The protozoan parasite Entamoeba histolytica is the etiological agent of human amebiasis. Trophozoites colonize the colonic mucus layer and may invade the epithelium subsequent to overcoming the mucus barrier. MUC2 is the major gel-forming mucin secreted by goblet cells in the colon and serves to maintain epithelial barrier function as well as acting as a major host defense against invading pathogens. The polymerization of MUC2 monomers via the N- and C- terminal cysteine rich D-domains is essential for mucus gel formation and confers protection to the underlying mucosa. Amoebae secrete cysteine proteinases, glycosidases and an unidentified mucus secretagogue, which may play a role in overcoming the protective mucus barrier. We hypothesize that E. histolytica cysteine proteinases as well as glycosidases are involved in mucus degradation and weakening of the mucus barrier by disrupting mucin polymerization. Amoebae secreted cysteine proteinases were shown to degrade the cysteine rich regions of MUC2 involved in polymerization and abrogate its protective function. More importantly, the major E. histolytica surface proteinase, cysteine proteinase 5 (EhCP5) was shown to specifically degrade [35S]cysteine labeled colonic mucin as effectively as secreted components. Moreover, trophozoites genetically engineered to express low levels of CP activity were incapable of traversing a mucus barrier and destroying the underlying epithelium, indicating a strong dependence between amebic invasiveness and cysteine protease activity. In addition, we have demonstrated that EhCPs specifically target the MUC2 C-terminus resulting in destabilization of the mucin polymeric network. Parasite glycosidase activity was also shown to contribute to mucin oligosaccharide degradation. Taken together, these results indicate that E. histolytica can substantially weaken the colonic mucus barrier via proteolytic degradation and glycosidase activity to compromise the gel and
Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.85940 |
Date | January 2005 |
Creators | Moncada, Darcy Marie |
Publisher | McGill University |
Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
Language | English |
Detected Language | English |
Type | Electronic Thesis or Dissertation |
Format | application/pdf |
Coverage | Doctor of Philosophy (Institute of Parasitology.) |
Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
Relation | alephsysno: 002268350, proquestno: AAINR21677, Theses scanned by UMI/ProQuest. |
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