown to be important in regulating stress resistance and the production of TNF alpha.