title: RhoA is involved in LFA-1 extension triggered by CXCL12 but not in a novel outside-in LFA-1 activation facilitated by CXCL9.
abstract: Chemokines presented on endothelial tissues instantaneously trigger LFA-1-mediated arrest on ICAM-1 via rapid inside-out and outside-in (ligand-driven) LFA-1 activation. The GTPase RhoA was previously implicated in CCL21-triggered LFA-1 affinity triggering in murine T lymphocytes and in LFA-1-dependent adhesion strengthening to ICAM-1 on Peyer's patch high endothelial venules stabilized over periods of at least 10 s. In this study, we show that a specific RhoA 23/40 effector region is vital for the initial LFA-1-dependent adhesions of lymphocytes on high endothelial venules lasting 1-3 s. Blocking the RhoA 23/40 region in human T lymphocytes in vitro also impaired the subsecond CXCL12-triggered LFA-1-mediated T cell arrest on ICAM-1 by eliminating the rapid induction of an extended LFA-1 conformational state. However, the inflammatory chemokine CXCL9 triggered robust LFA-1-mediated T lymphocyte adhesion to ICAM-1 at subsecond contacts independently of the RhoA 23/40 region. CXCL9 did not induce conformational changes in the LFA-1 ectodomain, suggesting that particular chemokines can activate LFA-1 through outside-in post ligand binding stabilization changes. Like CXCL9, the potent diacylglycerol-dependent protein kinase C agonist PMA was found to trigger LFA-1 adhesiveness to ICAM-1 also without inducing integrin extension or an a priori clustering and independently of the RhoA 23/40 region. Our results collectively suggest that the 23/40 region of RhoA regulates chemokine-induced inside-out LFA-1 extension before ligand binding, but is not required for a variety of chemokine and non-chemokine signals that rapidly strengthen LFA-1-ICAM-1 bonds without an a priori induction of high-affinity extended LFA-1 conformations.
authors.affiliation: Department of Immunology, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Ronit
authors.initials: R
authors.lastname: Pasvolsky
authors.forename: Valentin
authors.initials: V
authors.lastname: Grabovsky
authors.forename: Cinzia
authors.initials: C
authors.lastname: Giagulli
authors.forename: Ziv
authors.initials: Z
authors.lastname: Shulman
authors.forename: Revital
authors.initials: R
authors.lastname: Shamri
authors.forename: Sara W
authors.initials: SW
authors.lastname: Feigelson
authors.forename: Carlo
authors.initials: C
authors.lastname: Laudanna
authors.forename: Ronen
authors.initials: R
authors.lastname: Alon
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000276:immunology; D054377:Chemokine CXCL12 / Q000502:physiology*; D054370:Chemokine CXCL9 / Q000502:physiology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D006706:Homeostasis / Q000276:immunology; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D036904:Leukocyte Rolling / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D010581:Peyer's Patches / Q000098:blood supply / Q000166:cytology / Q000276:immunology; D017434:Protein Structure, Tertiary; D020742:rhoA GTP-Binding Protein / Q000502:physiology*
chemical_list: C515255:CXCL12 protein, human; C080810:CXCL9 protein, human; D054377:Chemokine CXCL12; D054370:Chemokine CXCL9; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1; D020742:rhoA GTP-Binding Protein