Involvement of p21racA, phosphoinositide 3-kinase, and vacuolar ATPase in phagocytosis of bacteria and erythrocytes by Entamoeba histolytica: suggestive evidence for coincidental evolution of amebic invasiveness

Abstract

Trophozoites of Entamoeba histolytica, the protozoan parasite that causes amebic dysentery, phagocytose bacteria in the colonic lumen and erythrocytes (RBC) in host tissues. Because tissue invasion is an evolutionary dead end, it is likely that amebic pathogenicity is coincidentally selected, i.e., the same methods used to kill bacteria in the colonic lumen are used by parasites to damage host cells and cause disease. In support of this idea, the amebic lectin and pore-forming peptide are involved in binding and killing, respectively, bacteria and host epithelial cells. Here amebic phagocytosis of bacteria, RBC, and mucin-coated beads was disrupted by overexpression of E. histolytica p21 racA-V12 , a ras-family protein involved in selection of sites of actin polymerization, which had been mutated to eliminate its GTPase activity. p21 racA-V12 transformants were also defective in capping and cytokinesis, while pinocytosis of fluorescent dextrans was not affected. Wortmannin, a fungal inhibitor of phosphoinositide 3-kinase, markedly inhibited phagocytosis of bacteria, RBC, and mucin-coated beads by wild-type amebae. In contrast to p21 racA-V12 overexpression, wortmannin abolished amebic pinocytosis of dextrans but had no inhibitory effects on capping. Inhibition of amebic vacuolar acidification by bafilomycin also decreased bacterial and RBC uptake. These results, which demonstrate similarities between mechanisms of phagocytosis of bacteria and RBC by amebae and macrophages, support the idea of coincidental selection of amebic genes encoding proteins that mediate destruction of host cells.

Signalization and cytoskeleton activity through myosin IB during the early steps of phagocytosis in Entamoeba histolytica: a proteomic approach

“…A comparative bioinformatic analysis led to the identification of amoebic proteins that are involved in cytoskeleton activity, signalling, endocytosis, lytic activity and proteins present at the surface of the parasite. With this study, we confirmed previous data on proteins already shown to be involved in erythrophagocytosis in E. histolytica as PI3-K and Rac A (Ghosh and Samuelson, 1997). We identified compounds of the cytoskeleton including actin, myosin II and several actin-binding proteins.…”

Antisense inhibition of expression of cysteine proteinases does not affect Entamoeba histolytica cytopathic or haemolytic activity but inhibits phagocytosis

“…For example, for some clones isolated from HM-1:IMSS or in strain HK-9, low virulence is correlated with a low level of CP and low phagocytosis rate (Orozco et al 1988). On the other hand, arguments against such a conclusion have also been raised (Monfort et al, 1992;Gosh and Samuelson, 1997). Comparison between hrbcs phagocytosis rates of HM1-pEhAct-Neo and pSA8 transfectants clearly shows a difference that suggests some correlation between the level of CP and the phagocytosis rates.…”

Chemotaxis ofEntamoeba histolyticatowards the pro-inflammatory cytokine TNF is based on PI3K signalling, cytoskeleton reorganization and the GalactoseN-acetylgalactosamine lectin activity

“…We hypothesize that in Wm-treated cells, the PI3K signalling cascade could no longer be activated and the cell would no longer polarize in an efficient manner in order to protrude a dominant leading edge. Interestingly, Wm affects phagocytosis and endocytosis but not capping and random motility (Ghosh and Samuelson, 1997;Rivière et al, 2007). Studies to determine PI3K activation and the direct target of PI3K involved in chemotaxis are under investigation.…”