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Restoration of W1282X CFTR Activity by Enhanced Expression

Departments of Medicine, Pediatrics, and Physiology and Biophysics, the Gregory Fleming James Cystic Fibrosis Research Center; and Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama

Correspondence and requests for reprints should be addressed to Steven M. Rowe, M.D., M.S.P.H., Assistant Professor, University of Alabama at Birmingham, THT 215, 1900 University Blvd., Birmingham, AL 35294-0006. E-mail: smrowe{at}uab.edu

Cystic fibrosis results from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Premature termination codons represent a common minority of CFTR mutations, and are caused by base pair substitutions that produce abnormal stop codons in the coding sequence. Select aminoglycosides induce "translational readthrough" of premature stop codons and have been shown to restore full-length functional protein in a number of preclinical and clinical settings. We studied two well-described premature termination codons found in the distal open reading frame of CFTR, W1282X and R1162X, expressed in polarizing and nonpolarizing cells. Our findings indicate that W1282X CFTR–expressing cells demonstrate significantly greater CFTR activity when overexpressed compared with R1162X CFTR cells, even when truncated protein is the predominant form. In addition, our results show that the combination of stimulated expression and stop codon suppression produces additive effects on CFTR-mediated ion transport. These findings provide evidence that W1282X CFTR exhibits membrane localization and retained chloride channel function after enhanced expression, and suggest that patients harboring this mutation may be more susceptible to CFTR rescue.

Key Words: cystic fibrosis • cystic fibrosis transmembrane conductance regulator • premature termination codons • nonsense mutations • aminoglycosides

CLINICAL RELEVANCE Evidence that W1282X cystic fibrosis transmembrane conductance regulator (CFTR) retains chloride channel function improves our understanding of CFTR biology, and may explain why subjects harboring W1282X CFTR appear more susceptible to the strategy of premature termination codon suppression.

 

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