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Type: Book chapter
Title: Phosphorylation of the Protein Phosphatase Type 1 Inhibitor Protein CPI-17 by Protein Kinase C
Author: Walsh, M.
Susnjar, M.
Deng, J.
Sutherland, C.
Kiss, E.
Wilson, D.
Citation: Protein Phosphatase Protocols, 2007 / Greg Moorhead (ed./s), vol.365, pp.209-224
Publisher: Humana Press
Publisher Place: Totowa, NJ
Issue Date: 2007
Series/Report no.: Methods in Molecular Biology ; 367
ISBN: 158829711X
Editor: Greg Moorhead
Statement of
Michael P. Walsh, Marija Susnjar, Jingti Deng, Cindy Sutherland, Enikö Kiss, and Divid P. Wilson
Abstract: CPI-17 is a cytosolic protein of 17 kDa that becomes a potent inhibitor of certain type 1 protein serine/threonine phosphatases, including smooth muscle myosin light-chain phosphatase (MLCP), when phosphorylated at Thr38. Several protein kinases are capable of phosphorylating CPI-17 at this site in vitro; however, in intact tissue, compelling evidence only exists for phosphorylation by protein kinase C (PKC). Agonist-induced activation of heterotrimeric G proteins of the Gq/11 family via seven-transmembrane domain-containing, G protein-coupled receptors results in phospholipase Cbeta-mediated hydrolysis of membrane phosphatidylinositol 4,5-bisphosphate to generate inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol (DAG). IP3 triggers Ca2+ release from the sarcoplasmic reticulum. DAG and Ca2+ together activate classical isoforms of PKC, and DAG activates novel PKC isoforms without a requirement for Ca2+. Activated PKC phosphorylates CPI-17 at Thr38, enhancing its potency of inhibition of MLCP approx 1000-fold. The myosin light-chain kinase (MLCK):MLCP activity ratio is thereby increased at the prevailing cytosolic free-Ca2+ concentration ([Ca2+]i), resulting in an increase in phosphorylation of the 20-kDa light chains of myosin II (LC20) catalyzed by Ca2+- and calmodulin-dependent MLCK and contraction of the smooth muscle. Physiologically, this mechanism can account for some instances of Ca2+ sensitization of smooth muscle contraction (i.e., an increase in force in response to agonist stimulation without a change in [Ca2+]i).
Keywords: Animals
Myosin-Light-Chain Phosphatase
Myosin-Light-Chain Kinase
Protein Kinase C
Phosphoprotein Phosphatases
Description: © 2007 Humana Press
DOI: 10.1385/1-59745-267-X:209
Appears in Collections:Aurora harvest 6
Molecular and Biomedical Science publications

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