Interaction of cholera toxin with cloned human goblet cells in monolayer culture

Abstract

Exposure of the intestinal mucosa to Vibrio cholerae enterotoxin (CT) results in mucus secretion from intestinal goblet cells. On the other hand, there is evidence that elevation of intracellular adenosine 3',5'-cyclic monophosphate levels is not sufficient to induce rapid mucin secretion. To determine whether CT has direct effects on human goblet cells and whether CT alone can elicit rapid exocytosis of apical mucin granules, purified CT was applied to monolayer cultures of well-differentiated HT-29-18 N2 cells, a goblet cell subclone derived from the human colon carcinoma line HT-29. CT bound with high affinity (dissociation constant = 10.5 +/- 1.9 nM) to receptors on these cells (approximately 60,000/apical membrane). Binding of radiolabeled CT was inhibited by excess CT or B subunit but not by A subunit. Preincubation of goblet cells with CT blocked the subsequent CT-specific ribosylation of a 45-kDa protein in membrane fractions of the cells and increased the activity of adenylate cyclase by 2- and 10-fold after 1 and 20 h, respectively. Light micrographs revealed that goblet cells incubated with CT, like control cells, contained abundant apical mucin granules. In contrast, goblet cells incubated with Ca2+ inophore A23187 and phorbol ester were rapidly depleted of mucin granules. Thus CT has direct physiological effects on HT-29 goblet cells, but these do not lead to rapid mucin secretion. These results raise the possibility that CT may accelerate mucin secretion in intact mucosa by an indirect mechanism perhaps mediated by mucosal nerves or other cell types.