The ΔF508 mutation results in loss of CFTR function and mature protein in native human colon

M Mall, SM Kreda, A Mengos, TJ Jensen, S Hirtz… - Gastroenterology, 2004 - Elsevier
M Mall, SM Kreda, A Mengos, TJ Jensen, S Hirtz, HH Seydewitz, J Yankaskas…
Gastroenterology, 2004Elsevier
Background & Aims: Deletion of the codon for phenylalanine at position 508 (ΔF508) is the
most frequent disease-causing mutation in the cystic fibrosis transmembrane conductance
regulator (CFTR) gene. In heterologous cells, defective processing of the ΔF508 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 ΔF508 protein in native …
Background & Aims
Deletion of the codon for phenylalanine at position 508 (ΔF508) is the most frequent disease-causing mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In heterologous cells, defective processing of the ΔF508 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 ΔF508 protein in native epithelia are limited and conflicting.
Methods
To characterize both the fate and function of ΔF508 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 ΔF508 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 ΔF508 homozygous patients with CF. By immunohistochemistry, we detected wild-type but not ΔF508 CFTR at the luminal membrane of crypt colonocytes. By sequential immunoprecipitation and immunoblotting analyses, mature CFTR protein was detected in normal but not in ΔF508 homozygous tissues.
Conclusions
Collectively, these data show that there is insufficient maturation and transport of ΔF508 CFTR from the endoplasmic reticulum to the apical membrane to support CFTR-mediated Cl secretion in the CF colon.
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