We have shown that RGS proteins modulate signaling through a variety of G-protein coupled receptors including chemokine receptors. Chemokine receptors signal predominantly by triggering G alpha i nucleotide exchange. Humans and mice have three Gi isoforms although Gi alpha2 (encoded by Gnai2) and Gi alpha3 (encoded by Gnai3) predominate in lymphoid cells. We have found that Gnai2 -/- T and B cells have severe defects in chemokine-receptor signaling while Gnai2 +/- T and B cells exhibit modest defects. In vivo, the Gnai2-/- B cells fail to properly access lymph node follicles and the Gnai2-/- T cells failing to properly enter the T cell zone. We have studies the immune system with a focus on immune cell trafficking in various RGS deficient mice. We have supplemented these studies with in vitro studies using mRNA knock-downs as well as over expression studies using RGS proteins fused to a fluorescent marker. The recognition of the importance of both G-protein signaling and RGS proteins in the regulation of lymphocyte responses to chemokines has led us some of our studies to hematopoietic cell types. RGS1 has been linked to type 1 diabetes, celiac disease, multiple sclerosis, and melanoma progression. A prominent site of Rgs1 expression is in intraepithelial lymphocytes (IELs) in the gastrointestinal tract (GI). IEL dysfunction has also been implicated in inflammatory diseases of the GI tract and Rgs1 deficient mice have IELs that respond inappropriately to chemoattractants. RGS2 has been linked to hypertension and anxiety disorders and mice lacking Rgs2 exhibit reduced T cell proliferation and IL-2 production, which translates in an impaired antiviral immunity in vivo. Rgs2 is well expressed in B and T lymphocytes and neutrophils while high levels are found in mast and dendritic cells. We have recently acquired Rgs2-/- mice to analyze neutrophil and B cell function in these mice. The Rgs2-/- mice have increased numbers of neutrophils and constitutive germinal center formation. Rgs3 is a broadly expressed RGS protein involved in the regulation of neuronal cell migration. We have recently found that an isoform of RGS3 termed PDZ-RGS3 functions in the Wnt signaling pathway and its overexpression leads to epithelial to mescenchymal cell transition (EMT). Rgs10 is among the best expressed RGS proteins found in numerous hematopoietic cell types. However, immune phenotyping of these mice has revealed surprisingly little. Recently we have found that these mice have T cells with enhanced intracellular calcium responses following CD3 crosslinking. In addition patch clamping of T cells from these mice has revealed that CD3 stimulation results in a prolonged activation of CRAC channels in these mice. RGS13 is strongly expressed in both human and mouse germinal center B cells and is often found highly expressed in human B cell lymphomas of germinal center origin. Rgs13 is also well expressed in mast cells and in adult T cell leukemia cells. To facilitate our studies of RGS13 and to provide a potential resource for in vivo imaging endogenous germinal center B cells we have generated mice where GFP (green fluorescent protein) has been knocked-in (KI) into the Rgs13 locus replacing the RGS13 coding sequence. Flow cytometry revealed high levels of GFP expression in germinal center centroblasts and centrocytes. Intravital microscopy documented the presence of brightly GFP positive cells in the interfollicular region and at the T-B border within a day of immunization. Later strong expression is observed in B cells located in germinal centers. Immune phenotyping of these mice revealed a minor defect in early B cell development with a normal peripheral lymphoid compartment with the exception of a 25% expansion in the number of Peyers patches. Upon immunization the Rgs13-/- mice exhibited an enhanced extra-follicular antibody response, an exaggerated germinal center response, and a disturbance of germinal center architecture. Analysis of mRNA expression in Rgs13GFP positive B cells revealed a marked enrichment in germinal center specific genes as well as genes involved in cell proliferation. Analysis of irradiated mice reconstituted with 1:1 mix of wild type and Rgs13-/- bone marrow revealed an expansion of Rgs13-/- GC B cells at the expense of wild type cells. These studies are aimed at understanding the role RGS13 plays in germinal center B cell function. Rgs14 is well expressed in lymphocytes and initially targeting in mice indicated that its absence resulted in embryonic lethality at the two cell stage. To analyze the role of Rgs14 in immune cells we created Rgs14LoxP mice. However, deletion of Rgs14 was not deleterious so we have analyzed mice globally lacking Rgs14 expression. Initial analysis of the immune system of these mice was unrevealing. Rgs19 is well expressed in B lymphocytes and less so in T cells. It is also well expressed in stem cells and hematopoietic progenitors. GFP has been inserted into the RGS19 locus and appropriated targeted mice identified. Flow cytometry revealed that GFP is well expressed in mature B and T cells and in progenitors in the bone marrow. Consistently the Rgs19 GFP KI mice had an enlarged spleen and thymus compared to wild type mice. Chemotaxis experiments comparing wild type and RGS19-/- lymphocytes indicate significant increases to a panel of chemokines with the KO B cells. Serum levels of IgM, IgG2a, and IgG2b are elevated in these mice. Current studies are aimed understanding the pathogenesis of the splenomegaly and enhanced B cell responsiveness in the Rgs19-/- mice. In bone marrow mixed chimeras the Rgs19-/- deficient B cells and neutrophils expand preferentially. Intriguing the wild type cells also expand in the mixed chimera mice suggesting that some bone marrow derived Rgs19-/- cell is responsible for the expansion. As another approach to assessing the role of RGS proteins we have begun the analysis of mice with a Gnai2 G184S knock-in obtained from Richard Neubig (University of Michigan). This mutation renders Gi alpha2 resistant to the effect of RGS proteins. The Gnai2 G184S KI mice possess a striking phenotype verifying the overall important of RGS proteins in G-protein regulation. They have a marked reduction in peripheral T cells;an increase in mature T cells in the thymus;a thymocyte egress defect;an absence of many peripheral lymph nodes;a disorganized spleen architecture;splenomegaly;abnormal lymphocyte responses to chemokines;and reduced serum levels of IgG3, but increased levels of Ig2b. We have shown that neutrophils with a genomic knock-in of a mutation that disables RGS protein-Galphai2 interactions accumulate in the bone marrow and mobilize poorly to inflammatory sites. These defects are attributable to enhanced sensitivity to background signals, prolonged chemoattractant receptor signaling, and inappropriate CXCR2 downregulation. Intravital imaging revealed a failure of the mutant neutrophils to accumulate at and stabilize sites of sterile inflammation. Furthermore, these mice could not control a non-lethal Staphylococcus aureus infection. Neutrophil RGS proteins establish a threshold for Gi alpha activation helping to coordinate desensitization mechanisms. Their loss renders neutrophils functionally incompetent.
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