MISSENSE MUTATION (G480C) IN THE CFTR GENE ASSOCIATED WITH PROTEIN MISLOCALIZATION BUT NORMAL CHLORIDE CHANNEL ACTIVITY

We have identified a novel CFTR missense mutation associated with a pr otein trafficking defect in mammalian cells but normal chloride channe l properties in a Xenopus oocyte assay. The mutation, a cysteine for g lycine substitution at residue 480 (G480C), was detected in a pancreat ic insufficient, African-American, cystic fibrosis (CF) patient. G480C was found on one additional CF chromosome and on none of 220 normal c hromosomes, including 160 chromosomes from normal African-American ind ividuals. Western blot analysis and immunofluorescence studies reveale d that, in 293T cells, the encoded mutant protein was not fully glycos ylated and failed to reach the plasma membrane, suggesting that the G4 80C protein was subject to defective intracellular processing. However , in Xenopus oocytes, a system in which mutant CFTR proteins are less likely to experience an intracellular processing/trafficking deficit, expression of G480C CFTR was associated with a chloride conductance th at exhibited a sensitivity to activation by forskolin and 3-isobutyl-1 -methylxanthine (IBMX) that was similar to that of wild-type CFTR. Thi s appears to be the first identification of a CFTR mutant with a singl e amino acid substitution in which the sole basis for disease is mislo calization of the protein.