Functional interaction between angiotensin ii and grk5 in cultured vascular smooth muscle cells (vsmc) and rat aorta

G protein receptor kinases (GRKs) are involved in receptor desensitization. In HEK293 cells overexpressing the angiotensin II (ang U) ATiA receptor (ATjAR) and GRK5, the ATjAR is a substrate for GRK5 and coupling to phospholipase C (PLC) is diminished. In the current study, we examined the interaction between ang II and GRKS in cultured VSMC from rat aorta, both in terms of functional consequences and long-term regulation. We stably transfected VSMC with a 1.8 kb fragment of bovine antisense GRK5, and measured GRK5 mRNA and protein expression, as well as ang n activation of PLC and phospholipase D (PLD). In antisense transfected cells, GRK5 mRNA was reduced by 64%. Both PLC and PLD activity, as measured by [3H]inositol and [3H]choline release, were increased (129±19% and 144±14% nontransfected levels, respectively), suggesting that GRK5 may be involved in the normal termination of VSMC ATi A& signaling. We next examined ang II regulation of GRKS expression. In cultured VSMC, GRK5 mRNA and protein is upregulated by exposure to 100 nM ang n for 16 h (453±27%). In aortas from rats receiving continuous infusion of ang II (0.7mg/ kg/day), GRK5 is also upregulated after 5 days (303±20%). This upregulation is completely blocked by the ATiAR antagonist losartan, and partially by the nonspecific vasodilator hydralazine, implying that GRKS may be regulated both by ang II and elevated blood pressure. In conclusion, GRKS appears to modulate AT| AR signaling in VSMC, and is itself regulated by ang II, suggesting a novel mechanism for regulating VSMC sensitivity to ang H.

Duke Scholars

Author Robert J. Lefkowitz Medicine, Cardiology