title: Inhibition of zipper-interacting protein kinase function in smooth muscle by a myosin light chain kinase pseudosubstrate peptide.
abstract: As a regulator of smooth muscle contractility, zipper-interacting protein kinase (ZIPK) appears to phosphorylate the regulatory myosin light chain (RLC20), directly or indirectly, at Ser19 and Thr18 in a Ca(2+)-independent manner. The calmodulin-binding and autoinhibitory domain of myosin light chain kinase (MLCK) shares similarity to a sequence found in ZIPK. This similarity in sequence prompted an investigation of the SM1 peptide, which is derived from the autoinhibitory region of MLCK, as a potential inhibitor of ZIPK. In vitro studies showed that SM1 is a competitive inhibitor of a constitutively active 32-kDa form of ZIPK with an apparent K(i) value of 3.4 microM. Experiments confirmed that the SM1 peptide is also active against full-length ZIPK. In addition, ZIPK autophosphorylation was reduced by SM1. ZIPK activity is independent of calmodulin; however, calmodulin suppressed the in vitro inhibitory potential of SM1, likely as a result of nonspecific binding of the peptide to calmodulin. Treatment of ileal smooth muscle with exogenous ZIPK was accompanied by an increase in RLC20 diphosphorylation, distinguishing between ZIPK [and integrin-linked kinase (ILK)] and MLCK actions. Administration of SM1 suppressed steady-state muscle tension developed by the addition of exogenous ZIPK to Triton-skinned rat ileal muscle strips with or without calmodulin depletion by trifluoperazine. The decrease in contractile force was associated with decreases in both RLC20 mono- and diphosphorylation. In summary, we present the SM1 peptide as a novel inhibitor of ZIPK. We also conclude that the SM1 peptide, which has no effect on ILK, can be used to distinguish between ZIPK and ILK effects in smooth muscle tissues.
authors.affiliation: Smooth Muscle Research Group and Dept. of Biochemistry and Molecular Biology, University of Calgary, Faculty of Medicine, 3330 Hospital Dr. NW, Calgary, Alberta T2N 4N1, Canada.
authors.forename: Eikichi
authors.initials: E
authors.lastname: Ihara
authors.forename: Elena
authors.initials: E
authors.lastname: Edwards
authors.forename: Meredith A
authors.initials: MA
authors.lastname: Borman
authors.forename: David P
authors.initials: DP
authors.lastname: Wilson
authors.forename: Michael P
authors.initials: MP
authors.lastname: Walsh
authors.forename: Justin A
authors.initials: JA
authors.lastname: MacDonald
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007082:Ileum / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D066298:In Vitro Techniques; D020930:MAP Kinase Kinase Kinases; D008954:Models, Biological; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010455:Peptides / Q000378:metabolism / Q000494:pharmacology*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D014162:Transfection; D000099200:Scaffold Protein ILK
chemical_list: D002118:Calcium; D002147:Calmodulin; D020930:MAP Kinase Kinase Kinases; D018994:Myosin Light Chains; D009219:Myosin-Light-Chain Kinase; D010455:Peptides; D047428:Protein Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011994:Recombinant Proteins; D000099200:Scaffold Protein ILK; C090757:mitogen-activated protein kinase kinase kinase 12