RGS2 is a primary terminator of β2-adrenergic receptor-mediated Gi signaling

Abstract

Two major β-adrenergic receptor (βAR) subtypes, β1AR and β2AR, are expressed in mammalian heart with β1AR coupling to Gs and β2AR dually coupling to Gs and Gi proteins. In many types of chronic heart failure, myocardial contractile response to both β1AR and β2AR stimulation is severely impaired. The dysfunction of βAR signaling in failing hearts is largely attributable to an increase in Gi signaling, because disruption of the Gi signaling restores myocardial contractile response to β1AR as well as β2AR stimulation. However, the mechanism terminating the β2AR-Gi signaling remains elusive, while it has been shown activation of the Gi signaling is dependent on agonist stimulation and subsequent PKA-mediated phosphorylation of the receptor. Here we demonstrate that regulator of G protein signaling 2 (RGS2) is a primary terminator of the β2AR-Gi signaling. Specifically, prolonged absence of agonist stimulation for 24h impairs the β2AR-Gi signaling, resulting in enhanced β2AR- but not β1AR-mediated contractile response in cultured adult mouse cardiomyocytes. Increased β2AR contractile response is accompanied by a selective upregulation of RGS2 in the absence of alterations in other major cardiac RGS proteins (RGS3-5) or Gs, Gi or βAR subtypes. Administration of a βAR agonist, isoproterenol (ISO, 1.0 nM), prevents RGS2 upregulation and restores the β2AR-Gi signaling in cultured cells. Furthermore, RGS2 ablation, similar to βAR agonist stimulation, sustains the β2AR-Gi signaling in cultured cells, whereas adenoviral overexpression of RGS2 suppresses agonist-activated β2AR-Gi signaling in cardiomyocytes and HEK293 cells. These findings not only define RGS2 as a novel negative regulator of the β2AR-Gi signaling, but also provide a potential novel target for the treatment of chronic heart failure.

Digoxin-Mediated Upregulation of RGS2 Protein Protects against Cardiac Injury

“…These changes could be due to enhanced G i/o signaling in RGS2 2/2 mice. RGS2 has been shown to inhibit b 2 adrenergic receptor-mediated G i signaling in cardiomyocytes (Chakir et al, 2011). Hence, suppression of AC activity by isoproterenol could be enhanced in RGS2 2/2 mice, resulting in lower levels of cAMP induction.…”

Regulators of G-Protein-Signaling Proteins: Negative Modulators of G-Protein-Coupled Receptor Signaling

“…This fact suggests that these mice have increased vascular tone from elevated signaling responses to angiotensin. Even though there was hypertension, there was not any cardiac hypertrophy or differences in cardiac systolic contractility that might have contributed to the elevated blood pressure in these mice (Biesemann et al, 2014;Chakir et al, 2011b;Ji et al, 2010;Jones et al, 2012;Momen et al, 2014;Sjogren et al, 2012;Takimoto et al, 2009;Tsang et al, 2010;Yue et al, 2010;Zhang et al, 2006). RGS2 knockout mice had other abnormalities that might contribute to their hypertension.…”

“…Although no changes in cardiac contractility or evidence of cardiac hypertrophy were observed in RGS2 À/À mice, several studies have shown that lower levels and abnormal regulation of RGS2 could lead to heart failure in mice (Biesemann et al, 2014;Chakir et al, 2011b;Ji et al, 2010;Jones et al, 2012;Sjogren et al, 2012;Tsang et al, 2010) and humans (Chakir et al, 2011a;Sjogren et al, 2012;Zhang and Mende, 2014). RGS4 has been found to be elevated in humans with heart failure (Mittmann et al, 2002;Owen et al, 2001), yet in contrast, models of mouse cardiac hypertrophy such as transverse aortic constriction (banding) or transgenic overexpression of constitutively active Gaq were associated with significantly decreased RGS2 mRNA and protein levels prior to the development of hypertrophy with no parallel differences or alterations found in expression of RGS3e5 .…”

The evolution of regulators of G protein signalling proteins as drug targets – 20 years in the making: IUPHAR Review 21

“…In the early days of RGS proteins, the Gilman lab demonstrated that RGS4 has high affinity for all members of the Gα i/o subtypes, while showing lower affinity for Gα q and no activity towards Gα s and Gα 12 (Berman et al, 1996a). RGS2, on the other hand, was demonstrated to be selective for Gα q over all other Gα subtypes tested (Heximer et al, 1997), although later studies demonstrated that RGS2 can also inhibit Gα i -mediated signalling in vivo (Chakir et al, 2011). Furthermore, all members of the R7 family of RGS proteins (RGS6, 7, 9 and 11) are selective for Gα i/o proteins (Anderson et al, 2009) while other RGS proteins are more promiscuous in their selectivity, for example, RGS1, RGS8, RGS13, RGS16 (Johnson and Druey, 2002;Soundararajan et al, 2008).…”