Gα13 stimulates gene expression and increases cell size in cultured neonatal rat ventricular myocytes

Objectives: Constitutively-active Ga,, causes permissive cell types to proliferate or undergo phenotypic transformation implying a role for G(13) in the control of cell growth. Cardiac myocytes are terminally-differentiated cells which respond to growth stimuli by increasing in size rather than by cell division. The objective of this study was to determine whether constitutively-active G alpha(13) is able to induce a hypertrophic phenotype in cardiac myocytes. Methods: Cultured neonatal rat ventricular myocytes were transiently transfected with an expression vector (pRC/RSV) encoding wild-type G alpha(13) or constitutively-active G(alpha 13)Q226L. Effects on transcription were monitored by co-transfected luciferase (LUX) reporter genes under the control of promoters responsive to hypertrophic stimuli. Cell size was determined by planimetry. Results: Transfection of neonatal myocytes with G alpha(13)Q226L, but not wild-type G alpha(13), stimulated ANF638LUX and ANF3003LUX expression to 3.0+/-0.3- and 4.3+/-0.6-fold of the control, respectively. Likewise, G alpha(12)Q226L stimulated vMLC250LUX and vMLC2700LUX expression to 3.9+/-1.0- and to 7.7+/-1.7-fold of controls, respectively, but there was relatively little effect of G alpha(13)Q226L on c-fos-SRE- and beta-MHC promoter activity. The effects of G alpha(13)Q226L on ANF3003LUX were inhibited by expression of C3 exoenzyme. Wild-type G alpha(13) and G alpha(13)Q226L increased myocyte area from 869+/-43 mu m(2) in control transfections to 1287+/-64 mu m(2) and 1278+/-59 mu m(2), respectively. Conclusion: We conclude that G alpha(13)Q226L is able to induce gene expression and morphological changes associated with a hypertrophic response in cardiac myocytes and that the transcriptional effects may be mediated through a Rho-dependent mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.