title: Functional UDP-xylose transport across the endoplasmic reticulum/Golgi membrane in a Chinese hamster ovary cell mutant defective in UDP-xylose Synthase.
abstract: In mammals, xylose is found as the first sugar residue of the tetrasaccharide GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser, initiating the formation of the glycosaminoglycans heparin/heparan sulfate and chondroitin/dermatan sulfate. It is also found in the trisaccharide Xylalpha1-3Xylalpha1-3Glcbeta1-O-Ser on epidermal growth factor repeats of proteins, such as Notch. UDP-xylose synthase (UXS), which catalyzes the formation of the UDP-xylose substrate for the different xylosyltransferases through decarboxylation of UDP-glucuronic acid, resides in the endoplasmic reticulum and/or Golgi lumen. Since xylosylation takes place in these organelles, no obvious requirement exists for membrane transport of UDP-xylose. However, UDP-xylose transport across isolated Golgi membranes has been documented, and we recently succeeded with the cloning of a human UDP-xylose transporter (SLC25B4). Here we provide new evidence for a functional role of UDP-xylose transport by characterization of a new Chinese hamster ovary cell mutant, designated pgsI-208, that lacks UXS activity. The mutant fails to initiate glycosaminoglycan synthesis and is not capable of xylosylating Notch. Complementation was achieved by expression of a cytoplasmic variant of UXS, which proves the existence of a functional Golgi UDP-xylose transporter. A approximately 200 fold increase of UDP-glucuronic acid occurred in pgsI-208 cells, demonstrating a lack of UDP-xylose-mediated control of the cytoplasmically localized UDP-glucose dehydrogenase in the mutant. The data presented in this study suggest the bidirectional transport of UDP-xylose across endoplasmic reticulum/Golgi membranes and its role in controlling homeostasis of UDP-glucuronic acid and UDP-xylose production.
authors.affiliation: Zelluläre Chemie, Zentrum Biochemie, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany. bakker.hans@mh-hannover.de
authors.forename: Hans
authors.initials: H
authors.lastname: Bakker
authors.forename: Takuji
authors.initials: T
authors.lastname: Oka
authors.forename: Angel
authors.initials: A
authors.lastname: Ashikov
authors.forename: Ajit
authors.initials: A
authors.lastname: Yadav
authors.forename: Monika
authors.initials: M
authors.lastname: Berger
authors.forename: Nadia A
authors.initials: NA
authors.lastname: Rana
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Bai
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Jigami
authors.forename: Robert S
authors.initials: RS
authors.lastname: Haltiwanger
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Esko
authors.forename: Rita
authors.initials: R
authors.lastname: Gerardy-Schahn
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D002262:Carboxy-Lyases / Q000235:genetics / Q000378:metabolism*; D002469:Cell Separation / Q000379:methods*; D006224:Cricetinae; D003412:Cricetulus; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006025:Glycosaminoglycans / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D051880:Receptors, Notch / Q000737:chemistry / Q000378:metabolism; D014540:Uridine Diphosphate Xylose / Q000378:metabolism*
chemical_list: D006025:Glycosaminoglycans; D051880:Receptors, Notch; D014540:Uridine Diphosphate Xylose; D002262:Carboxy-Lyases; C023257:UDPglucuronate decarboxylase