title: Azathioprine suppresses ezrin-radixin-moesin-dependent T cell-APC conjugation through inhibition of Vav guanosine exchange activity on Rac proteins.
abstract: We have shown recently that the azathioprine metabolite 6-Thio-GTP causes immunosuppression by blockade of GTPase activation in T lymphocytes. In the present study, we describe a new molecular mechanism by which 6-Thio-GTP blocks GTPase activation. Although 6-Thio-GTP could bind to various small GTPases, it specifically blocked activation of Rac1 and Rac2 but not of closely related Rho family members such as Cdc42 and RhoA in primary T cells upon stimulation with alphaCD28 or fibronectin. Binding of 6-Thio-GTP to Rac1 did not suppress Rac effector coupling directly but blocked Vav1 exchange activity upon 6-Thio-GTP hydrolysis, suggesting that 6-Thio-GTP loading leads to accumulation of 6-Thio-GDP-loaded, inactive Rac proteins over time by inhibiting Vav activity. In the absence of apoptosis, blockade of Vav-mediated Rac1 activation led to a blockade of ezrin-radixin-moesin dephosphorylation in primary T cells and suppression of T cell-APC conjugation. Azathioprine-generated 6-Thio-GTP thus prevents the development of an effective immune response via blockade of Vav activity on Rac proteins. These findings provide novel insights into the immunosuppressive effects of azathioprine and suggest that antagonists of the Vav-Rac signaling pathway may be useful for suppression of T cell-dependent pathogenic immune responses.
authors.affiliation: Laboratory of Immunology, I. Department of Medicine, University of Mainz, Mainz, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Poppe
authors.forename: Imke
authors.initials: I
authors.lastname: Tiede
authors.forename: Gerhard
authors.initials: G
authors.lastname: Fritz
authors.forename: Christoph
authors.initials: C
authors.lastname: Becker
authors.forename: Brigitte
authors.initials: B
authors.lastname: Bartsch
authors.forename: Stefan
authors.initials: S
authors.lastname: Wirtz
authors.forename: Dennis
authors.initials: D
authors.lastname: Strand
authors.forename: Shinya
authors.initials: S
authors.lastname: Tanaka
authors.forename: Peter R
authors.initials: PR
authors.lastname: Galle
authors.forename: Xosé R
authors.initials: XR
authors.lastname: Bustelo
authors.forename: Markus F
authors.initials: MF
authors.lastname: Neurath
mesh_terms: D000328:Adult; D000938:Antigen-Presenting Cells / Q000187:drug effects / Q000276:immunology; D017209:Apoptosis; D001379:Azathioprine / Q000494:pharmacology*; D015153:Blotting, Western; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects* / Q000276:immunology; D002450:Cell Communication / Q000187:drug effects / Q000276:immunology; D004789:Enzyme Activation / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D025581:Neurofibromin 2 / Q000187:drug effects*; D051567:Proto-Oncogene Proteins c-vav / Q000187:drug effects* / Q000276:immunology; D020744:rac GTP-Binding Proteins / Q000187:drug effects* / Q000276:immunology
chemical_list: D007166:Immunosuppressive Agents; D025581:Neurofibromin 2; D051567:Proto-Oncogene Proteins c-vav; D020744:rac GTP-Binding Proteins; D001379:Azathioprine