title: Analysis of functional selectivity through G protein-dependent and -independent signaling pathways at the adrenergic α(2C) receptor.
abstract: Although G protein-coupled receptors (GPCRs) are traditionally categorized as Gs-, Gq-, or Gi/o-coupled, their signaling is regulated by multiple mechanisms. GPCRs can couple to several effector pathways, having the capacity to interact not only with more than one G protein subtype but also with alternative signaling or effector proteins such as arrestins. Moreover, GPCR ligands can have different efficacies for activating these signaling pathways, a characteristic referred to as biased agonism or functional selectivity. In this work our aim was to detect differences in the ability of various agonists acting at the α2C type of adrenergic receptors (α2C-ARs) to modulate cAMP accumulation, cytoplasmic Ca(2+) release, β-arrestin recruitment and receptor internalization. A detailed comparative pharmacological characterization of G protein-dependent and -independent signaling pathways was carried out using adrenergic agonists (norepinephrine, phenylephrine, brimonidine, BHT-920, oxymetazoline, clonidine, moxonidine, guanabenz) and antagonists (MK912, yohimbine). As initial analysis of agonist Emax and EC50 values suggested possible functional selectivity, ligand bias was quantified by applying the relative activity scale and was compared to that of the endogenous agonist norepinephrine. Values significantly different from 0 between pathways indicated an agonist that promoted different level of activation of diverse effector pathways most likely due to the stabilization of a subtly different receptor conformation from that induced by norepinephrine. Our results showed that a series of agonists acting at the α2C-AR displayed different degree of functional selectivity (bias factors ranging from 1.6 to 36.7) through four signaling pathways. As signaling via these pathways seems to have distinct functional and physiological outcomes, studying all these stages of receptor activation could have further implications for the development of more selective therapeutics with improved efficacy and/or fewer side effects.
authors: Pharmacological and Drug Safety Research, Gedeon Richter Plc., Budapest, Hungary. Electronic address: d.kurko@richter.hu.
authors: Dalma
authors: D
authors: Kurko
authors: Pharmacological and Drug Safety Research, Gedeon Richter Plc., Budapest, Hungary.
authors: Zoltán
authors: Z
authors: Kapui
authors: Pharmacological and Drug Safety Research, Gedeon Richter Plc., Budapest, Hungary.
authors: József
authors: J
authors: Nagy
authors: Pharmacological and Drug Safety Research, Gedeon Richter Plc., Budapest, Hungary.
authors: Balázs
authors: B
authors: Lendvai
authors: Pharmacological and Drug Safety Research, Gedeon Richter Plc., Budapest, Hungary.
authors: Sándor
authors: S
authors: Kolok
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000494:pharmacology; D058669:Adrenergic alpha-2 Receptor Antagonists / Q000494:pharmacology; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D016466:CHO Cells; D020013:Calcium Signaling; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism; D006801:Humans; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D015398:Signal Transduction; D000071557:beta-Arrestins
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D019390:Arrestins; D044385:GTP-Binding Protein alpha Subunits; D018341:Receptors, Adrenergic, alpha-2; D043562:Receptors, G-Protein-Coupled; D000071557:beta-Arrestins; D000242:Cyclic AMP
keywords: Bias factor; Functional selectivity; Receptor internalization; cAMP accumulation; α(2C)-AR; β-Arrestin recruitment