title: Involvement of protein phosphatase-1-mediated MARCKS translocation in myogenic differentiation of embryonic muscle cells.
abstract: Myristoylated alanine-rich C kinase substrate (MARCKS) translocates from the cytosol to the plasma membrane while mononucleated myoblasts fuse to form multinucleated myotubes. Here, we show that protein phosphatase-1-mediated dephosphorylation of MARCKS largely influences its subcellular localization and the fusion process. Treatment with okadaic acid or tautomycin, which are potent inhibitors of protein phosphatases and cell fusion, was found to reversibly block the MARCKS translocation. Moreover, the dephosphorylating activity against MARCKS markedly increased during myogenesis, and this increase was closely correlated with the membrane fusion of the cells. In addition, protein phosphatase-1 was identified as a major enzyme that is responsible for dephosphorylation of MARCKS. Furthermore, a mutation preventing MARCKS phosphorylation and thus facilitating MARCKS translocation resulted in promotion of the cell fusion. In contrast, overexpression of MARCKS carrying a mutation that blocks myristoylation and thus prevents the MARCKS translocation impaired the myoblast fusion. Together with the fact that MARCKS regulates the cytoskeleton dynamics by crosslinking the actin filaments in the plasma membrane and that myoblast fusion accompanies massive cytoskeleton reorganization, these results suggest that protein phosphatase-1-mediated MARCKS localization at the membrane is required for the fusion of embryonic muscle cells.
authors.affiliation: NRL of Protein Biochemistry, School of Biological Sciences, Seoul National University, 56-1 Shinreem-dong, Kwanak-gu, Seoul 151-742, Korea.
authors.forename: Sang Soo
authors.initials: SS
authors.lastname: Kim
authors.forename: Jung Hwa
authors.initials: JH
authors.lastname: Kim
authors.forename: Seung-Hye
authors.initials: SH
authors.lastname: Lee
authors.forename: Sung Soo
authors.initials: SS
authors.lastname: Chung
authors.forename: Ok-Sun
authors.initials: OS
authors.lastname: Bang
authors.forename: Dongeun
authors.initials: D
authors.lastname: Park
authors.forename: Chin Ha
authors.initials: CH
authors.lastname: Chung
mesh_terms: D000595:Amino Acid Sequence / Q000187:drug effects / Q000235:genetics; D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D003402:Creatine Kinase / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000196:embryology* / Q000201:enzymology; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D032448:Myoblasts, Skeletal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D054645:Protein Phosphatase 1; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D011506:Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011506:Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D019319:Okadaic Acid; D003402:Creatine Kinase; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D018995:Myosin Heavy Chains