title: Selective reentry of recycling cell surface glycoproteins to the biosynthetic pathway in human hepatocarcinoma HepG2 cells.
abstract: Return of cell surface glycoproteins to compartments of the secretory pathway has been examined in HepG2 cells comparing return to the trans-Golgi network (TGN), the trans/medial- and cis-Golgi. Transport to these sites was studied by example of the transferrin receptor (TfR) and the serine peptidase dipeptidylpeptidase IV (DPPIV) after labeling these proteins with the N-hydroxysulfosuccinimide ester of biotin on the cell surface. This experimental design allowed to distinguish between glycoproteins that return to these biosynthetic compartments from the cell surface and newly synthesized glycoproteins that pass these compartments during biosynthesis en route to the surface. Reentry to the TGN was measured in that surface glycoproteins were desialylated with neuraminidase and were monitored for resialylation during recycling. Return to the trans-Golgi was traced measuring the transfer of [3H]fucose residues to recycling surface proteins by fucosyltransferases. To study return to the cis-Golgi, surface proteins were metabolically labeled in the presence of the mannosidase I inhibitor deoxymannojirimycin (dMM). As a result surface proteins retained N-glycans of the oligomannosidic type. Return to the site of mannosidase I in the medial/cis-Golgi was measured monitoring conversion of these glycans to those of the complex type after washout of dMM. Our data demonstrate that DPPIV does return from the cell surface not only to the TGN, but also to the trans-Golgi thus linking the endocytic to the secretory pathway. In contrast, no reentry to sites of mannosidase I could be detected indicating that the early secretory pathway is not or is only at insignificant rates accessible to recycling DPPIV. In contrast to DPPIV, TfR was very efficiently sorted from endosomes to the cell surface and did not return to the TGN or to other biosynthetic compartments in detectable amounts, indicating that individual surface proteins are subject to different sorting mechanisms or sorting efficiencies during recycling.
authors.affiliation: Institut für Klinische Chemie und Biochemie, Universitätsklinikum Rudolf-Virchow, Freie Universität Berlin, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Volz
authors.forename: G
authors.initials: G
authors.lastname: Orberger
authors.forename: S
authors.initials: S
authors.lastname: Porwoll
authors.forename: H P
authors.initials: HP
authors.lastname: Hauri
authors.forename: R
authors.initials: R
authors.lastname: Tauber
mesh_terms: D000818:Animals; D001692:Biological Transport; D001710:Biotin / Q000031:analogs & derivatives / Q000494:pharmacology; D002240:Carbohydrate Sequence; D002277:Carcinoma; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism*; D018819:Dipeptidyl Peptidase 4 / Q000378:metabolism; D005643:Fucose / Q000378:metabolism; D005647:Fucosyltransferases / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008113:Liver Neoplasms; D008297:Male; D008361:Mannosidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000378:metabolism*; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid; D051381:Rats; D017208:Rats, Wistar; D011990:Receptors, Transferrin / Q000378:metabolism; D012794:Sialic Acids / Q000378:metabolism; D013388:Succinimides / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D008562:Membrane Glycoproteins; D011990:Receptors, Transferrin; D012794:Sialic Acids; D013388:Succinimides; C094773:sulfosuccinimidyl-2-(biotinamido)ethyl-1,3-dithiopropionate; D005643:Fucose; D001710:Biotin; D005647:Fucosyltransferases; D008361:Mannosidases; C046090:mannosyl-oligosaccharide 1,2-alpha-mannosidase; D018819:Dipeptidyl Peptidase 4; D019158:N-Acetylneuraminic Acid