Hybrid transgenic mice reveal in vivo specificity of G protein-coupled receptor kinases in the heart

G protein-coupled receptor kinases (GRKs) phosphorylate activated G protein -coupled receptors, including alpha(1B)-adrenergic receptors (ARs), resulti ng in desensitization. In vivo analysis of GRK substrate selectivity has be en limited. Therefore, we generated hybrid transgenic mice with myocardium- targeted overexpression of 1 of 3 GRKs expressed in the heart (GRK2 [common ly known as the beta-AR kinase I], GRK3, or GRK5) with concomitant cardiac expression of a constitutively activated mutant (CAM) or wild-type cr(1B)AR . Transgenic mice with cardiac CAM alpha(1B)AR overexpression had enhanced myocardial alpha(1)AR signaling and elevated heart-to-body weight ratios wi th ventricular atrial natriuretic factor expression denoting myocardial hyp ertrophy. Transgenic mouse hearts overexpressing only GRK2, GRK3, or GRK5 h ad no hypertrophy, In hybrid transgenic mice, enhanced in vivo signaling th rough CAM alpha(1B)ARs, as measured by myocardial diacylglycerol content, w as attenuated by concomitant overexpression of GRK3 but not GRK2 or GRKS. C AM alpha(1B)AR-induced hypertrophy and ventricular atrial natriuretic facto r expression were significantly attenuated with either concurrent GRK3 or G RK5 overexpression. Similar GRK selectivity was seen in hybrid transgenic m ice with wild-type alpha(1B)AR overexpression concurrently with a GRK. GRK2 overexpression was without effect on any in vivo CAM or wild-type alpha(1B )AR cardiac phenotype, which is in contrast to previously reported in vitro findings. Furthermore, endogenous myocardial alpha(1)AR mitogen-activated protein kinase signaling in single-GRK transgenic mice also exhibited selec tivity, as GRK3 and GRK5 desensitized in vivo alpha(1)AR mitogen-activated protein kinase responses that were unaffected by GRK2 overexpression. Thus, these results demonstrate that GRKs differentially interact with alpha(1B) ARs in vivo such that GRK3 desensitizes all alpha(1B)AR signaling, whereas GRK5 has partial effects and, most interestingly, GRK2 has no effect on in vivo alpha(1B)AR signaling in the heart.