Regulators of G-protein signalling: multifunctional proteins with impact on signalling in the cardiovascular system

doi:10.1016/S0163-7258(02)00326-1

Pharmacology & Therapeutics

Volume 97, Issue 2, February 2003, Pages 95-115

https://doi.org/10.1016/S0163-7258(02)00326-1 Get rights and content

Abstract

Regulator of G-protein signalling (RGS) proteins form a superfamily of at least 25 proteins, which are highly diverse in structure, expression patterns, and function. They share a 120 amino acid homology domain (RGS domain), which exhibits GTPase accelerating activity for α-subunits of heterotrimeric G-proteins, and thus, are negative regulators of G-protein-mediated signalling. Based on the organisation of the Rgs genes, structural similarities, and differences in functions, they can be divided into at least six subfamilies of RGS proteins and three more families of RGS-like proteins. Many of these proteins regulate signalling processes within cells, not only via interaction with G-protein α-subunits, but are G-protein-regulated effectors, Gβγ scavenger, or scaffolding proteins in signal transduction complexes as well. The expression of at least 16 different RGS proteins in the mammalian or human myocardium have been described. A subgroup of at least eight was detected in a single atrial myocyte. The exact functions of these proteins remain mostly elusive, but RGS proteins such as RGS4 are involved in the regulation of G_i-protein βγ-subunit-gated K⁺ channels. An up-regulation of RGS4 expression has been consistently found in human heart failure and some animal models. Evidence is increasing that the enhanced RGS4 expression counter-regulates the G_q/11-induced signalling caused by hypertrophic stimuli. In the vascular system, RGS5 seems to be an important signalling regulator. It is expressed in vascular endothelial cells, but not in cultured smooth muscle cells. Its down-regulation, both in a model of capillary morphogenesis and in an animal model of stroke, render it a candidate gene, which may be involved in the regulation of capillary growth, angiogenesis, and in the pathophysiology of stroke.

Introduction

G-protein-coupled receptors (GPCRs) play a pivotal role in cardiovascular signal transduction and are targets for many drugs used in the treatment of cardiovascular diseases. All of these receptors are proteins with seven membrane-spanning elements that use intracellular loops and their C-terminal tails for interaction with heterotrimeric (Gαβγ) guanine-nucleotide-binding proteins (G-proteins) to transmit extracellular signals. Ligand-activated receptors catalyse the GDP/GTP-exchange at a coupled G-protein, and thereby promote the dissociation of the heterotrimer into a free GTP-liganded Gα-subunit and a Gβγ dimer. Both the Gα-subunit and Gβγ dimer regulate the activity of effectors, e.g., second messenger-producing enzymes and ion channels. The duration of G-protein activation is controlled by the intrinsic GTPase activity of Gα. By GTP hydrolysis, Gα returns to the GDP-bound conformation and reassembles with the Gβγ dimer.

For a long time, researchers in the field thought that the interactions of the GPCR, G-protein, and effector molecule are sufficient to explain the main principles of such signal transduction cascades. Therefore, the discovery of the “Regulators of G-protein signalling” (RGS) proteins in mammals created new interest in this field. First evidence for this new class of proteins, which negatively regulate the activity of heterotrimeric G-proteins, was obtained from genetic studies in yeast (Saccharomyces cerevisiae) (Dohlman et al., 1992), the filamentous fungus Aspergillus nidulans (Lee & Adams, 1994), and the nematode Caenorhabditis elegans (Koelle & Horvitz, 1996). The gene products Sst2, FblA, and Egl-10 share a distinct sequence homology in a ≈ 120 amino acid (aa) region with a human protein named Gα-interacting protein (GAIP) (De Vries et al., 1995). Rapidly, ∼20 different mammalian proteins, which share this RGS homology domain, were identified (see Dohlman & Thorner, 1997). Moreover, the RGS box was found to act as an GTPase-activating protein (GAP) for G-protein α-subunits. It accelerates GTP hydrolysis and signal termination Berman et al., 1996a, Berman et al., 1996b, Popov et al., 1997.

Meanwhile, at least 25 different mammalian proteins containing an RGS or RGS-like domain are known. They form a superfamily of highly diverse proteins with unique expression patterns and variable expression levels strongly regulated by signalling events. The evidence is increasing that besides G-protein inactivation, many RGS proteins possess other properties, with impact on signal transduction. Some RGS proteins additionally act as G-protein-regulated effectors. Others are Gβγ scavengers or scaffold proteins that are involved in the assembly of large signalling complexes. Recent reviews on RGS proteins Hepler, 1999, Wieland & Chen, 1999, De Vries et al., 2000, Burchett, 2000, Druey, 2001, Zhong & Neubig, 2001 dealt with general aspects such as G-protein specificity or mechanism of GAP activity, or focused on specific topics such as the use of RGS proteins as potential drug targets. This review will first update the reader on new information regarding the currently, at least 25, known RGS or RGS-like proteins and will explain the division into several subfamilies based on the organisation of the Rgs genes, structural similarities, and different functions. The second part will focus on the expression and impact of these proteins on signal transduction in the cardiovascular system.

Section snippets

“Small” or R4 regulator of G-protein signalling proteins

This subfamily of RGS proteins with 7 different members (Table 1) is the largest known thus far. Each of these RGS proteins is encoded by a different gene (Sierra et al., 2002). At first glance, these small proteins (M_r 20–30 kDa), which mainly consist of the C-terminal RGS homology domain (Fig. 1), appear to be relatively nonspecific negative regulators of signalling events mediated by G_i/o and G_q/11 family members. An interaction with Gα_s or Gα₁₂ family members has not been detected. With the

Proteins with regulator of G-protein signalling-like domains and GTPase-activating protein activity for Gα-subunits

Besides the proteins encoded by the Rgs gene family (Sierra et al., 2002), there are three different protein families (see 3.1 GTPase-activating protein activity of G-protein-coupled receptor kinases, 3.2 Regulator of G-protein signalling-PX1, the specific GTPase-activating protein for Gα, 3.3 Guanine nucleotide exchange factors with GTPase-activating protein activity for G) that contain RGS-like domains. These domains are similar to the RGS core domains in the Rgs gene family products with

Mammalian myocardium

At least 13 different members of the RGS family, with some additional mRNA variants, are expressed in the mammalian myocardium (Table 7). The majority of studies were performed in the rat heart, but most data in other animals essentially supported or complemented these findings. The expression of six RGS proteins in the rat ventricular myocardium and cardiomyocytes was sufficiently high to allow detection by northern blot (NB) and/or immunoblot: RGS1, -3, -4, -5, -6, and -16 Kardestuncer et

Expression of regulators of G-protein signalling proteins in vascular tissues

The vascular expression of RGS5 has been studied in detail in different species Panetta et al., 1999, Adams et al., 2000, Kirsch et al., 2001. RGS5 was detectable in all investigated cardiovascular tissues (aorta, carotid artery, caval vein, capillaries, and atrial and ventricular myocardium). The aorta showed by far the highest expression in macaques and humans (Adams et al., 2000). RGS5 was specifically enriched in endothelial cells from rat brain capillaries and from the plexus chorioideus

Conclusion

Although RGS proteins share a common preserved functional domain, they obviously comprise different protein families. The variety of domains found in RGS and RGS-like proteins endows them with multiple functions and makes them versatile regulators of signalling events within a cell. Because of these heterogeneous functions, however, it is difficult to derive a uniform and complete concept of the importance of RGS proteins for the physiologic regulation and the pathophysiological changes in the

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Associate editor: M. AvkiranRegulators of G-protein signalling: multifunctional proteins with impact on signalling in the cardiovascular system

Abstract

Introduction

Section snippets

“Small” or R4 regulator of G-protein signalling proteins

Proteins with regulator of G-protein signalling-like domains and GTPase-activating protein activity for Gα-subunits

Mammalian myocardium

Expression of regulators of G-protein signalling proteins in vascular tissues

Conclusion

Genomics

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

Cell

J Biol Chem

J Biol Chem

J Biol Chem

Biochem Biophys Res Commun

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

FEBS Lett

Neuron

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

Neuropharmacology

Biochim Biophys Acta

J Biol Chem

J Biol Chem

J Mol Cell Cardiol

Brain Res Mol Brain Res

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

J Biol Chem

Trends Pharmacol Sci

J Biol Chem

J Biol Chem

FEBS Lett

J Biol Chem

Brain Res

Exp Cell Res

Cell

J Biol Chem

Life Sci

J Biol Chem

A comparison of aorta and vena cava medial message expression by cDNA array analysis identifies a set of 68 consistently differentially expressed genes, all in aortic media

Circ Res

A novel G protein-coupled receptor kinase gene cloned from 4p16.3

Hum Mol Genet

Differential recruitment of Dishevelled provides signaling specificity in the planar cell polarity and Wingless signaling pathways

Genes Dev

Phosphorylation of the regulator of G protein signaling RGS9-1 by protein kinase A is a potential mechanism of light- and Ca2+-mediated regulation of G protein function in photoreceptors

Biochemistry

Regulators of G protein signaling exhibit distinct patterns of gene expression and target G protein specificity in human lymphocytes

J Immunol

Differential gene expression during capillary morphogenesis in 3D collagen matrices: regulated expression of genes involved in basement membrane matrix assembly, cell cycle progression, cellular differentiation and G-protein signaling

J Cell Sci

Associate editor: M. Avkiran
Regulators of G-protein signalling: multifunctional proteins with impact on signalling in the cardiovascular system

Phosphorylation of the regulator of G protein signaling RGS9-1 by protein kinase A is a potential mechanism of light- and Ca²⁺-mediated regulation of G protein function in photoreceptors