Cystic fibrosis transmembrane conductance regulator activation is reduced in the small intestine of Na+/H+ exchanger 3 regulatory factor 1 (NHERF-1)-but not NHERF-2-deficient mice

Binding of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel to the Na+/H+ exchanger 3 regulatory factor 1 (NHERF-1) and NHERF-2 scaffolding proteins has been shown to affect its localization and activation. We have for the first time studied the physiological role of these proteins in CFTR regulation in native tissue by determining CFTR-dependent chloride current in NHERF-1-and NHERF-2-deficient mice. The cAMP-and cGMP-activated chloride current and the basal chloride current in basolaterally permeabilized jejunum were reduced by similar to 30% in NHERF-1-deficient mice but not in NHERF-2-deficient mice. The duodenal bicarbonate secretion was affected in a similar way, whereas no significant differences in CFTR activity were observed in ileum. CFTR abundance as determined by Western blotting was unaltered in jejunal epithelial cells and brush border membranes of NHERF-1 and NHERF-2 mutant mice. However, semi-quantitative detection of CFTR by confocal microscopy showed that the level of apically localized CFTR in jejunal crypts was reduced by similar to 35% in NHERF-1-deficient and NHERF-1/ 2 double deficient mice but not in NHERF-2 null mice. Together our results indicate that NHERF-1 is required for full activation of CFTR in murine duodenal and jejunal mucosa and that NHERF-1 affects the local distribution of CFTR in or near the plasma membrane. These studies provide the first evidence in native intestinal epithelium that NHERF-1 but not NHERF-2 is involved in the formation of CFTR-containing functional complexes that serve to position CFTR in the crypt apical membrane and/ or to optimize its function as a cAMP-and cGMP-regulated anion channel.