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.
Penmatsa
Himabindu
H
Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA.
Frederick
Carla A
CA
Nekkalapu
Sunitha
S
Conoley
Veronica G
VG
Zhang
Weiqiang
W
Li
Chunying
C
Kappes
John
J
Stokes
Dennis C
DC
Naren
Anjaparavanda P
AP
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