Regulator of G-protein signaling subtype 4 mediates antihypertrophic effect of locally secreted natriuretic peptides in the heart

Background - Mice lacking guanylyl cyclase- A ( GC- A), a natriuretic peptide receptor, have pressure- independent cardiac hypertrophy. However, the mechanism underlying GC- A - mediated inhibition of cardiac hypertrophy remains to be elucidated. In the present report, we examined the role of regulator of G- protein signaling subtype 4 ( RGS4), a GTPase activating protein for G(q) and G(i), in the antihypertrophic effects of GC- A. Methods and Results - In cultured cardiac myocytes, treatment of atrial natriuretic peptide stimulated the binding of guanosine 3', 5'- cyclic monophosphate- dependent protein kinase ( PKG) I-alpha to RGS4, PKG- dependent phosphorylation of RGS4, and association of RGS4 and G alpha(q). In contrast, blockade of GC- A by an antagonist, HS- 142- 1, attenuated the phosphorylation of RGS4 and association of RGS4 and G alpha(q). Moreover, overexpressing a dominant negative form of RGS4 diminished the inhibitory effects of atrial natriuretic peptide on endothelin- 1 - stimulated inositol 1,4,5-triphosphate production, [(3)H] leucine incorporation, and atrial natriuretic peptide gene expression. Furthermore, expression and phosphorylation of RGS4 were significantly reduced in the hearts of GC- A knockout ( GC- A- KO) mice compared with wild- type mice. For further investigation, we constructed cardiomyocyte- specific RGS4 transgenic mice and crossbred them with GC- A- KO mice. The cardiac RGS4 overexpression in GC- A- KO mice significantly reduced the ratio of heart to body weight ( P < 0.001), cardiomyocyte size ( P < 0.01), and ventricular calcineurin activity ( P < 0.05) to 80%, 76%, and 67% of nontransgenic GC- A- KO mice, respectively. It also significantly suppressed the augmented cardiac expression of hypertrophy- related genes in GC- A- KO mice. Conclusions - These results provide evidence that GC- A activates cardiac RGS4, which attenuates G alpha(q) and its downstream hypertrophic signaling, and that RGS4 plays important roles in GC- A - mediated inhibition of cardiac hypertrophy.