Inhibition of GTPase Rac1 in endothelium by 6-mercaptopurine results in immunosuppression in nonimmune cells: new target for an old drug

J Immunol. 2014 May 1;192(9):4370-8. doi: 10.4049/jimmunol.1302527. Epub 2014 Mar 26.


Azathioprine and its metabolite 6-mercaptopurine (6-MP) are well established immunosuppressive drugs. Common understanding of their immunosuppressive properties is largely limited to immune cells. However, in this study, the mechanism underlying the protective role of 6-MP in endothelial cell activation is investigated. Because 6-MP and its derivative 6-thioguanosine-5'-triphosphate (6-T-GTP) were shown to block activation of GTPase Rac1 in T lymphocytes, we focused on Rac1-mediated processes in endothelial cells. Indeed, 6-MP and 6-T-GTP decreased Rac1 activation in endothelial cells. As a result, the compounds inhibited TNF-α-induced downstream signaling via JNK and reduced activation of transcription factors c-Jun, activating transcription factor-2 and, in addition, NF κ-light-chain-enhancer of activated B cells (NF-κB), which led to decreased transcription of proinflammatory cytokines. Moreover, 6-MP and 6-T-GTP selectively decreased TNF-α-induced VCAM-1 but not ICAM-1 protein levels. Rac1-mediated generation of cell membrane protrusions, which form docking structures to capture leukocytes, also was reduced by 6-MP/6-T-GTP. Consequently, leukocyte transmigration was inhibited after 6-MP/6-T-GTP treatment. These data underscore the anti-inflammatory effect of 6-MP and 6-T-GTP on endothelial cells by blocking Rac1 activation. Our data provide mechanistic insight that supports development of novel Rac1-specific therapeutic approaches against chronic inflammatory diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Western
  • Cell Adhesion / drug effects
  • Cells, Cultured
  • Coculture Techniques
  • Endothelial Cells / drug effects*
  • Endothelial Cells / enzymology
  • Enzyme Activation / drug effects
  • Humans
  • Immunosuppressive Agents / pharmacology*
  • Mercaptopurine / pharmacology*
  • Microscopy, Confocal
  • Microscopy, Electron, Scanning
  • Neutrophils / drug effects
  • Neutrophils / metabolism
  • Signal Transduction / drug effects*
  • Transcriptome
  • Transendothelial and Transepithelial Migration / drug effects
  • rac1 GTP-Binding Protein / metabolism*


  • Immunosuppressive Agents
  • RAC1 protein, human
  • Mercaptopurine
  • rac1 GTP-Binding Protein