Background & aims: Mucins form an integral part of innate host defenses against intestinal pathogens and irritants. However, the mechanisms whereby mucin secretion is regulated during inflammation are poorly understood. Because prostaglandin E(2) (PGE(2)) is prominent during intestinal inflammation, we investigated its receptor-signaling pathway coupled to mucin exocytosis in the colonic epithelial cell line LS174T and rat colon.
Methods: Reverse-transcription polymerase chain reaction (RT-PCR) and [(3)H]PGE(2) binding assays were used to identify the PGE(2) receptors (EP). Intracellular cyclic adenosine monophosphate ([cAMP](i)) was quantified by enzyme immunoassay. Mucins were metabolically labeled with [(3)H]glucosamine, and mucin secretion was quantified by Sepharose 4B column chromatography, immunoblot analysis, and cesium chloride density gradient centrifugation.
Results: RT-PCR and DNA sequence analysis identified EP(2), EP(3), and EP(4) receptors. Mucin secretion and [cAMP](i) production by LS174T cells were stimulated dose-dependently by PGE(2), the EP(4)-receptor agonist 1-OH-PGE(1), and the EP(3)/EP(4) agonist M&B28767 and were inhibited with the adenylate cyclase inhibitor SQ22536. The EP(1), EP(2), and EP(3)/EP(1)-receptor agonists iloprost, butaprost, and sulprostone, respectively, had no effect. Similar results were obtained in rat colonic loop studies confirming that the EP(4) receptor is linked to mucin exocytosis in vivo. [(3)H]PGE(2) binding to cell membranes identified a high-affinity binding site that was competitively inhibited by M&B28767 (EP(3)/EP(4)) > 1-OH-PGE(1) (EP(4)) > sulprostone (EP(3)/EP(1)) > butaprost (EP(2)).
Conclusions: PGE(2) coupling to the EP(4) receptor stimulates [cAMP](i)-dependent mucin exocytosis.