Localization of cystic fibrosis transmembrane conductance regulator signaling complexes in human salivary gland striated duct cells

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-dependent protein kinase (PKA) regulated Cl− channel crucial for epithelial cell regulation of salt and water transport. Previous studies showed that ezrin, an actin binding and A-kinase anchoring protein (AKAP), facilitates association of PKA with CFTR. We used immunohistochemistry and immunogold transmission electron microscopy to localize CFTR, ezrin, and PKA type II regulatory (RII) and catalytic (C) subunits in striated duct cells of human parotid and submandibular glands. Immunohistochemistry localized the four proteins mainly to the apical membrane and apical cytoplasm of striated duct cells. In acinar cells, ezrin localized to the luminal membrane, and RII was present in secretory granules as previously described. Immunogold labeling showed that CFTR, PKA RII and C subunits were localized to the luminal membrane and associated with apical granules and vesicles of striated duct cells. Ezrin was present along the luminal membrane, on microvilli and along the junctional complexes between cells. Double labeling showed specific protein associations with apical granules and vesicles and along the luminal membrane. Ezrin, CFTR and PKA RII and C subunits are co-localized in striated duct cells, suggesting the presence of signaling complexes that serve to regulate CFTR activity.