Exogenous ganglioside GD1a enhances epidermal growth factor receptor binding and dimerization.
Gangliosides are shed by tumor cells and can bind to normal cells in the tumor microenvironment and affect their function. Exposure of fibroblasts to exogenous gangliosides increases epidermal growth factor (EGF)-induced fibroblast proliferation and enhances EGF receptor (EGFR)-mediated activation of the mitogen-activated protein kinase signaling pathway (Li, R., Liu, Y., and Ladisch, S. (2001) J. Biol. Chem. 276, 42782-42792). Here we report that the EGFR itself is the target of this ganglioside effect: Preincubation of normal human dermal fibroblasts with G(D1a) ganglioside enhanced both EGF-induced EGFR autophosphorylation and receptor-tyrosine kinase activity. The enhancement was rapid (within 30 min), not due to alteration of time kinetics of the EGFR response to EGF, and reproduced in purified G(D1a)-enriched cell membranes isolated from ganglioside-preincubated fibroblasts. Evaluating the initial steps underlying activation, EGF binding, and EGFR dimerization, we found that G(D1a) enrichment of the cell membrane increased EGFR dimerization and the effective number of high affinity EGFR without increasing total receptor protein. Unexpectedly, G(D1a) enrichment also triggered increased EGFR dimerization in the absence of growth factor. This resulted in enhanced activation of the EGFR signal transduction cascade when EGF was added. We conclude that membrane ganglioside enrichment of normal fibroblasts (such as by tumor cell ganglioside shedding) facilitates receptor-receptor interactions (possibly by altering membrane topology), causing ligand-independent EGFR dimerization and, in turn, enhanced EGF signaling.
Liu
Yihui
Y
Glycobiology Program, Center for Cancer and Immunology Research, Children's Research Institute, Children's National Medical Center, 111 Michigan Avenue NW, Washington, D. C. 20010, USA.
Li
Ruixiang
R
Ladisch
Stephan
S
D000818:Animals; D015153:Blotting, Western; D002455:Cell Division; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D005677:G(M1) Ganglioside / Q000031:analogs & derivatives* / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D020935:MAP Kinase Signaling System; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D015398:Signal Transduction; D013997:Time Factors
D008024:Ligands; C064020:ganglioside GD1alpha; D005677:G(M1) Ganglioside; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases