Unraveling the mechanism on how Entamoeba histolytica evokes MUC2 exocytosis (152.3)

Abstract

MUC2 is the major secreted gel‐forming mucin produced by goblet cells that form the protective mucus blanket covering the colonic epithelium. This mucus barrier confers the first line of innate host defence against invasion by the protozoan parasite Entamoeba histolytica (Eh). During Eh infection, a subset of individuals develop infectious colitis when the parasite degrades and/or deplete mucin stores. In this study we quantified the exocytosis SNARE complex that regulated mucin secretion in vitro in response to Eh using human colonic LS174T goblet cells. Unlike MUC2, SNARE components were not transcriptionally regulated or specifically degraded in response to live Eh. Rather, mucin exocytosis occurred through a protein kinase C and calcium dependent manner. Furthermore, we have characterized the Eh surface virulent factor, cysteine protease 5, as the predominant component that mediated mucin secretion. Interestingly, only viable Eh but not heat‐killed and/or glutaraldehyde fixed Eh evoked mucin exocytosis upon contact with colonic cells. These studies were confirmed using live cell confocal microscopy imaging with fluorescent SNAREs and Eh. Predictably, shRNA silencing of a putative SNARE, SNAP23, markedly decreased mucin exocytosis and rendered the colonic monolayer susceptible to Eh degradation. This work sheds light into the pathogenesis of Eh and the regulatory mechanisms of the host which act to subvert infection.Grant Funding Source: Supported by CIHR and NSERC CREATE HPI