P-ARRESTINS AND GRKs IN CARDIOVASCULAR FUNCTION. G protein coupled receptors (GPCRs) such as those for catecholamines and angiotensin II regulate cardiovascular functions including vasoconstriction and vasodilation;vascular smooth muscle cell (VSM) mitogenesis and migration;and cardiac inotropy and chronotropy. These functions may be perturbed in hypertension, in pathological intimal hyperplasia as after bypass surgery or angioplasty, or in heart failure. Following GPCR activation, the receptors are phosphorylated by one of several G protein coupled receptor kinases (GRKs) and then bind one of the two isoforms of p-arrestin. p-arrestin binding sterically interdicts further signaling to G proteins leading to receptor desensitization and attenuation of second messenger generation, p-arrestins also play positive roles in signaling, serving as adaptors and scaffolds to organize receptor-mediated activation of MAP kinase cascades and other pathways. These MAP kinases regulate mitogenesis and migration of vascular smooth muscle cells. Recently we have found that receptor ligands may vary dramatically in their ability to stimulate G protein versus p-arrestin-mediated signaling. However, the cellular and physiological consequences of p-arrestin/GRK mediated signaling in cardiovascular (or other) systems are largely unknown. Accordingly, we will use several approaches to test our central hypothesis that p-arrestin/GRK- mediated signaling contributes significantly to the short and long-term regulation of cardiovascular function. Our approaches will include the use of mutant receptors and specific agonists which can selectively activate p-arrestin but not G protein signaling;siRNA to p-arrestins and GRKs;knock-out mice which we have previously developed lacking each of the p-arrestins and GRKs;and cells derived there from. Utilizing the p-adrenergic receptors and angiotensin IMA receptor as our models our specific aims are to determine: 1) the specificity of individual p-arrestins and GRKs in desensitizing G protein mediated second messenger generation and to compare this with their roles in mediating signaling, as for example through ERK activation. 2) The physiological effects of P-arrestin-mediated signaling, a) In vitro on cardiac myocytes and vascular smooth muscle cells, and b) In vivo on cardiac inotropy and chronotropy and on systemic blood pressure, c) The in vivo consequences of cardiac signaling by mutant p-adrenergic receptors and angiotensin II1A receptors which are uncoupled from G proteins but signal through p-arrestins. 3) The chronic effects of an ang analog (SII ang) which signals only through p-arrestins, on the development and course of CHF in a transgenic mouse overexpressing calsequestrin in the heart. These experiments have the potential to delineate an entirely novel and general mode of receptor-mediated signaling and to point the way to the development of novel therapeutics which target this recently discovered signaling mechanism.
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