MR60/ERGIC-53, a mannose-specific shuttling intracellular membrane lectin

Perturbation of free oligosaccharide trafficking in endoplasmic reticulum glucosidase I-deficient and castanospermine-treated cells

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.

Ecdysone triggers the expression of Golgi genes in Drosophila imaginal discs via broad-complex

One of the most significant morphogenic events in the development of Drosophila melanogaster is the elongation of imaginal discs during puparium formation. We have shown that this macroscopic event is accompanied by the formation of Golgi stacks from small Golgi larval clusters of vesicles and tubules that are present prior to the onset of disc elongation. We have shown that the fly steroid hormone 20-hydroxyecdysone triggers both the elongation itself and the formation of Golgi stacks (V. Kondylis, S. E. Goulding, J. C. Dunne, and C. Rabouille, 2001, Mol. Biol. Cell, 12, 2308). Using mRNA in situ hybridisation, we show here that ecdysone triggers the upregulation of a subset of genes encoding Golgi-related proteins (such as dnsf1, dsec23, dsed5, and drab1) and downregulates the expression of others (such as dergic53, dbeta'COP, and drab6). We show that the transcription factor Broad-complex, itself an "early" ecdysone target, mediates this regulation. And we show that the ecdysone-independent upregulation of dnsf1 and dsnap prior to the ecdysone peak leads to a precocious formation of large Golgi stacks. The ecdysone-triggered biogenesis of Golgi stacks at the onset of imaginal disc elongation offers the exciting possibility of advancing our understanding of the relationship between gene expression and organelle biogenesis.

Gene therapy of cystic fibrosis: the glycofection approach

Many cells express surface membrane lectins that selectively bind and carry glycoconjugates into intracellular endosomes; in addition, various intracellular membrane and soluble lectins act as shuttles between different compartments. On this basis, we developed glycosylated polycations, now called glycofectins (glycosylated polylysine and polyethyleneimine). Recently, we set up a simple way to transform oligosaccharides into glycosynthons suitable to substitute proteins or polymers. Glycofectins bind plasmid DNA leading to compact glycoplexes. Glycoplexes prepared with glycofectins were found to be much more active than naked plasmid to transfer genes to various types of cells including human airway epithelial and serous cells. The gene transfer efficiency was found to depend on the nature of the sugars borne by glycofectins. It appeared that the sugar-dependent efficiency was not only related to the uptake but also to the intracellular traffic of glycoplexes.