Products of Cultured Neuroglial Cells. III. Release of an 85,000 Molecular Weight Glycoprotein by C6 Glioma Cells In Vitro

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Abstract
With [3H]fucose as a marker, C6 [rat] glioma cells in culture released an 85,000 MW molecule into the medium as the major extracellular glycoprotein. The quantity and extracellular/cytoplasmic ratio of this glycoprotein suggest that its cellular processing is different from that of 5 other released glycoproteins of MW 55,000, 115,000, 130,000, 150,000 and 170,000. Nearly 40% of newly synthesized glycoproteins in the cells was released into the culture medium. Major glycoproteins retained by the cells migrated electrophoretically to MW positions of 82,000, 110,000, 120,000, 140,000 and 160,000, and .apprx. 1/3 of these retained glycoproteins were labile to trypsinization. Both synthesis and release of these macromolecules were inhibited > 95% with cycloheximide treatment, demonstrating that nearly all fucosylation was linked to protein synthesis. Since 40% of all glycoproteins was released under conditions of > 99% cellular viability, it is likely that these extracellular glycoproteins are physiological products of membrane turnover and secretion, but not of cell lysis. A basis for further study of glial differentiation and of shed glioma antigens is provided.