Overexpression of cysteine proteinase 2 in Entamoeba histolytica or Entamoeba dispar increases amoeba-induced monolayer destruction in vitro but doesnot augment amoebic liver abscess formation in gerbils

To study the role of cysteine proteinases in the pathogenicity of Entamoeba histolytica, we have attempted to overexpress the three main cysteine prot einases (EhCP1, EhCP2, EhCP5) of this parasite in trophozoites of E. histol ytica as well as in non-pathogenic Entamoeba dispar by episomal transfectio n. Although each of the corresponding coding sequences were cloned in ident ical expression plasmids, we were unable to overexpress EhCP1 and EhCP5, re spectively, but could substantially induce expression of EhCP2 in both amoe ba species by sevenfold, leading to a threefold increase in total cysteine proteinase activity. Overexpression of EhCP2 did not influence expression o f other cysteine proteinases and could be attributed to an increase of a si ngle 35 kDa activity band in substrate gel electrophoresis. In contrast to previous findings, which indicated that amoeba cysteine proteinases are inv olved in erythrophagocytosis and liver abscess formation, cells overexpress ing EhCP2 showed no difference in erythrophagocytosis or liver abscess form ation compared with respective controls. However, overexpression of EhCP2 i n both amoeba species resulted in a marked increase of in vitro monolayer d estruction.