The major neutral proteinase of Entamoeba histolytica.

Abstract

Although an infection with Entamoeba histolytica is most commonly asymptomatic, the potential for invasive, metastatic disease, coupled with its high prevalence, makes amoebiasis a major health problem throughout much of the world. Most amoebiasis-related mortality stems from extra-intestinal infection. In these cases, trophozoites penetrate the epithelial layer and lamina propria of the bowel mucosa, enter the bloodstream, and then disseminate to almost any organ or tissue, most commonly the liver.The mechanisms that allow tissue penetration are not well understood. Ultrastructural and histopathological studies (reviewed in reference 1) have shown that, during invasion of the bowel wall, trophozoites are seen at the margin of ulcerative lesions adjacent to healthy tissue. Degeneration of epithelial cells adjacent to invading trophozoites and dissolution of the basement membrane of the mucosa have been observed (2-4). These findings suggest that histolytic and proteolytic factors may be elaborated to facilitate mucosal damage and invasion.Two general types of histolytic factors have been proposed: cytotoxic factors which may directly damage cells, such as a secreted "amoebapore" ion channel (5, 6) and proteolytic enzymes, which may attack both cells and extracellular matrix.The virulence ~ of axenically cultured E. histolytica strains has been correlated with the presence of proteolytic enzymes found on the amoeba surface, in secretions, or in extracts of whole trophozoites (9-14). Unfortunately, as none of these proteinases has been purified to homogeneity, important questions remain as to how many are present and how they may contribute to the pathogenesis of amoebiasis.To determine what role secreted proteinases may play in tissue invasion, we assayed the degradation of extracellular matrix by live trophozoites and their secretory products, using an in vitro model of extracellular matrix successfully used to study other invasive parasites (15-18). These studies allowed us to For axenic amoebae in culture, "virulence" is defined in terms of ability to induce lesions in animals (7) or cytopathic effect on cell monolayers (8).

Cloning of a virulence factor of Entamoeba histolytica. Pathogenic strains possess a unique cysteine proteinase gene.

“…Factors associated with the virulence of E. histolytica include surface lectins (1 1, 12), cytolytic ion channel-forming proteins (13)(14)(15), phospholipases ( 11 ), and proteinases (10, [16][17][18]. The major proteinase of E. histolytica is a cysteine proteinase biochemically similar to cathepsin B (17)(18)(19)(20).…”

“…The major proteinase of E. histolytica is a cysteine proteinase biochemically similar to cathepsin B (17)(18)(19)(20). Ex-perimental evidence supporting the role of this cysteine proteinase in the pathogenesis of amebiasis includes its ability to degrade fibronectin, collagen, and basement membrane matrix and to activate the third component of complement (17)(18)(19)21).…”

“…The major proteinase of E. histolytica is a cysteine proteinase biochemically similar to cathepsin B (17)(18)(19)(20). Ex-perimental evidence supporting the role of this cysteine proteinase in the pathogenesis of amebiasis includes its ability to degrade fibronectin, collagen, and basement membrane matrix and to activate the third component of complement (17)(18)(19)21). Purified proteinase reproduces the cytopathic effect of pathogenic amebae (17)(18)(19)(20), and a specific irreversible inhibitor ofthe proteinase prevents destruction of cell monolayers by live axenic amebae (22).…”

Mechanisms of Hepatocellular Dysfunction and Regeneration: Enzyme Inhibition by Nitroimidazole and Human Liver Regeneration

“…Author proposed a comparative enzyme database of amoeba and hepatocellular cells in culture (see Table 1 and Figure 1). Of specific mention, cysteine proteinase enzymes are secreted in large quantities by the parasite during immune response and can cleave extracellular matrix proteins, which might facilitate amoebic invasion [Scholze et al 1988, Keene 1986. Mainly carbohydrate metabolizing, energy metabolizing enzymes and lyssomal enzymes are abundant and participate in amoebic -host liver cell interaction as shown in Figures 2,3a,3b and 3c.…”

Purification and Characterization of an Extracellular Serine Proteinase from Acanthamoeba castellanii

“…Eventually, the parasite invades the corneal stroma, resulting in necrosis, edema, disruption of the stromal lamellae, and an intense polymorphonuclear in ammatory response (7). These considerable damages are known to induced by cytopathogenic substances, such as oxygen radicals and several different enzymes, released by Acanthamoeba trophozoites (8)(9)(10)(11).…”