The DeltaF508 mutation results in loss of CFTR function and mature protein in native human colon.
OBJECTIVE
Deletion of the codon for phenylalanine at position 508 (DeltaF508) is the most frequent disease-causing mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In heterologous cells, defective processing of the DeltaF508 protein results in endoplasmic reticulum retention, proteolytic degradation, and absence of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent plasma membrane Cl(-) conductance. However, data with respect to the processing block of DeltaF508 protein in native epithelia are limited and conflicting.


METHODS
To characterize both the fate and function of DeltaF508 protein in a native epithelium, we measured CFTR-mediated Cl(-) secretion, localization of the CFTR protein, and CFTR maturation in rectal biopsy specimens from normal individuals and DeltaF508 homozygous patients with cystic fibrosis (CF).


RESULTS
Ussing chamber studies showed that cAMP-dependent and cholinergic Cl(-) secretion was absent from rectal tissues freshly excised from DeltaF508 homozygous patients with CF. By immunohistochemistry, we detected wild-type but not DeltaF508 CFTR at the luminal membrane of crypt colonocytes. By sequential immunoprecipitation and immunoblotting analyses, mature CFTR protein was detected in normal but not in DeltaF508 homozygous tissues.


CONCLUSIONS
Collectively, these data show that there is insufficient maturation and transport of DeltaF508 CFTR from the endoplasmic reticulum to the apical membrane to support CFTR-mediated Cl(-) secretion in the CF colon.
Mall
Marcus
M
School of Medicine, University of North Carolina at Chapel Hill, NC 27599, USA.
Kreda
Silvia M
SM
Mengos
April
A
Jensen
Timothy J
TJ
Hirtz
Stephanie
S
Seydewitz
Hans H
HH
Yankaskas
James
J
Kunzelmann
Karl
K
Riordan
John R
JR
Boucher
Richard C
RC
D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D002712:Chlorides / Q000378:metabolism; D018679:Cholinergic Agonists / Q000494:pharmacology; D003106:Colon / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D003550:Cystic Fibrosis / Q000235:genetics* / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D006720:Homozygote; D006801:Humans; D007158:Immunologic Techniques; D007223:Infant; D007231:Infant, Newborn; D007413:Intestinal Mucosa / Q000378:metabolism; D008297:Male; D009154:Mutation / Q000502:physiology*; D012007:Rectum / Q000378:metabolism / Q000473:pathology; D014018:Tissue Distribution
C505032:CFTR protein, human; D002712:Chlorides; D018679:Cholinergic Agonists; C093349:cystic fibrosis transmembrane conductance regulator delta F508; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000242:Cyclic AMP