Regulator of G protein signaling 2 is a key modulator of airway hyperresponsiveness

Department of Pharmacology, Creighton University School of Medicine, Omaha, Neb.
The Journal of allergy and clinical immunology (Impact Factor: 11.48). 06/2012; 130(4):968-976.e3. DOI: 10.1016/j.jaci.2012.05.004
Source: PubMed


Drugs targeting individual G protein-coupled receptors are used as asthma therapies, but this strategy is limited because of G protein-coupled receptor signal redundancy. Regulator of G protein signaling 2 (RGS2), an intracellular selective inhibitor of multiple bronchoconstrictor receptors, may play a central role in the pathophysiology and treatment of asthma.
We defined functions and mechanisms of RGS2 in regulating airway hyperresponsiveness (AHR), the pathophysiologic hallmark of asthma.
Real-time PCR and Western blot were used to determine changes in RGS2 expression in ovalbumin-sensitized/-challenged mice. We also used immunohistochemistry and real-time PCR to compare RGS2 expression between human asthmatic and control subjects. The AHR of RGS2 knockout mice was assessed by using invasive tracheostomy and unrestrained plethysmography. Effects of loss of RGS2 on mouse airway smooth muscle (ASM) remodeling, contraction, intracellular Ca(2+), and mitogenic signaling were determined in vivo and in vitro.
RGS2 was highly expressed in human and murine bronchial epithelium and ASM and was markedly downregulated in lungs of ovalbumin-sensitized/-challenged mice. Lung tissues and blood monocytes from asthma patients expressed significantly lower RGS2 protein (lung) and mRNA (monocytes) than from nonasthma subjects. The extent of reduction of RGS2 on human monocytes correlated with increased AHR. RGS2 knockout caused spontaneous AHR in mice. Loss of RGS2 augmented Ca(2+) mobilization and contraction of ASM cells. Loss of RGS2 also increased ASM mass and stimulated ASM cell growth via extracellular signal-regulated kinase and phosphatidylinositol 3-kinase pathways.
We identified RGS2 as a potent modulator of AHR and a potential novel therapeutic target for asthma.

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    • " ( RGS2 ) , a Ga q - selective GTPase - activating protein ( Heximer , 2004 ; Kimple et al . , 2009 ) , is synergistically enhanced by glucocorticoid plus LABA ( Holden et al . , 2011 ) . Because RGS2 attenuates responses from Ga q - linked G protein - coupled receptors ( GPCRs ) , such as airway smooth muscle contraction ( Holden et al . , 2011 ; Xie et al . , 2012 ) , we reasoned that relevant responses in other cells that express the b 2 - adrenoceptor , including airway epithelia , might be affected similarly . Agonists of various GPCRs , including acetylcholine , hista - mine , cysteinyl - leukotrienes and certain prostanoids , activate phospholipase Cb ( PLCb ) via Ga q and increase the intra"
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    ABSTRACT: In asthma and chronic obstructive pulmonary disease (COPD) multiple mediators act on Gαq-linked G protein coupled receptors (GPCRs) to cause bronchoconstriction. However, acting on the airway epithelium, such mediators may also elicit inflammatory responses. In human bronchial epithelial BEAS-2B cells, regulator of G protein signalling (RGS) 2 mRNA and protein was synergistically induced in response to combinations of long-acting β2-adrenoceptor agonist (LABA) (salmeterol, formoterol) plus glucocorticoid (dexamethasone, fluticasone propionate, budesonide). Equivalent responses occurred in primary human bronchial epithelial cells. Concentrations of glucocorticoid plus LABA required to induce RGS2 expression in BEAS-2B cells were consistent with the levels achieved therapeutically in the lungs. As RGS2 is a GTPase-activating protein that switches off Gαq, intracellular free calcium ([Ca(2+)]i) flux was used as a surrogate of responses induced by histamine, methacholine and the thromboxane receptor agonist, U46619. This was significantly attenuated by salmeterol plus dexamethasone pre-treatment, or RGS2 over-expression, and the protective effect of salmeterol plus dexamethasone was abolished by RGS2 RNA silencing. While methacholine and U46619 induced IL-8 release and this was inhibited by RGS2 over-expression, the repression of U46619-induced IL-8 release by salmeterol plus dexamethasone was unaffected by RGS2 knockdown. Given a role for Gαq-mediated pathways in inducing IL-8 release, we propose that RGS2 acts redundantly with other effector processes to repress IL-8 expression. Thus, RGS2 expression is a novel effector mechanism, in the airway epithelium, that is induced by glucocorticoid/LABA combinations. This could contribute to the efficacy of glucocorticoid/LABA combinations in asthma and COPD.
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    ABSTRACT: Mucus hypersecretion is a common pathological feature of inflammatory airway diseases. Previous studies have shown that acidic microenvironment of inflamed airways may provoke the pathophysiology of inflammatory airway diseases. However, the acidic-sensing and negative regulatory mechanisms that mediate mucus hypersecretion in inflamed airway remain elusive. Thus, we sought to explore the role of ovarian cancer G-protein-coupled receptor 1 (OGR1) in acid-induced mucin5AC (MUC5AC) hypersecretion in human airway epithelium and the inhibitory effect of regulator of G-protein signaling 2 (RGS2) in this process. We found that airway acidification increased [Ca(2+)](i), which was required for MUC5AC secretion. Knocking-down OGR1 and G(q) with siRNAs and pretreating cells with phospholipase C inhibitor effectively attenuated acid-induced cellular responses. Moreover, the overexpression of wild-type RGS2 attenuated acid-induced cellular responses. In contrast, reducing RGS2 with siRNA enhanced the increases in acid-induced cellular responses. These data suggest that airway acidification can induce MUC5AC hypersecretion through an OGR1-mediated mechanism and RGS2 can inhibit acid-induced MUC5AC hypersecretion at OGR1 receptor level.
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    ABSTRACT: It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features including 1) [Ca(2+)]i, contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types such as epithelium, fibroblasts and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening and fibrosis that influences compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard, and helps set the stage for future research towards understanding the pathways regulating ASM, and in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, COPD and pulmonary fibrosis.
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