Impaired desensitization of a human polymorphic α2B-adrenergic receptor variant enhances its sympatho-inhibitory activity in chromaffin cells

Kristy Nguyen,Theodoros Kassimatis,Anastasios Lymperopoulos

doi:10.1186/1478-811x-9-5

Abstract

Backgroundα2-adrenergic receptors (ARs) mediate many cellular actions of epinephrine and norepinephrine and inhibit their secretion from adrenal chromaffin cells. Like many other G-protein coupled receptors (GPCRs), they undergo agonist-dependent phopshorylation and desensitization by GPCR Kinases (GRKs), a phenomenon recently shown to play a major role in the sympathetic overdrive that accompanies and aggravates chronic heart failure. A deletion polymorphism in the human α2B-AR gene (Glu301-303) causes impaired agonist-promoted receptor phosphorylation and desensitization in heterologous cell lines. Given the importance of α2-ARs in regulation of catecholamine secretion from chromaffin cells, we sought to investigate, in the present study, the desensitization properties and the sympatho-inhibitory activity of this variant in a chromaffin cell line. For this purpose, we expressed this variant and its wild type counterpart in the well-established chromaffin cell line PC12, and performed receptor phosphorylation and desensitization studies, as well as in vitro catecholamine secretion assays.ResultsBoth the agonist-induced phosphorylation and agonist-dependent desensitization of the human Glu301-303 deletion polymorphic α2B-AR are significantly impaired in PC12 cells, resulting in enhanced signaling to inhibition of cholinergic-induced catecholamine secretion in vitro.ConclusionThis α2B-AR gene polymorphism (Glu301-303 deletion) might confer better protection against conditions characterized and aggravated by sympathetic/catecholaminergic overstimulation in vivo.

Highlights

Three distinct a2-adrenergic receptor (a2-adrenergic receptors (ARs)) subtypes (a2A, a2B, a2C) that mediate many of the physiological actions of the catecholamines (CAs) epinephrine (Epi) and norepinephrine (NE) have been described [1]
They belong to the family of G-protein coupled or seven transmembrane-spanning receptors (GPCRs or 7TMRs) and they are linked to the inhibitory Gi/o proteins [1]
Like many other G-protein coupled receptors (GPCRs), the a2B-AR undergoes agonist promoted desensitization [3] initiated by the phosphorylation of the receptor in its third intracellular loop by a well-characterized family of serine/threonine kinases termed G protein-coupled receptor kinases (GRKs), the most prominent member of which is the ubiquitously expressed GRK2 [4]

Summary

Introduction

Three distinct a2-adrenergic receptor (a2-AR) subtypes (a2A, a2B, a2C) that mediate many of the physiological actions of the catecholamines (CAs) epinephrine (Epi) and norepinephrine (NE) have been described [1]. They belong to the family of G-protein coupled or seven transmembrane-spanning receptors (GPCRs or 7TMRs) and they are linked to the inhibitory Gi/o proteins [1]. Its role in the Central Nervous System (CNS) remains largely elusive. It may be important in developmental processes, since homozygous a2B-KO mice do not breed well [2]. The phosphorylated receptor interacts with a certain family of proteins termed arrestins, which physically uncouple the receptor from G proteins, terminating receptor signaling [4]

Methods

Results

Conclusion