Signal transduction in Entamoeba histolytica induced by interaction with fibronectin: presence and activation of phosphokinase A and its possible relation to invasiveness

Low molecular weight protein tyrosine phosphatase (LMW-PTP2) protein can potentially modulate virulence of the parasite Entamoeba histolytica

The Entamoeba histolytica parasite is the causative agent of amebiasis, infecting approximately 1% of the world population and causing 100,000 deaths per year. It binds to Fibronectin (FN), activating signaling pathways regulated by kinases and phosphatases. EhLMW-PTPs genes from E. histolytica encode for Low Molecular Weight Tyrosine Phosphatases expressed in trophozoites and amoebic cysts. The role of these phosphatases in the virulence of the parasite has not yet been well characterized. Our results showed a differential expression of the EhLMW-PTPs, at the mRNA and protein levels, in an asynchronous trophozoites culture. Furthermore, we observed that trophozoites transfected that overexpressed EhLMW-PTP2 phagocytized fewer erythrocytes, possibly due to decreased phagocytic cups, and showed deficiencies in adherence to FN and less cytopathic effect. These analyzes suggest that the parasite's EhLMW-PTPs have an essential role in the mechanisms of proliferation, adhesion, and phagocytosis, regulating its pathogenicity.

cAMP-dependent signal pathways in unicellular eukaryotes

The review summarizes current data about mechanisms of signal transduction with participation of cAMP (cyclic adenosine monophosphate) and elements of the complex cAMP-protein kinase A (PKA) signal pathway in unicellular eukaryotes. Conceptions of evolutionary origin of eukaryotic signal transduction systems are developed.

Initiation of Plasmodium sporozoite motility by albumin is associated with induction of intracellular signalling

Malaria infection is initiated when a mosquito injects Plasmodium sporozoites into a mammalian host. Sporozoites exhibit gliding motility both in vitro and in vivo. This motility is associated with the secretion of at least two proteins, circumsporozoite protein (CSP) and thrombospondin-related anonymous protein (TRAP). Both derive from micronemes, which are organelles that empty out of the apical end of the sporozoite. Sporozoite motility can be initiated in vitro by albumin added to the medium. To investigate how albumin functions in this process, we studied second messenger signalling within the sporozoite. Using pharmacological activators and inhibitors, we have concluded that gliding motility is initiated when albumin interacts with the surface of the sporozoite and that this leads to a signal transduction cascade within the sporozoite, including the elevation of intracellular cAMP, the modulation of sporozoite motility by Ca(2+) and the release of microneme proteins.

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.

Entamoeba histolytica: lipid rafts are involved in adhesion of trophozoites to host extracellular matrix components

Adhesion is an important virulence function for Entamoeba histolytica, the causative agent of amoebic dysentery. Lipid rafts, cholesterol-rich domains, function in compartmentalization of cellular processes. In E. histolytica, rafts participate in parasite-host cell interactions; however, their role in parasite-host extracellular matrix (ECM) interactions has not been explored. Disruption of rafts with a cholesterol extracting agent, methyl-beta-cyclodextrin (MbetaCD), resulted in inhibition of adhesion to collagen, and to a lesser extent, to fibronectin. Replenishment of cholesterol in MbetaCD-treated cells, using a lipoprotein-cholesterol concentrate, restored adhesion to collagen. Confocal microscopy revealed enrichment of rafts at parasite-ECM interfaces. A raft-resident adhesin, the galactose/N-acetylgalactosamine-inhibitable lectin, mediates interaction to host cells by binding to galactose or N-acetylgalactosamine moieties on host glycoproteins. In this study, galactose inhibited adhesion to collagen, but not to fibronectin. Together these data suggest that rafts participate in E. histolytica-ECM interactions and that raft-associated Gal/GalNAc lectin may serve as a collagen receptor.

Analysis of the protein kinome of Entamoeba histolytica

Protein kinases play important roles in almost all major signaling and regulatory pathways of eukaryotic organisms. Members in the family of protein kinases make up a substantial fraction of eukaryotic proteome. Analysis of the protein kinase repertoire (kinome) would help in the better understanding of the regulatory processes. In this article, we report the identification and analysis of the repertoire of protein kinases in the intracellular parasite Entamoeba histolytica. Using a combination of various sensitive sequence search methods and manual analysis, we have identified a set of 307 protein kinases in E. histolytica genome. We have classified these protein kinases into different subfamilies originally defined by Hanks and Hunter and studied these kinases further in the context of noncatalytic domains that are tethered to catalytic kinase domain. Compared to other eukaryotic organisms, protein kinases from E. histolytica vary in terms of their domain organization and displays features that may have a bearing in the unusual biology of this organism. Some of the parasitic kinases show high sequence similarity in the catalytic domain region with calmodulin/calcium dependent protein kinase subfamily. However, they are unlikely to act like typical calcium/calmodulin dependent kinases as they lack noncatalytic domains characteristic of such kinases in other organisms. Such kinases form the largest subfamily of kinases in E. histolytica. Interestingly, a PKA/PKG-like subfamily member is tethered to pleckstrin homology domain. Although potential cyclins and cyclin-dependent kinases could be identified in the genome the likely absence of other cell cycle proteins suggests unusual nature of cell cycle in E. histolytica. Some of the unusual features recognized in our analysis include the absence of MEK as a part of the Mitogen Activated Kinase signaling pathway and identification of transmembrane region containing Src kinase-like kinases. Sequences which could not be classified into known subfamilies of protein kinases have unusual domain architectures. Many such unclassified protein kinases are tethered to domains which are Cysteine-rich and to domains known to be involved in protein-protein interactions. Our kinome analysis of E. histolytica suggests that the organism possesses a complex protein phosphorylation network that involves many unusual kinases.

The Cytoskeleton of Entamoeba histolytica: Structure, Function, and Regulation by Signaling Pathways

Pathogenesis in the parasite Entamoeba histolytica has been related to motility of the trophozoites. Motility is an important feature in amebas as they perform multiple motile functions during invasion of host tissues. As motility depends on the organization and regulation of the cytoskeleton elements, in particular of the actin cytoskeleton, the study of the molecular components of the machinery responsible for movement has been a key aspect to study in this parasite. Although many of the components have high homology in amino acid sequence and function to those characterized in higher eukaryotic cells, there are important differences to suggest that parasitic organisms may have developed adaptative differences that could be useful as targets to stop invasion. The purpose of this review is to evaluate current knowledge about the cytoskeleton of E. histolytica and the ways in which the parasite controls motility.

Entamoeba histolytica sequences and their relationship with experimental liver abscesses in hamsters

The purpose of the present paper was to analyse the association between sequences of Entamoeba histolytica and their relationship with the development of hepatic abscesses in hamsters, using a complementary DNA library for E. histolytica. From the sequences obtained, we designed oligonucleotides for amplification by PCR. Trophozoites were isolated from faeces of 11 patients in whom cysts from E. histolytica were identified, and these trophozoites were then subjected to monoaxenic culture. Then 1 x 10(5) trophozoites were inoculated into hamster liver, with three hamsters used for every culture. Sequences were obtained for ubiquitin, lectin surface precursor, replication factor MCM3 and surface antigen. The associations between sequences and hepatic abscesses were: 11/11 for ubiquitin, 9/11 for lectin precursor, 4/11 for replication factor and 1/11 for surface antigen. These results suggest that ubiquitin could be an important protein involved in the mechanism of E. histolytica invasion.

An anti-inflammatory oligopeptide produced by Entamoeba histolytica down-regulates the expression of pro-inflammatory chemokines

Axenically grown Entamoeba histolytica produces a pentapeptide (Met-Gln-Cys-Asn-Ser) with anti-inflammatory properties that, among others, inhibits the in vitro and in vivo locomotion of human monocytes, sparing polymorphonuclear leucocytes from this effect [hence the name originally given. Monocyte Locomotion Inhibitory Factor (MLIF)]. A synthetic construct of this peptide displays the same effects as the native material. We now added MLIF to resting and PMA-stimulated cells of a human monocyte cell line and measured the effect upon mRNA and protein expression of pro-inflammatory chemokines (RANTES, IP-10, MIP-1alpha, MIP-1beta, MCP-1, IL-8, I-309 and lymphotactin) and the shared CC receptor repertoire. The constitutive expression of these chemokines and the CC receptors was unaffected, whereas induced expression of MIP-1alpha, MIP-1beta, and I-309, and that of the CCR1 receptor--all involved in monocyte chemotaxis--was significantly inhibited by MLIF. This suggests that the inhibition of monocyte functions by MLIF may not only be exerted directly on these cells, but also--and perhaps foremost--through a conglomerate down-regulation of endogenous pro-inflammatory chemokines.