Molecular mechanisms of Trypanosoma cruzi survival using host apoptosis inhibitor

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Trypanosoma cruzi is a protozoan parasite that causes Chagas' disease in South America. We demonstrated that the parasite infection inhibits death receptor-mediated apoptosis in host cells. This inhibition is thought to be a defense strategy for the parasite to escape from host immune responses. We clarified that the parasite dramatically up-regulates cellular FLICE-like inhibitory protein (c-FLIP), the only known mammalian inhibitor specific for death receptor signaling. We also found that c-FLIP knock-down with a small interfering RNA significantly restores Fas-mediated apoptosis in infected cells. To elucidate the mechanisms of c-FLIP up-regulation, we examined posttranscriptional regulation of c-FLIP expression in T. cruzi infected cells. It has been reported that c-FLIP is a key target for S-nitrosylation by nitric oxide (NO) in cancer cells. HT1080 or THP-1 cells were infected with T. cruzi or treated with NO donors, and further cultured for 1-3 days. Cell lysates were immunoprecipitated and analyzed by Western blot using anti-S-nitrosocysteine antibody in control and infected cells. By the addition of the NO donors, sodium nitroprusside, the nitrosylated level of FLIP was strongly increased. In infected cells nitrosylated c-FLIP was clearly detected in supernatant. These findings suggest that endogenously produced NO synthesized by NO synthase is a mediator of T. cruzi infection. S-nitrosylation of FLIP is an important mechanism utilized by NO rendering FLIP resistant to ubiquitination and proteasomal degradation by FasL.