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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS
1Pulmonary Research Unit, Faculty of Medicine, Université de Sherbrooke, Sherbrooke; and 2Department of Physiology, McGill University, Montreal, Quebec, Canada
Submitted 17 February 2005 ; accepted in final form 1 September 2005
Epithelial mucous membranes are repeatedly exposed to oxidants and xenobiotics. CFTR plays a role in glutathione transepithelial flux and in defining the hydration and viscoelasticity of protective mucus. We therefore hypothesized that CFTR expression and function may be modulated by oxidant stress. A sublethal oxidant stress (tert-butylhydroquinone, BHQ) in CFTR-expressing epithelial cells (T84) induced a significant increase in cellular glutathione that was associated with an increase in expression of the gene encoding the heavy subunit of the rate-limiting enzyme for glutathione synthesis, 
-glutamylcysteine synthetase (-GCShs). CFTR gene expression was markedly decreased according to a time course that mirrored the changes in -GCShs. Western blot analysis confirmed that the decrease in CFTR gene expression was associated with a decrease in CFTR protein. cAMP-dependent iodide efflux was also decreased by the oxidant stress. Nuclear run-on assays indicated that the oxidant stress had no effect on CFTR gene transcription, but the mRNA stability in the oxidant-stressed cells was markedly reduced. Furthermore, BHQ increased -GCShs mRNA while decreasing CFTR mRNA in Calu-3 cells, and taurine chloramine induced similar effects in T84 cells. We conclude that suppression of CFTR expression may represent an adaptive response of mucosal epithelium to an exogenous oxidant stress.
antioxidants; chloride channels; epithelial cells; cystic fibrosis; reactive oxygen species
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