Protein kinase C-mediated phosphorylation of troponin I and C-protein in isolated myocardial cells is associated with inhibition of myofibrillar actomyosin MgATPase.
Phosphorylation of cardiac myofibrillar proteins by protein kinase C (PKC) in isolated adult rat cardiomyocytes has been compared with that mediated by the cAMP-dependent protein kinase (PKA). PKA activation by beta-adrenoreceptor (isoproterenol) stimulation results in stoichiometric phosphorylation of troponin I (TnI) and C-protein. PKC activation by either 12-O-tetradecanoylphorbol-13-acetate (TPA) or by alpha-adrenoreceptor (phenylephrine plus propranolol) stimulation results in phosphorylation of the same two proteins to similar extents. Two-dimensional phosphopeptide mapping shows that the same sites in TnI are modified by PKC in vitro and in TPA- or alpha-agonist-stimulated cells. These sites are distinct from those phosphorylated in isoproterenol-stimulated cells or by PKA in vitro. Phosphopeptide mapping analysis of C-protein shows that PKC and PKA phosphorylate identical residues in this protein in vitro and in situ. TPA-stimulated phosphorylation in myocytes is associated with a reduction in maximal activity of myofibrillar Ca(2+)-dependent actomyosin MgATPase. Isoproterenol-stimulated phosphorylation has no effect on maximal activity but reduces the Ca2+ sensitivity of the MgATPase. These data demonstrate that TnI and C-protein are phosphorylated in myocardial cells by both PKA and PKC, resulting in different functional consequences in each case.
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
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Venema
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Kuo
D000205:Actomyosin / Q000037:antagonists & inhibitors*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000201:enzymology*; D009218:Myosins / Q000037:antagonists & inhibitors*; D010449:Peptide Mapping; D010750:Phosphoproteins / Q000737:chemistry; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014336:Troponin / Q000378:metabolism*; D019209:Troponin C; D019210:Troponin I
D010750:Phosphoproteins; D011942:Receptors, Adrenergic, alpha; D014336:Troponin; D019209:Troponin C; D019210:Troponin I; D000205:Actomyosin; D011494:Protein Kinases; D011493:Protein Kinase C; D009218:Myosins; D007545:Isoproterenol; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium