Ca2+-independent smooth muscle contraction. a novel function for integrin-linked kinase.
Smooth muscle contraction follows an increase in cytosolic Ca(2+) concentration, activation of myosin light chain kinase, and phosphorylation of the 20-kDa light chain of myosin at Ser(19). Several agonists acting via G protein-coupled receptors elicit a contraction without a change in [Ca(2+)](i) via inhibition of myosin light chain phosphatase and increased myosin phosphorylation. We showed that microcystin (phosphatase inhibitor)-induced contraction of skinned smooth muscle occurred in the absence of Ca(2+) and correlated with phosphorylation of myosin light chain at Ser(19) and Thr(18) by a kinase distinct from myosin light chain kinase. In this study, we identify this kinase as integrin-linked kinase. Chicken gizzard integrin-linked kinase cDNA was cloned, sequenced, expressed in E. coli, and shown to phosphorylate myosin light chain in the absence of Ca(2+) at Ser(19) and Thr(18). Subcellular fractionation revealed two distinct populations of integrin-linked kinase, including a Triton X-100-insoluble component that phosphorylates myosin in a Ca(2+)-independent manner. These results suggest a novel function for integrin-linked kinase in the regulation of smooth muscle contraction via Ca(2+)-independent phosphorylation of myosin, raise the possibility that integrin-linked kinase may also play a role in regulation of nonmuscle motility, and confirm that integrin-linked kinase is indeed a functional protein-serine/threonine kinase.
Deng
J T
JT
Smooth Muscle Research Group and Canadian Institutes of Health Research Group in Regulation of Vascular Contractility, Department of Biochemistry, University of Calgary Faculty of Medicine, Calgary, Alberta T2N 4N1, Canada.
Van Lierop
J E
JE
Sutherland
C
C
Walsh
M P
MP
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D002645:Chickens; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005895:Gizzard, Avian; D006801:Humans; D007700:Kinetics; D052998:Microcystins; D008954:Models, Biological; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000201:enzymology / Q000502:physiology*; D009219:Myosin-Light-Chain Kinase / Q000737:chemistry* / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D000099200:Scaffold Protein ILK
D002118:Calcium; D004791:Enzyme Inhibitors; D052998:Microcystins; D009219:Myosin-Light-Chain Kinase; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D010768:Phosphoserine; D010769:Phosphothreonine; D017346:Protein Serine-Threonine Kinases; D000099200:Scaffold Protein ILK; C078588:microcystin