Differential β‐arrestin2 binding of the human β 1 ‐adrenoceptor Arg389Gly polymorphic variants in cardiac myocytes

Abstract

Rationale The β1-adrenergic receptor (AR) is the primary receptor in cardiomyocytes through which catecholamines increase cardiac function, i.e. contractility and heart rate (positive inotropy and chronotropy). The human β1AR gene (Adrb1), which encodes a G protein-coupled receptor (GPCR), displays high nucleotide sequence variability. One of its several non-synonymous polymorphisms identified to date is the Gly/Arg variation at aminoacid position 389 (C1165G in the open reading frame's nucleotide sequence), with the Arg389 variant being much less frequent in African-Americans than in Caucasians (58% vs. 73%, respectively). Since amino acid 389 is located in the intracellular C-terminus of the encoded receptor, this polymorphism is expected, and has been shown to affect both signaling/function and desensitization of the β1AR. Indeed, Arg389 β1AR has been found to be hyperfunctional, compared to its Gly389 counterpart, in transfected cell lines and in cardiomyocytes in vitro. It is also known to affect the response of individuals to the cardiac stimulant (β1AR-agonist) dobutamine, as well as the responses of heart failure patients to several β-blockers (β1AR-antagonists), including carvedilol, to which the Arg allele confers greater responses. Consistent with this, homozygous Arg389 heart failure patients seem to fare much better than their homozygous Gly389 or heterozygous Arg389Gly counterparts when treated with the same β-blocker drug, a finding that has led to the idea of utilizing genotyping for the β1AR Arg389Gly polymorphism for the purposes of stratification of heart failure patients and of tailoring their b-blocker therapy. Objective To examine the interaction of the two β1AR variants with the signal transducers β-arrestins in neonatal rat ventricular myocytes (NRVMs), in order to identify molecular mechanisms underlying their functional differences. Methods We tested the interaction of the polymorphic β1ARs with β-arrestins via β1AR immunoprecipitation followed by β-arrestin immunoblotting in NRVM protein extracts. Results The β-arrestin1 isoform binds both variants equally well in NRVMs. Conversely, the potentially beneficial in the heart β-arrestin2 isoform interacts only with the Arg389 receptor (not with the Gly389 allele) in NRVMs. Conclusion Arg389 confers unique β-arrestin2-interacting properties to the β1AR in cardiac myocytes, potentially underlying this variant's gain-of-function phenotype.