The enteric protozoan parasite Entamoeba histolytica is the etiologic agent of the disease amebiasis which is characterized by colitis or hepatic lesions. Amebae colonize the colon by binding to mucous glycoproteins (mucins). Secretory mucins provide the gel nature to mucus and are a vital component of epithelial barrier function. Mucins prevent contact-dependent cytolysis of colonic cells by E. histolytica. To possibly circumvent this barrier, the parasite secretes a potent yet unidentified mucin secretagogue, which could deplete the stored mucin pool and render the mucous layer less protective. The objective of this study was to investigate the molecular mechanisms by which E. histolytica modulates colonic mucin exocytosis. We showed that E. histolytica converts exogenous arachidonic acid to prostaglandin E2 (PGE2), a known mucin secretagogue and potential mechanism by which the parasite evokes mucin secretion. Conversion was via a novel cyclooxygenase-like activity and was inhibitable with the known cyclooxygenase inhibitor aspirin. To study E. histolytica-mucin interactions, we developed an in vitro model of LS174T human colonic epithelial cells that secrete mucin constitutively and in response to mucin agonists. Highly purified mucins isolated from LS174T cells markedly inhibited amebic adherence to target cells and the mucous barrier protected the LS174T monolayers from amebic cytolysis. We have identified that Gal and GalNAc residues (O-linked sugars) of mucins are the protective moiety as O- but not N-linked glycosylation inhibitors decreased their protective effect. To understand how mucins are regulated during intestinal amebiasis and in the inflamed gut, we determined that PGE2 binds the EP4 receptor on LS174T cells and in rat colon to stimulate cyclic adenosine monophosphate-dependent mucin exocytosis. Taken together, these studies delineate how E. histolytica modulates host responses during infection to allow the parasite to survive and persist in th
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36752 |
| Date | January 2000 |
| Creators | Belley, Adam. |
| Contributors | Chadee, Kris (advisor) |
| 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: 001782158, proquestno: NQ69853, Theses scanned by UMI/ProQuest. |
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