MAP kinase-activated protein kinase-2 (MAPKAPK-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. MAPKAPK-2 is activated in response to stress, IL-1 and TNF, possibly catalyzed by p38/Hog-dependent phosphorylation. One of the major substrates of MAPKAPK-2 is hsp27, which stimulates actin polymerization in order to facilitate recovery from destruction of cytoskeleton during cellular stresses. Two isoforms are produced due to alternative splicing of the same gene which differs in their C-terminals. This antibody recognizes both isoforms.