Gangliosides Inhibit Platelet‐Derived Growth Factor‐Stimulated Receptor Dimerization in Human Glioma U‐1242MG and Swiss 3T3 Cells

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Abstract
We previously showed that gangliosides inhibit DNA synthesis in Swiss 3T3 cells stimulated with platelet-derived growth factor (PDGF) in a dose-responsive manner. This correlated with the inhibitory effects of several gangliosides (except GM3) on tyrosine phosphorylation of the PDGF receptor (PDGFR). [35S]Methionine-labeled Swiss 3T3 cells were incubated either with or without gangliosides and stimulated with PDGF, and proteins were cross-linked with bis(sulfosuccinimidyl) suberate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that two protein bands (170 and 350 kDa) were specifically immunoprecipitated with an anti-PDGFR antibody. Using both Swiss 3T3 and human glioma U-1242MG cells, western blots with anti-PDGFR and anti-phosphotyrosine antibodies confirmed that these bands were the PDGFR monomer and dimer, respectively, and that phosphotyrosine was present in these bands only after cells were stimulated with PDGF. Of the gangliosides tested, GM1, GM2, GD1a, GD1b, GD3, and GT1b, but not GM3, inhibited the formation of the 350-kDa band. These results demonstrate that all gangliosides tested, except GM3, probably inhibit PDGF-mediated growth by preventing dimerization of PDGFR monomers. Loss of more complex gangliosides in human gliomas would permit unregulated activation of the PDGFR, contributing to uncontrolled growth stimulation. We propose that ganglioside inhibition of receptor dimerization is a novel mechanism for regulating and coordinating several trophic factor-mediated cell functions.

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