beta-Adrenergic stimulation of rat cardiac fibroblasts promotes protein synthesis via the activation of phosphatidylinositol 3-kinase.
beta -adrenergic agonists stimulate neonatal rat cardiac fibroblast growth, albeit the identity of the signaling event(s) remains equivocal. Isoproterenol (ISO) treatment increased intracellular cyclic AMP levels; however, cyclic AMP-elevating agents had no effect on protein synthesis. The tyrosine kinase inhibitor tyrphostin A25, and the inhibition of ras processing by the farnesyltransferase inhibitor BMS-191563 attenuated ISO-stimulated protein synthesis. Concomitant with increased protein synthesis, ISO stimulated extracellular signal-regulated protein kinase (ERK) and phosphatidylinositol 3-kinase (PI3-K) activity. The MEK1/2 inhibitor PD098059 abrogated ISO-stimulated ERK activity, albeit the increase in protein synthesis was unaffected. By contrast, LY294002 inhibited both ISO-stimulated PI3-K activity, and protein synthesis. ISO treatment did not increase the expression of transforming growth factor-beta(1)(TGF-beta(1)) mRNA, whereas a significant decrease in the steady-state mRNA level of TGF- beta(3)was observed. This latter effect was mimicked by cyclic AMP-elevating agents. Angiotensin II (AII) activation of the AT(1)receptor increased protein synthesis, but in contrast to ISO, the growth response was not inhibited by either tyrphostin A25 or BMS-191563, and was associated with the concomitant expression of both TGF-beta(1)and TGF-beta(3)mRNAs. Analogous to ISO, AII treatment increased ERK and PI3-K activity, and PI3-K was required for protein synthesis. These findings are the first to highlight the activation of PI3-K by a Gs(alpha)-coupled receptor, and its essential role in beta -adrenergic as well as AT(1)receptor-mediated protein synthesis in neonatal rat cardiac fibroblasts. However, despite the conserved role of PI3-K, additional disparate signaling pathways are recruited by ISO and AII, which may differentially influence fibroblast phenotype.
Colombo
F
F
Departément de Physiologie, Université de Montréal, Montréal, Québec, Canada.
Noël
J
J
Mayers
P
P
Mercier
I
I
Calderone
A
A
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D014176:Protein Biosynthesis; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000378:metabolism; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D053782:Transforming Growth Factor beta3; D020032:Tyrphostins / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D004791:Enzyme Inhibitors; D018343:Receptors, Adrenergic, beta-2; C508962:Tgfb1 protein, rat; C509046:Tgfb3 protein, rat; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D053782:Transforming Growth Factor beta3; D020032:Tyrphostins; D000804:Angiotensin II; C079836:tyrphostin 25; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D007545:Isoproterenol