The epithelial anion channel CFTR interacts with multiple PDZ domain–containing proteins. Heterologous expression studies have demonstrated that the Na+/H+ 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 Nherf1, Nherf2, and Pdzk1 loss of function. We found that Nherf1 ablation strongly reduced basal as well as forskolin-stimulated (FSK-stimulated) HCO3– secretory rates and blocked β2-adrenergic receptor (β2-AR) stimulation. Conversely, Nherf2–/– 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 Nherf2–/– mice. Pdzk1 ablation reduced basal, but not FSK-stimulated, HCO3– secretion. In addition, laser microdissection and quantitative PCR revealed that the β2-AR and the type 2 LPA receptor were expressed together with CFTR in duodenal crypts and that colocalization of the β2-AR and CFTR was reduced in the Nherf1–/– mice. These data suggest that the NHERF proteins differentially modulate duodenal HCO3– secretion: while NHERF1 is an obligatory linker for β2-AR stimulation of CFTR, NHERF2 confers inhibitory signals by coupling the LPA receptor to CFTR.
Anurag Kumar Singh, Brigitte Riederer, Anja Krabbenhöft, Brigitte Rausch, Janina Bonhagen, Ulrich Lehmann, Hugo R. de Jonge, Mark Donowitz, Chris Yun, Edward J. Weinman, Olivier Kocher, Boris M. Hogema, Ursula Seidler
Basal and FSK-stimulated HCO3– secretion in