Downregulated in adenoma and putative anion transporter are regulated by CFTR in cultured pancreatic duct cells

The mechanism of the pancreatic ductal HCO3- secretion defect in cystic fibrosis (CF) is not well defined. However, a lack of apical Cl-/HCO3- exchange may exist in CF. To test this hypothesis, we examined the expression of Cl-/HCO3- exchangers in cultured pancreatic duct epithelial cells with physiological features prototypical of CF [CFPAC-1 cells lacking a functional CF transmembrane conductance regulator (CFTR)] or normal duct cells (CFPAC-1 cells transfected with functional wild-type CFTR, CFPAC-WT). Cl-/HCO3- exchange activity, assayed with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein in cells grown on coverslips, increased about twofold in cells transfected with functional CFTR. This correlated with increased apical Cl-36 influx in cells expressing functional CFTR and grown on permeable support. Northern hybridizations indicated the induction of downregulated in adenoma (DRA) in cells expressing functional CFTR. The expression of putative anion transporter PAT1 also increased significantly in cells expressing functional CFTR. DRA was detected at high levels in native mouse pancreas by Northern hybridization and localized to the apical domain of the duct cells by immunohistochemical studies. In conclusion, CFTR upregulates DRA and PAT1 expression in cultured pancreatic duct cells. We propose that the pancreatic HCO3- secretion defect in CF patients is partly due to the downregulation of apical Cl-/ HCO3- exchange activity mediated by DRA (and possibly PAT1).