Overexpression of R domain eliminates cAMP-stimulated Cl- secretion in 9/HTEo(-) cells in culture

The intracellular hydrophilic region of the cystic fibrosis transmembrane conductance regulator (CFTR), the R domain, has been postulated to be a regulator of the Cl- channel. Under basal conditions R blocks the channel, but when phosphorylated, R undergoes conformational change to open the channel. Overexpression of R in 9/HTEo(-) cells, a human tracheal epithelial cell line with adenosine 3',5'-cyclic monophosphate (cAMP)-regulated Cl- conductance due to CFTR, caused reduced basal Cl- conductance and elimination of its response to isoproterenol, but ionomycin-stimulated Cl- efflux was preserved. Cells which overexpressed R showed no downregulation of endogenous CFTR mRNA and had normal cAMP production and protein kinase A (PKA) activity, so R did not act at these levels. Although the precise mechanism by which R affects CFTR conductance is undetermined, these cell lines could be useful in separating the cell biological consequences of impaired Cl- transport from those of mutant CFTR per se.