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Intracellular trafficking of cell surface sialoglycoconjugates
J S Reichner1, S W Whiteheart, G W Hart
1Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
The Journal of Biological Chemistry
|November 5, 1988
Summary
Cell surface glycoproteins are primarily resialylated through new protein synthesis, not recycling. This study shows most sialic acids return to the cell surface via de novo synthesis, not Golgi recycling.
Area of Science:
- Cell Biology
- Glycobiology
- Membrane Trafficking
Background:
- Recent studies suggest Golgi apparatus traffic is dominated by recycling molecules.
- The role of molecular recycling in cell surface glycoprotein turnover remains unclear.
Purpose of the Study:
- To investigate the contribution of recycling versus de novo synthesis to cell surface glycoprotein sialylation.
- To determine the extent of glycoprotein recycling through the Golgi apparatus.
Main Methods:
- Utilized EL-4 (murine T-cell lymphoma) and K562 (human erythroleukemia) cell lines.
- Sialic acids were removed using Vibrio cholerae sialidase and resialylation monitored via HPLC thiobarbituric acid assay.
- Tracked glycoprotein movement using rat liver alpha 2-6Gal beta 1-4GlcNAc sialyltransferase and CMP-[3H]NeuAc.
Main Results:
- Resialylation of cell surface glycoproteins was dependent on de novo protein synthesis.
- Internalization of surface sialoglycoproteins was slow and unaffected by cycloheximide.
- Only a small fraction of internalized glycoproteins returned to a trans-Golgi compartment for recycling.
Conclusions:
- The majority of cell surface sialic acid replacement occurs through de novo glycoprotein synthesis.
- Limited recycling of glycoproteins through the trans-Golgi compartment contributes minimally to surface sialylation.
- Cell surface glycoprotein turnover relies predominantly on synthesis rather than extensive recycling.