Non-conventional Trafficking of the Cystic Fibrosis Transmembrane Conductance Regulator through the Early Secretory Pathway*
- From the Departments of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, the§Institute for Childhood and Neglected Diseases, and‡Mayo Foundation and S. C. Johnson Medical Research Center, Mayo Clinic, Scottsdale, Arizona 85259
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-ΔF508 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 SNApREceptor (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.
Footnotes
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↵* This work was supported by an NRSA post-doctoral fellowship from the National Institutes of Health (to B. D. M.) and National Institutes of Health Grant DK 51870 (to J. R.). This is TSRI manuscript 14614-CB.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵¶ To whom correspondence should be addressed. Tel.: 858-784-2310; Fax: 858-784-9126; E-mail: webalch@scripps.edu.
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Published, JBC Papers in Press, January 17, 2002, DOI 10.1074/jbc.M110263200
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↵2 J.-S. Yoo and W. E. Balch, unpublished observations.
- Abbreviations:
- CFTR
-
cystic fibrosis transmembrane conductance regulator
- Arf
-
ADP-ribosylation factor
- BFA
-
brefeldin A
- CF
-
cystic fibrosis
- COPII
-
coat protein complex II
- COPI
-
coat protein complex I
- ER
-
endoplasmic reticulum
- VSV-G
-
vesicular stomatitis virus G protein
- Syn
-
syntaxin
- endo H
-
endoglycosidase H
- DMEM
-
Dulbecco's modified Eagle's medium
- BFA
-
brefeldin A
- VTCs
-
vesicular tubular elements
- TGN
-
trans-Golgi network
- CHO
-
Chinese hamster ovary
- SNARE
-
solubleN-ethylmaleimide-sensitive factor attachment protein receptors
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- Received October 25, 2001.
- Revision received January 15, 2002.
- The American Society for Biochemistry and Molecular Biology, Inc.
