NHE-RF1 protein rescues ΔF508-CFTR function

Abstract

In cystic fibrosis (CF), the ΔF508-CFTR anterograde trafficking from the endoplasmic reticulum to the plasma membrane is inefficient. New strategies for increasing the delivery of ΔF508-CFTR to the apical membranes are thus pathophysiologically relevant targets to study for CF treatment. Recent studies have demonstrated that PDZ-containing proteins play an essential role in determining polarized plasma membrane expression of ionic transporters. In the present study we have hypothesized that the PDZ-containing protein NHE-RF1, which binds to the carboxy terminus of CFTR, rescues ΔF508-CFTR expression in the apical membrane of epithelial cells. The plasmids encoding ΔF508-CFTR and NHE-RF1 were intranuclearly injected in A549 or Madin-Darby canine kidney (MDCK) cells, and ΔF508-CFTR channel activity was functionally assayed using SPQ fluorescent probe. Cells injected with ΔF508-CFTR alone presented a low chloride channel activity, whereas its coexpression with NHE-RF1 significantly increased both the basal and forskolin-activated chloride conductances. This last effect was lost with ΔF508-CFTR deleted of its 13 last amino acids or by injection of a specific NHE-RF1 antisense oligonucleotide, but not by NHE-RF1 sense oligonucleotide. Immunocytochemical analysis performed in MDCK cells transiently transfected with ΔF508-CFTR further revealed that NHE-RF1 specifically determined the apical plasma membrane expression of ΔF508-CFTR but not that of a trafficking defective mutant potassium channel (KCNQ1). These data demonstrate that the modulation of the expression level of CFTR protein partners, like NHE-RF1, can rescue ΔF508-CFTR activity.