title: Non-conventional trafficking of the cystic fibrosis transmembrane conductance regulator through the early secretory pathway.
abstract: The mechanism(s) of cystic fibrosis transmembrane conductance regulator (CFTR) trafficking from the endoplasmic reticulum (ER) through the Golgi apparatus, the step impaired in individuals afflicted with the prevalent CFTR-DeltaF508 mutation leading to cystic fibrosis, is largely unknown. Recent morphological observations suggested that CFTR is largely absent from the Golgi in situ (Bannykh, S. I., Bannykh, G. I., Fish, K. N., Moyer, B. D., Riordan, J. R., and Balch, W. E. (2000) Traffic 1, 852-870), raising the possibility of a novel trafficking pathway through the early secretory pathway. We now report that export of CFTR from the ER is regulated by the conventional coat protein complex II (COPII) in all cell types tested. Remarkably, in a cell type-specific manner, processing of CFTR from the core-glycosylated (band B) ER form to the complex-glycosylated (band C) isoform followed a non-conventional pathway that was insensitive to dominant negative Arf1, Rab1a/Rab2 GTPases, or the SNAp REceptor (SNARE) component syntaxin 5, all of which block the conventional trafficking pathway from the ER to the Golgi. Moreover, CFTR transport through the non-conventional pathway was potently blocked by overexpression of the late endosomal target-SNARE syntaxin 13, suggesting that recycling through a late Golgi/endosomal system was a prerequisite for CFTR maturation. We conclude that CFTR transport in the early secretory pathway can involve a novel pathway between the ER and late Golgi/endosomal compartments that may influence developmental expression of CFTR on the cell surface in polarized epithelial cells.
authors.affiliation: Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Jin-San
authors.initials: JS
authors.lastname: Yoo
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Moyer
authors.forename: Sergei
authors.initials: S
authors.lastname: Bannykh
authors.forename: Hyeon-Mi
authors.initials: HM
authors.lastname: Yoo
authors.forename: John R
authors.initials: JR
authors.lastname: Riordan
authors.forename: William E
authors.initials: WE
authors.lastname: Balch
mesh_terms: D020823:ADP-Ribosylation Factor 1 / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D009154:Mutation; D021381:Protein Transport; D050765:Qa-SNARE Proteins; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D020761:rab1 GTP-Binding Proteins / Q000378:metabolism
chemical_list: C505032:CFTR protein, human; D008164:Luminescent Proteins; D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D049452:Green Fluorescent Proteins; D020823:ADP-Ribosylation Factor 1; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae; D020761:rab1 GTP-Binding Proteins