RAS AND RHO ARE REQUIRED FOR G-ALPHA-Q-INDUCED HYPERTROPHIC GENE-EXPRESSION IN NEONATAL RAT CARDIAC MYOCYTES

The hypertrophic response is characterized by increased myofibril/sarc omere organization, induction of the cardiac specific atrial natriuret ic factor (ANF) and myosin light chain-2 (MLC-2v) genes, and an increa se in total cell volume. The alpha(1)-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-prot ein, G alpha q, for a subset of the hypertrophic phenotypes. The small GTPases Ras and Rho have also been implicated in phenylephrine-induce d hypertrophy. To further delineate the role of G alpha q in hypertrop hy, a constitutively active mutant of G alpha q was transiently transf ected in primary rat ventricular cardiomyocytes. This molecule was suf ficient to induce ANF-, AP1-, and MLC-2-driven gene expression. Cotran sfection of G alpha q and dominant negative Ras or dominant negative R af resulted in dose-dependent inhibition of ANF-driven expression. Bot h dominant negative Rho, and the Rho inhibitor C3-transferase, also at tenuated G alpha q- and Ras-induced ANF-driven gene expression. Cells transfected with active G alpha q did not show a detectable increase i n activation of the mitogen activated protein kinases ERK or SAPK. How ever, activity of the MAP-kinases appears to be important for G alpha q-induced gene expression since the MAP-kinase phosphatase Clone 100 a nd catalytically inactive SAPK strongly inhibited G alpha q-induced AN F expression. Thus, our studies indicate G alpha q-induced hypertrophi c gene expression requires the small G-proteins Ras and Rho. The data also indicates that G alpha q mediated gene expression is dependent on functional MAP-kinases and that multiple signaling pathways contribut e to G alpha q-mediated cardiac cell hypertrophy. (C) 1998 Academic Pr ess Limited.