title: CD28-dependent Rac1 activation is the molecular target of azathioprine in primary human CD4+ T lymphocytes.
abstract: Azathioprine and its metabolite 6-mercaptopurine (6-MP) are immunosuppressive drugs that are used in organ transplantation and autoimmune and chronic inflammatory diseases such as Crohn disease. However, their molecular mechanism of action is unknown. In the present study, we have identified a unique and unexpected role for azathioprine and its metabolites in the control of T cell apoptosis by modulation of Rac1 activation upon CD28 costimulation. We found that azathioprine and its metabolites induced apoptosis of T cells from patients with Crohn disease and control patients. Apoptosis induction required costimulation with CD28 and was mediated by specific blockade of Rac1 activation through binding of azathioprine-generated 6-thioguanine triphosphate (6-Thio-GTP) to Rac1 instead of GTP. The activation of Rac1 target genes such as mitogen-activated protein kinase kinase (MEK), NF-kappaB, and bcl-x(L) was suppressed by azathioprine, leading to a mitochondrial pathway of apoptosis. Azathioprine thus converts a costimulatory signal into an apoptotic signal by modulating Rac1 activity. These findings explain the immunosuppressive effects of azathioprine and suggest that 6-Thio-GTP derivates may be useful as potent immunosuppressive agents in autoimmune diseases and organ transplantation.
authors.affiliation: Laboratory of Immunology, Department of Medicine, University of Mainz, Langenbeckstrasse 1, 55101 Mainz, Germany.
authors.forename: Imke
authors.initials: I
authors.lastname: Tiede
authors.forename: Gerhard
authors.initials: G
authors.lastname: Fritz
authors.forename: Susanne
authors.initials: S
authors.lastname: Strand
authors.forename: Daniela
authors.initials: D
authors.lastname: Poppe
authors.forename: Radovan
authors.initials: R
authors.lastname: Dvorsky
authors.forename: Dennis
authors.initials: D
authors.lastname: Strand
authors.forename: Hans Anton
authors.initials: HA
authors.lastname: Lehr
authors.forename: Stefan
authors.initials: S
authors.lastname: Wirtz
authors.forename: Christoph
authors.initials: C
authors.lastname: Becker
authors.forename: Raja
authors.initials: R
authors.lastname: Atreya
authors.forename: Jonas
authors.initials: J
authors.lastname: Mudter
authors.forename: Kai
authors.initials: K
authors.lastname: Hildner
authors.forename: Brigitte
authors.initials: B
authors.lastname: Bartsch
authors.forename: Martin
authors.initials: M
authors.lastname: Holtmann
authors.forename: Richard
authors.initials: R
authors.lastname: Blumberg
authors.forename: Henning
authors.initials: H
authors.lastname: Walczak
authors.forename: Heiko
authors.initials: H
authors.lastname: Iven
authors.forename: Peter R
authors.initials: PR
authors.lastname: Galle
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Ahmadian
authors.forename: Markus F
authors.initials: MF
authors.lastname: Neurath
mesh_terms: D000328:Adult; D000368:Aged; D017209:Apoptosis / Q000187:drug effects; D001379:Azathioprine / Q000494:pharmacology*; D018106:CD28 Antigens / Q000502:physiology*; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects* / Q000276:immunology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology; D006801:Humans; D051550:I-kappa B Kinase; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects; D008875:Middle Aged; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000502:physiology; D020830:rac1 GTP-Binding Protein / Q000502:physiology*
chemical_list: D018106:CD28 Antigens; D004268:DNA-Binding Proteins; D007166:Immunosuppressive Agents; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D017346:Protein Serine-Threonine Kinases; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496560:IKBKB protein, human; C496565:IKBKE protein, human; D020830:rac1 GTP-Binding Protein; D001379:Azathioprine