Cell-matrix interactions of Entamoeba histolytica and E. dispar. A comparative study by electron-, atomic force- and confocal microscopy

Effect of Stevioside (Stevia rebaudiana) on Entamoeba histolytica Trophozoites

Human amoebiasis still represents a major health problem worldwide. Metronidazole has been used as the most common drug to treat the disease; however, it is also known that the drug causes undesirable side effects. This has led to the search for new pharmacological alternatives which include phytochemical compounds with antiamoebic effects. We analyzed the amoebicidal activity of stevioside (STV), a diterpene glycoside present in Stevia rebaudiana, on trophozoites of E. histolytica. Different concentrations of STV were tested, and an inhibitory concentration of 50% of cell viability (IC50) was determined with an exposition of 9.53 mM for 24 h. Trophozoites exposed to STV showed morphological changes evidenced by the decrease in the basic structures related to the movement and adherence to the substrate, as well as ultrastructural features characterized by a loss of regularity on the cell membrane, an increase in cytoplasmic granularity, and an increase in apparent autophagic vacuoles. Also, the decrease in cysteine protease expression and the proteolytic activity of trophozoites to degrade the cell monolayer were analyzed. A histological analysis of hamster livers inoculated with trophozoites and treated with STV showed changes related to the granulomatous reaction of the liver parenchymal tissue. Our results constitute the first report related to the possible use of STV as a therapeutic alternative in amoebiasis.

Characterization of low molecular weight protein tyrosine phosphatases of Entamoeba histolytica

Entamoeba histolytica is an intestinal protozoan parasite of humans and is endemic in developing countries. E. histolytica has two low molecular weight protein tyrosine phosphatase (LMW-PTP) genes, EhLMW-PTP1 and EhLMW-PTP2, which are expressed in cultured trophozoites, clinical isolates, and cysts. The amino acid sequences of proteins EhLMW-PTP1 and EhLMW-PTP2 showed only one amino acid difference between them at position A85V, respectively. Both genes are expressed in cultured trophozoites, mainly EhLMW-PTP2, and in trophozoites recovered from amoebic liver abscess, the expression of EhLMW-PTP1 is downregulated. We cloned the two genes and purified the corresponding recombinant (rEhLMW-PTPs) proteins. Antibodies anti-rEhLMW-PTP2 showed that during red blood cells uptake by E. histolytica, the EhLMW-PTPs were found in the phagocytic cups based on analysis of fluorescence signals. On the other hand, rEhLMW-PTPs showed an optimum phosphatase activity at pH 6.0 with p-nitrophenyl phosphate as the substrate. They dephosphorylate phosphotyrosine and 3-O-methylfluorescein phosphate, but not phosphoserine or phosphothreonine, and the enzymatic activity is inhibited by orthovanadate. rEhLMW-PTP1 and rEhLMW-PTP2 exhibited optimum temperatures of activities at 60 °C and 58 °C, respectively, with high thermal stability at 50 °C. Also, the rEhLMW-PTPs showed high specific activities and specific km value with pNPP or OMFP as the substrates at the physiological temperature (37 °C).

Entamoeba histolytica and Entamoeba dispar: Morphological and Behavioral Differences Induced by Fibronectin through GTPases Activation and Actin-Binding Proteins

Early steps of tissue invasion by Entamoeba histolytica are mediated by adhesion and migration through matrix components such as fibronectin with the participation of the actin cytoskeleton. Striking differences in their produced structures, movement, and migration were found. These observations suggest differential changes in their ability to organize the actin cytoskeleton and, therefore, to modify its morphology after adhesion to fibronectin. To understand these observations, we explore deeper the cytoskeleton pathway of E. histolytica compared to Entamoeba dispar, analyzing the activation and involvement of actin cytoskeleton regulatory proteins such as small GTPases (Rho, Rac1 and Cdc42), myosin IB, paxillin, alpha-actinin, and ARP2/3 during interaction with fibronectin. Results showed a higher activation of Rac1 in E. histolytica compared to E. dispar, while Cdc42 and RhoA were equally activated in both amebae; besides, variations in the amount of myosin IB, paxillin, and ARP2/3 were detected among these species, coinciding and reflected in formation of lamellipodia in E. histolytica and filopodia in E. dispar. These could partially explain the higher invasive capacity of E. histolytica compared to E. dispar, due to its pleomorphic ability, high motility, migration, activation, and abundance of proteins involved in the cytoskeleton arrangement.

Reduced expression of a rhomboid protease, EhROM1, correlates with changes in the submembrane distribution and size of the Gal/GalNAc lectin subunits in the human protozoan parasite, Entamoeba histolytica

Entamoeba histolytica is a food- and waterborne parasite that causes amebic dysentery and amoebic liver abscesses. Adhesion is one of the most important virulence functions as it facilitates motility, colonization of host, destruction of host tissue, and uptake of nutrients by the parasite. The parasite cell surface adhesin, the Gal/GalNAc lectin, facilitates parasite-host interaction by binding to galactose or N-acetylgalactosamine residues on host components. It is composed of heavy (Hgl), intermediate (Igl), and light (Lgl) subunits. Igl is constitutively localized to lipid rafts (cholesterol-rich membrane domains), whereas Hgl and Lgl transiently associate with rafts. When all three subunits are localized to rafts, galactose-sensitive adhesion is enhanced. Thus, submembrane location may regulate the function of this adhesion. Rhomboid proteases are a conserved family of intramembrane proteases that also participate in the regulation of parasite-host interactions. In E. histolytica, one rhomboid protease, EhROM1, cleaves Hgl as a substrate, and knockdown of its expression inhibits parasite-host interactions. Since rhomboid proteases are found within membranes, it is not surprising that lipid composition regulates their activity and enzyme-substrate binding. Given the importance of the lipid environment for both rhomboid proteases and the Gal/GalNAc lectin, we sought to gain insight into the relationship between rhomboid proteases and submembrane location of the lectin in E. histolytica. We demonstrated that EhROM1, itself, is enriched in highly buoyant triton-insoluble membranes reminiscent of rafts. Reducing rhomboid protease activity, either pharmacologically or genetically, correlated with an enrichment of Hgl and Lgl in rafts. In a mutant cell line with reduced EhROM1 expression, there was also a significant augmentation of the level of all three Gal/GalNAc subunits on the cell surface and an increase in the molecular weight of Hgl and Lgl. Overall, the study provides insight into the molecular mechanisms governing parasite-host adhesion for this pathogen.

Influence of Micropatterned Grill Lines on Entamoeba histolytica Trophozoites Morphology and Migration

Entamoeba histolytica, the causal agent of human amoebiasis, has two morphologically different phases: a resistant cyst and a trophozoite responsible for the invasion of the host tissues such as the colonic mucosa and the intestinal epithelium. During in vitro migration, trophozoites usually produce protuberances such as pseudopods and rarely filopodia, structures that have been observed in the interaction of trophozoites with human colonic epithelial tissue. To study the different membrane projections produced by the trophozoites, including pseudopods, filopodia, uropods, blebs, and others, we designed an induction system using erythrocyte extract or fibronectin (FN) in micropatterned grill lines (each micro-line containing multiple micro-portions of FN or erythrocyte extract) on which the trophozoites were placed in culture for migration assays. Using light, confocal, and scanning electron microscopy, we established that E. histolytica trophozoites frequently produce short and long filopodia, large retractile uropods in the rear, pseudopods, blebs, and others structures, also showing continuous migration periods. The present study provides a simple migration method to induce trophozoites to generate abundant membrane protrusion structures that are rarely obtained in normal or induced cultures, such as long filopodia; this method will allow a–better understanding of the interactions of trophozoites with FN and cell debris. E. histolytica trophozoites motility plays an important role in invasive amoebiasis. It has been proposed that both physical forces and chemical signals are involved in the trophozoite motility and migration. However, the in vivo molecules that drive the chemotactic migration remain to be determined. We propose the present assay to study host molecules that guide chemotactic behavior because the method is highly reproducible, and a live image of cell movement and migration can be quantified.

Invadosome-Mediated Human Extracellular Matrix Degradation by Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite that causes invasive amoebiasis when it invades the human colon. Tissue invasion requires a shift from an adhesive lifestyle in the colonic lumen to a motile and extracellular matrix (ECM) degradative lifestyle in the colonic tissue layers. How the parasite regulates these two lifestyles is largely unknown. Previously, we showed that silencing the E. histolytica surface metalloprotease EhMSP-1 results in parasites that are hyperadherent and less motile. To better understand the molecular mechanism of this phenotype, we now show that the parasites with EhMSP-1 silenced cannot efficiently form specialized dot-like polymerized actin (F actin) structures upon interaction with the human ECM component fibronectin. We characterized these F actin structures and found that they are very short-lived structures that are the sites of fibronectin degradation. Motile mammalian cells form F actin structures called invadosomes that are similar in stability and function to these amoebic actin dots. Therefore, we propose here that E. histolytica forms amoebic invadosomes to facilitate colonic tissue invasion.

Structural and functional characterization of the divergent Entamoeba Src using Src inhibitor-1

Background

The abundant number of kinases that Entamoeba histolytica possesses allows us to assume that the regulation of cellular functions by phosphorylation-dephosphorylation processes is very important. However, the kinases responsible for the phosphorylation in Entamoeba spp. vary in the structure of their domains and, therefore, could be responsible for the unusual biological characteristics of this parasite. In higher eukaryotes, Src kinases share conserved structural domains and are very important in the regulation of the actin cytoskeleton. In both Entamoeba histolytica and Entamoeba invadens, the major Src kinase homologue of higher eukaryotes lacks SH3 and SH2 domains, but does have KELCH domains; the latter are part of actin cross-linking proteins in higher eukaryotic cells.

Methods

The function of the EhSrc protein kinase of Entamoeba spp. was evaluated using Src inhibitor-1, microscopy assays, Src kinase activity and western blot. In addition, to define the potential inhibitory mechanism of Src-inhibitor-1 for the amoebic EhSrc protein kinase, molecular dynamic simulations using NAnoscale Molecular Dynamics (NAMD2) program and docking studies were performed with MOE software.

Results

We demonstrate that Src inhibitor-1 is able to prevent the activity of EhSrc protein kinase, most likely by binding to the catalytic domain, which affects cell morphology via the disruption of actin cytoskeleton remodeling and the formation of phagocytic structures without an effect on cell adhesion. Furthermore, in E. invadens, Src inhibitor-1 inhibited the encystment process by blocking RhoA GTPase activity, a small GTPase protein of Rho family.

Conclusions

Even though the EhSrc molecule of Entamoeba is not a typical Src, because its divergent amino acid sequence, it is a critical factor in the biology of this parasite via the regulation of actin cytoskeleton remodeling via RhoA GTPase activation. Based on this, we conclude that EhSrc could become a target molecule for the future design of drugs that can prevent the transmission of the disease.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2461-5) contains supplementary material, which is available to authorized users.