title: Most F508del-CFTR is targeted to degradation at an early folding checkpoint and independently of calnexin.
abstract: Biosynthesis and folding of multidomain transmembrane proteins is a complex process. Structural fidelity is monitored by endoplasmic reticulum (ER) quality control involving the molecular chaperone calnexin. Retained misfolded proteins undergo ER-associated degradation (ERAD) through the ubiquitin-proteasome pathway. Our data show that the major degradation pathway of the cystic fibrosis transmembrane conductance regulator (CFTR) with F508del (the most frequent mutation found in patients with the genetic disease cystic fibrosis) from the ER is independent of calnexin. Moreover, our results demonstrate that inhibition of mannose-processing enzymes, unlike most substrate glycoproteins, does not stabilize F508del-CFTR, although wild-type (wt) CFTR is drastically stabilized under the same conditions. Together, our data support a novel model by which wt and F508del-CFTR undergo ERAD from two distinct checkpoints, the mutant being disposed of independently of N-glycosidic residues and calnexin, probably by the Hsc70/Hsp70 machinery, and wt CFTR undergoing glycan-mediated ERAD.
authors.affiliation: Department of Chemistry and Biochemistry, Faculty of Sciences, University of Lisboa, 1749-016 Lisboa, Portugal.
authors.forename: Carlos M
authors.initials: CM
authors.lastname: Farinha
authors.forename: Margarida D
authors.initials: MD
authors.lastname: Amaral
mesh_terms: D017485:1-Deoxynojirimycin / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D037281:Calnexin / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D005959:Glucosidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D007212:Indolizines / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D034622:RNA Interference; D054836:Indolizidines
chemical_list: D017485:1-Deoxynojirimycin; D037281:Calnexin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004791:Enzyme Inhibitors; D005959:Glucosidases; D007212:Indolizines; D008565:Membrane Proteins; D011134:Polysaccharides; C505032:CFTR protein, human; C486654:EDEM1 protein, human; C037806:castanospermine; D054836:Indolizidines