title: Analysis of polarized secretion of fucosylated alpha-fetoprotein in HepG2 cells.
abstract: Fucosylated alpha-fetoprotein (AFP) is a more specific biomarker for hepatocellular carcinoma (HCC) than AFP. However, the mechanisms underlying the increase in fucosylated AFP in sera of HCC patients remain largely unknown. Recently, we reported that fucosylation is a possible signal for the secretion of hepatic glycoproteins into bile and that the fucosylation-based sorting machinery might be disrupted in the liver bearing HCC. In this study, we investigated the selective secretion of fucosylated AFP into bile canaliculus (BC) structures of the human hepatoma cell line HepG2. The proportion of fucosylated AFP in BC structures was higher than that in the medium, as judged by lectin affinity electrophoresis. Suppression of fucosylation by the double knock-down of GDP-mannose-4,6-dehydratase and the human homologue of GDP-4-keto-6-deoxymannose-3,5-epimerase-4-reductase, which contribute to the synthesis of GDP-fucose, a donor substrate for fucosyltransferases, did not decrease the proportion of fucosylated AFP in BC structures but decreased this proportion in conditioned medium. Furthermore, increased AFP fucosylation was observed in medium, but not in BC structures, upon adding free fucose. These results suggest that saturation of fucosylated AFP in BC structures is accompanied by its increase in conditioned medium, probably leading to increased fucosylated AFP in sera of HCC patients.
authors.affiliation: Department of Molecular Biochemistry and Clinical Investigation, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Kenta
authors.initials: K
authors.lastname: Moriwaki
authors.forename: Naoko
authors.initials: N
authors.lastname: Terao
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Yasuhide
authors.initials: Y
authors.lastname: Miyamoto
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kamada
authors.forename: Eiji
authors.initials: E
authors.lastname: Miyoshi
mesh_terms: D001648:Bile Canaliculi / Q000378:metabolism / Q000473:pathology*; D014408:Biomarkers, Tumor / Q000378:metabolism*; D005643:Fucose / Q000378:metabolism; D005647:Fucosyltransferases / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006023:Glycoproteins / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D006836:Hydro-Lyases / Q000235:genetics / Q000378:metabolism; D009844:Oligosaccharides / Q000378:metabolism; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D000509:alpha-Fetoproteins / Q000378:metabolism*
chemical_list: C097353:AFP protein, human; D014408:Biomarkers, Tumor; D006023:Glycoproteins; D009844:Oligosaccharides; D034741:RNA, Small Interfering; D000509:alpha-Fetoproteins; D005643:Fucose; D005647:Fucosyltransferases; D006836:Hydro-Lyases; C044971:GDPmannose 4,6-dehydratase