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Durrant C, Moore SE Biochem J. 2002 Jul 1;365(Pt 1):239-47
Perturbation of free oligosaccharide trafficking in
endoplasmic reticulum glucosidase I-deficient and
castanospermine - treated cells.
Unité de Glycobiologie et Signalisation Cellulaire, U504,
Bâtiment INSERM, 16 avenue Paul Vaillant-Couturier, 94807
Villejuif Cedex, France.
Free oligosaccharides (FOS) are generated both in the
endoplasmic reticulum (ER) and in the cytosol during
glycoprotein biosynthesis. ER lumenal FOS possessing the
di-N-acetylchitobiose moiety at their reducing termini (FOSGN2)
are exported into the cytosol where they, along with their
cytosolically generated counterparts possessing a single
N-acetylglucosamine residue at their reducing termini (FOSGN1),
are trimmed in order to be imported into lysosomes for final
degradation. Both the ER and lysosomal FOS transport processes
are unable to translocate triglucosylated FOS across membranes.
In the present study, we have examined FOS trafficking in HepG2
cells treated with the glucosidase inhibitor castanospermine. We
have shown that triglucosylated FOSGN2 generated in the ER are
transported to the Golgi apparatus where they are deglucosylated
by endomannosidase and acquire complex, sialic acid-containing
structures before being secreted into the extracellular space by
a Brefeldin A-sensitive pathway. FOSGN2 are also secreted from
glucosidase I-deficient Lec23 cells and from the
castanospermine-treated parental Chinese-hamster ovary cell
line. Despite the secretion of FOSGN2 from Lec23 cells, we noted
a transient intracellular accumulation (60 nmol/g cells) of
triglucosylated FOSGN1 in these cells. Finally, in glucosidase
I-compromised cells, FOS trafficking was severely perturbed
leading to both the secretion of FOSGN2 into the extracellular
space and a growth-dependent pile up of triglucosylated FOSGN1
in the cytosol. The possibility that these abnormalities
contributed to the severe and rapidly progressive pathology in a
patient with congenital disorders of glycosylation type IIb
(glucosidase I deficiency) is discussed.
PMID: 11942856 |
