Ras and rho are required for galphaq-induced hypertrophic gene expression in neonatal rat cardiac myocytes.
The hypertrophic response is characterized by increased myofibril/sarcomere organization, induction of the cardiac specific atrial natriuretic factor (ANF) and myosin light chain-2 (MLC-2v) genes, and an increase in total cell volume. The alpha1-adrenergic agonist phenylephrine induces both the morphological and biochemical markers of hypertrophy in cultured neonatal rat ventricular cardiomyocytes. Previous studies have suggested a functional requirement for the heterotrimeric G-protein, Galphaq, for a subset of the hypertrophic phenotypes. The small GTPases Ras and Rho have also been implicated in phenylephrine-induced hypertrophy. To further delineate the role of Galphaq in hypertrophy, a constitutively active mutant of Galphaq was transiently transfected in primary rat ventricular cardiomyocytes. This molecule was sufficient to induce ANF-, AP1-, and MLC-2-driven gene expression. Co-transfection of Galphaq and dominant negative Ras or dominant negative Raf resulted in dose-dependent inhibition of ANF-driven expression. Both dominant negative Rho, and the Rho inhibitor C3-transferase, also attenuated Galphaq- and Ras-induced ANF-driven gene expression. Cells transfected with active Galphaq did not show a detectable increase in activation of the mitogen activated protein kinases ERK or SAPK. However, activity of the MAP-kinases appears to be important for Galphaq-induced gene expression since the MAP-kinase phosphatase Clone 100 and catalytically inactive SAPK strongly inhibited Galphaq-induced ANF expression. Thus, our studies indicate Galphaq-induced hypertrophic gene expression requires the small G-proteins Ras and Rho. The data also indicates that Galphaq mediated gene expression is dependent on functional MAP-kinases and that multiple signaling pathways contribute to Galphaq-mediated cardiac cell hypertrophy.
Hines
W A
WA
Department of Human Genetics, Program in Human Molecular Biology and Genetics, Eccles Institute of Human Genetics, Bldg. 533, Rm. 4220, University of Utah, Salt Lake City, UT 84112, USA.
Thorburn
A
A
D000818:Animals; D000831:Animals, Newborn; D009320:Atrial Natriuretic Factor / Q000235:genetics; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D024722:Cardiac Myosins; D006332:Cardiomegaly / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D018994:Myosin Light Chains / Q000235:genetics; D011401:Promoter Regions, Genetic; D051381:Rats; D012234:Rho Factor / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000235:genetics; D014162:Transfection; D018631:ras Proteins / Q000235:genetics* / Q000378:metabolism
D004791:Enzyme Inhibitors; D005419:Flavonoids; D018994:Myosin Light Chains; D012234:Rho Factor; D018808:Transcription Factor AP-1; C107184:myosin light chain 2; D009320:Atrial Natriuretic Factor; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D024722:Cardiac Myosins; D019204:GTP-Binding Proteins; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one