title: The regulation of smooth muscle contractility by zipper-interacting protein kinase.
abstract: Smooth muscle contractility is mainly regulated by phosphorylation of the 20 kDa myosin light chains (LC20), a process that is controlled by the opposing activities of myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP). Recently, intensive research has revealed that various protein kinase networks including Rho-kinase, integrin-linked kinase, zipper-interacting protein kinase (ZIPK), and protein kinase C (PKC) are involved in the regulation of LC20 phosphorylation and have important roles in modulating smooth muscle contractile responses to Ca2+ (i.e., Ca2+ sensitization and Ca2+ desensitization). Here, we review the general background and structure of ZIPK and summarize our current understanding of its involvement in a number of cell processes including cell death (apoptosis), cell motility, and smooth muscle contraction. ZIPK has been found to induce the diphosphorylation of LC20 at Ser-19 and Thr-18 in a Ca2+-independent manner and to regulate MLCP activity directly through its phosphorylation of the myosin-targeting subunit of MLCP or indirectly through its phosphorylation of the PKC-potentiated inhibitory protein of MLCP. Future investigations of ZIPK function in smooth muscle will undoubtably focus on determining the mechanisms that regulate its cellular activity, including the identification of upstream signaling pathways, the characterization of autoinhibitory domains and regulatory phosphorylation sites, and the development of specific inhibitor compounds.
authors.affiliation: Smooth Muscle Research Group and Department of Biochemistry and Molecular Biology, University of Calgary, Faculty of Medicine, 3330 Hospital Drive N.W, Calgary, AB T2N 4N1, Canada.
authors.forename: Eikichi
authors.initials: E
authors.lastname: Ihara
authors.forename: Justin A
authors.initials: JA
authors.lastname: MacDonald
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002465:Cell Movement / Q000502:physiology; D064550:Death-Associated Protein Kinases; D015195:Drug Design; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D016350:Leucine Zippers; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000201:enzymology*; D018994:Myosin Light Chains / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D051017:Apoptosis Regulatory Proteins; D004791:Enzyme Inhibitors; D018994:Myosin Light Chains; D010446:Peptide Fragments; D064550:Death-Associated Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D043263:Myosin-Light-Chain Phosphatase; D002118:Calcium