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Endoplasmic reticulum/golgi nucleotide sugar transporters contribute to the cellular release of UDP-sugar signaling molecules.

ABSTRACT: 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.

SUBMITTER: Sesma JI

PROVIDER: S-EPMC2673323 | biostudies-literature | 2009 May

REPOSITORIES: biostudies-literature

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Endoplasmic reticulum/golgi nucleotide sugar transporters contribute to the cellular release of UDP-sugar signaling molecules.

Sesma Juliana I JI Esther Charles R CR Kreda Silvia M SM Jones Lisa L O'Neal Wanda W Nishihara Shoko S Nicholas Robert A RA Lazarowski Eduardo R ER

The Journal of biological chemistry 20090310 18

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 ...[more]

PMID: 19276090

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Project description:Background: Herpesvirus capsids are assembled in the nucleus, translocated to the perinuclear space by budding, acquiring tegument and envelope, or released to the cytoplasm via impaired nuclear envelope. One model proposes that envelopment, "de-envelopment" and "re-envelopment" is essential for production of infectious virus. Glycoproteins gB/gH were reported to be essential for de-envelopment, by fusion of the "primary" envelope with the outer nuclear membrane. Yet, a high proportion of enveloped virions generated from genomes with deleted gB/gH were found in the cytoplasm and extracellular space, suggesting the existence of alternative exit routes. Methods: We investigated the relatedness between the nuclear envelope and membranes of the endoplasmic reticulum and Golgi complex, in cells infected with either herpes simplex virus 1 (HSV-1) or a Us3 deletion mutant thereof, or with bovine herpesvirus 1 (BoHV-1) by transmission and scanning electron microscopy, employing freezing technique protocols. Results: The Golgi complex is a compact entity in a juxtanuclear position covered by a membrane on the cis face. Golgi membranes merge with membranes of the endoplasmic reticulum forming an entity with the perinuclear space. All compartments contained enveloped virions. After treatment with brefeldin A, HSV-1 virions aggregated in the perinuclear space and endoplasmic reticulum, while infectious progeny virus was still produced. Conclusions: The data suggest that virions derived by budding at nuclear membranes are intraluminally transported from the perinuclear space via Golgi -endoplasmic reticulum transitions into Golgi cisternae for packaging. Virions derived by budding at nuclear membranes are infective like Us3 deletion mutants, which accumulate in the perinuclear space. Therefore, i) de-envelopment followed by re-envelopment is not essential for production of infective progeny virus, ii) the process taking place at the outer nuclear membrane is budding not fusion, and iii) naked capsids gain access to the cytoplasmic matrix via impaired nuclear envelope as reported earlier.

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Endoplasmic reticulum/golgi nucleotide sugar transporters contribute to the cellular release of UDP-sugar signaling molecules.

Publications

Endoplasmic reticulum/golgi nucleotide sugar transporters contribute to the cellular release of UDP-sugar signaling molecules.

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