Hierarchy of Polymorphic Variation and Desensitization Permutations Relative to β1- and β2-Adrenergic Receptor Signaling

Abstract

Agonist-promoted desensitization of G-protein-coupled receptors results in partial uncoupling of receptor from cognate G-protein, a process that provides for rapid adaptation to the signaling environment. This property plays important roles in physiologic and pathologic processes as well as therapeutic efficacy. However, coupling is also influenced by polymorphic variation, but the relative impact of these two mechanisms on signal transduction is not known. To determine this we utilized recombinant cells expressing the human ␤ 1 -adrenergic receptor (␤ 1 AR) or a gain-of-function polymorphic variant (␤ 1 AR-Arg 389 ), and the ␤ 2 -adrenergic receptor (␤ 2 AR) or a loss-of-function polymorphic receptor (␤ 2 AR-Ile 164 ). Adenylyl cyclase activities were determined with multiple permutations of the possible states of the receptor: genotype, basal, or agonist stimulated and with or without agonist pre-exposure. For the ␤ 1 AR, the enhanced function of the Arg 389 receptor underwent less agonist-promoted desensitization compared with its allelic counterpart. Indeed, the effect of polymorphic variation on absolute adenylyl cyclase activities was such that desensitized ␤ 1 AR-Arg 389 signaling was equivalent to non-desensitized wild-type ␤ 1 AR; that is, the genetic component had as much impact as desensitization on receptor coupling. In contrast, the enhanced signaling of wild-type ␤ 2 AR underwent less desensitization compared with ␤ 2 AR-Ile 164 , thus the heterogeneity in absolute signaling was markedly broadened by this polymorphism. Inverse agonist function was not affected by polymorphisms of either subtype. A general model is proposed whereby up to 10 levels of signaling by G-protein-coupled receptors can be present based on the influences of desensitization and genetic variation on coupling.Like a number of other G-protein-coupled receptors, the ␤ 1 -and ␤ 2 -adrenergic receptors (␤ 1 AR and ␤ 2 AR, 1 respectively) undergo desensitization during continuous exposure to agonist.Such desensitization occurs maximally after several minutes of agonist exposure and is due to decreased interaction with G s , which is evoked by receptor phosphorylation (1). Thus the signal transduction of these receptors can be characterized as one of two potential conditions or states, defined here as "control" (no recent exposure to agonist) and "desensitized." However, we have recently shown that an alteration in receptor-G s coupling can also be imposed by genetic mechanisms. A single nucleotide polymorphism found in the ␤ 1 AR gene in the human population (2, 3) results in either Gly or Arg being encoded at amino acid position 389 of the proximal portion of the cytoplasmic tail. In studies using transfected cells with equivalent expression of the two receptors, the ␤ 1 AR-Arg 389 displays an increase in G s coupling compared with ␤ 1 AR-Gly 389 (2). So, one can consider that the human ␤ 1 AR can exist in four agoniststimulated states: Gly 389 control and desensitized, and Arg 389 control and desensitized. And, since basal (non-ag...

Differential coupling of Arg- and Gly389 polymorphic forms of the β1-adrenergic receptor leads to pathogenic cardiac gene regulatory programs

“…In recombinantly expressing cell lines (12) and transgenic mice (14), the ␤ 1 -Arg389 has been found to exhibit increased stimulation of adenylyl cyclase compared with ␤ 1 -Gly389. In addition, in a model cell-based system ␤ 1 -Arg389 underwent greater agonist-promoted desensitization [of the adenylyl cyclase (AC) response] compared with ␤ 1 -Gly389 (17). This polymorphic variation of the ␤ 1 AR has been associated with a number of human cardiovascular phenotypes including risk for hypertension (1), exercise capacity in heart failure (30), the inotropic response to dobutamine (3,8), ventricular remodeling in heart failure (29), ␤-blocker survival in heart failure (11,14), and the blood pressure response to ␤-blockers in hypertension (7,26).…”

Development of an enzyme‐linked immunosorbent assay and a beta‐1 adrenergic receptor–based assay for monitoring the drug atenolol

“…Such mutated receptors are capable of selectively binding a drug such as ATL, without identifying native adrenergic agonists of this family. Indeed, several studies were carried out in a variety of stably expressed cell lines (with the exception of Sf9) in which cloned and mutated b1A-and b2ARs were characterized and the interactions with their ligands and G-proteins were determined [41]. However, despite the many advantages presented by cloned and expressed receptors, so far only a few G-protein coupled receptor-based assays have been developed for environmental or food diagnostics.…”

Os polimorfismos dos receptores adrenérgicos na insuficiência cardíaca: o que a genética explica?

“…Additionally, β1-Arg389 presents a faster desensitization, has higher affinity for the G s protein and produces an activation of the effector enzyme adenylyl cyclase that is three-fold higher than the one induced by the Gly389 allele 4,14 .…”