Heterotrimeric G Protein Signaling In Allergic Inflammation

National Institute Of Allergy And Infectious Diseases

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Abstract

Mast cells (MCs), granulocytes, and lymphocytes are integral to the development of an allergic response. Allergic inflammation may also be generated through activation of receptors coupled to heterotrimeric G proteins (GPCRs). The purpose of this study is to understand mechanisms of G protein-mediated signal transduction in immune cells, with a focus on GPCR-mediated trafficking of leukocytes to sites of allergic inflammation. GPCRs activate a core pathway of heterotrimeric G proteins. G protein alpha subunits oscillate between GDP- (inactive) and GTP- (active) bound forms based on ligand occupancy of the associated receptor. The GTP-bound form of the G protein alpha subunit induces downstream signaling cascades, including intracellular calcium flux responsible for MC/basophil degranulation. This project focuses on a family of regulators of G protein signaling (RGS proteins), which inhibit the function of G alpha-i and G alpha-q, but not G alpha-s, proteins by increasing their intrinsic GTPase activity, a property that promotes deactivation of the signaling pathway. The GTPase accelerating (GAP) activity of RGS proteins limits the time of interaction of active G-alpha and its effectors, resulting in desensitization of GPCR signaling. Despite a growing body of knowledge concerning the biochemical mechanisms of RGS action, relatively little is known about the physiological role of these proteins in allergic inflammation. A major area of investigation is the recruitment of inflammatory leukocytes to sites of inflammation. Chemokines are a major class of compounds acting on leukocyte GPCRs, which orchestrate immune cell trafficking, and RGS proteins including RGS10, RGS13, and RGS16 inhibit chemokine signaling by desensitizing GPCR signals. In Fiscal Year (FY) 21, we characterized the phenotype of patients with undefined immunodeficiencies and novel mutations in G proteins and/or RGS proteins in collaborative studies with Drs. Chinn, Orange and Su. We reported the clinical and molecular phenotype of three siblings from one family, who presented with short stature and immunodeficiency and carried novel, uncharacterized variants in RGS10 (c.489_491del:p.E163del and c.G511T:p.A171S). The affected subjects exhibited systemic abnormalities including recurrent infections, hypergammaglobulinemia, profoundly reduced lymphocyte chemotaxis, abnormal lymph node architecture, and short stature due to growth hormone deficiency, several of which are directly related mechanistically to the RGS10 mutations. Although the GAP activity of each RGS10 variant was intact, each protein exhibited aberrant phosphorylation by protein kinase A (PKA), which was associated with increased cytosolic and cell membrane localization and activity compared to the wild-type protein. We propose that the RGS10 p.E163del and p.A171S mutations lead to mis-localization of the RGS10 protein, resulting in a unique syndrome of short stature and immunodeficiency. This study reveals the critical importance of RGS10 for immune competence and normal hormonal metabolism in humans and suggests that rare RGS variants can cause systemic genetic disorders.