Functional UDP-xylose transport across the endoplasmic reticulum/Golgi membrane in a Chinese hamster ovary cell mutant defective in UDP-xylose Synthase.
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.
Bakker
Hans
H
Zelluläre Chemie, Zentrum Biochemie, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany. bakker.hans@mh-hannover.de
Oka
Takuji
T
Ashikov
Angel
A
Yadav
Ajit
A
Berger
Monika
M
Rana
Nadia A
NA
Bai
Xiaomei
X
Jigami
Yoshifumi
Y
Haltiwanger
Robert S
RS
Esko
Jeffrey D
JD
Gerardy-Schahn
Rita
R
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*
D006025:Glycosaminoglycans; D051880:Receptors, Notch; D014540:Uridine Diphosphate Xylose; D002262:Carboxy-Lyases; C023257:UDPglucuronate decarboxylase