Opposing effects of calcium entry and phorbol esters on fusion of chick muscle cells.
Studies utilizing cultured muscle cells have shown that myoblast fusion requires extracellular Ca2+ and involves transient coordinated changes in cell membrane topography and cytoskeletal organization. However, neither the mechanisms by which Ca2+ influences these changes nor its cellular sites of action are known. We have investigated the effects of Ca2+ channel modulators and phorbol esters on fusion of embryonic chick myoblasts in culture. Myoblast fusion was inhibited by the Ca2+ channel blockers D600 and nitrendipine and stimulated by the Ca2+ channel activator Bay K 8644. We have obtained evidence that the tumor promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibits fusion through activation of protein kinase C. Myoblasts prevented from fusing by Ca2+ channel blockers or TPA display a distinctive elongated morphology that is characteristic of cells prevented from fusion by Ca2+ deprivation. The inhibition of fusion by D600 and TPA is significantly diminished in the presence of the Ca2+ ionophore A23187. TPA arrest of myoblast fusion was found to be accompanied by an increase in phosphorylation of the 20-kDa light chain of cytoplasmic myosin in a dose- and time-dependent manner. The effects of TPA on myoblast fusion and phosphorylation of myosin light chain were mimicked by the cell permeant diacylglycerol sn-1,2-dioctanoylglycerol, a potent activator of protein kinase C. The present results suggest that activators of protein kinase C block fusion by interfering with a Ca2+ signal transduction pathway and that this interference may be associated with a protein kinase C catalyzed inhibitory phosphorylation of myosin light chain.
Rapuano
M
M
Cellular and Developmental Biology Program, State University of New York, Stony Brook 11794.
Ross
A F
AF
Prives
J
J
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002459:Cell Fusion / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D004533:Egtazic Acid / Q000494:pharmacology; D005711:Gallopamil / Q000494:pharmacology; D007700:Kinetics; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D015879:Myosin Subfragments; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism; D009568:Nitrendipine / Q000494:pharmacology; D010446:Peptide Fragments / Q000302:isolation & purification / Q000378:metabolism; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015879:Myosin Subfragments; D010446:Peptide Fragments; D010703:Phorbol Esters; C008874:phorbol-12,13-diacetate; D015240:Phorbol 12,13-Dibutyrate; D000001:Calcimycin; D005711:Gallopamil; D004533:Egtazic Acid; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009568:Nitrendipine; D009219:Myosin-Light-Chain Kinase; D009218:Myosins; D013755:Tetradecanoylphorbol Acetate