Trypanosoma cruzi TcHTE protein expression is regulated by intracellular heme levels

EVELYN TEVERE; CECILIA B. DI CAPUA; JULIA A. CRICCO

Mar de Plata

Congreso; XXXII Reunión Anual de la Sociedad Argentina de Protozoologúa; 2019

Sociedad Argentina de Protozoología

Trypanosoma cruzi is a heme auxotroph, therefore it must scavenge heme (as free heme or as hemoglobin) from their hosts. The protein TcHTE (T. cruzi Heme Transport Enhancer) is involved in the uptake of this cofactor. It is localized to the flagellar pocket of the parasite and there is evidence that it forms a homotrimer. Conversely to other trypanosomatids, no hemoglobin (Hb) receptor has been found in T. cruzi yet. Given these precedents, we investigated if TcHTE has a role in Hb uptake from the extracellular medium or in Hb-derived heme transport.At mRNA and protein level, TcHTE is higher in heme starved Wild Type epimastigotes, and it gradually decreases when increasing amounts of a heme source (hemin or Hb) are added to the media. However, this response is faster when hemin is used as heme source, which may be related to the different biodisponibilities and/or uptake mechanisms of both heme sources. Surprisingly, epimastigotes that overexpress rTcHTE.His-GFP incubated in media supplemented with Hb have a significantly higher intracellular heme content compared to control epimastigotes; as previously reported using hemin as heme source. Altogether, these results mean that TcHTE is also involved in Hb uptake. Conversely to Trypanosoma brucei ortholog rTbHRG, rTcHTE.His-GFP does not change its localization when Hb is used as heme source, which discards that TcHTE has a role in the salvage of Hb-derived heme in internal compartments. We concluded that T. cruzi is able to sense intracellular heme level and regulates TcHTE expression according to it. Based on these and our previous results we propose two models of heme uptake in T. cruzi. In the first one, Hb is endocyted via a non-canonical Hb receptor and Hb-derived heme is transported through an unknown protein, meanwhile heme enters the cell via TcHTE. In the other model, Hb is degraded by external proteases in the parasite?s surface, heme is released and enters the cell via TcHTE.