GANGLIOSIDE GM1 ACTIVATES THE MITOGEN-ACTIVATED PROTEIN-KINASE ERK2 AND P70 S6 KINASE IN U-1242 MG HUMAN GLIOMA-CELLS

Gangliosides are implicated in the regulation of cellular proliferatio n as evidenced by differences in ganglioside composition associated wi th malignant transformation and density of cells in culture, as well a s their inhibitory effects when added to cells growing in culture. Exo genously added gangliosides have a bimodal effect on proliferation in U-1242 MG glioma cells, inhibiting DNA synthesis in growing cells and stimulating it in quiescent cells. We investigated the mechanisms invo lved in stimulation of DNA synthesis using [H-3]thymidine incorporatio n and immune complex kinase assays to identify responsible signal tran sduction pathways. Treatment of quiescent U-1242 MG cells with GM1 cau sed activation of the mitogen-activated protein (MAP) kinase isoform E rk2. Pretreatment with the specific MAP kinase kinase inhibitor PD9805 9 prevented the GM1-stimulated Erk2 activation and GM1-stimulated DNA synthesis. GM1 treatment stimulated another distinct signaling pathway leading to activation of p70 S6 kinase (p70(s6k)), and this was preve nted by pretreatment with rapamycin. Rapamycin also inhibited GM1-stim ulated DNA synthesis. Activation of both pathways and stimulation of D NA synthesis were inhibited by forskolin treatment; however, GM1 had n o effect on cyclic AMP levels, Platelet-derived growth factor also act ivated both Erk2 and p70(s6k) but did not cause DNA synthesis, suggest ing that GM1 may stimulate additional cascades, which also contribute to GM1-mediated DNA synthesis.