Trypanosoma cruzi: cloning and characterization of two genes whose expression is up-regulated in metacyclic trypomastigotes

Secreted trypanosome cyclophilin inactivates lytic insect defense peptides and induces parasite calcineurin activation and infectivity

The mechanisms by which Trypanosoma cruzi survives antimicrobial peptides and differentiates during its transit through the gastrointestinal tract of the reduviid vector are unknown. We show that cyclophilin, a peptidyl-prolyl isomerase secreted from T. cruzi epimastigotes, binds to and neutralizes the reduviid antimicrobial peptide trialysin promoting parasite survival. This is dependent on a singular proline residue in trialysin and is inhibited by the cyclophilin inhibitor cyclosporine A. In addition, cyclophilin-trialysin complexes enhance the production of ATP and reductase responses of parasites, which are inhibited by both calcineurin-specific inhibitors cyclosporine A and FK506. Calcineurin phosphatase activity of cyclophilin-trialysin-treated parasites was higher than in controls and was inhibited by preincubation by either inhibitor. Parasites exposed to cyclophilin-trialysin have enhanced binding and invasion of host cells leading to higher infectivity. Leishmanial cyclophilin also mediates trialysin protection and metabolic stimulation by T. cruzi, indicating that extracellular cyclophilin may be critical to adaptation in other insect-borne protozoa. This work demonstrates that cyclophilin serves as molecular sensor leading to the evasion and adaptive metabolic response to insect defense peptides.

Quantitative proteomics of Trypanosoma cruzi during metacyclogenesis

Trypanosoma cruzi is the etiologic agent of Chagas disease, which is estimated to affect over eight million people around the world. Trypanosoma cruzi has a complex life cycle, involving insect and mammalian hosts and four distinct developmental stages: epimastigotes, metacyclic trypomastigotes, amastigotes, and bloodstream trypomastigotes. Metacyclogenesis is the process by which T. cruzi epimastigotes differentiate into metacyclic trypomastigotes and acquire infectivity, and involves differential gene expression associated with acquisition of virulence. In T. cruzi, gene expression regulation is achieved mainly posttranscriptionally. Therefore, proteomics-based approaches are extremely useful for gaining a better understanding of the changes that occur in the stage-regulated gene expression program of the parasite at the molecular level. Here, we performed an in-depth quantitative MS-based proteomic study of T. cruzi metacyclogenesis and quantified almost 3000 proteins expressed during the process of differentiation. To the best of our knowledge, this work is the most comprehensive quantitative proteomics study of different cell populations of T. cruzi available so far. We identified relevant proteins and pathways involved in the parasite's differentiation and infectivity acquisition, opening new perspectives for further studies that could, ultimately, lead to the identification of new targets for chemotherapy.

Aspects of Trypanosoma cruzi stage differentiation

Trypanosoma cruzi alternates between different morphological and functional types during its life cycle. Since the discovery of this parasite at the beginning of the twentieth century, efforts have been made to determine the basis of its pathogenesis in the course of Chagas disease and its biochemical constituents. There has also been work to develop tools and strategies for prophylaxis of the important disease caused by these parasites which affects millions of people in Latin America. The identification of axenic conditions allowing T. cruzi growth and differentiation has led to the identification and characterization of stage-specific antigens as well as a better characterization of the biological properties and biochemical particularities of each individual developmental stage. The recent availability of genomic data should pave the way to new progress in our knowledge of the biology and pathogenesis of T. cruzi. This review addresses the differentiation and major stage-specific antigens of T. cruzi and attempts to describe the complexity of the parasite and of the disease it causes.

Posttranscriptional mechanisms involved in the control of expression of the stage-specific GP82 surface glycoprotein in Trypanosoma cruzi

Trypanosoma cruzi metacyclic trypomastigotes express the developmentally regulated GP82 glycoprotein, which is implicated in host cell invasion. Although GP82 mRNA and protein are not present and the mRNAs barely detectable in epimastigotes, nuclear run-on analysis showed that it is transcribed in both stages. This result indicates that accumulation of transcripts in metacyclic forms is not due to increased transcription of the GP82 gene. To investigate whether mRNA stability may be responsible for the differences in the steady-state levels of this mRNA, parasites were treated with actinomycin D or cycloheximide. When treated with actinomycin D, the half-lives estimated for GP82 transcripts were about 6h in metacyclic trypomastigotes and 0.5h in epimastigotes. In the presence of cycloheximide, the levels of GP82 mRNA decayed slightly after 8h in metacyclic trypomastigotes, whereas in epimastigotes the levels of this mRNA increased. This effect suggests a stabilizing mechanism acting in metacyclic trypomastigotes and a destabilizing mechanism in epimastigotes which could be mediated by an element present in the 3'-UTR of the transcripts. Consistent with this finding, northern blot analysis showed that GP82 mRNAs were mobilized to polysomes and consequently translated, but only in metacyclic trypomastigotes.

Active transcription and ultrastructural changes during Trypanosoma cruzi metacyclogenesis

The differentiation of proliferating epimastigote forms of Trypanosoma cruzi , the protozoan parasite that causes Chagas disease, into the infective and non-proliferating metacyclic forms can be reproduced in the laboratory by incubating the cells in a chemically-defined medium that mimics the urine of the insect vector. Epimastigotes have a spherical nucleus, a flagellum protruding from the middle of the protozoan cell, and a disk-shaped kinetoplast -- an organelle that corresponds to the mitochondrial DNA. Metacyclic trypomastigotes have an elongated shape with the flagellum protruding from the posterior portion of the cell and associated with a spherical kinetoplast. Here we describe the morphological events of this transformation and characterize a novel intermediate stage by three-dimensional reconstruction of electron microscope serial sections. This new intermediate stage is characterized by a kinetoplast compressing an already elongated nucleus, indicating that metacyclogenesis involves active movements of the flagellar structure relative to the cell body. As transcription occurs more intensely in proliferating epimastigotes than in metacyclics, we also examined the presence of RNA polymerase II and measured transcriptional activity during the differentiation process. Both the presence of the enzyme and transcriptional activity remain unchanged during all steps of metacyclogenesis. RNA polymerase II levels and transcriptional activity only decrease after metacyclics are formed. We suggest that transcription is required during the epimastigote-to-metacyclic trypomastigote differentiation process, until the kinetoplast and flagellum reach the posterior position of the parasites in the infective form.

The Trypanosoma cruzi metacyclic-specific protein Met-III associates with the nucleolus and contains independent amino and carboxyl terminal targeting elements

Metacyclogenesis in Trypanosoma cruzi involves the differentiation of replicating non-infective epimastigotes into non-replicating metacyclic trypomastigotes. This pre-adapts parasites for infection of the mammalian host and is characterised by several morphological changes and structural alterations to the nucleus, including nucleolar disaggregation. Experimental investigation of these developmental processes has been hampered by a lack of robust molecular markers. Here, we describe the precise temporal expression of the T. cruzi-specific protein Met-III, in the genome reference strain CL Brener. Expression is restricted to metacyclics in the insect stages of the life-cycle and is rapidly down-regulated following invasion of mammalian cells. Met-III localises to dispersed foci typical of the disassembled nucleolus in metacyclics and to the discrete single nucleolus of cells soon after macrophage invasion. To identify elements that target Met-III, we generated a series of tagged green fluorescent protein fusion proteins and examined their sub-nuclear location in transformed parasites. These experiments demonstrated that amino and carboxyl terminal fragments, characterised by clusters of basic residues, could independently mediate nucleolar sequestration. To investigate the function of Met-III, we used gene deletion. This showed that Met-III is not required for the development of metacyclic trypomastigotes and that null mutants can complete the life-cycle in vitro.

TcZFP1: a CCCH zinc finger protein of Trypanosoma cruzi that binds poly-C oligoribonucleotides in vitro

We have identified two zinc finger proteins of Trypanosoma cruzi, the protozoan parasite that causes Chagas disease in humans. These proteins, named tcZFP1 and tcZFP2, share the unusual zinc finger motif (CCCH) found in a diverse range of RNA-binding proteins involved in various aspects of the control of cell homeostasis and differentiation. We report here the functional expression of a recombinant tcZFP1, and the relative affinity and stability of the specific complexes formed between the protein and synthetic oligoribonucleotides containing C-rich sequences.