title: Beta-adrenergic receptor-mediated DNA synthesis in neonatal rat cardiac fibroblasts proceeds via a phosphatidylinositol 3-kinase dependent pathway refractory to the antiproliferative action of cyclic AMP.
abstract: The following study was undertaken to elucidate the cytoskeletal phenotype of neonatal rat cardiac fibroblasts (NNCF) and the signaling pathways coupled to beta-adrenergic receptor stimulated DNA synthesis. The cytoskeletal proteins vimentin, and smooth muscle alpha-actin were detected in NNCF, suggestive of a myofibroblast phenotype. Isoproterenol (ISO) treatment stimulated (3)H-thymidine uptake, and concomitantly increased intracellular cyclic AMP levels. However, cyclic AMP-elevating agents markedly decreased DNA synthesis. Coincident with growth, ISO-stimulated phosphatidylinositol 3-kinase (PI3-K) activity, and the PI3-K inhibitor LY294002 abrogated enzyme activity, and DNA synthesis. Unexpectedly, the serine/threonine kinase protein kinase Balpha (PKBalpha), a putative downstream target of PI3-K, was dephosphorylated following ISO treatment. Despite PKBalpha inactivation, the phosphorylation of its putative downstream target, the pro-apoptotic enzyme glycogen synthase kinase-3alpha was significantly increased in response to ISO. These latter effects of ISO were mimicked by the cyclic AMP-elevating agent forskolin. Lastly, ISO treatment increased p70 ribosomal S6 kinase (p70S6K) phosphorylation, as reflected by an upward electrophoretic mobility shift. The pretreatment with rapamycin abrogated the ISO-mediated mobility shift of p70S6K, and DNA synthesis. Collectively, these data demonstrate that NNCF express a myofibroblast phenotype, and beta-adrenergic agonists promote DNA synthesis via a PI3-K-dependent pathway involving p70S6K. Although unable to suppress ISO-stimulated DNA synthesis, cyclic AMP can influence specific downstream targets of PI3-K highlighting a novel crosstalk between these signaling pathways.
authors.affiliation: Centre de Recherche de l'Institut de Cardiologie de Montréal, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Federico
authors.initials: F
authors.lastname: Colombo
authors.forename: Hugues
authors.initials: H
authors.lastname: Gosselin
authors.forename: Viviane
authors.initials: V
authors.lastname: El-Helou
authors.forename: Angelino
authors.initials: A
authors.lastname: Calderone
mesh_terms: D000199:Actins / Q000378:metabolism; D000322:Adrenergic Agonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000187:drug effects / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014746:Vimentin / Q000378:metabolism
chemical_list: D000199:Actins; D000322:Adrenergic Agonists; D005576:Colforsin; D000242:Cyclic AMP; D003598:Cytoskeletal Proteins; D004247:DNA; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011943:Receptors, Adrenergic, beta; D014746:Vimentin