EhRho1 regulates phagocytosis by modulating actin dynamics through EhFormin1 and EhProfilin1 inEntamoeba histolytica

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.

Transmembrane formins as active cargoes of membrane trafficking

Formins are a large, evolutionarily old family of cytoskeletal regulators whose roles include actin capping and nucleation, as well as modulation of microtubule dynamics. The plant class I formin clade is characterized by a unique domain organization, as most of its members are transmembrane proteins with possible cell wall-binding motifs exposed to the extracytoplasmic space-a structure that appears to be a synapomorphy of the plant kingdom. While such transmembrane formins are traditionally considered mainly as plasmalemma-localized proteins contributing to the organization of the cell cortex, we review, from a cell biology perspective, the growing evidence that they can also, at least temporarily, reside (and in some cases also function) in endomembranes including secretory and endocytotic pathway compartments, the endoplasmic reticulum, the nuclear envelope, and the tonoplast. Based on this evidence, we propose that class I formins may thus serve as 'active cargoes' of membrane trafficking-membrane-embedded proteins that modulate the fate of endo- or exocytotic compartments while being transported by them.

Dynamic Association of ESCRT-II Proteins with ESCRT-I and ESCRT-III Complexes during Phagocytosis of Entamoeba histolytica

By their active movement and voraux phagocytosis, the trophozoites of Entamoeba histolytica constitute an excellent system to investigate the dynamics of the Endosomal Sorting Complex Required for Transport (ESCRT) protein interactions through phagocytosis. Here, we studied the proteins forming the E. histolytica ESCRT-II complex and their relationship with other phagocytosis-involved molecules. Bioinformatics analysis predicted that EhVps22, EhVps25, and EhVps36 are E. histolytica bona fide orthologues of the ESCRT-II protein families. Recombinant proteins and specific antibodies revealed that ESCRT-II proteins interact with each other, with other ESCRT proteins, and phagocytosis-involved molecules, such as the adhesin (EhADH). Laser confocal microscopy, pull-down assays, and mass spectrometry analysis disclosed that during phagocytosis, ESCRT-II accompanies the red blood cells (RBCs) from their attachment to the trophozoites until their arrival to multivesicular bodies (MVBs), changing their interactive patterns according to the time and place of the process. Knocked-down trophozoites in the Ehvps25 gene presented a 50% lower rate of phagocytosis than the controls and lower efficiency to adhere RBCs. In conclusion, ESCRT-II interacts with other molecules during prey contact and conduction throughout the phagocytic channel and trophozoites membranous system. ESCRT-II proteins are members of the protein chain during vesicle trafficking and are fundamental for the continuity and efficiency of phagocytosis.

Molecular Dissection of Phagocytosis by Proteomic Analysis in Entamoeba histolytica

Entamoeba histolytica is the enteric protozoan parasite responsible for amebiasis. Trophozoites of E. histolytica ingest human cells in the intestine and other organs, which is the hallmark of its pathogenesis. Phagocytosis and trogocytosis are pivotal biological functions for its virulence and also contribute to the proliferation of nutrient uptake from the environment. We previously elucidated the role of a variety of proteins associated with phagocytosis and trogocytosis, including Rab small GTPases, Rab effectors, including retromer, phosphoinositide-binding proteins, lysosomal hydrolase receptors, protein kinases, and cytoskeletal proteins. However, a number of proteins involved in phagocytosis and trogocytosis remain to be identified, and mechanistic details of their involvement must be elucidated at the molecular level. To date, a number of studies in which a repertoire of proteins associated with phagosomes and potentially involved in phagocytosis have been conducted. In this review, we revisited all phagosome proteome studies we previously conducted in order to reiterate information on the proteome of phagosomes. We demonstrated the core set of constitutive phagosomal proteins and also the set of phagosomal proteins recruited only transiently or in condition-dependent fashions. The catalogs of phagosome proteomes resulting from such analyses can be a useful source of information for future mechanistic studies as well as for confirming or excluding a possibility of whether a protein of interest in various investigations is likely or is potentially involved in phagocytosis and phagosome biogenesis.

Insights into the Mechanisms of Lactobacillus acidophilus Activity against Entamoeba histolytica by Using Thiol Redox Proteomics

Amebiasis is an intestinal disease transmitted by the protist parasite, Entamoeba histolytica. Lactobacillus acidophilus is a common inhabitant of healthy human gut and a probiotic that has antimicrobial properties against a number of pathogenic bacteria, fungi, and parasites. The aim of this study was to investigate the amebicide activity of L. acidophilus and its mechanisms. For this purpose, E. histolytica and L. acidophilus were co-incubated and the parasite's viability was determined by eosin dye exclusion. The level of ozidized proteins (OXs) in the parasite was determined by resin-assisted capture RAC (OX-RAC). Incubation with L. acidophilus for two hours reduced the viability of E. histolytica trophozoites by 50%. As a result of the interaction with catalase, an enzyme that degrades hydrogen peroxide (H2O2) to water and oxygen, this amebicide activity is lost, indicating that it is mediated by H2O2 produced by L. acidophilus. Redox proteomics shows that L. acidophilus triggers the oxidation of many essential amebic enzymes such as pyruvate: ferredoxin oxidoreductase, the lectin Gal/GalNAc, and cysteine proteases (CPs). Further, trophozoites of E. histolytica incubated with L. acidophilus show reduced binding to mammalian cells. These results support L. acidophilus as a prophylactic candidate against amebiasis.

EhRho6 mediated actin degradation in Entamoeba histolytica is associated with compromised pathogenicity

Entamoeba histolytica causes amoebiasis which is a major health concern in developing countries. E. histolytica pathogenicity has been implicated to a large repertoire of small GTPases which switch between the inactive GDP bound state and the active GTP bound state with the help of guanine nucleotide exchange factors (GEFs) and GTPase activating protein (GAPs). Rho family of small GTPases are well known to modulate the actin cytoskeletal dynamics which plays a major role in E. histolytica pathogenicity. Here we report an atypical amoebic RhoGEF, and its preferred substrate EhRho6, which, upon overexpression abrogated the pathogenic behavior of the amoeba such as adhesion to host cell, monolayer destruction, erythrophagocytosis, and formation of actin dots. A causative immunoblot analysis revealed actin degradation in the EhRho6 overexpressing trophozoites that could be inhibited by blocking the amoebic proteasomal pathway. A careful analysis of the results from a previously published transcriptomics study, in conjunction with our observations, led to the identification of a clade of Rho GTPases in this pathogenic amoeba which we hypothesize to have implications during the amoebic encystation.

Unravelling the Biology of EhActo as the First Cofilin From Entamoeba histolytica

Actin-depolymerising factors (ADF) are a known family of proteins that regulate actin dynamics. Actin regulation is critical for primitive eukaryotes since it drives their key cellular processes. Entamoeba histolytica, a protist human pathogen harbours eleven proteins within this family, however, with no actin depolymerising protein reported to date. We present here the NMR model of EhActo, the first Cofilin from E. histolytica that severs actin filaments and also participates in cellular events like phagocytosis and pseudopod formation. The model typically represents the ADF-homology domain compared to other cofilins. Uniquely, EhActo lacks the critical Serine3 residue present in all known actophorins mediating its phospho-regulation. The second mode of regulation that cofilin’s are subjected to is via their interaction with 14-3-3 proteins through the phosphorylated Serine residue and a consensus binding motif. We found a unique interaction between EhActo and 14-3-3 without the presence of the consensus motif or the phosphorylated Serine. These interesting results present unexplored newer mechanisms functional in this pathogen to regulate actophorin. Through our structural and biochemical studies we have deciphered the mechanism of action of EhActo, implicating its role in amoebic biology.

An atypical EhGEF regulates phagocytosis in Entamoeba histolytica through EhRho1

The parasite Entamoeba histolytica is the etiological agent of amoebiasis, a major cause of morbidity and mortality due to parasitic diseases in developing countries. Phagocytosis is an essential mode of obtaining nutrition and has been associated with the virulence behaviour of E. histolytica. Signalling pathways involved in activation of cytoskeletal dynamics required for phagocytosis remains to be elucidated in this parasite. Our group has been studying initiation of phagocytosis and formation of phagosomes in E. histolytica and have described some of the molecules that play key roles in the process. Here we showed the involvement of non-Dbl Rho Guanine Nucleotide Exchange Factor, EhGEF in regulation of amoebic phagocytosis by regulating activation of EhRho1. EhGEF was found in the phagocytic cups during the progression of cups, until closure of phagosomes, but not in the phagosomes themselves. Our observation from imaging, pull down experiments and down regulating expression of different molecules suggest that EhGEF interacts with EhRho1 and it is required during initiation of phagocytosis and phagosome formation. Also, biophysical, and computational analysis reveals that EhGEF mediates GTP exchange on EhRho1 via an unconventional pathway. In conclusion, we describe a non-Dbl EhGEF of EhRho1 which is involved in endocytic processes of E. histolytica.

Trogocytosis in Unicellular Eukaryotes

Trogocytosis is a mode of internalization of a part of a live cell by nibbling and is mechanistically distinct from phagocytosis, which implies internalization of a whole cell or a particle. Trogocytosis has been demonstrated in a broad range of cell types in multicellular organisms and is also known to be involved in a plethora of functions. In immune cells, trogocytosis is involved in the "cross-dressing" between antigen presenting cells and T cells, and is thus considered to mediate intercellular communication. On the other hand, trogocytosis has also been reported in a variety of unicellular organisms including the protistan (protozoan) parasite Entamoeba histolytica. E. histolytica ingests human T cell line by trogocytosis and acquires complement resistance and cross-dresses major histocompatibility complex (MHC) class I on the cell surface. Furthermore, trogocytosis and trogocytosis-like phenomena (nibbling of a live cell, not previously described as trogocytosis) have also been reported in other parasitic protists such as Trichomonas, Plasmodium, Toxoplasma, and free-living amoebae. Thus, trogocytosis is conserved in diverse eukaryotic supergroups as a means of intercellular communication. It is depicting the universality of trogocytosis among eukaryotes. In this review, we summarize our current understanding of trogocytosis in unicellular organisms, including the history of its discovery, taxonomical distribution, roles, and molecular mechanisms.

Coordinated activity of amoebic formin and profilin are essential for phagocytosis

For the protist parasite Entamoeba histolytica, endocytic processes, such as phagocytosis, are essential for its survival in the human gut. The actin cytoskeleton is involved in the formation of pseudopods and phagosomal vesicles by incorporating a number of actin-binding and modulating proteins along with actin in a temporal manner. The actin dynamics, which comprises polymerization, branching, and depolymerization is very tightly regulated and takes place directionally at the sites of initiation of phagocytosis. Formin and profilin are two actin-binding proteins that are known to regulate actin cytoskeleton dynamics and thereby, endocytic processes. In this article, we report the participation of formin and profilin in E. histolytica phagocytosis and propose that these two proteins interact with each other and their sequential recruitment at the site is required for the successful completion of phagocytosis. The evidence is based on detailed microscopic, live imaging, interaction studies, and expression downregulation. The cells downregulated for expression of formin show absence of profilin at the site of phagocytosis, whereas downregulation of profilin does not affect formin localization.

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.

Rab7D small GTPase is involved in phago-, trogocytosis and cytoskeletal reorganization in the enteric protozoan Entamoeba histolytica

Rab small GTPases regulate membrane traffic between distinct cellular compartments of all eukaryotes in a tempo‐spatially specific fashion. Rab small GTPases are also involved in the regulation of cytoskeleton and signalling. Membrane traffic and cytoskeletal regulation play pivotal role in the pathogenesis of Entamoeba histolytica, which is a protozoan parasite responsible for human amebiasis. E. histolytica is unique in that its genome encodes over 100 Rab proteins, containing multiple isotypes of conserved members (e.g., Rab7) and Entamoeba‐specific subgroups (e.g., RabA, B, and X). Among them, E. histolytica Rab7 is the most diversified group consisting of nine isotypes. While it was previously demonstrated that EhRab7A and EhRab7B are involved in lysosome and phagosome biogenesis, the individual roles of other Rab7 members and their coordination remain elusive. In this study, we characterised the third member of Rab7, Rab7D, to better understand the significance of the multiplicity of Rab7 isotypes in E. histolytica. Overexpression of EhRab7D caused reduction in phagocytosis of erythrocytes, trogocytosis (meaning nibbling or chewing of a portion) of live mammalian cells, and phagosome acidification and maturation. Conversely, transcriptional gene silencing of EhRab7D gene caused opposite phenotypes in phago/trogocytosis and phagosome maturation. Furthermore, EhRab7D gene silencing caused reduction in the attachment to and the motility on the collagen‐coated surface. Image analysis showed that EhRab7D was occasionally associated with lysosomes and prephagosomal vacuoles, but not with mature phagosomes and trogosomes. Finally, in silico prediction of structural organisation of EhRab7 isotypes identified unique amino acid changes on the effector binding surface of EhRab7D. Taken together, our data suggest that EhRab7D plays coordinated counteracting roles: a inhibitory role in phago/trogocytosis and lyso/phago/trogosome biogenesis, and an stimulatory role in adherence and motility, presumably via interaction with unique effectors. Finally, we propose the model in which three EhRab7 isotypes are sequentially involved in phago/trogocytosis.

EhC2B, a C2 domain-containing protein, promotes erythrophagocytosis in Entamoeba histolytica via actin nucleation

Remodelling of the actin cytoskeleton in response to external stimuli is obligatory for many cellular processes in the amoebic cell. A rapid and local rearrangement of the actin cytoskeleton is required for the development of the cellular protrusions during phagocytosis, trogocytosis, migration, and invasion. Here, we demonstrated that EhC2B, a C2 domain-containing protein, is an actin modulator. EhC2B was first identified as an effector of EhRab21 from E. histolytica. In vitro interaction studies including GST pull-down, fluorescence-based assay and ITC also corroborated with our observation. In the amoebic trophozoites, EhC2B accumulates at the pseudopods and the tips of phagocytic cups. FRAP based studies confirmed the recruitment and dynamics of EhC2B at the phagocytic cup. Moreover, we have shown the role of EhC2B in erythrophagocytosis. It is well known that calcium-dependent signal transduction is essential for the cytoskeletal dynamics during phagocytosis in the amoebic parasite. Using liposome pelleting assay, we demonstrated that EhC2B preferentially binds to the phosphatidylserine in the presence of calcium. The EhC2B mutants defective in calcium or lipid-binding failed to localise beneath the plasma membrane. The cells overexpressing these mutants have also shown a significant reduction in erythrophagocytosis. The role of EhC2B in erythrophagocytosis and pseudopod formation was also validated by siRNA-based gene knockdown approach. Finally, with the help of in vitro nucleation assay using fluorescence spectroscopy and total internal reflection fluorescence microscopy, we have established that EhC2B is an actin nucleator. Collectively, based on the results from the study, we propose that EhC2B acts like a molecular bridge which promotes membrane deformation via its actin nucleation activity during the progression of the phagocytic cup in a calcium-dependent manner.

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.

Phosphatidylinositol Kinases and Phosphatases in Entamoeba histolytica

Phosphatidylinositol (PtdIns) metabolism is indispensable in eukaryotes. Phosphoinositides (PIs) are phosphorylated derivatives of PtdIns and consist of seven species generated by reversible phosphorylation of the inositol moieties at the positions 3, 4, and 5. Each of the seven PIs has a unique subcellular and membrane domain distribution. In the enteric protozoan parasite Entamoeba histolytica, it has been previously shown that the PIs phosphatidylinositol 3-phosphate (PtdIns3P), PtdIns(4,5)P₂, and PtdIns(3,4,5)P₃ are localized to phagosomes/phagocytic cups, plasma membrane, and phagocytic cups, respectively. The localization of these PIs in E. histolytica is similar to that in mammalian cells, suggesting that PIs have orthologous functions in E. histolytica. In contrast, the conservation of the enzymes that metabolize PIs in this organism has not been well-documented. In this review, we summarized the full repertoire of the PI kinases and PI phosphatases found in E. histolytica via a genome-wide survey of the current genomic information. E. histolytica appears to have 10 PI kinases and 23 PI phosphatases. It has a panel of evolutionarily conserved enzymes that generate all the seven PI species. However, class II PI 3-kinases, type II PI 4-kinases, type III PI 5-phosphatases, and PI 4P-specific phosphatases are not present. Additionally, regulatory subunits of class I PI 3-kinases and type III PI 4-kinases have not been identified. Instead, homologs of class I PI 3-kinases and PTEN, a PI 3-phosphatase, exist as multiple isoforms, which likely reflects that elaborate signaling cascades mediated by PtdIns(3,4,5)P₃ are present in this organism. There are several enzymes that have the nuclear localization signal: one phosphatidylinositol phosphate (PIP) kinase, two PI 3-phosphatases, and one PI 5-phosphatase; this suggests that PI metabolism also has conserved roles related to nuclear functions in E. histolytica, as it does in model organisms.

EhP3, a homolog of 14-3-3 family of protein participates in actin reorganization and phagocytosis in Entamoeba histolytica

The highly conserved proteins of the 14-3-3 family are universal adaptors known to regulate an enormous range of cellular processes in eukaryotes. However, their biological functions remain largely uncharacterized in pathogenic protists comprising of several 14-3-3 protein isoforms. In this study, we report the role of 14-3-3 in coordinating cytoskeletal dynamics during phagocytosis in a professional phagocytic protist Entamoeba histolytica, the etiological agent of human amebiasis. There are three isoforms of 14-3-3 protein in amoeba and here we have investigated Eh14-3-3 Protein 3 (EhP3). Live and fixed cell imaging studies revealed the presence of this protein throughout the parasite phagocytosis process, with high rate of accumulation at the phagocytic cups and closed phagosomes. Conditional suppression of EhP3 expression caused significant defects in phagocytosis accompanied by extensive diminution of F-actin at the site of cup formation. Downregulated cells also exhibited defective recruitment of an F-actin stabilizing protein, EhCoactosin at the phagocytic cups. In addition, mass spectrometry based analysis further revealed a large group of EhP3-associated proteins, many of these proteins are known to regulate cytoskeletal architecture in E histolytica. The dynamics of these proteins may also be controlled by EhP3. Taken together, our findings strongly suggest that EhP3 is a novel and a key regulatory element of actin dynamics and phagocytosis in E. histolytica.

Phagocytosis of host cells is central to pathogenesis of protist parasite Entamoeba histolytica, the etiological agent of human amebiasis. It is a complex and multistep process that requires dynamic remodelling of the actin cytoskeleton by a large number of scaffolding, signaling and actin-binding proteins (ABPs). Although several parasite ligands such as EhC2PK, EhCaBP1, EhCaBP3, EhAK1, Arp2/3 complex and EhCoactosin that participate in the phagocytic machinery have been identified, the mechanistic insights to their regulation process remain largely elusive. We have in this study identified and characterized the important role of scaffolding protein EhP3 in modulating cytoskeletal dynamics and regulating phagocytosis in E. histolytica. Expression knockdown, imaging and interaction studies suggest that EhP3 function as an adaptor molecule that controls the localization of an F-actin stabilizing protein EhCoactosin and thus the dynamics of F-actin rearrangement during phagocytosis. EhP3 also interact with other actin dynamics regulating proteins that may in coordination regulate cytoskeletal dynamics and thereby phagocytosis in Entamoeba.

Stress-induced nuclear depletion of Entamoeba histolytica 3'-5' exoribonuclease EhRrp6 and its role in growth and erythrophagocytosis

The 3'-5' exoribonuclease Rrp6 is a key enzyme in RNA homeostasis involved in processing and degradation of many stable RNA precursors, aberrant transcripts, and noncoding RNAs. We previously have shown that in the protozoan parasite Entamoeba histolytica, the 5'-external transcribed spacer fragment of pre-rRNA accumulates under serum starvation-induced growth stress. This fragment is a known target of degradation by Rrp6. Here, we computationally and biochemically characterized EhRrp6 and found that it contains the catalytically important EXO and HRDC domains and exhibits exoribonuclease activity with both unstructured and structured RNA substrates, which required the conserved DEDD-Y catalytic-site residues. It lacked the N-terminal PMC2NT domain for binding of the cofactor Rrp47, but could functionally complement the growth defect of a yeast rrp6 mutant. Of note, no Rrp47 homologue was detected in E. histolytica Immunolocalization studies revealed that EhRrp6 is present both in the nucleus and cytosol of normal E. histolytica cells. However, growth stress induced its complete loss from the nuclei, reversed by proteasome inhibitors. EhRrp6-depleted E. histolytica cells were severely growth restricted, and EhRrp6 overexpression protected the cells against stress, suggesting that EhRrp6 functions as a stress sensor. Importantly EhRrp6 depletion reduced erythrophagocytosis, an important virulence determinant of E. histolytica This reduction was due to a specific decrease in transcript levels of some phagocytosis-related genes (Ehcabp3 and Ehrho1), whereas expression of other genes (Ehcabp1, Ehcabp6, Ehc2pk, and Eharp2/3) was unaffected. This is the first report of the role of Rrp6 in cell growth and stress responses in a protozoan parasite.