title: Expression of constitutively active phosphatidylinositol 3-kinase inhibits activation of caspase 3 and apoptosis of cardiac muscle cells.
abstract: Apoptosis of cardiac muscle cells contributes to the development of cardiomyopathy. Recent studies showed that insulin-like growth factor I (IGF-I) inhibits apoptosis of cardiac muscle cells and improves myocardial function in experimental heart failure. This study was carried out to elucidate the role of phosphatidylinositol 3-kinase (PI 3-kinase) in the anti-apoptotic actions of IGF-I in cardiomyocytes and to explore whether expression of constitutively active PI 3-kinase can inhibit apoptosis in cardiomyocytes. Apoptosis of primary cardiomyocytes was induced by doxorubicin treatment and serum withdrawal. Transduction of cardiomyocytes with constitutively active PI 3-kinase specifically lead to serine phosphorylation of Akt, whereas phosphorylation of IGF-I receptor, IRS1/2 and p44/42 mitogen-activated protein kinase were not increased. In the cardiomyocytes transduced with constitutively active PI 3-kinase, activation of the pro-apoptotic caspase 3 was attenuated and fragmentation of DNA was reduced. Preincubating cells with PI 3-kinase inhibitor LY294002 was associated with loss of anti-apoptotic actions of IGF-I and PI 3-kinase. Neither IGF-I nor constitutively active PI 3-kinase lead to serine phosphorylation of Bad, suggesting that the anti-apoptotic effects of PI 3-kinase are not mediated through Bad phosphorylation in cardiac muscle cells. To determine whether activation of caspase 3 is sufficient to induce apoptosis in cardiomyocytes, an engineered TAT-caspase 3 protein was introduced to cardiomyocytes. Significant reduction of cell viability occurred in the cardiomyocytes transduced with active caspase 3, indicating that activation of caspase 3 is sufficient to cause cardiomyocyte death. These findings indicate the existence of an IGF-I receptor-PI 3-kinase-caspase 3 pathway in cardiomyocytes that plays an important role in the anti-apoptotic actions of IGF-I in heart. Moreover, these data suggest that modulation of PI 3-kinase activities may represent a potential therapeutic strategy to counteract the occurrence of apoptosis in cardiomyopathy.
authors.affiliation: Department of Medicine and Biological Chemistry, Division of Endocrinology, Diabetes, and Metabolism, University of California, Irvine, California 92697, USA.
authors.forename: W
authors.initials: W
authors.lastname: Wu
authors.forename: W L
authors.initials: WL
authors.lastname: Lee
authors.forename: Y Y
authors.initials: YY
authors.lastname: Wu
authors.forename: D
authors.initials: D
authors.lastname: Chen
authors.forename: T J
authors.initials: TJ
authors.lastname: Liu
authors.forename: A
authors.initials: A
authors.lastname: Jang
authors.forename: P M
authors.initials: PM
authors.lastname: Sharma
authors.forename: P H
authors.initials: PH
authors.lastname: Wang
mesh_terms: D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology* / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
chemical_list: D061945:Caspase Inhibitors; D002867:Chromones; D009025:Morpholines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases