Protein Sumoylation Is Crucial for Phagocytosis in Entamoeba histolytica Trophozoites.

Posttranslational modifications provide Entamoeba histolytica proteins the timing and signaling to intervene during different processes, such as phagocytosis. However, SUMOylation has not been studied in E. histolytica yet. Here, we characterized the E. histolytica SUMO gene, its product (EhSUMO), and the relevance of SUMOylation in phagocytosis. Our results indicated that EhSUMO has an extended N-terminus that differentiates SUMO from ubiquitin. It also presents the GG residues at the C-terminus and the ΨKXE/D binding motif, both involved in target protein contact. Additionally, the E. histolytica genome possesses the enzymes belonging to the SUMOylation-deSUMOylation machinery. Confocal microscopy assays disclosed a remarkable EhSUMO membrane activity with convoluted and changing structures in trophozoites during erythrophagocytosis. SUMOylated proteins appeared in pseudopodia, phagocytic channels, and around the adhered and ingested erythrocytes. Docking analysis predicted interaction of EhSUMO with EhADH (an ALIX family protein), and immunoprecipitation and immunofluorescence assays revealed that the association increased during phagocytosis; whereas the EhVps32 (a protein of the ESCRT-III complex)-EhSUMO interaction appeared stronger since basal conditions. In EhSUMO knocked-down trophozoites, the bizarre membranous structures disappeared, and EhSUMO interaction with EhADH and EhVps32 diminished. Our results evidenced the presence of a SUMO gene in E. histolytica and the SUMOylation relevance during phagocytosis. This is supported by bioinformatics screening of many other proteins of E. histolytica involved in phagocytosis, which present putative SUMOylation sites and the ΨKXE/D binding motif.

Epithelial Cells Expressing EhADH, An Entamoeba histolytica Adhesin, Exhibit Increased Tight Junction Proteins.

In Entamoeba histolytica, the EhADH adhesin together with the EhCP112 cysteine protease, form a 124 kDa complex named EhCPADH. This complex participates in trophozoite adherence, phagocytosis and cytolysis of target cells. EhCPADH and EhCP112 are both involved on epithelium damage, by opening tight junctions (TJ) and reaching other intercellular junctions. EhADH is a scaffold protein belonging to the ALIX family that contains a Bro1 domain, expresses at plasma membrane, endosomes and cytoplasm of trophozoites, and is also secreted to the medium. Contribution of EhADH to TJ opening still remains unknown. In this paper, to elucidate the role of EhADH on epithelium injury, we followed two strategies: producing a recombinant protein (rEhADH) and transfecting the ehadh gene in MDCK cells. Results from the first strategy revealed that rEhADH reached the intercellular space of epithelial cells and co-localized with claudin-1 and occludin at TJ region; later, rEhADH was mainly internalized by clathrin-coated vesicles. In the second strategy, MDCK cells expressing EhADH (MDCK-EhADH) showed the adhesin at plasma membrane. In addition, MDCK-EHADH cells exhibited adhesive features, producing epithelial aggregation and adherence to erythrocytes, as described in trophozoites. Surprisingly, the adhesin expression produced an increase of claudin-1, occludin, ZO-1 and ZO-2 at TJ, and also the transepithelial electric resistance (TEER), which is a measure of TJ gate function. Moreover, MDCK-EhADH cells resulted more susceptible to trophozoites attack, as showed by TEER and cytopathic experiments. Overall, our results indicated that EhADH disturbed TJ from the extracellular space and also intracellularly, suggesting that EhADH affects by itself TJ proteins, and possibly synergizes the action of other parasite molecules during epithelial invasion.