Abstract 179: EGFR Transactivation Triggered by Alpha1a-Adrenergic Receptor Genetic Variant is Generalizable Phenomenon in Cardiovascular Cells

Abstract

Alpha 1 -Adrenergic Receptors (α 1 AR) are G protein-coupled transmembrane receptors (GPCRs) that mediate actions of the sympathetic nervous system through binding of endogenous catecholamines epinephrine and norepinephrine. Three subtypes of α 1 ARs (α 1a , α 1b , α 1d ) are expressed within most sympathetic tissues and in the human heart and they couple predominantly to the G q/11 family of G proteins. α 1a ARs play a major role in regulating vascular tone, in blood vessel repair and in cardiovascular diseases like hypertension, myocardial hypertrophy, ischemia and heart failure. Recently, we discovered a novel, unique mechanism of hypertension triggered by naturally occurring human α 1a AR-G247R (247R) genetic variant, identified in the 3 rd intracellular loop (3iL) of the receptor in hypertensive patient. 247R signals in Gq-independent but βarrestin1-dependent manner leading to transactivation of epidermal growth factor receptor (EGFR) via constitutive active coupling to the βarrestin1 /MMP7/EGFR pathway. We also demonstrated that expression of 247R in cardiomyoblasts leads to phenotypical and morphological changes of the cells to novel fibroblast-like phenotype. Here we examine if the 247R-triggered hyperproliferation is generalizable in other cell types such as smooth muscle cells (SMC). Our preliminary results reveal that constitutive expression of 247R in human coronary artery SMCs and in A-10 rat cell line leads to ~2-fold increased hyperproliferation and ERK-kinase activation. The increased proliferation of 247R cells is reduced by EGFR specific inhibitor AG1478 and general MMP inhibitor GM6001, indicating involvement of EGFR transactivation pathway in 247R-triggered hyperproliferation. We elucidate molecular mechanisms and signal transduction pathways responsible for increased cell proliferation and hypertrophy in SMCs. Search of SNP databases revealed several additional SNPs in the same 3iL of human α 1a AR. The structure modeling reveals that 247R is a representative of these SNPs, and novel EGFR transactivation pathway triggered by 247R may represent general mechanism for SNPs identified in the 3iL of α 1a AR involved in development of hypertension.