title: Inhibition of G alpha i2 activation by G alpha i3 in CXCR3-mediated signaling.
abstract: G protein-coupled receptors (GPCRs) convey extracellular stimulation into dynamic intracellular action, leading to the regulation of cell migration and differentiation. T lymphocytes express G alpha(i2) and G alpha(i3), two members of the G alpha(i/o) protein family, but whether these two G alpha(i) proteins have distinguishable roles guiding T cell migration remains largely unknown because of a lack of member-specific inhibitors. This study details distinct G alpha(i2) and G alpha(i3) effects on chemokine receptor CXCR3-mediated signaling. Our data showed that G alpha(i2) was indispensable for T cell responses to three CXCR3 ligands, CXCL9, CXCL10, and CXCL11, as the lack of G alpha(i2) abolished CXCR3-stimulated migration and guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) incorporation. In sharp contrast, T cells isolated from G alpha(i3) knock-out mice displayed a significant increase in both GTPgammaS incorporation and migration as compared with wild type T cells when stimulated with CXCR3 agonists. The increased GTPgammaS incorporation was blocked by G alpha(i3) protein in a dose-dependent manner. G alpha(i3)-mediated blockade of G alpha(i2) activation did not result from G alpha(i3) activation, but instead resulted from competition or steric hindrance of G alpha(i2) interaction with the CXCR3 receptor via the N terminus of the second intracellular loop. A mutation in this domain abrogated not only G alpha(i2) activation induced by a CXCR3 agonist but also the interaction of G alpha(i3) to the CXCR3 receptor. These findings reveal for the first time an interplay of G alpha(i) proteins in transmitting G protein-coupled receptor signals. This interplay has heretofore been masked by the use of pertussis toxin, a broad inhibitor of the G alpha(i/o) protein family.
authors.affiliation: Wellman Center for Photomedicine, Department of Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Brian D
authors.initials: BD
authors.lastname: Thompson
authors.affiliation: Wellman Center for Photomedicine, Department of Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Yongzhu
authors.initials: Y
authors.lastname: Jin
authors.affiliation: Wellman Center for Photomedicine, Department of Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Kevin H
authors.initials: KH
authors.lastname: Wu
authors.affiliation: Center for Immunology and Inflammatory Diseases, Division of Rheumatology, Allergy and Immunology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Colvin
authors.affiliation: Center for Immunology and Inflammatory Diseases, Division of Rheumatology, Allergy and Immunology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Luster
authors.affiliation: NIEHS, Transmembrane Signaling Group, Laboratory of Signal Transduction, National Institutes of Health, Research Triangle Park, North Carolina 27709.
authors.forename: Lutz
authors.initials: L
authors.lastname: Birnbaumer
authors.affiliation: Wellman Center for Photomedicine, Department of Dermatology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114. Electronic address: mwu2@partners.org.
authors.forename: Mei X
authors.initials: MX
authors.lastname: Wu
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D054357:Chemokine CXCL10; D054371:Chemokine CXCL11; D054370:Chemokine CXCL9; D019743:Chemokines, CXC / Q000378:metabolism; D005260:Female; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000037:antagonists & inhibitors* / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D054367:Receptors, CXCR3; D019707:Receptors, Chemokine / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism
chemical_list: D054357:Chemokine CXCL10; D054371:Chemokine CXCL11; D054370:Chemokine CXCL9; D019743:Chemokines, CXC; C485433:Cxcl10 protein, mouse; C515203:Cxcl11 protein, mouse; C485969:Cxcl9 protein, mouse; C515188:Cxcr3 protein, mouse; D054367:Receptors, CXCR3; D019707:Receptors, Chemokine; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C417708:Gnai3 protein, mouse