Cysteine proteinases are hypothesized to be important virulence factors of Entamoeba histolytica, the causative agent of amebic dysentery and liver abscesses. The release of a histolytic cysteine prot Show more
Cysteine proteinases are hypothesized to be important virulence factors of Entamoeba histolytica, the causative agent of amebic dysentery and liver abscesses. The release of a histolytic cysteine proteinase from E. histolytica correlates with the pathogenicity of both axenic strains and recent clinical isolates as determined by clinical history of invasive disease, zymodeme analysis, and cytopathic effect. We now show that pathogenic isolates have a unique cysteine proteinase gene (ACP1). Two other cysteine proteinase genes (ACP2, ACP3) are 85% identical to each other and are present in both pathogenic and nonpathogenic isolates. ACP1 is only 35 and 45% identical in sequence to the two genes found in all isolates and is present on a distinct chromosome-size DNA fragment. Presence of the ACP1 gene correlates with increased proteinase expression and activity in pathogenic isolates as well as cytopathic effect on a fibroblast monolayer, an in vitro assay of virulence. Analysis of the predicted amino acid sequence of the ACP1 proteinase gene reveals homology with cysteine proteinases released by activated macrophages and invasive cancer cells, suggesting an evolutionarily conserved mechanism of tissue invasion. The observation that a histolytic cysteine proteinase gene is present only in pathogenic isolates of E. histolytica suggests that this aspect of virulence in amebiasis is genetically predetermined. Show less
Extracellular neutral cysteine proteinases are an important virulence factor of E. histolytica. Experimental evidence supporting its role in invasion includes the ability to degrade components of the Show more
Extracellular neutral cysteine proteinases are an important virulence factor of E. histolytica. Experimental evidence supporting its role in invasion includes the ability to degrade components of the extracellular matrix and activate complement by specifically cleaving C3. We had previously reported the isolation of fragments encoding cysteine proteinase genes from HM-1 (ACP1) and a nonpathogenic strain (REF291, ACP2) by PCR using consensus sequences based on conserved structural motifs of eukaryotic cysteine proteinases. Using similar techniques, we have now identified a third gene encoding a cysteine proteinase which is present in both pathogenic and nonpathogenic strains and have correlated cysteine proteinase specific-mRNA levels with enhanced proteolytic activity and cytopathic effect on a fibroblast cell monolayer, a quantitative assay of virulence. Show less