Negative iron regulation of the CP65 cysteine proteinase cytotoxicity in Trichomonas vaginalis

Several cysteine proteinases (CPs) participate in the virulence of Trichomonas vaginalis. One of them is a 65 kDa CP, CP65, involved in cytotoxicity. The aim of this work was to investigate the effect of iron on the trichomonal CP65-dependent cytotoxicity using parasites grown under distinct iron concentrations. Cytotoxicity and cell-binding assays, and zymograms were performed. At the highest iron concentration (250 μM), parasites exhibited the lowest levels of cytotoxicity and less CP65 proteolytic activity. Other cations in the culture medium did not affect the trichomonal CP65-dependent cytotoxicity as iron did. Another four trichomonad fresh isolates presented similar iron negative effect over cytotoxicity. Western blot and RT-PCR experiments also showed reduction in the amount of protein and transcript of CP65 in trichomonads grown under iron-rich conditions, as compared with parasites grown in normal and iron-depleted media. Indirect immunofluorescence using the anti-CP65 antibody showed that parasites grown in iron-rich medium expressed less CP65 than those grown in normal and iron-depleted media. Cytotoxicity inhibition experiments with the anti-CP65 antibody confirmed the iron negative effect over the CP65-dependent cytotoxicity. In conclusion, our data show that iron specifically down-regulates proteolytic activity, expression, and transcription of CP65, negatively affecting trichomonal cytotoxicity in vitro.