Endocytosis of cholera toxin by human enterocytes is developmentally regulated

Abstract

Many secretory diarrheas including cholera are more prevalent and fulminant in young infants than in older children and adults. Cholera toxin (CT) elicits a cAMP-dependent chloride secretory response in intestinal epithelia, which accounts for the fundamental pathogenesis of this toxigenic diarrhea. We have previously reported that the action of this bacterial enterotoxin is excessive in immature enterocytes and under developmental regulation. In this study, we tested the hypothesis that enhanced endocytosis by immature human enterocytes may, in part, account for the excessive secretory response to CT noted in the immature intestine and that enterocyte endocytosis of CT is developmentally regulated. To test this hypothesis, we used specific inhibitors to define endocytic pathways in mature and immature cell lines. We showed that internalization of CT in adult enterocytes is less and occurs via the caveolae/raft-mediated pathway in contrast to an enhanced immature human enterocyte CT uptake that occurs via a clathrin pathway. We also present evidence that this clathrin pathway is developmentally regulated as demonstrated by its response to corticosteroids, a known maturation factor that causes a decreased CT endocytosis by this pathway.