Identification of a new form of death-associated protein kinase that promotes cell survival

In this study, two alternatively spliced forms of the mouse death-associate d protein kinase (DAPK) have been identified and their roles in apoptosis e xamined. The mouse DAPK-alpha sequence is 95% identical to the previously d escribed human DAPK, and it has a kinase domain and calmodulin-binding regi on closely related to the 130-150 kDa myosin light chain kinases. A beta -r esidue extension of the carboxyl terminus of DAPK-beta distinguishes it fro m the human and mouse DAPK-alpha. DAPK phosphorylates at least one substrat e in vitro and in vivo, the myosin II regulatory light chain. This phosphor ylation occurs preferentially at Ser-19 and is stimulated by calcium and ca lmodulin. The mRNA encoding DAPK is widely distributed and detected in mous e embryos and most adult tissues, although the expression of the encoded 16 0-kDa DAPK protein is more restricted. Overexpression of DAPK-alpha, the mo use homolog of human DAPK has a negligible effect on tumor necrosis factor (TNF)-induced apoptosis. Overexpression of DAPK-beta has a strong cytoprote ctive effect on TNF-treated cells. Biochemical analysis of TNF-treated cell lines expressing mouse DAPK-beta suggests that the cytoprotective effect o f DAPK is mediated through both intrinsic and extrinsic apoptotic signaling pathways and results in the inhibition of cytochrome c release from the mi tochondria as well as inhibition of caspase-3 and caspase-9 activity. These results suggest that the mouse DAPK-beta is a negative regulator of TNF-in duced apoptosis.