Cadmium-dependent expression of a new metallothionein identified in Trichomonas vaginalis

Metallothioneins (MTs) have been identified in a wide variety of organisms from bacteria to humans. The biological functions of these MTs have a key role in metalloregulatory metabolism and its expression is induced in response to different stimuli, particularly by divalent metal cations. Also, the action of MTs have been implicated in the survival of pathogens in presence of microbicidal concentration of divalent cations, which allows the establishment of the infection. Trichomonas vaginalis is a protozoan parasite that adapts to the microenvironment of the male urogenital tract, where cations such as zinc (Zn²⁺) and cadmium (Cd²⁺) are present. Nevertheless, the molecular mechanisms of metal tolerance and homeostasis is not yet dilucidated in this parasite. In this study, we have identified 4 potential MT-like sequences (tvmt´s) in T. vaginalis genome. Because tvmt-2, -3, and -4 corresponds to truncated partial genes, we characterized the trichomonad tvmt-1 gene. The bioinformatic analyses and the predicted protein (TvMT-1) show similar properties to the reported in other MTs. The expression patterns of tvmt-1 in the presence of several divalent cations (Fe²⁺, Mn²⁺, Zn²⁺ and Cd²⁺) were analyzed and we demonstrated that Cd²⁺ induce significantly their expression. By indirect immunofluorescence assays, we corroborated this positive regulation of TvMT-1 in the cytoplasm of parasites grown in the presence of Cd²⁺. The tvmt-1 promoter contains putative metal responsive elements, which are probably the responsible for the Cd²⁺-dependent expression of this gene. Our results suggest that tvmt-1 gene encode a metallothionein that may be responsible for the homeostatis and detoxification of Cd⁺² in T. vaginalis.