Host tissue invasion by Entamoeba histolytica is powered by motility and phagocytosis

Effects of nocodazole and latrunculin B on locomotion of amoeboid cells of Rhizochromulina sp. strain B44 (Heterokontophyta, Dictyochophyceae)

Rhizochromulina is a genus of unicellular dictyochophycean algae (Heterokontophyta), comprising a single species R. marina and numerous strains. Recently, we described the first arctic rhizochromuline-Rhizochromulina sp. strain B44. Amoeboid cells of this algae are able to transform into flagellates, and this transition can be triggered by prolonged mechanical disturbance. Thin branching pseudopodia of the neighboring rhizochromuline cells fuse to form a meroplasmodium. The pseudopodia contain microtubules, but do not contain actin microfilaments; actin forms the cytoplasmic cytoskeleton and extends only to the bases of the pseudopodia. Microtubule-driven pseudopodia are characteristic to a plethora of eukaryotes, but the role of microtubular and actin cytoskeleton in locomotion of these organisms remains poorly understood. We conducted a series of experiments where amoeboid cells of Rhizochromulina sp. B44 were treated with either 10 µM nocodazole, 10 µM latrunculin B, or both drugs simultaneously. Cellular locomotion was captured on camera, tracked, and then analyzed with the help of the generalized additive mixed model. The obtained results indicate that both drugs, when applied separately, decrease the motility of the studied cells. Unexpectedly, the combined treatment had the opposite effect, as the cells became more motile. The analysis also revealed a non-linear pattern of relationship between motility of amoeboid cells of rhizochromulines and density of their population.

Understanding the pathogenicity of Naegleria fowleri in association with N. fowleri antigen-1 (Nfa1)

Naegleria fowleri, a brain-eating amoeba, thrives in lakes and rivers with aquatic vegetation and causes primary amoebic meningoencephalitis (PAM) in humans. Most recently, it has become such a serious problem that N. fowleri was detected in tap water in Houston, USA. Several pathogenic factors are considered very important to destroy target cells in the brain. In particular, the food-cup where N. fowleri antigen-1 (Nfa1) is located, is strongly expressed in pseudopodia involved in the movement of N. fowleri, and is involved in phagocytosis by attaching to target cells. In this article, we reviewed the role of the Nfa1 protein and its associated pathogenicity. The nfa1 gene was cloned by cDNA library immunoscreening using infection serum and immune serum. Nfa1 protein is mainly distributed in pseudopodia important to movement and vacuoles. Moreover, heat shock protein 70, cathepsin-like proteare and Nf-actin are also associated with pseudopodia in which Nfa1 is localized. Interestingly, the amount of the nfa1 gene changed as N. fowleri trophozoites transformed into cysts. Polyclonal antiserum against Nfa1 showed a protective effect against cytotoxicity of approximately 19.7%. Nfa1-specific IgA antibodies prevent N. fowleri trophozoites from adhering to the nasal mucosa, delaying invasion. The nfa1-vaccinated mice showed significantly higher levels of Nfa1-specific antibody. The duration of anti-Nfa1 IgG in the vaccinated mice lasted 12 weeks, strongly suggesting that nfa1 is a significant pathogenic gene and that Nfa1 is a pathogenic protein. Several factors related to pseudopodia and locomotion have been linked to Nfa1. A clearer function of N. fowleri targeting nfa1 with other genes might enable target-based inhibition of N. fowleri pathogenicity.

Ancestral TALE homeobox protein transcription factor regulates actin dynamics and cellular activities of protozoan parasite Entamoeba invadens

Entamoeba histolytica causes invasive amoebiasis, an important neglected tropical disease with a significant global health impact. The pathogenicity and survival of E. histolytica and its reptilian equivalent, Entamoeba invadens, relies on its ability to exhibit efficient motility, evade host immune responses, and exploit host resources, all of which are governed by the actin cytoskeleton remodeling. Our study demonstrates the early origin and the regulatory role of TALE homeobox protein EiHbox1 in actin-related cellular processes. Several genes involved in different biological pathways, including actin dynamics are differentially expressed in EiHbox1 silenced cells. EiHbox1 silenced parasites showed disrupted F-actin organization and loss of cellular polarity. EiHbox1's presence in the anterior region of migrating cells further suggests its involvement in maintaining cellular polarity. Loss of polarized morphology of EiHbox1 silenced parasites leads to altered motility from fast, directionally persistent, and highly chemotactic to slow, random, and less chemotactic, which subsequently leads to defective aggregation during encystation. EiHbox1 knockdown also resulted in a significant reduction in phagocytic capacity and poor capping response. These findings highlight the importance of EiHbox1 of E. invadens in governing cellular processes crucial for their survival, pathogenicity, and evasion of the host immune system.

Immunogens in Balamuthia mandrillaris: a proteomic exploration

Balamuthia mandrillaris is the causative agent of granulomatous amoebic encephalitis, a rare and often fatal infection affecting the central nervous system. The amoeba is isolated from diverse environmental sources and can cause severe infections in both immunocompromised and immunocompetent individuals. Given the limited understanding of B. mandrillaris, our research aimed to explore its protein profile, identifying potential immunogens crucial for early granulomatous amoebic encephalitis diagnosis. Cultures of B. mandrillaris and other amoebas were grown under axenic conditions, and total amoebic extracts were obtained. Proteomic analyses, including two-dimensional electrophoresis and mass spectrometry, were performed. A 50-kDa band showed a robust recognition of antibodies from immunized BALB/c mice; peptides contained in this band were matched with elongation factor-1 alpha, which emerged as a putative key immunogen. Besides, lectin blotting revealed the presence of glycoproteins in B. mandrillaris, and confocal microscopy demonstrated the focal distribution of the 50-kDa band throughout trophozoites. Cumulatively, these observations suggest the participation of the 50-kDa band in adhesion and recognition mechanisms. Thus, these collective findings demonstrate some protein characteristics of B. mandrillaris, opening avenues for understanding its pathogenicity and developing diagnostic and therapeutic strategies.

De Novo Transcriptome Profiling of Naegleria fowleri Trophozoites and Cysts via RNA Sequencing

Naegleria fowleri is a pathogenic free-living amoeba, commonly found around the world in warm, fresh water and soil. N. fowleri trophozoites can infect humans by entering the brain through the nose and causing usually fatal primary amebic meningoencephalitis (PAM). Trophozoites can encyst to survive under unfavorable conditions such as cold temperature, starvation, and desiccation. Recent technological advances in genomics and bioinformatics have provided unique opportunities for the identification and pre-validation of pathogen-related and environmental resistance through improved understanding of the biology of pathogenic N. fowleri trophozoites and cysts at a molecular level. However, genomic and transcriptomic data on differential expression genes (DEGs) between trophozoites and cysts of N. fowleri are very limited. Here, we report transcriptome Illumina RNA sequencing (RNA-seq) for N. fowleri trophozoites and cysts and de novo transcriptome assembly. RNA-seq libraries were generated from RNA extracted from N. fowleri sampled from cysts, and a reference transcriptome was generated through the assembly of trophozoite data. In the database, the assembly procedure resulted in 42,220 contigs with a mean length of 11,254 nucleotides and a C+G content of 37.21%. RNA sequencing showed that 146 genes in cysts of N. fowleri indicated 2-fold upregulation in comparison with trophozoites of N. fowleri, and 163 genes were downregulated; these genes were found to participate in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. The KEGG pathway included metabolic (131 sequences) and genetic information processing (66 sequences), cellular processing (43 sequences), environmental information processing (22 sequences), and organismal system (20 sequences) pathways. On the other hand, an analysis of 11,254 sequences via the Gene Ontology database showed that their annotations contained 1069 biological processes including the cellular process (228 sequences) and metabolic process (214 sequences); 923 cellular components including cells (240 sequences) and cell parts (225 sequences); and 415 molecular functions including catalytic activities (195 sequences) and binding processes (186 sequences). Differential expression levels increased in cysts of N. fowleri compared to trophozoites of N. fowleri, which were mainly categorized as serine/threonine protease, kinase, and lipid metabolism-related proteins. These results may provide new insights into pathogen-related genes or environment-resistant genes in the pathogenesis of N. fowleri.

Molecular interplays of the Entamoeba histolytica endosomal sorting complexes required for transport during phagocytosis

Entamoeba histolytica, the causative agent of human amoebiasis, exhibits a continuous membrane remodelling to exert its virulence properties. During this dynamic process, the Endosomal Sorting Complexes Required for Transport (ESCRT) machinery is a key player, particularly in phagocytosis, a virulence hallmark of this parasite. In addition to ESCRT, other molecules contribute to membrane remodelling, including the EhADH adhesin, EhRabs, actin, and the lysobisphosphatidic acid (LBPA). The endocytosis of a prey or molecules induces membrane invaginations, resulting in endosome and multivesicular bodies (MVBs) formation for cargo delivery into lysosomes. Alternatively, some proteins are recycled or secreted. Most of these pathways have been broadly characterized in other biological systems, but poorly described in protozoan parasites. Here, we encompass 10 years of ESCRT research in E. histolytica, highlighting the role of the ESCRT-I and ESCRT-III components and the EhADH and EhVps4-ATPase accessory proteins during phagocytosis. In particular, EhADH exhibits a multifunctional role along the endocytic pathway, from cargo recognition to endosome maturation and lysosomal degradation. Interestingly, the interaction of EhADH with EhVps32 seems to shape a concurrent route to the conventional one for MVBs biogenesis, that could optimize their formation. Furthermore, this adhesin is secreted, but its role in this event remains under study. Other components from the endosomal pathway, such as EhVps23 and LBPA, are also secreted. A proteomic approach performed here, using an anti-LBPA antibody, revealed that some proteins related to membrane trafficking, cellular transport, cytoskeleton dynamics, and transcriptional and translational functions are secreted and associated to LBPA. Altogether, the accumulated knowledge around the ESCRT machinery in E. histolytica, points it out as a dynamic platform facilitating the interaction of molecules participating in different cellular events. Seen as an integrated system, ESCRTs lead to a better understanding of E. histolytica phagocytosis.

PTEN differentially regulates endocytosis, migration, and proliferation in the enteric protozoan parasite Entamoeba histolytica

PTEN is a lipid phosphatase that is highly conserved and involved in a broad range of biological processes including cytoskeletal reorganization, endocytosis, signal transduction, and cell migration in all eukaryotes. Although regulation of phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3] signaling via PTEN has been well established in model organisms and mammals, it remains elusive in the parasitic protist E. histolytica, which heavily relies on PtdIns phosphate(s)-dependent membrane traffic, migration, and phago- and trogocytosis for its pathogenesis. In this study, we characterized the major PTEN from E. histolytica, EhPTEN1, which shows the highest expression at the transcript level in the trophozoite stage among 6 possible PTENs, to understand the significance of PtdIns(3,4,5)P3 signaling in this parasite. Live imaging of GFP-EhPTEN1 expressing amebic trophozoites showed localization mainly in the cytosol with a higher concentration at pseudopods and the extending edge of the phago- and trogocytic cups. Furthermore, quantitative analysis of phago- and trogocytosis using a confocal image cytometer showed that overexpression of EhPTEN1 caused reduction in trogo- and phagocytosis while transcriptional gene silencing of EhPTEN1 gene caused opposite phenotypes. These data suggest that EhPTEN1 has an inhibitory role in these biological processes. Conversely, EhPTEN1 acts as a positive regulator for fluid-phase and receptor-mediated endocytosis in E. histolytica trophozoites. Moreover, we showed that EhPTEN1 was required for optimal growth and migration of this parasite. Finally, the phosphatase activity of EhPTEN1 towards PtdIns(3,4,5)P3 was demonstrated, suggesting that the biological roles of EhPTEN1 are likely linked to its catalytic function. Taken together, these results indicate that EhPTEN1 differentially regulates multiple cellular activities essential for proliferation and pathogenesis of the organism, via PtdIns(3,4,5)P3 signaling. Elucidation of biological roles of PTEN and PtdIns(3,4,5)P3 signaling at the molecular levels promotes our understanding of the pathogenesis of this parasite.

Immune Response to the Enteric Parasite Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite responsible for amoebiasis, a disease with a high prevalence in developing countries. Establishing an amoebic infection involves interplay between pathogenic factors for invasion and tissue damage, and immune responses for protecting the host. Here, we review the pathogenicity of E. histolytica and summarize the latest knowledge on immune response and immune evasion mechanisms during amoebiasis.

Host Invasion by Pathogenic Amoebae: Epithelial Disruption by Parasite Proteins

The epithelium represents the first and most extensive line of defence against pathogens, toxins and pollutant agents in humans. In general, pathogens have developed strategies to overcome this barrier and use it as an entrance to the organism. Entamoeba histolytica, Naegleriafowleri and Acanthamoeba spp. are amoebae mainly responsible for intestinal dysentery, meningoencephalitis and keratitis, respectively. These amoebae cause significant morbidity and mortality rates. Thus, the identification, characterization and validation of molecules participating in host-parasite interactions can provide attractive targets to timely intervene disease progress. In this work, we present a compendium of the parasite adhesins, lectins, proteases, hydrolases, kinases, and others, that participate in key pathogenic events. Special focus is made for the analysis of assorted molecules and mechanisms involved in the interaction of the parasites with epithelial surface receptors, changes in epithelial junctional markers, implications on the barrier function, among others. This review allows the assessment of initial host-pathogen interaction, to correlate it to the potential of parasite invasion.

Tyrosine phosphorylation/dephosphorylation of myosin II essential light chains of Entamoeba histolytica trophozoites regulates their motility

Entamoeba histolytica trophozoites dwell in the human intestine as comensals although under still unclear circumstances become invasive and destroy the host tissues. For these activities, trophozoites relay on remarkable motility provided by the cytoskeleton organization. Amebic actin and some of its actin-associated proteins are well known, while components of the myosin II molecule, although predicted from the E. histolytica genome, need biochemical and functional characterization. Recently, an amebic essential light myosin II chain, named EhMLCI, was identified and reported to be phosphorylated in tyrosines. The phosphorylated form of the protein was associated with the soluble assembly incompetent conformation of the heavy myosin chains, while the non-phosphorylated protein was identified with filamentous heavy chains, organized in an assembly competent conformation. It was postulated that EhMLCI tyrosine phosphorylation could act as a negative regulator of myosin II activity by its phosphorylation/dephosphorylation cycles. To test this hypothesis, we constructed an expression vector containing an EhMLCI DNA sequence where two tyrosine residues, with strong probability of phosphorylation and fall within the single EF-hand domain that interacts with the N-terminus of myosin II heavy chains, were replaced by phenylalanines. Transfected trophozoites, expressing the mutant MutEhMLCI protein cannot process it, thereby not incorporated into the phosphorylation/dephosphorylation cycles required for myosin II activity, results in motility defective trophozoites.

Magnetic resonance imaging of pathogenic protozoan parasite Entamoeba histolytica labeled with superparamagnetic iron oxide nanoparticles

OBJECTIVES

The aim of this study was to establish a noninvasive tracking of the pathogenic parasite Entamoeba histolytica (Eh) after superparamagnetic iron oxide (SPIO) labeling by magnetic resonance imaging (MRI) on a single-cell level in vitro and in vivo in a mouse model for amebic liver abscess (ALA).

MATERIALS AND METHODS

Local institutional review committee on animal care approved all animal experiments. Entamoeba histolytica trophozoites were labeled with SPIO nanoparticles (SPIO-Eh). The uptake of SPIO by Eh was optimized using flow cytometry and visualized by bright field, fluorescence, and transmission electron microscopy. The viability of SPIO-Eh was assessed in vitro by determination of growth and ingestion rate of red blood cells. Migration of SPIO-Eh was proven by in vitro MRI in a preclinical 7 T MRI system using continually repeated MRI scans. In vivo distribution of SPIO-Eh within the mouse liver was assessed qualitatively and quantitatively by serial respiration-triggered T2*-weighted MRI, T2-weighted MRI, and R2* MR relaxometry up to 5 days after injection and correlated with immunohistology of the liver sections after removal.

RESULTS

Entamoeba histolytica can be efficiently labeled with SPIO without influence on parasite growth rate or phagocytic capacity. In vitro dynamic MRI allowed real-time migration monitoring and determination of velocity of single SPIO-Eh. In vivo SPIO-Eh showed signal decrease in T2*-weighted and increase of R2* in ALA formations. Motility of SPIO-Eh was necessary to induce ALA formations.

CONCLUSIONS

The present study demonstrates the feasibility of an efficient magnetic labeling and a noninvasive in vitro and in vivo MR tracking of the pathogenic protozoan Eh in a mouse model for ALA, thus representing in future a noninvasive imaging tool to study parasite, as well as on host-specific pathomechanisms.

Detection of beta-tubulin in the cytoplasm of the interphasic Entamoeba histolytica trophozoites

It is known that the microtubules (MT) of Entamoeba histolytica trophozoites form an intranuclear mitotic spindle. However, electron microscopy studies and the employment of anti-beta-tubulin (β-tubulin) antibodies have not exhibited these cytoskeletal structures in the cytoplasm of these parasites. The purpose of this work was to detect β-tubulin in the cytoplasm of interphasic E. histolytica trophozoites. Activated or non-activated HMI-IMSS-strain E. histolytica trophozoites were used and cultured for 72 h at 37 °C in TYI-S-33 medium, and then these were incubated with the anti-β-tubulin antibody of E. histolytica. The anti-β-tubulin antibody reacted with the intranuclear mitotic spindle of E. histolytica-activated trophozoites as control. In contrast, in non-activated interphasic parasites, anti-β-tubulin antibody reacted with diverse puntiform structures in the cytoplasm and with ring-shaped structures localized in the cytoplasm, cellular membrane and endocytic stomas. In this work, for the first time, the presence of β-tubulin is shown in the cytoplasm of E. histolytica trophozoites.

Proteomic Identification of Oxidized Proteins in Entamoeba histolytica by Resin-Assisted Capture: Insights into the Role of Arginase in Resistance to Oxidative Stress

Entamoeba histolytica is an obligate protozoan parasite of humans, and amebiasis, an infectious disease which targets the intestine and/or liver, is the second most common cause of human death due to a protozoan after malaria. Although amebiasis is usually asymptomatic, E. histolytica has potent pathogenic potential. During host infection, the parasite is exposed to reactive oxygen species that are produced and released by cells of the innate immune system at the site of infection. The ability of the parasite to survive oxidative stress (OS) is essential for a successful invasion of the host. Although the effects of OS on the regulation of gene expression in E. histolytica and the characterization of some proteins whose function in the parasite's defense against OS have been previously studied, our knowledge of oxidized proteins in E. histolytica is lacking. In order to fill this knowledge gap, we performed a large-scale identification and quantification of the oxidized proteins in oxidatively stressed E. histolytica trophozoites using resin-assisted capture coupled to mass spectrometry. We detected 154 oxidized proteins (OXs) and the functions of some of these proteins were associated with antioxidant activity, maintaining the parasite's cytoskeleton, translation, catalysis, and transport. We also found that oxidation of the Gal/GalNAc impairs its function and contributes to the inhibition of E. histolytica adherence to host cells. We also provide evidence that arginase, an enzyme which converts L-arginine into L-ornithine and urea, is involved in the protection of the parasite against OS. Collectively, these results emphasize the importance of OS as a critical regulator of E. histolytica's functions and indicate a new role for arginase in E. histolytica's resistance to OS.

Reactive oxygen species are the most studied of environmental stresses generated by the host immune defense against pathogens. Although most of the studies that have investigated the effect of oxidative stress on an organism have focused on changes which occur at the protein level, only a few studies have investigated the oxidation status of these proteins. Infection with Entamoeba histolytica is known as amebiasis. This condition occurs worldwide, but is most associated with crowded living conditions and poor sanitation. The parasite is exposed inside the host to oxidative stress generated by cells of the host immune system. The nature of oxidized proteins in oxidatively stressed E. histolytica has never been studied. In this report, the authors present their quantitative results of a proteome-wide analysis of oxidized proteins in the oxidatively stressed parasite. They identified crucial redox-regulated proteins that are linked to the virulence of the parasite, such as the Gal/GalNAc lectin. They also discovered that arginase, a protein involved in ornithine synthesis, is also involved in the parasite's resistance to oxidative stress.

Amoeboid movement in protozoan pathogens

Entamoeba histolytica, the causative agent of amoebiasis, is a protozoan parasite characterised by its amoeboid motility, which is essential to its survival and invasion of the human host. Elucidating the molecular mechanisms leading to invasion of human tissues by E. histolytica requires a quantitative understanding of how its cytoskeleton deforms and tailors its mode of migration to the local microenvironment. Here we review the wide range of methods available to extract biophysical information from amoeboid cells, from interventional techniques to computational modelling approaches, and discuss how recent developments in bioimaging and bioimage informatics can complement our understanding of cellular morphodynamics at the intracellular level.

A surface membrane protein of Entamoeba histolytica functions as a receptor for human chemokine IL-8: its role in the attraction of trophozoites to inflammation sites

Entamoeba histolytica trophozoites respond to the presence of IL-8, moving by chemotaxis towards the source of the chemokine. IL-8 binds to the trophozoite membrane and triggers a response that activates signaling pathways that in turn regulate actin/myosin cytoskeleton organisation to initiate migration towards the chemokine, suggesting the presence of a receptor for IL-8 in the parasite. Antibodies directed to the human IL-8 receptor (CXCR1) specifically recognised a 29 kDa protein in trophozoite membrane fractions. The same protein was immunoprecipitated by this antibody from total amebic extracts. Peptide analysis of the immunoprecipitated protein revealed a sequence with high homology to a previously identified amebic outer membrane peroxiredoxin and a motif within the third loop of human CXCR1, which is an important site for IL-8 binding and activation of signaling processes. Immunodetection assays demonstrated that the anti-human CXCR1 antibody binds to the 29 kDa protein in a different but close site to where IL-8 binds to the trophozoite surface membrane, suggesting that human and amebic receptors for this chemokine share common epitopes. In the context of the human intestinal environment, a receptor for IL-8 could be a great advantage for E. histolytica trophozoite survival, as they could reach an inflammatory milieu containing abundant nutrients. In addition, it has been suggested that the high content of accessible thiol groups of the protein and its peroxidase activity could provide protection in the oxygen rich milieu of colonic lesions, allowing trophozoite invasion of other tissues and escape from the host immune response.

EhVps32 Is a Vacuole-Associated Protein Involved in Pinocytosis and Phagocytosis of Entamoeaba histolytica

Here, we investigated the role of EhVps32 protein (a member of the endosomal-sorting complex required for transport) in endocytosis of Entamoeba histolytica, a professional phagocyte. Confocal microscopy, TEM and cell fractionation revealed EhVps32 in cytoplasmic vesicles and also located adjacent to the plasma membrane. Between 5 to 30 min of phagocytosis, EhVps32 was detected on some erythrocytes-containing phagosomes of acidic nature, and at 60 min it returned to cytoplasmic vesicles and also appeared adjacent to the plasma membrane. TEM images revealed it in membranous structures in the vicinity of ingested erythrocytes. EhVps32, EhADH (an ALIX family member), Gal/GalNac lectin and actin co-localized in the phagocytic cup and in some erythrocytes-containing phagosomes, but EhVps32 was scarcely detected in late phagosomes. During dextran uptake, EhVps32, EhADH and Gal/GalNac lectin, but not actin, co-localized in pinosomes. EhVps32 recombinant protein formed oligomers composed by rings and filaments. Antibodies against EhVps32 monomers stained cytoplasmic vesicles but not erythrocytes-containing phagosomes, suggesting that in vivo oligomers are formed on phagosome membranes. The involvement of EhVps32 in phagocytosis was further study in pNeoEhvps32-HA-transfected trophozoites, which augmented almost twice their rate of erythrophagocytosis as well as the membranous concentric arrays built by filaments, spirals and tunnel-like structures. Some of these structures apparently connected phagosomes with the phagocytic cup. In concordance, the EhVps32-silenced G3 trophozoites ingested 80% less erythrocytes than the G3 strain. Our results suggest that EhVps32 participates in E. histolytica phagocytosis and pinocytosis. It forms oligomers on erythrocytes-containing phagosomes, probably as a part of the scission machinery involved in membrane invagination and intraluminal vesicles formation.

Trophozoites of E. histolytica represent an excellent model to study endosomal-sorting complex required for transport components due to their high endocytic activity and vesicle trafficking. The key role of EhVps32 on phagocytosis is supported by: i) its presence on phagosomes, ii) its interaction with EhADH (an erythrocytes receptor), Gal/GalNac lectin and actin, iii) the higher rate of erythrophagocytosis showed by EhVps32 overexpressing trophozoites, iv) the diminish rate of phagocytosis in EhVps32-silenced G3 trophozoites, and v) its location in erythrocytes-containing acidic phagosomes. Here, we discovered the presence of membranous concentric helicoidally and tunnel-like structures constituted by EhVps32 and EhADH that may have a dynamic role in membrane remodeling and in the generation of intraluminal vesicles in the phagosomes. Elucidating molecular mechanisms of endocytosis-exocytosis pathways will help us to better understand the pathogenic process of E. histolytica and develop new drugs for diagnosis and vaccine methods.

Entamoeba histolytica rhomboid protease 1 has a role in migration and motility as validated by two independent genetic approaches

Rhomboid proteins represent a recently discovered family of intramembrane proteases present in a broad range of organisms and with increasing links to human diseases. The enteric parasite Entamoeba histolytica has evolved multiple mechanisms to adapt to the human host environment and establish infection. Our recent studies identified EhROM1 as a functional E. histolytica rhomboid protease with roles in adhesion to and phagocytosis of host cells. Since those studies were performed in a non-virulent strain, roles in parasite virulence could not be assessed. We focused this study on the comparison and validation of two genetic manipulation techniques: overexpression of a dominant-negative catalytic mutant of EhROM1 and knock down of EhROM1 using a RNAi-based silencing approach followed by functional studies of phenotypic analyses in virulent parasites. Both the EhROM1 catalytic mutant and parasites with EhROM1 downregulation were reduced in cytotoxicity, hemolytic activity, and directional and non-directional transwell migration. Importantly, the role for EhROM1 in cell migration mimics similar roles for rhomboid proteases from mammalian and apicomplexan systems. However, the EhROM1 catalytic mutant and EhROM1 downregulation parasites had different phenotypes for erythrophagocytosis, while complement resistance was not affected in either strain. In summary, in this study we genetically manipulated E. histolytica rhomboid protease EhROM1 by two different approaches and identified similarly attenuated phenotypes by both approaches, suggesting a novel role for EhROM1 in amebic motility.

Identification and characterization of microRNAs from Entamoeba histolytica HM1-IMSS

BACKGROUND

Entamoeba histolytica is the causative agent of amebiasis, a disease that is a major source of morbidity and mortality in the developing world. MicroRNAs (miRNAs) are a large group of non-coding RNAs that play important roles in regulating gene expression and protein translation in animals. Genome-wide identification of miRNAs is a critical step to facilitating our understanding of genome organization, genome biology, evolution, and post-transcriptional regulation.

METHODOLOGY/PRINCIPAL FINDINGS

We sequenced a small RNA library prepared from a culture of trophozoites of Entamoeba histolytica Strain HM1-IMSS using a deep DNA sequencing approach. Deep sequencing yielded 16 million high-quality short sequence reads containing a total of 5 million non-redundant sequence reads. Based on a bioinformatics pipeline, we found that only 0.5% of these non-redundant small RNA reads were a perfect match with the drafted E. histolytica genome. We did not find miRNA homologs in plant or animal miRNAs. We discovered 199 new potential Entamoeba histolytica miRNAs. The expression and sequence of these Ehi-miRNAs were further validated through microarray by µParaflo Microfluidic Biochip Technology. Ten potential miRNAs were additionally confirmed by real time RT-PCR analysis. Prediction of target genes matched 32 known genes and 34 hypothetical genes.

CONCLUSIONS/SIGNIFICANCE

These results show that there is a number of regulatory miRNAs in Entamoeba histolytica. The collection of miRNAs in this parasite could be used as a new platform to study genomic structure, gene regulation and networks, development, and host-parasite interactions.

G protein signaling in the parasite Entamoeba histolytica

The parasite Entamoeba histolytica causes amebic colitis and systemic amebiasis. Among the known amebic factors contributing to pathogenesis are signaling pathways involving heterotrimeric and Ras superfamily G proteins. Here, we review the current knowledge of the roles of heterotrimeric G protein subunits, Ras, Rho and Rab GTPase families in E. histolytica pathogenesis, as well as of their downstream signaling effectors and nucleotide cycle regulators. Heterotrimeric G protein signaling likely modulates amebic motility and attachment to and killing of host cells, in part through activation of an RGS-RhoGEF (regulator of G protein signaling-Rho guanine nucleotide exchange factor) effector. Rho family GTPases, as well as RhoGEFs and Rho effectors (formins and p21-activated kinases) regulate the dynamic actin cytoskeleton of E. histolytica and associated pathogenesis-related cellular processes, such as migration, invasion, phagocytosis and evasion of the host immune response by surface receptor capping. A remarkably large family of 91 Rab GTPases has multiple roles in a complex amebic vesicular trafficking system required for phagocytosis and pinocytosis and secretion of known virulence factors, such as amebapores and cysteine proteases. Although much remains to be discovered, recent studies of G protein signaling in E. histolytica have enhanced our understanding of parasitic pathogenesis and have also highlighted possible targets for pharmacological manipulation.

Src and PI3 K inhibitors affect the virulence factors of Entamoeba histolytica

Protein kinases (PKs) of parasitic protozoa are being evaluated as drug targets. A large number of protein kinases within the protein kinome of Entamoeba histolytica strongly suggest that protein phosphorylation is a key component of pathogenesis regulation by this parasite. PI3 K and Src are kinases previously described in this parasite, but their role is poorly understood. Here, the effect of Src-1-inhibitor and PI3 K inhibitor (Wortmannin) on the virulence factors of E. histolytica was evaluated. Results show that both inhibitors affect the actin cytoskeleton and the amoebic movement. Also, the proteolytic activity is diminished by Wortmannin, but not by Src-inhibitor-1; however, the phagocytic capacity is diminished by Wortmannin and Src-1-inhibitor. Finally, we found that the virulence in vivo of E. histolytica is affected by Wortmannin but not by Src-1-inhibitor. This study opens the way for the design of anti-amoebic drugs based on kinase inhibition.

Oxidative stress resistance genes contribute to the pathogenic potential of the anaerobic protozoan parasite, Entamoeba histolytica

The protozoan parasite, Entamoeba histolytica, invades the host colon causing significant tissue destruction and inflammation. Upon host infection, the parasite is confronted with reactive oxygen and nitrogen species (ROS/RNS) that cause large-scale changes in gene expression profiles, which likely support the parasite's adaptation to the host environment. We have previously identified oxidative and nitrosative stress responsive genes using whole-genome expression profiling. Functional studies on two such genes are now reported and demonstrate that they have roles in parasite virulence. EHI_056680 encodes a small hypothetical protein named E. histolytica stress-induced adhesion factor (EhSIAF); EHI_188210 encodes a putative phospholipid transporting P-type ATPase/flippase (EhPTPA). Over-expression of each protein in E. histolytica trophozoites enhanced parasite survival in response to oxidative stress. Exposure to oxidative and nitrosative stress did not affect the localization of EhSIAF or EhPTPA but markedly increased EhPTPA protein levels. Interestingly, over-expression of each gene resulted in parasites with increased adherence to healthy mammalian cells, but increased adherence to apoptotic cells was noted only in EhSIAF over-expressing parasites. However, despite having increased adherence to both healthy and apoptotic host cells, EhSIAF-over-expressing parasites were reduced in their ability to destroy mammalian cell monolayers, raising the intriguing possibility that EhSIAF over-expression caused signaling defects or resulted in a dominant negative phenotype. Over-expression of EhSIAF and EhPTPA also resulted in decreased motility in a transwell motility assay. Thus, we have confirmed that two genes that are upregulated by ROS confer increased resistance to oxidative stress and have identified an unexpected role of EhSIAF and EhPTPA in host cell adherence and a role of EhSIAF in parasite virulence. Our data imply that stress response genes may play multi-factorial roles in amoebic pathogenesis.

Downregulation of an Entamoeba histolytica rhomboid protease reveals roles in regulating parasite adhesion and phagocytosis

Entamoeba histolytica is a deep-branching eukaryotic pathogen. Rhomboid proteases are intramembrane serine proteases, which cleave transmembrane proteins in, or in close proximity to, their transmembrane domain. We have previously shown that E. histolytica contains a single functional rhomboid protease (EhROM1) and has unique substrate specificity. EhROM1 is present on the trophozoite surface and relocalizes to internal vesicles during erythrophagocytosis and to the base of the cap during surface receptor capping. In order to further examine the biological function of EhROM1 we downregulated EhROM1 expression by >95% by utilizing the epigenetic silencing mechanism of the G3 parasite strain. Despite the observation that EhROM1 relocalized to the cap during surface receptor capping, EhROM1 knockdown [ROM(KD)] parasites had no gross changes in cap formation or complement resistance. However, ROM(KD) parasites demonstrated decreased host cell adhesion, a result recapitulated by treatment of wild-type parasites with DCI, a serine protease inhibitor with activity against rhomboid proteases. The reduced adhesion phenotype of ROM(KD) parasites was noted exclusively with healthy cells, and not with apoptotic cells. Additionally, ROM(KD) parasites had decreased phagocytic ability with reduced ingestion of healthy cells, apoptotic cells, and rice starch. Decreased phagocytic ability is thus independent of the reduced adhesion phenotype, since phagocytosis of apoptotic cells was reduced despite normal adhesion levels. The defect in host cell adhesion was not explained by altered expression or localization of the heavy subunit of the Gal/GalNAc surface lectin. These results suggest no significant role of EhROM1 in complement resistance but unexpected roles in parasite adhesion and phagocytosis.

Current and future perspectives on the chemotherapy of the parasitic protozoa Trichomonas vaginalis and Entamoeba histolytica

Trichomonas vaginalis and Entamoeba histolytica are clinically important protozoa that affect humans. T. vaginalis produces sexually transmitted infections and E. histolytica is the causative agent of amebic dysentery. Metronidazole, a compound first used to treat T. vaginalis in 1959, is still the main drug used worldwide to treat these pathogens. It is essential to find new biochemical differences in these organisms that could be exploited to develop new antiprotozoal chemotherapeutics. Recent findings associated with T. vaginalis and E. histolytica biochemistry and host–pathogen interactions are surveyed. Knowledge concerning the biochemistry of these parasites is serving to form the foundation for the development of new approaches to control these important human pathogens.

The endoplasmic reticulum chaperone calreticulin is recruited to the uropod during capping of surface receptors in Entamoeba histolytica

Calreticulin (CRT), an intracellular chaperone protein, is crucial for proper folding and transport of proteins through the endoplasmic reticulum (ER). It has recently been identified as a critical regulator of some several different cellular functions such as migration, phagocytosis of apoptotic cells and cytotoxic T lymphocyte- or natural killer cell-mediated lysis. Characterization of CRT isolated from parasites may thus help to decipher the contribution of this protein in the parasites' biology and host-parasite interactions. Here, we report descriptive data on the localization of Entamoeba histolytica's CRT at rest and following cap formation by Concanavalin A. As expected, CRT from E. histolytica localizes in the ER. However, the protein was surprisingly found to localize to the parasite surface and, furthermore, to concentrate in the uropod following activation of surface receptors by capping with Concanavalin A.

Characterization of Entamoeba histolytica α-actinin2

We have cloned and characterized a second alpha-actinin isoform in Entamoeba histolytica. This protein, alpha-actinin2, has a N-terminal actin-binding domain, a C-terminal calcium-binding domain and an intervening rod domain containing two spectrin repeats. The protein binds and cross-links actin filaments in a calcium-dependent manner. Therefore alpha-actinin2 is a genuine alpha-actinin except for the shorter rod domain compared to the rod domain of isoforms of higher organisms. A alpha-actinin-like protein has previous been implicated in the adherence to the host cell and infection. It is therefore possible that alpha-actinin2 is involved in mechanism of infection, and in particular in reorganisation of the parasite's cytoskeleton that follows on adherence. E. histolytica alpha-actinin2 represents one of the first members of the spectrin superfamily where well defined spectrin repeats are found. The isolation and characterization of this second alpha-actinin isoform is valuable not only into the study of E. histolytica infection mechanisms, but also for understanding the evolution processes of the spectrin superfamily.

Progress in research on Entamoeba histolytica pathogenesis

Entamoeba histolytica is a protozoan parasite of humans that causes 40,000-100,000 deaths annually. Clinical amoebiasis results from the spread of the normally luminal parasite into the colon wall and beyond; the key development in understanding this complex multistage process has been the publication of the E. histolytica genome, from which has come an explosion in the use of microarrays to examine changes in gene expression that result from changes in growth conditions. The genome has also revealed a unique arrangement of tRNA genes and an extraordinary number of genes for putative virulence factors, many unexpressed under the artificial conditions of growth in culture. The ability to induce apoptosis of mammalian cells and a useful, but as yet little-understood, technique for epigenetic irreversible gene silencing are other exciting developments.