Tunicamycin inhibits ganglioside biosynthesis in neuronal cells

The antibiotic tunicamycin blocks the transfer of GlcNAc-1-P from UDP-GlcNAc to dolichol phosphate, thereby blocking the synthesis of N-linked oligosaccharide chains on glycoproteins. Its effect on the biosynthesis of gangliosides has not been reported. We report that tunicamycin caused a 70-80% reduction in incorporation of [(3)H]GlcN into gangliosides and neutral glycosphingolipids of the neuroblastoma-glioma hybrid cell line NG 108-15 at antibiotic concentrations that caused a 90% reduction of the radiolabel incorporation into glycoproteins. The effect of tunicamycin on ganglioside biosynthesis was apparent after only 4 hr of incubation, and maximum inhibition was seen within 6 hr. When control or tunicamycin-treated (5 mug/ml) cells were collected and fractionated to separate glycoproteins, neutral glycosphingolipids, gangliosides, and nucleotide sugar-precursor pools, the following results were obtained: (i) UDP-GlcNAc and UDP-GalNAc pool sizes increased >3-fold, and specific activities decreased 50% upon treatment with tunicamycin; (ii) when corrected for this value, the percentage inhibition of GlcN incorporation into various glycoconjugates by tunicamycin in these cells was 82% for glycoproteins, 54% for neutral glycosphingolipids, and 50% for gangliosides; and (iii) the different gangliosides were affected differentially, with the most striking inhibition apparent in GM(3) biosynthesis, which was decreased 78% in the presence of tunicamycin. These data suggest that the effects of tunicamycin on glycosphingolipids as well as on glycoproteins must be considered when interpreting its effects on intact cells and organisms.