Possible role of calcium ions, calcium channels and calmodulin in excystation and metacystic development of Entamoeba invadens

Functional Innovation in the Evolution of the Calcium-Dependent System of the Eukaryotic Endoplasmic Reticulum

The origin of eukaryotes was marked by the emergence of several novel subcellular systems. One such is the calcium (Ca²⁺)-stores system of the endoplasmic reticulum, which profoundly influences diverse aspects of cellular function including signal transduction, motility, division, and biomineralization. We use comparative genomics and sensitive sequence and structure analyses to investigate the evolution of this system. Our findings reconstruct the core form of the Ca²⁺-stores system in the last eukaryotic common ancestor as having at least 15 proteins that constituted a basic system for facilitating both Ca²⁺ flux across endomembranes and Ca²⁺-dependent signaling. We present evidence that the key EF-hand Ca²⁺-binding components had their origins in a likely bacterial symbiont other than the mitochondrial progenitor, whereas the protein phosphatase subunit of the ancestral calcineurin complex was likely inherited from the asgard archaeal progenitor of the stem eukaryote. This further points to the potential origin of the eukaryotes in a Ca²⁺-rich biomineralized environment such as stromatolites. We further show that throughout eukaryotic evolution there were several acquisitions from bacteria of key components of the Ca²⁺-stores system, even though no prokaryotic lineage possesses a comparable system. Further, using quantitative measures derived from comparative genomics we show that there were several rounds of lineage-specific gene expansions, innovations of novel gene families, and gene losses correlated with biological innovation such as the biomineralized molluscan shells, coccolithophores, and animal motility. The burst of innovation of new genes in animals included the wolframin protein associated with Wolfram syndrome in humans. We show for the first time that it contains previously unidentified Sel1, EF-hand, and OB-fold domains, which might have key roles in its biochemistry.

Bioinformatics Analysis and Functional Prediction of Transmembrane Proteins in Entamoeba histolytica

Entamoeba histolytica is an invasive, pathogenic parasite causing amoebiasis. Given that proteins involved in transmembrane (TM) transport are crucial for the adherence, invasion, and nutrition of the parasite, we conducted a genome-wide bioinformatics analysis of encoding proteins to functionally classify and characterize all the TM proteins in E. histolytica. In the present study, 692 TM proteins have been identified, of which 546 are TM transporters. For the first time, we report a set of 141 uncharacterized proteins predicted as TM transporters. The percentage of TM proteins was found to be lower in comparison to the free-living eukaryotes, due to the extracellular nature and functional diversification of the TM proteins. The number of multi-pass proteins is larger than the single-pass proteins; though both have their own significance in parasitism, multi-pass proteins are more extensively required as these are involved in acquiring nutrition and for ion transport, while single-pass proteins are only required at the time of inciting infection. Overall, this intestinal parasite implements multiple mechanisms for establishing infection, obtaining nutrition, and adapting itself to the new host environment. A classification of the repertoire of TM transporters in the present study augments several hints on potential methods of targeting the parasite for therapeutic benefits.

A Calcium/Cation Exchanger Participates in the Programmed Cell Death and in vitro Virulence of Entamoeba histolytica

Entamoeba histolytica is the etiologic agent of human amoebiasis, disease that causes 40,000 to 100,000 deaths annually worldwide. The cytopathic activity as well as the growth and differentiation of this microorganism is dependent on both, extracellular and free cytoplasmic calcium. However, few is known about the proteins that regulate the calcium flux in this parasite. In many cells, the calcium extrusion from the cytosol is performed by plasma membrane Ca²⁺-ATPases and calcium/cation exchangers. The aim of this work was to identify a calcium/cation exchanger of E. histolytica and to analyze its possible role in some cellular processes triggered by calcium flux, such as the programmed cell death and in vitro virulence. By searching putative calcium/cation exchangers in the genome database of E. histolyica we identified a protein belonging to the CCX family (EhCCX). We generated a specific antibody against EhCCX, which showed that this protein was expressed in higher levels in E. histolytica than its orthologous in the non-pathogenic amoeba E. dispar. In addition, the expression of EhCCX was increased in trophozoites incubated with hydrogen peroxide. This E. histolytica exchanger was localized in the plasma membrane and in the membrane of some cytoplasmic vesicles. However, after 10 min of erythrophagocytosis, EhCCX was found predominantly in the plasma membrane of the trophozoites. On the other hand, the parasites that overexpress this exchanger contained higher cytosolic calcium levels than control, but the extrusion of calcium after the addition of hydrogen peroxide was more efficient in EhCCX-overexpressing trophozoites; consequently, the programmed cell death was retarded in these parasites. Interestingly, the overexpression of EhCCX increased the in vitro virulence of trophozoites. These results suggest that EhCCX plays important roles in the programmed cell death and in the in vitro virulence of E. histolytica.

A putative calcium-ATPase of the secretory pathway family may regulate calcium/manganese levels in the Golgi apparatus of Entamoeba histolytica

Calcium regulates many cellular processes in protozoa, including growth, differentiation, programmed cell death, exocytosis, endocytosis, phagocytosis, fusion of the endosomes of distinct stages with phagosomes, fusion of phagosomes with lysosomes, and recycling the membrane. In Entamoeba histolytica, the protozoa responsible for human amoebiasis, calcium ions are essential for signaling pathways that lead to growth and development. In addition, calcium is crucial in the modulation of gene expression in this microorganism. However, there is scant information about the proteins responsible for regulating calcium levels in this parasite. In this work, we characterized a protein of E. histolytica that shows a close phylogenetic relationship with Ca²⁺ pumps that belong to the family of secretory pathway calcium ATPases (SPCA), which for several organisms are located in the Golgi apparatus. The amoeba protein analyzed herein has several amino acid residues that are characteristic of SPCA members. By an immunofluorescent technique using specific antibodies and immunoelectron microscopy, the protein was detected on the membrane of some cytoplasmic vacuoles. Moreover, this putative calcium-ATPase was located in vacuoles stained with NBD C6-ceramide, a Golgi marker. Overall, the current findings support the hypothesis that the presently analyzed protein corresponds to the SPCA of E. histolytica.

Divalent Metal Cations Potentiate the Predatory Capacity of Amoeba for Cryptococcus neoformans

Among the best-studied interactions between soil phagocytic predators and a human-pathogenic fungus is that of Acanthamoeba castellanii and Cryptococcus neoformans The experimental conditions used in amoeba-fungus confrontation assays can have major effects on whether the fungus or the protozoan is ascendant in the interaction. In the presence of Mg²⁺ and Ca²⁺ in phosphate-buffered saline (PBS), C. neoformans was consistently killed when incubated with A. castellaniiA. castellanii survived better in the presence of Mg²⁺ and Ca²⁺, even when incubated with C. neoformans In the absence of Mg²⁺ and Ca²⁺, C. neoformans survived when incubated with A. castellanii, and the percentage of dead amoebae was higher than when incubated without yeast cells. These results show that the presence of Mg²⁺ and Ca²⁺ can make a decisive contribution toward tilting the outcome of the interaction in favor of the amoeba. Of the two metals, Mg²⁺ had a stronger effect than Ca²⁺ The cations enhanced A. castellanii activity against C. neoformans via enhanced phagocytosis, which is the major mechanism by which amoebae kill fungal cells. We found no evidence that amoebae use extracellular killing mechanisms in their interactions with C. neoformans In summary, the presence of Mg²⁺ and Ca²⁺ enhanced the cell adhesion on the surfaces and the motility of the amoeba, thus increasing the chance for contact with C. neoformans and the frequency of phagocytosis. Our findings imply that the divalent cation concentration in soils could be an important variable for whether amoebae can control C. neoformans in the environment.IMPORTANCE The grazing of soil organisms by phagocytic predators such as amoebae is thought to select for traits that enable some of them to acquire the capacity for virulence in animals. Consequently, knowledge about the interactions between amoebae and soil microbes, such as pathogenic fungi, is important for understanding how virulence can emerge. We show that the interaction between an amoeba and the pathogenic fungus C. neoformans is influenced by the presence in the assay of magnesium and calcium, which potentiate amoebae. The results may also have practical applications, since enriching soils with divalent cations may reduce C. neoformans numbers in contaminated soils.

Proteome analysis of excretory-secretory proteins of Entamoeba histolytica HM1:IMSS via LC-ESI-MS/MS and LC-MALDI-TOF/TOF

BACKGROUND

Excretory-secretory (ES) proteins of E. histolytica are thought to play important roles in the host invasion, metabolism, and defence. Elucidation of the types and functions of E. histolytica ES proteins can further our understanding of the disease pathogenesis. Thus, the aim of this study is to use proteomics approach to better understand the complex ES proteins of the protozoa.

METHODS

E. histolytica ES proteins were prepared by culturing the trophozoites in protein-free medium. The ES proteins were identified using two mass spectrometry tools, namely, LC-ESI-MS/MS and LC-MALDI-TOF/TOF. The identified proteins were then classified according to their biological processes, molecular functions, and cellular components using the Panther classification system (PantherDB).

RESULTS

A complementary list of 219 proteins was identified; this comprised 201 proteins detected by LC-ESI-MS/MS and 107 proteins by LC-MALDI-TOF/TOF. Of the 219 proteins, 89 were identified by both mass-spectrometry systems, while 112 and 18 proteins were detected exclusively by LC-ESI-MS/MS and LC-MALDI-TOF/TOF respectively. Biological protein functional analysis using PantherDB showed that 27% of the proteins were involved in metabolic processes. Using molecular functional and cellular component analyses, 35% of the proteins were found to be involved in catalytic activity, and 21% were associated with the cell parts.

CONCLUSION

This study showed that complementary use of LC-ESI-MS/MS and LC-MALDI-TOF/TOF has improved the identification of ES proteins. The results have increased our understanding of the types of proteins excreted/secreted by the amoeba and provided further evidence of the involvement of ES proteins in intestinal colonisation and evasion of the host immune system, as well as in encystation and excystation of the parasite.

Balamuthia mandrillaris in South America: an emerging potential hidden pathogen in Perú

Balamuthia mandrillaris is a free living amoeba that can be isolated from soil. It is an emerging pathogen causing skin lesions as well as CNS involvement with a fatal outcome if untreated. Further, infections can sometimes can also appear in peripheral areas such as extremities (usually knee), or trunk. Moreover, it often progresses to an infiltrative lesion that occasionally becomes ulcerated. In countries like Peru, a skin lesion will precede other symptoms. This primary cutaneous lesion can be present for weeks or even months. However, the appearance of neurological disease predicts a poor prognosis. Diagnosis requires a high level of suspicion.

Identification of putative potassium channel homologues in pathogenic protozoa

K⁺ channels play a vital homeostatic role in cells and abnormal activity of these channels can dramatically alter cell function and survival, suggesting that they might be attractive drug targets in pathogenic organisms. Pathogenic protozoa lead to diseases such as malaria, leishmaniasis, trypanosomiasis and dysentery that are responsible for millions of deaths each year worldwide. The genomes of many protozoan parasites have recently been sequenced, allowing rational design of targeted therapies. We analyzed the genomes of pathogenic protozoa and show the existence within them of genes encoding putative homologues of K⁺ channels. These protozoan K⁺ channel homologues represent novel targets for anti-parasitic drugs. Differences in the sequences and diversity of human and parasite proteins may allow pathogen-specific targeting of these K⁺ channel homologues.

Efficacy of antiamebic drugs in a mouse model

Nitroimidazole antibiotics are the mainstay of treatment of invasive amebiasis; however, few comparative studies of applicable antibiotics are available. Evidence of sporadic clinical failure and rare reports of metronidazole resistance have led to the investigation of novel antiamebic therapeutics. The goal of this study was to examine drug efficacy in both in vitro and in vivo models of intestinal amebiasis. We studied six current and three novel drugs. Many drugs, including metronidazole, nitazoxanide, and nitazoxanide derivatives, were shown to be potently inhibitory in vitro. However, metronidazole remained the most effective in vivo, both in preventative and curative regimens, underscoring the value of animal models in evaluating future therapies.

Phospholipid-binding protein EhC2A mediates calcium-dependent translocation of transcription factor URE3-BP to the plasma membrane of Entamoeba histolytica

The Entamoeba histolytica upstream regulatory element 3-binding protein (URE3-BP) is a transcription factor that binds DNA in a Ca(2+)-inhibitable manner. The protein is located in both the nucleus and the cytoplasm but has also been found to be enriched in the plasma membrane of amebic trophozoites. We investigated the reason for the unusual localization of URE3-BP at the amebic plasma membrane. Here we identify and characterize a 22-kDa Ca(2+)-dependent binding partner of URE3-BP, EhC2A, a novel member of the C2-domain superfamily. Immunoprecipitations of URE3-BP and EhC2A showed that the proteins interact and that such interaction was enhanced in the presence of Ca(2+). Recombinant and native EhC2A bound phospholipid liposomes in a Ca(2+)-dependent manner, with half-maximal binding occurring at 3.4 muM free Ca(2+). A direct interaction between EhC2A and URE3-BP was demonstrated by the ability of recombinant EhC2A to recruit recombinant URE3-BP to phospholipid liposomes in a Ca(2+)-dependent manner. URE3-BP and EhC2A were observed to translocate to the amebic plasma membrane upon an increase in the intracellular Ca(2+) concentration of trophozoites, as revealed by subcellular fractionation and immunofluorescent staining. Short hairpin RNA-mediated knockdown of EhC2A protein expression significantly modulated the mRNA levels of URE3-BP-regulated transcripts. Based on these results, we propose a model for EhC2A-mediated regulation of the transcriptional activities of URE3-BP via Ca(2+)-dependent anchoring of the transcription factor to the amebic plasma membrane.

Compounds of the upper gastrointestinal tract induce rapid and efficient excystation of Entamoeba invadens

The infective stage of Entamoeba parasites is an encysted form. This stage can be readily generated in vitro, which has allowed identification of stimuli that trigger the differentiation of the parasite trophozoite stage into the cyst stage. Studies of the second differentiation event, emergence of the parasite from the cyst upon infection of a host, have been hampered by the lack of an efficient means to excyst the parasite and complete the life cycle in vitro. We have determined that a combination of exposures to water, bicarbonate and bile induces rapid excystment of Entamoeba invadens cysts. The high efficiency of this method has allowed the visualization of the dynamics of the process by electron and confocal microscopy, and should permit the analysis of stage-specific gene expression and high-throughput screening of inhibitory compounds.

Recent insights into Entamoeba development: identification of transcriptional networks associated with stage conversion

Entamoeba histolytica is an important human pathogen and a leading parasitic cause of death globally. The parasite life cycle alternates between the trophozoite form, which is motile and causes invasive disease and the cyst stage, which is environmentally resistant and transmits infection. Understanding the triggers that initiate stage conversion is an important yet understudied area of investigation. Recent progress in dissecting the transcriptional networks that regulate E. histolytica development is outlined in this paper.

Identification of developmentally regulated genes in Entamoeba histolytica: insights into mechanisms of stage conversion in a protozoan parasite

Developmental switching between life-cycle stages is a common feature among many pathogenic organisms. The protozoan parasite Entamoeba histolytica converts between cysts (essential for disease transmission) and trophozoites (responsible for tissue invasion). Identification of genes involved in the developmental pathway has been severely hindered by the inability to generate E. histolytica cysts in vitro. Using parasite strains derived from recent human infections and whole-genome transcriptional profiling, we determined that 1439 genes (approximately 15% of annotated genes) were potentially developmentally regulated. Genes enriched in cysts (672 in total) included cysteine proteinases and transmembrane protein kinases, which may be involved in signal transduction. Genes enriched in trophozoites (767 in total) included genes typically thought of as important in tissue invasion by trophozoites, including the Gal/GalNAc lectin light subunit and cysteine protease 1. Putative regulators of differentiation including possible G-protein coupled receptors, signal transduction proteins and transcription factors were identified. A number of E. histolytica stage-specific genes were also developmentally regulated in the reptilian parasite E. invadens, indicating that they likely have conserved functions in Entamoeba development. These advances lay the groundwork for dissection of the molecular signals that initiate stage conversion and development of novel diagnostic and therapeutic measures targeting E. histolytica cysts.