Inhibition of DNA synthesis in C6 glioma cells following cellular incorporation of GM1 ganglioside and choleragenoid exposure.
The B subunit of cholera toxin, which is multivalent and binds specifically to GM1 ganglioside on the cell surface, has previously been used as a ganglioside-specific probe to regulate DNA synthesis in thymocytes and fibroblasts. To explore in more detail this growth-regulatory action of gangliosides, C6 glioma cells (which are GM1 ganglioside deficient) were used as a model system. When cultures of C6 cells were first treated with GM1, followed by exposure to the B subunit, proliferation was inhibited, as measured by 3H-labeled thymidine incorporation into DNA. Pretreatment of the cells with 50 microM GM1 for 15 min (followed by washing with fetal calf serum) and incubation with 1 microgram/ml of B subunit for 21 h was sufficient to reduce DNA synthesis to 15% of control values (and confirmed by autoradiographic analysis), although maximal inhibition could be achieved with as little as 30 min exposure to B, followed by washing. Furthermore, the B subunit inhibited the response of the C6 cells to basic fibroblast growth factor only following GM1 pretreatment. The B subunit-induced inhibition of DNA synthesis was specific for the ganglioside GM1, and was unrelated to increases of cyclic AMP. These results demonstrate that cell-incorporated GM1 ganglioside may act as a receptor capable of undergoing a specific ligand interaction, subsequently affecting molecular processes at the nuclear level.
Skaper
S D
SD
Fidia Research Laboratories, Department of CNS Research, Abano Terme, Italy.
Facci
L
L
Favaron
M
M
Leon
A
A
D000818:Animals; D002772:Cholera Toxin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D004247:DNA / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D005677:G(M1) Ganglioside / Q000378:metabolism* / Q000494:pharmacology; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000378:metabolism*
D010446:Peptide Fragments; D005677:G(M1) Ganglioside; C050310:cholera toxin, B subunit (50-64); D004247:DNA; D002772:Cholera Toxin; D000242:Cyclic AMP