INTERFERON-GAMMA MODULATES CAMP-INDUCED MUCIN EXOCYTOSIS WITHOUT AFFECTING MUCIN GENE-EXPRESSION IN A HUMAN COLONIC GOBLET CELL-LINE

The regulation of intestinal mucin secretion by cytokines, soluble fac tors released by mucosal activated immune cells, is so far unknown. Th e aim of the present study was (1) to investigate the regulatory effec ts of interferon-gamma on baseline and stimulated mucin secretion elic ited by an increase in intracellular cAMP, either a short-ter-m increa se (induced by vasoactive intestinal peptide or by forskolin) or a lon g-term increase (cholera toxin-induced), and (2) to attempt to delinea te the site of action of interferon-gamma. The in vitro model used was the human colonic goblet cell line Cl.16E, which has already been sho wn to respond to physiological secretagogues in terms of mucin secreti on. We examined the effects of interferon-gamma 1) on mucin exocytosis , measured as release of [H-3]glucosamine-labeled macromolecules trapp ed at the stacking/running gel interface of polyacrylamide gels, and 2 ) on mucin biosynthesis, examined at the RNA level using a cDNA probe directed to the MUC2 mucin gene. We demonstrated that, while interfero n-gamma did not alter baseline Cl.16E mucin secretion and MUC2 gene ex pression, it strongly inhibited the protein kinase A-dependent secreto ry response to VIP, forskolin, or cholera toxin. However, interferon-g amma had no effect on the protein kinase A-dependent MUC2 over-express ion induced by cholera toxin. We thus concluded that the target for in terferon-gamma inhibition of cAMP-stimulated C1.16E mucin secretion is distal to protein kinase A and might be a component of the exocytotic machinery. Together, our results establish interferon-gamma as a phar macologically powerful tool to specifically inhibit stimulated secreto ry processes without affecting baseline secretion.