A method for measuring Cl efflux from dispersed cells of airway epithelium

Efficient expression of CFTR function with adeno-associated virus vectors that carry shortened CFTR genes

Adeno-associated virus (AAV)-based vectors have been shown to be effective in transferring the cystic fibrosis gene (CFTR) into airway epithelial cells in animal models and in patients. However, the level of CFTR gene expression has been low because the vector cannot accommodate the CFTR gene together with a promoter. In this study, we described a strategy to reduce the size of the CFTR cDNA to allow the incorporation of an effective promoter with the CFTR gene into AAV vectors. We engineered and tested 20 CFTR mini-genes containing deletions that were targeted to regions that may contain nonessential sequences. Functional analyses showed that four of the shortened CFTRs (one with combined deletions) retained the function and the characteristics of a wild-type CFTR, as measured by open probability, time voltage dependence, and regulation by cAMP. By using an AAV vector with a P5 promoter, we transduced these short forms of CFTR genes into target cells and demonstrated high levels of CFTR expression. We also demonstrated that smaller AAV/CFTR vectors with a P5 promoter expressed the CFTR gene more efficiently than larger vectors or a vector in which CFTR gene was expressed from the AAV inverted terminal repeat sequence. The CFTR mini-gene with combined deletions was packaged into AAV virions more efficiently, generated higher titers of transducing virions, and more effectively transferred CFTR function into target cells. These new vectors should circumvent the limitations of AAV vector for CFTR expression. Our strategy also may be applicable to other genes, the sizes of which exceed the packaging limit of an AAV vector.

Effects of lovastatin on trafficking of cystic fibrosis transmembrane conductance regulator in human tracheal epithelium

Genetic defects in the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel, cause cystic fibrosis. Most defective forms of CFTR show improper intracellular trafficking. Because isoprenylated, small GTP-binding proteins are involved in the vesicular trafficking of other integral membrane proteins, we have investigated the role of isoprenylation in the trafficking of CFTR to the apical membranes of primary cultures of human airway epithelium and of Calu-3 cells, a human lung carcinoma cell line. CFTR function was measured as short circuit current, 125I efflux, and conductance of cell sheets with permeabilized basolateral membranes. Lovastatin, an inhibitor of isoprenyl lipid biosynthesis, markedly inhibited all measures of CFTR function. The lovastatin-induced declines in CFTR function were corrected by the simultaneous addition of mevalonate or the isoprenyl lipids geranylgeranyl and farnesyl but not cholesterol. Lovastatin reduced total cellular CFTR as assessed by immunoprecipitation. Mevalonate or isoprenyl lipids protected CFTR levels from the actions of lovastatin. Together, these results suggest a role for isoprenyl lipids, presumably through the actions of small GTP-binding proteins, in the trafficking of CFTR to the apical membrane of human airway epithelium.