Characterization, cloning and immunolocalization of a coronin homologue in Trichomonas vaginalis

Revisiting fecal metatranscriptomics analyses of macaques with idiopathic chronic diarrhoea with a focus on trichomonad parasites

Trichomonads, anaerobic microbial eukaryotes members of the phylum Parabasalia, are common obligate extracellular symbionts that can lead to pathological or asymptomatic colonization of various mucosal surfaces in a wide range of animal hosts. Results from previous in vitro studies have suggested a number of intriguing mucosal colonization strategies by Trichomonads, notably highlighting the importance of interactions with bacteria. However, in vivo validation is currently lacking. A previous metatranscriptomics study into the cause of idiopathic chronic diarrhoea in macaques reported the presence of an unidentified protozoan parasite related to Trichomonas vaginalis. In this work, we performed a reanalysis of the published data in order to identify the parasite species present in the macaque gut. We also leveraged the information-rich metatranscriptomics data to investigate the parasite behaviour in vivo. Our results indicated the presence of at least 3 genera of Trichomonad parasite; Tetratrichomonas, Pentatrichomonas and Trichomitus, 2 of which had not been previously reported in the macaque gut. In addition, we identified common in vivo expression profiles shared amongst the Trichomonads. In agreement with previous findings for other Trichomonads, our results highlighted a relationship between Trichomonads and mucosal bacterial diversity which could be influential in health and disease.

Biochemical and immunocytochemical characterization of coronins in platelets

Rapid reorganization of the actin cytoskeleton in response to receptor-mediated signaling cascades allows platelets to transition from a discoid shape to a flat spread shape upon adhesion to damaged vessel walls. Coronins are conserved regulators of the actin cytoskeleton turnover but they also participate in signaling events. To gain a better picture of their functions in platelets we have undertaken a biochemical and immunocytochemical investigation with a focus on Coro1. We found that class I coronins Coro1, 2 and 3 are abundant in human and mouse platelets whereas little Coro7 can be detected. Coro1 is mainly cytosolic, but a significant amount associates with membranes in an actin-independent manner and does not translocate from or to the membrane fraction upon exposure to thrombin, collagen or prostacyclin. Coro1 rapidly translocates to the Triton insoluble cytoskeleton upon platelet stimulation with thrombin or collagen. Coro1, 2 and 3 show a diffuse cytoplasmic localization with discontinuous accumulation at the cell cortex and actin nodules of human platelets, where all three coronins colocalize. Our data are consistent with a role of coronins as integrators of extracellular signals with actin remodeling and suggests a high extent of functional overlap among class I coronins in platelets.

In-Depth Quantitative Proteomic Analysis of Trophozoites and Pseudocysts of Trichomonas vaginalis

Trichomonas vaginalis is a sexually transmitted anaerobic parasite that infects humans causing trichomoniasis, a common and ubiquitous sexually transmitted disease. The life cycle of this parasite possesses a trophozoite form without a cystic stage. However, the presence of nonproliferative and nonmotile, yet viable and reversible spherical forms with internalized flagella, denominated pseudocysts, has been commonly observed for this parasite. To understand the mechanisms involved in the formation of pseudocysts, we performed a mass spectrometry-based high-throughput quantitative proteomics study using a label-free approach and functional assays by biochemical and flow cytometric methods. We observed that the morphological transformation of trophozoite to pseudocysts is coupled to (i) a metabolic shift toward a less glycolytic phenotype; (ii) alterations in the abundance of hydrogenosomal iron-sulfur cluster (ISC) assembly machinery; (iii) increased abundance of regulatory particles of the ubiquitin-proteasome system; (iv) significant alterations in proteins involved in adhesion and cytoskeleton reorganization; and (v) arrest in G2/M phase associated with alterations in the abundance of regulatory proteins of the cell cycle. These data demonstrate that pseudocysts experience important physiological and structural alterations for survival under unfavorable environmental conditions.

RNA-Binding Proteins in Trichomonas vaginalis: Atypical Multifunctional Proteins

Iron homeostasis is highly regulated in vertebrates through a regulatory system mediated by RNA-protein interactions between the iron regulatory proteins (IRPs) that interact with an iron responsive element (IRE) located in certain mRNAs, dubbed the IRE-IRP regulatory system. Trichomonas vaginalis, the causal agent of trichomoniasis, presents high iron dependency to regulate its growth, metabolism, and virulence properties. Although T. vaginalis lacks IRPs or proteins with aconitase activity, possesses gene expression mechanisms of iron regulation at the transcriptional and posttranscriptional levels. However, only one gene with iron regulation at the transcriptional level has been described. Recently, our research group described an iron posttranscriptional regulatory mechanism in the T. vaginalis tvcp4 and tvcp12 cysteine proteinase mRNAs. The tvcp4 and tvcp12 mRNAs have a stem-loop structure in the 5'-coding region or in the 3'-UTR, respectively that interacts with T. vaginalis multifunctional proteins HSP70, α-Actinin, and Actin under iron starvation condition, causing translation inhibition or mRNA stabilization similar to the previously characterized IRE-IRP system in eukaryotes. Herein, we summarize recent progress and shed some light on atypical RNA-binding proteins that may participate in the iron posttranscriptional regulation in T. vaginalis.

The biology of Trichomonas vaginalis in the light of urogenital tract infection

The human pathogen Trichomonas vaginalis is a parasitic protist. It is a representative of the eukaryotic supergroup Excavata that includes a few other protist parasites such as Leishmania, Trypanosoma and Giardia. T. vaginalis is the agent of trichomoniasis and in the US alone, one in 30 women tests positive for this parasite. The disease is easily treated with metronidazole in most cases, but resistant strains are on the rise. The biology of Trichomonas is remarkable: it includes for example the biggest protist genome currently sequenced, the expression of about 30,000 protein-encoding genes (and thousands of lncRNAs and pseudogenes), anaerobic hydrogenosomes, rapid morphogenesis during infection, the secretion of exosomes, the manipulation of the vaginal microbiota through phagocytosis and a rich strain-dependent diversity. Here we provide an overview of Trichomonas biology with a focus on its relevance for pathogenicity and summarise the most recent advances. With some respect this parasite offers the opportunity to serve as a model system to study certain aspects of cell and genome biology, but tackling the complex biology of T. vaginalis is also important to better understand the effects that accompany infection and direct symptoms.

The actin-based machinery of Trichomonas vaginalis mediates flagellate-amoeboid transition and migration across host tissue

Trichomonas vaginalis is the most widespread non-viral pathogen of the human urogenital tract, infecting ∼ 3% of the world's population annually. At the onset of infection the protist changes morphology within minutes: the flagellated free-swimming cell converts into the amoeboid-adherent stage. The molecular machinery of this process is not well studied, but is thought to involve actin reorganization. We have characterized amoeboid transition, focusing in particular on TvFim1, the only expressed protein of the fimbrin family in Trichomonas. Addition of TvFim1 to actin polymerization assays increases the speed of actin filament assembly and results in bundling of F-actin in a parallel and anti-parallel manner. Upon contact with vaginal epithelial cells, the otherwise diffuse localization of actin and TvFim1 changes dramatically. In the amoeboid TvFim1 associates with fibrous actin bundles and concentrates at protrusive structures opposing the trailing ends of the gliding amoeboid form and rapidly redistributes together with actin to form distinct clusters. Live cell imaging demonstrates that Trichomonas amoeboid stages do not just adhere to host tissue, rather they actively migrate across human epithelial cells. They do so in a concerted manner, with an average speed of 20 μm min(-1) and often using their flagella and apical tip as the leading edge.

Actin-interacting and flagellar proteins in Leishmania spp.: Bioinformatics predictions to functional assignments in phagosome formation

Several motile processes are responsible for the movement of proteins into and within the flagellar membrane, but little is known about the process by which specific proteins (either actin-associated or not) are targeted to protozoan flagellar membranes. Actin is a major cytoskeleton protein, while polymerization and depolymerization of parasite actin and actin-interacting proteins (AIPs) during both processes of motility and host cell entry might be key events for successful infection. For a better understanding the eukaryotic flagellar dynamics, we have surveyed genomes, transcriptomes and proteomes of pathogenic Leishmania spp. to identify pertinent genes/proteins and to build in silico models to properly address their putative roles in trypanosomatid virulence. In a search for AIPs involved in flagellar activities, we applied computational biology and proteomic tools to infer from the biological meaning of coronins and Arp2/3, two important elements in phagosome formation after parasite phagocytosis by macrophages. Results presented here provide the first report of Leishmania coronin and Arp2/3 as flagellar proteins that also might be involved in phagosome formation through actin polymerization within the flagellar environment. This is an issue worthy of further in vitro examination that remains now as a direct, positive bioinformatics-derived inference to be presented.

Ancient Leishmania coronin (CRN12) is involved in microtubule remodeling during cytokinesis

In general, coronins play an important role in actin-based processes, and are expressed in a variety of eukaryotic cells, including Leishmania. Here, we show that Leishmania coronin preferentially distributes to the distal tip during cytokinesis, and interacts with microtubules through a microtubule-based motor, kinesin K39. We further show that reduction in coronin levels by 40-50% in heterozygous coronin mutants results in generation of bipolar cells (25-30%), specifically in the log phase, owing to unregulated growth of the corset microtubules. Further analysis of bipolar cells revealed that the main cause of generation of bipolar cell morphology is the intrusion of the persistently growing corset microtubules into the other daughter cell corset from the opposite direction. This defect in cytokinesis, however, disappears upon episomal gene complementation. Additionally, our attempts to prepare homozygous mutants were unsuccessful, as only the aneuploid cells survive the selection process. These results indicate that coronin regulates microtubule remodeling during Leishmania cytokinesis and is essentially required for survival of these parasites in culture.

Electron microscopy and cytochemistry analysis of the endocytic pathway of pathogenic protozoa

Endocytosis is essential for eukaryotic cell survival and has been well characterized in mammal and yeast cells. Among protozoa it is also important for evading from host immune defenses and to support intense proliferation characteristic of some life cycle stages. Here we focused on the contribution of morphological and cytochemical studies to the understanding of endocytosis in Trichomonas, Giardia, Entamoeba, Plasmodium, and trypanosomatids, mainly Trypanosoma cruzi, and also Trypanosoma brucei and Leishmania.

Evolutionary and functional diversity of coronin proteins

This chapter discusses various aspects of coronin phylogeny, structure and function that are of specific interest. Two subfamilies of ancient coronins of unicellular pathogens such as Entamoeba, Trypanosoma, Leishmania and Acanthamoeba as well as of Plasmodium, Babesia, and Trichomonas are presented in the first two sections. Their coronins generally bind to F-actin and apparently are involved in proliferation, locomotion and phagocytosis. However, there are so far no studies addressing a putative role of coronin in the virulence of these pathogens. The following section delineates genetic anomalies like the chimeric coronin-fusion products with pelckstrin homology and gelsolin domains that are found in amoeba. Moreover, most nonvertebrate metazoa appear to encode CRN8, CRN9 and CRN7 representatives (for these coronin symbols see Chapter 2), but in e.g., Drosophila melanogaster and Caenorhabditis elegans a CRN9 is missing. The forth section deals with the evolutionary expansion of vertebrate coronins. Experimental data on the F-actin binding CRN2 of Xenopus (Xcoronin) including a Cdc42/Rac interactive binding (CRIB) motif that is also present in other members of the coronin protein family are discussed. Xenopus laevis represents a case for the expansion of the seven vertebrate coronins due to tetraploidization events. Other examples for a change in the number of coronin paralogs are zebrafish and birds, but (coronin) gene duplication events also occurred in unicellular protozoa. The fifth section of this chapter briefly summarizes three different cellular processes in which CRN4/CORO1A is involved, namely actin-binding, superoxide generation and Ca(2+)-signaling and refers to the largely unexplored mammalian coronins CRN5/CORO2A and CRN6/CORO2B, the latter binding to vinculin. The final section discusses how, by unveiling the aspects of coronin function in organisms reported so far, one can trace a remarkable evolution and diversity in their individual roles anticipating a rather complex and intricate involvement of coronins in a variety of cellular processes.

Differential soluble protein expression between Trichomonas vaginalis isolates exhibiting low and high virulence phenotypes

A comparative analysis of proteomic maps of long-term grown and fresh clinical Trichomonas vaginalis isolates exhibiting low and high virulence phenotypes, respectively, was performed using two-dimensional gel electrophoresis and mass spectrometry. Of 29 protein spots differentially expressed between the isolates, 19 were over-expressed in the isolate exhibiting high virulence phenotype: proteins associated with cytoskeletal dynamics, such as coronin and several isoforms of actin, as well as proteins involved in signal transduction, protein turnover, proteolysis, and energetic and polyamine metabolisms were identified. Some malate dehydrogenase, fructose-1,6-bisphosphate aldolase and ornithine cyclodeamidase isoforms were exclusively expressed by the highly virulent isolate. During interaction assays with VEC, parasites exhibiting high virulence phenotype rapidly adhered and switched to amoeboid forms. In contrast, low adhesion and no morphological transformation were observed in parasites displaying low virulence phenotype. Our findings demonstrate that expression of specific proteins by high and low virulence parasites could be associated with the ability of each isolate to undergo morphological transformation and interact with host cells. Such data represent an important step towards understanding of the complex interaction network of proteins that participate in the mechanism of pathogenesis of this protozoan.

Phagocytosis by Trichomonas vaginalis: new insights

BACKGROUND INFORMATION

The parasitic protozoan Trichomonas vaginalis is the causative agent of trichomoniasis, a sexually transmitted disease. The phagocytic activity of this parasite has not been completely elucidated. In order to better understand the mechanisms of trichomonal phagocytosis, we have studied the in vitro capacity of T. vaginalis to phagocytose and degrade Saccharomyces cerevisiae cells.

RESULTS AND CONCLUSIONS

To analyse the phagocytic ability and capacity, two isolates of T. vaginalis presenting different virulence grades were used. Complementary techniques, such as fluorescence microscopy, computer-based fluorescence analysis, scanning and transmission electron microscopy and the use of drugs that interfere with the actin microfilaments, were used in order to follow the behaviour of the actin cytoskeleton during phagocytosis of yeast cells by T. vaginalis. It was concluded that: (1) T. vaginalis changes its shape rapidly and engulfs the yeast cells, which are almost as large as the parasite; (2) long-term and fresh cultures are able to phagocytose, although the low-virulence strain JT demonstrated a lower activity when compared with the highly virulent T016 isolate; (3) the T016 strain exhibited an amoeboid morphology during the internalization of yeast cells in contrast with the JT strain; (4) attachment of yeast cells to the parasite occurs via the whole cell surface, including both anterior and recurrent flagella; (5) two forms of phagocytosis were observed: a 'sinking' process without any apparent participation of plasma membrane extensions and the classical phagocytosis where pseudopodia are extended toward the target cell; (6) the internalized S. cerevisiae are digested in lysosomes; (7) competitor sugars D-mannose or L-fucose inhibit the phagocytosis, and inhibition was 1.67 times higher in long-term cultured JT than that of the parasites from fresh isolate T016; (8) a thick layer of actin microfilaments was present underlying the plasma membrane, and especially in the pseudopodia and around the phagocytosed particles; (9) a dramatic change in the distribution pattern of fibrillar actin occurred during phagocytosis; (10) cytochalasin D depressed the phagocytosis; (11) a non-specific recognition and phagocytosis of yeast cells by T. vaginalis is mediated by a mannose receptor present on the parasite surface; (12) the phagocytic process may occur simultaneously during mitosis of the parasite.

A novel homologue of coronin colocalizes with actin in filament-like structures in Leishmania

The presence of actin in Leishmania has recently been demonstrated, but the functional form of this protein (filamentous actin) has not yet been identified. We report here that the putative coronin homologue identified in the Leishmania genome is invariably associated with the filament-like structures of actin in Leishmania promastigotes. The occurrence of filamentous structures is significantly increased upon overexpression of Leishmania coronin as its GFP fusion product in Leishmania cells. However, expression of Leishmania actin or coronin alone in mammalian cells does not result in formation of any filament-like structures of Leishmania actin or association of Leishmania coronin with mammalian filamentous actin, but coexpression of both the proteins in these cells leads to formation of filamentous structures containing Leishmania actin and coronin. The high specificity of Leishmania coronin for Leishmania actin could be attributed to its unique structure as it differs from other coronins not only in the unique region but also in the actin-binding site and leucine zipper motif. These results taken together indicate that Leishmania contains a novel form of coronin which colocalizes with actin in filament-like structures in these cells.

Acanthamoeba healyi: Molecular cloning and characterization of a coronin homologue, an actin-related protein

Coronin, described in organisms from yeasts to humans, has been found to be involved in various actin-associated activities. It has yet to be described in Acanthamoeba, medically significant as the causative agent of granulomatous amebic encephalitis and amoebic keratitis and used extensively in actin-related studies. We isolated and characterized a cDNA encoding a coronin-like protein in A. healyi by sequence analysis and demonstrated intracellular localization of the gene product by transient transfection. Named Ahcoronin, the gene is composed of 454 amino acids which contain the characteristic WD repeats of coronin and coronin-like proteins. The C-terminal region of the gene was also predicted to have a high tendency of forming a coiled-coil, another structural characteristic of coronin. The gene showed a 50% homology to coronins. Ahcoronin occurs as a single copy and expressed as a transcript of approximately 1.4kb in A. healyi. Results of transfection showed that Ahcoronin was localized in the cell's periphery and in the leading edge consistent to that of actin. The fusion protein has also been observed to localize around phagocytic cups but was disassembled later during phagocytosis. Sequence analysis of Ahcoronin homologue of A. healyi showed numerous potential for further studies and is sure to contribute in the growing interest toward the properties and functions of coronin and coronin-like proteins.

Trichomonads under Microscopy

Trichomonads are flagellate protists, and among them Trichomonas vaginalis and Tritrichomonas foetus are the most studied because they are parasites of the urogenital tract of humans and cattle, respectively. Microscopy provides new insights into the cell biology and morphology of these parasites, and thus allows better understanding of the main aspects of their physiology. Here, we review the ultrastructure of T. foetus and T. vaginalis, stressing the participation of the axostyle in the process of cell division and showing that the pseudocyst may be a new form in the trichomonad cell cycle and not simply a degenerative form. Other organelles, such as the Golgi and hydrogenosomes, are also reviewed. The virus present in trichomonads is discussed.

Trichomonas vaginalis virulence against epithelial cells and morphological variability: the comparison between a well-established strain and a fresh isolate

The FMVI strain of Trichomonas vaginalis was freshly isolated from an asymptomatic patient, and its morphological properties and virulence in vitro compared with the well-established JT strain. The morphological variability of the parasites was assessed by differential interference microscopy and both scanning and transmission electron microscopy. The FMV1 strain presented nearly 20% amoeboid cells whereas the JT strain presented high percentages of ellipsoid but no amoeboid cells. The FMV1 morphotype population was unaltered after at least 1 year of subculturing. Electron microscopy revealed that this strain produced numerous pseudopod structures which mediated intimate contact and interdigitation among trophozoites. Dead FMV1 parasites were often phagocytosed by conspecific cells. We also compared the cytolytic capacity of these two populations against epithelial MDCK cells and its contact dependence. The FMV1 strain rapidly adhered to plastic or glass surfaces and to MDCK monolayers. This strain destroyed about 93% of the epithelial cells in 90 min whereas the cytolytic activity of the JT parasites was very much lower (about 41%). Parasite supernatants displayed no cytolytic activity, indicating contact-mediated lysis. The protozoan virulence in vitro did not correlate well with the clinical observations. The implications of these results are discussed.

Two regions responsible for the actin binding of p57, a mammalian coronin family actin-binding protein

The actin-binding protein p57, a member of the coronin protein family, is expressed in a variety of immune cells. It has five WD repeats and a coiled-coil motif containing a leucine zipper, both of which are known to mediate protein-protein interactions. In order to identify the precise actin-binding regions in p57, and to assess the contribution of these structural motifs, we prepared various truncated p57 as fusion proteins with glutathione S-transferase (GST) and examined their actin-binding activity. A co-sedimentation assay demonstrated that p57(1-371) (C-terminal truncated p57) had the ability to bind F-actin, but p57(372-461) (a fragment containing the coiled-coil motif) did not. A segment consisting of the N-terminal 34 amino acids of p57 (p57(1-34)) was found to bind to F-actin in the co-sedimentation assay. Furthermore, fluorescence microscopic observation showed that p57(1-34) was co-localized with F-actin in COS-1 cells after the transfection with the p57(1-34) construct. Deletion of (10)KFRHVF(15), a sequence conserved among coronin-related proteins, from p57(1-34) abolished its actin-binding activity, suggesting that this sequence with basic and hydrophobic amino acids is crucial for p57 to bind to F-actin. However, the N-terminal deletion mutant p57(63-461) retained the binding ability to F-actin. This result suggests the presence of a second actin-binding region. Further deletion analysis revealed that p57(111-204), which includes the second and third WD repeats, also exhibited weak actin-binding activity in the co-sedimentation assay. Taken together, these data strongly suggest that at least two regions within Met-1 to Asp-34 and Ile-111 to Glu-204 of p57 are responsible for its binding to the actin cytoskeleton.