Differential regulation of UDP-GlcUA transport in endoplasmic reticulum and in Golgi membranes.
BACKGROUND
In the endoplasmic reticulum (ER), the stimulation of UDP-glucuronosyltransferase (UGT) by UDP-GlcNAc is based on the interaction of transport across the ER membrane of UDP-GlcUA with UDP-GlcNAc. Intramicrosomal UDP-GlcNAc stimulates influx of UDP-GlcUA and thereby enhances delivery of UDP-GlcUA to the catalytic center of UGT in the ER lumen.


OBJECTIVE
The aim of this study is to investigate whether the interactions between nucleotide sugars for transport across the ER membrane also occur in the Golgi apparatus, and thereby affect UGT activity in Golgi membranes.


RESULTS
We found that Golgi membrane preparations display UGT activity which, unlike in ER membranes, is not stimulated by UDP-GlcNAc. Efflux of intravesicular UDP-GlcNAc and UDP-Xyl marginally enhanced uptake of UDP-GlcUA in Golgi vesicles; such trans-stimulation was much more pronounced in the ER. Efflux of intravesicular UDP-GlcNAc was strongly trans-stimulated by cytosolic UDP-GlcUA in ER-derived vesicles but less so in Golgi-derived vesicles.


CONCLUSIONS
The interaction between transport of UDP-GlcUA and transport of UDP-GlcNAc or UDP-Xyl is different in Golgi vesicles compared with ER vesicles. This finding is consistent with the different effects of UDP-GlcNAc on glucuronidation in Golgi and ER.
Department of Molecular Cell Biology, Catholic University of Leuven, Belgium. xavier.bossuyt@uz.kuleuven.ac.be
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Bossuyt
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Blanckaert
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000378:metabolism; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism* / Q000494:pharmacology; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000378:metabolism / Q000494:pharmacology; D014540:Uridine Diphosphate Xylose / Q000378:metabolism / Q000494:pharmacology
D014535:Uridine Diphosphate Glucuronic Acid; D014540:Uridine Diphosphate Xylose; D014537:Uridine Diphosphate N-Acetylglucosamine; D014453:Glucuronosyltransferase