Nedd4–2 does not regulate wt-CFTR in human airway epithelial cells
The cystic fibrosis transmembrane conductance regulator (CFTR), a Cl− channel in airway epithelial cells, plays an important role in maintaining the volume of the airway surface liquid and therefore mucociliary clearance of respiratory pathogens. A recent study has shown that the E3 ubiquitin ligase Neural precursor cells expressed developmentally downregulated (Nedd4–2) ubiquitinates ΔF508-CFTR in pancreatic epithelial cells and that siRNA-mediated silencing of Nedd4–2 increases plasma membrane ΔF508-CFTR. Because the role of Nedd4–2 in regulating wild-type (wt)-CFTR in airway epithelial cells is unknown, studies were conducted to test the hypothesis that Nedd4–2 also ubiquitinates wt-CFTR and regulates its plasma membrane abundance. We found that Nedd4–2 did not affect wt-CFTR Cl− currents in Xenopus oocytes. Likewise, overexpression of Nedd4–2 in human airway epithelial cells did not alter the amount of ubiquitinated wt-CFTR. siRNA knockdown of Nedd4–2 in human airway epithelial cells had no effect on ubiquitination or apical plasma membrane abundance of wt-CFTR. Thus Nedd4–2 does not ubiquitinate and thereby regulate wt-CFTR in human airway epithelial cells.