AQPexpression on intestinal epithelial cells, relation to intestinal hormone and cytekine.

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Vasoactive intestinal polypeptide (VIP) plays an important role in water transport in the intestine. Several specialized channels termed aquaporins (AQPs) facilitate water transport in the gastrointestinal tract. AQP3 localizes to epithelial cells in the human small intestine and colon. However, the regulatory mechanisms underlying the functions of AQP3 remain unclear. To characterize the regulation of AQP3 expression by VIP, we studied mRNA expression, protein expression and DNA binding activity in a human colonic epithelial cell line HT-29. Human colonic epithelial cell, HT-29 was incubated with VIP (10^<-12> to 10^<-7> M). The cells were treated with the protein kinase-A (PK-A) inhibitors (H-89, H-9) or the Cl channel blockers (DPC, NPPB). The expression of AQP3 mRNA and protein was determined by Northern blot and Western blot, respectively. The DNA binding activities of cyclic-AMP response element (CRE/ATF) in the nuclear extract were determined by electrophoretic mobility shift assay (EMSA). AQP3 mRNA was upregulated at a concentration of 10^<-10> M VIP. The expression of AQP3 protein was enhanced at 3 hr after addition of VIP. The protein kinase-A (PK-A) inhibitohs (H-89, H-9) inhibited the expression of AQP3 mRNA enhanced by VIP and cAMP. The gel shift assay of CRE/ATF in HT-29 cells revealed a single band. These results indicate that VIP up-regulated the expression of AQP3 mRNA and protein, and a cAMP dependent pathway mediated this effect in a human colonic epithelial cell line HT-29.