ZIP kinase identified as a novel myosin regulatory light chain kinase in HeLa cells.

A novel myosin light chain kinase (MLCK) cDNA was isolated from a HeLa cell cDNA library. The deduced amino acid sequence was identical to that of a zipper-interacting protein kinase (ZIPK) which mediates apoptosis [Kawai et al. (1998) Mol. Cell. Biol. 18, 1642-1651]. Here we found that HeLa ZIPK phosphorylated the regulatory light chain of myosin II (MRLC) at both serine 19 and threonine 18 in a Ca2+/calmodulin independent manner. Phosphorylation of myosin II by HeLa ZIPK resulted in activation of actin-activated MgATPase activity of myosin II. HeLa ZIPK is the first non-muscle MLCK that phosphorylates MRLC at two sites.