Entamoeba histolytica: alterations in EhRabB protein in a phagocytosis deficient mutant correlate with the Entamoeba dispar RabB sequence

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.

Chew on this: amoebic trogocytosis and host cell killing by Entamoeba histolytica

Entamoeba histolytica was named 'histolytica' (from histo-, 'tissue'; lytic-, 'dissolving') for its ability to destroy host tissues. Direct killing of host cells by the amoebae is likely to be the driving factor that underlies tissue destruction, but the mechanism was unclear. We recently showed that, after attaching to host cells, amoebae bite off and ingest distinct host cell fragments, and that this contributes to cell killing. We review this process, termed 'amoebic trogocytosis' (trogo-, 'nibble'), and how this process interplays with phagocytosis, or whole cell ingestion, in this organism. 'Nibbling' processes have been described in other microbes and in multicellular organisms. The discovery of amoebic trogocytosis in E. histolytica may also shed light on an evolutionarily conserved process for intercellular exchange.

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.

Entamoeba histolytica: the over expression of a mutated EhRabB protein produces a decrease of in vitro and in vivo virulence

Vesicular trafficking, which is implicated in secretion of cytolytic molecules as well as in phagocytosis, plays an important role in the pathogenic mechanism of Entamoeba histolytica, the protozoan parasite causative of human amoebiasis. Thus, Rab GTPases, that are key regulators of vesicle trafficking, should be considered as molecules involved in the parasite virulence. EhRabB is a Rab protein located in cytoplasmic vesicles that are translocated to phagocytic mouths during ingestion of target cells, suggesting that this Rab protein is involved in phagocytosis. To prove this hypothesis, we over expressed the wild type EhrabB gene and a mutant gene encoding for a protein (RabBN118I) unable to bind guanine nucleotides and therefore constitutively inactive. The over expression of the mutated protein in E. histolytica trophozoites provoked a dominant negative effect, reflected in a significant decrease of both phagocytosis and cytopathic effect as well as in a failure to produce hepatic abscesses in hamsters. These results confirm that EhRabB is involved in phagocytosis and virulence of E. histolytica.

Heterotrimeric G-protein signaling is critical to pathogenic processes in Entamoeba histolytica

Heterotrimeric G-protein signaling pathways are vital components of physiology, and many are amenable to pharmacologic manipulation. Here, we identify functional heterotrimeric G-protein subunits in Entamoeba histolytica, the causative agent of amoebic colitis. The E. histolytica Gα subunit EhGα1 exhibits conventional nucleotide cycling properties and is seen to interact with EhGβγ dimers and a candidate effector, EhRGS-RhoGEF, in typical, nucleotide-state-selective fashions. In contrast, a crystal structure of EhGα1 highlights unique features and classification outside of conventional mammalian Gα subfamilies. E. histolytica trophozoites overexpressing wildtype EhGα1 in an inducible manner exhibit an enhanced ability to kill host cells that may be wholly or partially due to enhanced host cell attachment. EhGα1-overexpressing trophozoites also display enhanced transmigration across a Matrigel barrier, an effect that may result from altered baseline migration. Inducible expression of a dominant negative EhGα1 variant engenders the converse phenotypes. Transcriptomic studies reveal that modulation of pathogenesis-related trophozoite behaviors by perturbed heterotrimeric G-protein expression includes transcriptional regulation of virulence factors and altered trafficking of cysteine proteases. Collectively, our studies suggest that E. histolytica possesses a divergent heterotrimeric G-protein signaling axis that modulates key aspects of cellular processes related to the pathogenesis of this infectious organism.

Mechanisms of adherence, cytotoxicity and phagocytosis modulate the pathogenesis of Entamoeba histolytica

The unicellular parasite Entamoeba histolytica, the causative agent of the human disease amebiasis, has traditionally been distinguished from its nonpathogenic cousin Entamoeba dispar by its propensity for the ingestion of erythrocytes. This classic feature, along with the parasite’s ability to cause extensive host cell death, are critical mechanisms of pathogenesis during human infection. Recent advances have led to a greater understanding of the molecular components that allow E. histolytica to kill and phagocytose extracellular targets during human infection and include detailed studies of the role of the parasite’s cysteine proteinases and other effectors of cytotoxicity, as well as the mechanisms of ligand recognition, signaling and intracellular trafficking during phagocytosis.

Regulation of gene expression in protozoa parasites

Infections with protozoa parasites are associated with high burdens of morbidity and mortality across the developing world. Despite extensive efforts to control the transmission of these parasites, the spread of populations resistant to drugs and the lack of effective vaccines against them contribute to their persistence as major public health problems. Parasites should perform a strict control on the expression of genes involved in their pathogenicity, differentiation, immune evasion, or drug resistance, and the comprehension of the mechanisms implicated in that control could help to develop novel therapeutic strategies. However, until now these mechanisms are poorly understood in protozoa. Recent investigations into gene expression in protozoa parasites suggest that they possess many of the canonical machineries employed by higher eukaryotes for the control of gene expression at transcriptional, posttranscriptional, and epigenetic levels, but they also contain exclusive mechanisms. Here, we review the current understanding about the regulation of gene expression in Plasmodium sp., Trypanosomatids, Entamoeba histolytica and Trichomonas vaginalis.

Structural and functional analysis of the Entamoeba histolytica EhrabB gene promoter

BACKGROUND

The Entamoeba histolytica EhrabB gene encodes for a Rab GTPase involved in phagocytosis. It is located at a virulence locus where the Ehcp112 gene is in the complementary strand at 332 bp of EhrabB start codon, suggesting a finely regulated transcription of both genes. However, the transcription regulation in this parasite is poorly understood.

RESULTS

To initiate the knowledge of EhrabB gene expression regulation, here we studied the structural characteristics of its gene promoter and its control transcription elements. In silico searches of the EhrabB 5'-flanking region revealed that it contains a motif similar to the upstream regulatory element 1 (URE1) of the E. histolytica hgl5 gene. It also has sequences with homology to C/EBP and GATA1 binding sites, and heat shock elements (HSE). Primer extension experiments revealed that EhrabB has at least four transcription initiation sites. The elements at the 5'-flanking region that drive EhrabB gene expression were detected and characterized using transitory transfected trophozoites with a plasmid carrying the CAT reporter gene. EhrabB transcription is negatively regulated by a sequence located between positions -491 to -428 with respect to the first transcription initiation site. We also showed that the URE1-like motif activates EhrabB transcription. In addition, heat shock activated the EhrabB promoter in episomal constructs and lead to an increase in de novo EhrabB transcription.

CONCLUSION

The data suggest that EhrabB transcription is controlled negatively by an unidentified sequence, but it is activated by an URE1-like motif. Our analyses also revealed the presence of activator HSE that function under stress.

A phagocytosis mutant of Entamoeba histolytica is less virulent due to deficient proteinase expression and release

Cysteine proteinases are key virulence factors of Entamoeba histolytica that are released during the process of invasion. We used a chemical mutant of E. histolytica strain HM-1:IMSS, clone L6, which is deficient in virulence, phagocytosis, and cysteine proteinase activity to help define the mechanisms of cysteine proteinase release. All cysteine proteinase genes of wild type HM-1 were present in the L6 mutant genome, but three of the major expressed proteinases, ehcp1, ehcp2, and ehcp5 were both transcribed, translated, and released at lower levels in L6. We hypothesized that a central protein such as the calcium binding protein 1, EhCaBP1, which is required for both phagocytosis and exocytosis might be deficient in this mutant. We found that both mRNA and proteinase levels of EhCaBP1 were decreased in L6. These findings provide an important link between phagocytosis, passive release of multiple cysteine proteinases, and attenuated virulence of this E. histolytica mutant.

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.