title: Role of protein phosphatase 2A in the regulation of mitogen-activated protein kinase activity in ventricular cardiomyocytes.
abstract: Incubation of cultured, neonatal rat ventricular cardiomyocytes with 100 nM phorbol 12-myristate-13-acetate (PMA) induced a transient suppression of PP2A activity at 5 min, an effect that was reversed after 15 min of exposure to PMA. This inactivation was correlated with a transient increase in the phosphorylation level of the catalytic subunit of PP2A (193 +/- 38% of control levels at 5 min). Simultaneously to the transient inactivation of PP2A, we observed a rapid and reversible phosphorylation of 42-kDa MAP kinase (474 +/- 65% of control levels at 5 min, and 316 +/- 44% at 15 min) in cardiomyocytes treated with PMA. This transient phosphorylation was accompanied by a transient increase in cytosolic MAP kinase activity (209 +/- 17% of control values at 5 min and 125 +/- 7% at 15 min). Okadaic acid (1 microM ) completely blocked the decrease in the phosphorylation level and activity of MAP kinase occurring after 5 min of exposure to PMA. These data demonstrate that PP2A inactivation and MAP kinase activation are very strongly correlated in cardiomyocytes, indicating that PP2A plays a negative modulatory role in the regulation of MAP kinase activity.
authors.affiliation: Division of Endocrinology, University Hospital, Geneva, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Braconi Quintaje
authors.forename: D J
authors.initials: DJ
authors.lastname: Church
authors.forename: M
authors.initials: M
authors.lastname: Rebsamen
authors.forename: M B
authors.initials: MB
authors.lastname: Valloton
authors.forename: B A
authors.initials: BA
authors.lastname: Hemmings
authors.forename: U
authors.initials: U
authors.lastname: Lang
mesh_terms: D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D004789:Enzyme Activation; D004988:Ethers, Cyclic / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology / Q000201:enzymology*; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D054648:Protein Phosphatase 2; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004988:Ethers, Cyclic; D019319:Okadaic Acid; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D013755:Tetradecanoylphorbol Acetate