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Endoplasmic Reticulum/Golgi Nucleotide Sugar Transporters Contribute to the Cellular Release of UDP-sugar Signaling MoleculesS
Ist Teil von
The Journal of biological chemistry, 2009-05, Vol.284 (18), p.12572-12583
Ort / Verlag
American Society for Biochemistry and Molecular Biology
Erscheinungsjahr
2009
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
Extracellular UDP-sugars promote cellular responses by interacting with
widely distributed P2Y
14
receptors, but the mechanisms by which
these molecules are released from cells are poorly understood. Given the
active role of UDP-sugars in glycosylation reactions within the secretory
pathway, we hypothesized that UDP-sugar release includes an exocytotic
component. This hypothesis was tested by assessing the contribution of
endoplasmic reticulum (ER)/Golgi-resident UDP-GlcNAc transporters to the
cellular release of their cognate substrates. A sensitive and highly selective
assay for UDP-GlcNAc mass was developed using purified AGX2, an isoenzyme of
human UDP-GlcNAc pyrophosphorylase. Robust constitutive release of UDP-GlcNAc
was observed in yeast as well as in well differentiated human airway
epithelial cells. The human UDP-GlcNAc transporter HFRC1 was overexpressed in
human bronchial epithelial cells and was shown to localize in the Golgi and to
enhance the surface expression of
N
-acetylglucosamine-rich glycans.
HFRC1-overexpressing cells also displayed increased constitutive and hypotonic
stress-stimulated release of UDP-GlcNAc. Yeast mutants lacking Yea4 (the ER
UDP-GlcNAc transporter endogenously expressed in
Saccharomyces
cerevisiae
) showed reduced UDP-GlcNAc release. Yea4-deficient cells
complemented with Yea4 showed UDP-GlcNAc release rates at levels similar to or
higher than wild type cells. Our results illustrate that ER/Golgi lumen
constitutes a significant source of extracellular UDP-sugars and therefore
plays a critical role in nucleotide sugar-promoted cell signaling.