title: 6-Mercaptopurine reduces macrophage activation and gut epithelium proliferation through inhibition of GTPase Rac1.
abstract: BACKGROUND
  Inflammatory bowel disease is characterized by chronic intestinal inflammation. Azathioprine and its metabolite 6-mercaptopurine (6-MP) are effective immunosuppressive drugs that are widely used in patients with inflammatory bowel disease. However, established understanding of their immunosuppressive mechanism is limited. Azathioprine and 6-MP have been shown to affect small GTPase Rac1 in T cells and endothelial cells, whereas the effect on macrophages and gut epithelial cells is unknown.
  
  
  METHODS
  Macrophages (RAW cells) and gut epithelial cells (Caco-2 cells) were activated by cytokines and the effect on Rac1 signaling was assessed in the presence or absence of 6-MP.
  
  
  RESULTS
  Rac1 is activated in macrophages and epithelial cells, and treatment with 6-MP resulted in Rac1 inhibition. In macrophages, interferon-γ induced downstream signaling through c-Jun-N-terminal Kinase (JNK) resulting in inducible nitric oxide synthase (iNOS) expression. iNOS expression was reduced by 6-MP in a Rac1-dependent manner. In epithelial cells, 6-MP efficiently inhibited tumor necrosis factor-α-induced expression of the chemokines CCL2 and interleukin-8, although only interleukin-8 expression was inhibited in a Rac1-dependent manner. In addition, activation of the transcription factor STAT3 was suppressed in a Rac1-dependent fashion by 6-MP, resulting in reduced proliferation of the epithelial cells due to diminished cyclin D1 expression.
  
  
  CONCLUSIONS
  These data demonstrate that 6-MP affects macrophages and gut epithelial cells beneficially, in addition to T cells and endothelial cells. Furthermore, mechanistic insight is provided to support development of Rac1-specific inhibitors for clinical use in inflammatory bowel disease.
authors.affiliation: Department of Medical Biochemistry, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Goran
authors.initials: G
authors.lastname: Marinković
authors.forename: Anouk A J
authors.initials: AA
authors.lastname: Hamers
authors.forename: Carlie J M
authors.initials: CJ
authors.lastname: de Vries
authors.forename: Vivian
authors.initials: V
authors.lastname: de Waard
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000235:genetics / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism*; D048670:MAP Kinase Kinase 4 / Q000235:genetics / Q000378:metabolism; D008262:Macrophage Activation / Q000187:drug effects*; D008264:Macrophages / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D015122:Mercaptopurine / Q000494:pharmacology*; D051379:Mice; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
chemical_list: D018932:Chemokine CCL2; D007166:Immunosuppressive Agents; D016209:Interleukin-8; C107953:RAC1 protein, human; D050796:STAT3 Transcription Factor; D014409:Tumor Necrosis Factor-alpha; D015122:Mercaptopurine; D052247:Nitric Oxide Synthase Type II; D048670:MAP Kinase Kinase 4; D020830:rac1 GTP-Binding Protein