Mutations in CFTR associated with mild-disease-form Cl- channels with altered pore properties.
The cystic fibrosis transmembrane conductance regulator (CFTR) is a phosphorylation-regulated Cl- channel located in the apical membrane of epithelia. Although cystic fibrosis (CF) is caused by mutations in a single gene encoding CFTR, the disease has a variable clinical phenotype. The most common mutation associated with cystic fibrosis, deletion of a phenylalanine at position 508 (frequency, 67%), is associated with severe disease. But some missense mutations, for example ones in which arginine is replaced by histidine at residue at 117 (R117H; 0.8%), tryptophan at 334 (0.4%), or proline at 347 (0.5%), are associated with milder disease. These missense mutations affect basic residues located at the external end of the second (M2) and in the sixth (M6) putative membrane-spanning sequences. Here we report that, when expressed in heterologous epithelial cells, all three mutants were correctly processed and generated cyclic AMP-regulated apical Cl- currents. Although the macroscopic current properties were normal, the amount of current was reduced. Patch-clamp analysis revealed that all three mutants had reduced single-channel conductances. In addition, R117H showed altered sensitivity to external pH and had altered single-channel kinetics. These results explain the quantitative decrease in macroscopic Cl- current, and suggest that R117, R334 and R347 contribute to the pore of the CFTR Cl- channel. Our results also suggest why R117H, R334W and R347P produce less severe clinical disease and have implications for our understanding of cystic fibrosis.
Sheppard
D N
DN
Howard Hughes Medical Institute, Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242.
Rich
D P
DP
Ostedgaard
L S
LS
Gregory
R J
RJ
Smith
A E
AE
Welsh
M J
MJ
D000818:Animals; D002460:Cell Line; D018118:Chloride Channels; D000242:Cyclic AMP / Q000502:physiology; D003550:Cystic Fibrosis / Q000235:genetics / Q000503:physiopathology*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004848:Epithelium / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D051381:Rats; D011916:Rats, Inbred F344; D013961:Thyroid Gland / Q000502:physiology; D014162:Transfection
C505032:CFTR protein, human; D018118:Chloride Channels; D007473:Ion Channels; D008565:Membrane Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000242:Cyclic AMP