Clinical and molecular characterization of S1118F-CFTR.
BACKGROUND
Cystic fibrosis is a lethal autosomal recessive disorder usually associated with lung disease, pancreatic insufficiency and high sweat chloride levels.


METHODS
A patient admitted to Le Bonheur Children's Medical Center (LBCMC, Memphis, TN) showed symptoms of meconium ileus which required exploratory laparotomy, bowel resection and ileostomy. Genotyping showed DeltaF508/I1027T on one chromosome and S1118F on the other. Sweat testing on three different occasions gave negative and intermediate results (22.7, 24.6 mmol/L; 55.1, 58.6 mmol/L and 55.1, 58 mmol/L) and pancreatic elastase testing showed normal levels.


OBJECTIVE
To characterize S1118F-CFTR mutation at a molecular level to help understand the associated CF-phenotype.


METHODS
Molecular characterization of S1118F-CFTR mutant was studied in HEK-293 cells at 37 degrees C. Various biochemical methods such as Western blotting, real-time PCR, Pulse chase labeling and iodide efflux assay were employed.


RESULTS
S1118F-CFTR makes less than 10-15% of mature CFTR (band C) compared to WT-CFTR. The mRNA levels of S1118F-CFTR and WT-CFTR are comparable. S1118F-CFTR is functional but shows about 10-15% of WT-CFTR activity. S1118F-CFTR shows impaired maturation and CF-correctors can increase the amount of mature and functional CFTR by three- to fourfold.


CONCLUSIONS
S1118F-CFTR shows impaired maturation and an individual with S1118F-CFTR paired with DeltaF508-CFTR exhibits atypical CF symptoms with intermediate sweat chloride level and meconium ileus despite documented pancreatic sufficiency.
Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA.
Himabindu
H
Penmatsa
Carla A
CA
Frederick
Sunitha
S
Nekkalapu
Veronica G
VG
Conoley
Weiqiang
W
Zhang
Chunying
C
Li
John
J
Kappes
Dennis C
DC
Stokes
Anjaparavanda P
AP
Naren
D015153:Blotting, Western; D002478:Cells, Cultured; D002712:Chlorides / Q000032:analysis; D003550:Cystic Fibrosis / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics*; D010188:Exocrine Pancreatic Insufficiency / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D045823:Ileus / Q000235:genetics; D008297:Male; D009154:Mutation; D010641:Phenotype; D011336:Probability; D012313:RNA / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013542:Sweat / Q000737:chemistry / Q000378:metabolism
D002712:Chlorides; C093349:cystic fibrosis transmembrane conductance regulator delta F508; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012313:RNA