INCREASING EXPRESSION OF THE NORMAL HUMAN CFTR CDNA IN CYSTIC-FIBROSIS EPITHELIAL-CELLS RESULTS IN A PROGRESSIVE INCREASE IN THE LEVEL OF CFTR PROTEIN EXPRESSION, BUT A LIMIT ON THE LEVEL OF CAMP-STIMULATED CHLORIDE SECRETION

Cystic fibrosis (CF) results from mutations of the CF transmembrane co nductance regulator (CFTR) gene and the consequent defective regulatio n of cAMP-stimulated Cl- permeability across epithelial cell apical me mbranes. Given that in vitro transfer of normal CFTR cDNA corrects thi s defect and that recombinant adenovirus (Ad) vectors can transfer the normal human CFTR cDNA in vivo, Ad vectors have significant potential in the development of effective strategies for CF gene therapy. One c oncern is whether CFTR overexpression achievable with Ad vectors may h ave untoward effects on cAMP-stimulated Cl- efflux. To address this, t he CF pancreatic epithelial cell line CFPAC-1 was infected with increa sing doses of AdCFTR, a recombinant Ad containing the normal CFTR cDNA , and analyzed for CFTR mRNA and protein levels and CFTR function. As the AdCFTR dose increased [multiplicity of infection (mail 0-1,000], C FTR mRNA and protein levels increased. However, while CFTR function me asured by cAMP-stimulated Cl-36(-) efflux was observed with low doses of the vector (moi 20), there was no further increase in CFTR function with increasing doses of AdCFTR (moi from 20 to 1,000). These data su ggest that after AdCFTR-mediated gene transfer, epithelial cells limit the level of cAMP-stimulated Cl- secretion despite increasing levels of CFTR protein.