title: Heart-specific small subunit of myosin light chain phosphatase activates rho-associated kinase and regulates phosphorylation of myosin phosphatase target subunit 1.
abstract: Phosphorylation of myosin regulatory light chain (MLC) plays a regulatory role in muscle contraction, and the level of MLC phosphorylation is balanced by MLC kinase and MLC phosphatase (MLCP). MLCP consists of a catalytic subunit, a large subunit (MYPT1 or MYPT2), and a small subunit. MLCP activity is regulated by phosphorylation of MYPTs, whereas the role of small subunit in the regulation remains unknown. We previously characterized a human heart-specific small subunit (hHS-M(21)) that increased the sensitivity to Ca(2+) in muscle contraction. In this study, we investigated the role of hHS-M(21) in the regulation of MLCP phosphorylation. Two isoforms of hHS-M(21), hHS-M(21)A and hHS-M(21)B, preferentially bound the C-terminal one-third region of MYPT1 and MYPT2, respectively. Amino acid substitutions at a phosphorylation site of MYPT1, Ser-852, impaired the binding of MYPT1 and hHS-M(21). The hHS-M(21) increased the phosphorylation level of MYPT1 at Thr-696, which was attenuated by Rho-associated kinase (ROCK) inhibitors and small interfering RNAs for ROCK. In addition, hHS-M(21) bound ROCK and enhanced the ROCK activity. These findings suggest that hHS-M(21) is a heart-specific effector of ROCK and plays a regulatory role in the MYPT1 phosphorylation at Thr-696 by ROCK.
authors.affiliation: Department of Molecular Pathogenesis, Medical Research Institute, School of Biomedical Science, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo 113-8510, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Shichi
authors.forename: Takuro
authors.initials: T
authors.lastname: Arimura
authors.forename: Taisuke
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Akinori
authors.initials: A
authors.lastname: Kimura
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003598:Cytoskeletal Proteins / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry; D008840:Microfilament Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism*; D009218:Myosins; D010766:Phosphorylation; D020798:Two-Hybrid System Techniques; D054460:rho-Associated Kinases / Q000378:metabolism*; D000099149:Ezrin
chemical_list: D003598:Cytoskeletal Proteins; D008565:Membrane Proteins; D008840:Microfilament Proteins; D043263:Myosin-Light-Chain Phosphatase; D009218:Myosins; D054460:rho-Associated Kinases; D000099149:Ezrin; C071058:moesin; C071776:radixin
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