Differential roles of NHERF1, NHERF2, and PDZK1 in regulating CFTR-mediated intestinal anion secretion in mice

The epithelial anion channel CFTR interacts with multiple PDZ domain-containing proteins. Heterologous expression studies have demonstrated that the Na+/1H(+) exchanger regulatory factors, NHERF1, NHERF2, and PDZK1 (NHERF3), modulate CFTR membrane retention, conductivity, and interactions with other transporters. To study their biological roles in vivo, we investigated CFTR-dependent duodenal HCO3- secretion in mouse models of Nberf1, Nberf2, and Pdzk1 loss of function. We found that Nberf1 ablation strongly reduced basal as well as forskolin-stimulated (FSK-stimulated) HCO3- secretory rates and blocked beta(2)-adrenergic receptor (beta(2)-AR) stimulation. Conversely, Nberf2(-/-) mice displayed augmented FSK-stimulated HCO3- secretion. Furthermore, although lysophosphatidic acid (LPA) inhibited FSK-stimulated HCO3- secretion in WT mice, this effect was lost in Nberf2(-/-) mice. Pdzk1 ablation reduced basal, but not FSK-stimulated, HCO3- secretion. In addition, laser microdissection and quantitative PCR revealed that the beta(2)-AR and the type 2 LPA receptor were expressed together with CFTR in duodenal crypts and that colocalization of the beta(2)-AR and CFTR was reduced in the Nberf1(-/-) mice. These data suggest that the NHERF proteins differentially modulate duodenal HCO3- secretion: while NHERF1 is an obligatory linker for beta(2)-AR stimulation of CFTR, NHERF2 confers inhibitory signals by coupling the LPA receptor to CFTR.