title: Intracellular turnover of cystic fibrosis transmembrane conductance regulator. Inefficient processing and rapid degradation of wild-type and mutant proteins.
abstract: Mutant (delta F508) and wild-type cystic fibrosis transmembrane conductance regulator (CFTR) were synthesized initially as an approximately 140-kDa core-glycosylated precursor, which, in the case of wild-type CFTR, was chased to an approximately 160 kDa form bearing complex oligosaccharides. Mutant CFTR disappeared from the detergent-soluble cell extract with rapid (t1/2 = 27 min) kinetics. Only approximately 25% of the initially synthesized wild-type 140-kDa CFTR precursor was detected as mature protein; the remaining approximately 75% decayed with kinetics (t1/2 = 33 min) indistinguishable from those of the mutant. Rapid degradation kinetics and inefficient processing of wild-type CFTR were also observed in the colonic carcinoma lines HT29 and T84 and in stably transfected C127 cells, which express 5-50 times lower levels of CFTR. These results suggest that inefficient processing and rapid degradation of wild-type CFTR precursor are an intrinsic property of CFTR in these diverse cell types and are not an artifact of overexpression. Degradation of wild-type and mutant 140-kDa CFTR began without significant lag following synthesis. These data suggest that wild-type and delta F508 CFTR differ in the efficiency of folding of the core-glycosylated primary translation product.
authors.affiliation: Department of Biological Sciences, Stanford University, California 94305-5020.
authors.forename: C L
authors.initials: CL
authors.lastname: Ward
authors.forename: R R
authors.initials: RR
authors.lastname: Kopito
mesh_terms: D000595:Amino Acid Sequence; D020126:Brefeldin A; D002277:Carcinoma / Q000378:metabolism; D002451:Cell Compartmentation; D003110:Colonic Neoplasms / Q000378:metabolism; D003517:Cyclopentanes / Q000494:pharmacology; D003550:Cystic Fibrosis / Q000235:genetics / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D014176:Protein Biosynthesis; D017510:Protein Folding; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: C505032:CFTR protein, human; D003517:Cyclopentanes; D008565:Membrane Proteins; D011498:Protein Precursors; D011500:Protein Synthesis Inhibitors; D011994:Recombinant Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D020126:Brefeldin A