Ganglioside GM3 Blocks the Activation of Epidermal Growth Factor Receptor Induced by Integrin at Specific Tyrosine Sites

Abstract

The epidermal growth factor receptor (EGFR) can be activated by both direct ligand binding and cross-talk with other molecules, such as integrins. This integrinmediated cross-talk with growth factor receptors participates in regulating cell proliferation, survival, migration, and invasion. Previous studies have shown that ligand-dependent EGFR activation is inhibited by GM3, the predominant ganglioside of epithelial cells, but the effect of GM3 on ligand-independent, integrin-EGFR cross-talk is unknown. Using a squamous carcinoma cell line we show that endogenous accumulation of GM3 disrupts the ligand-independent association of the integrin ␤ 1 subunit with EGFR and results in inhibition of cell proliferation. Consistently, endogenous depletion of GM3 markedly increases the association of EGFR with tyrosine-phosphorylated integrin ␤ 1 and promotes cell proliferation. The ligand-independent stimulation of EGFR does not require focal adhesion kinase phosphorylation or cytoskeletal rearrangement. Stimulation of EGFR and mitogen-activated protein kinase signaling by GM3 depletion involves the phosphorylation of EGFR at tyrosine residues 845, 1068, and 1148 but not 1086 or 1173. The specific blockade of phosphorylation at Tyr-845 with Src family kinase inhibition and at Tyr-1148 with phosphatidylinositol 3-kinase inhibition suggests that GM3 inhibits integrin-induced, ligand-independent EGFR phosphorylation (cross-talk) through suppression of Src family kinase and phosphatidylinositol 3-kinase signaling.Integrins are cell surface-adhesive receptors formed by ␣ and ␤ subunits, which bind to extracellular matrix proteins. Integrin-mediated adhesion to extracellular matrix triggers intracellular signaling pathways to modulate cell proliferation, shape, migration, invasion, and survival (for review see Refs. 1 and 2). Integrin signaling is mediated by intracellular molecules, such as c-Src, small GTPases, adaptor molecules such as Shc, the protein-tyrosine phosphatases SHP-2, and phosphatidylinositol 3-kinase (3-5). Integrins can also cross-communicate with growth factor receptors, enabling growth factor receptor signaling upon extracellular matrix binding of the interacting integrin in the absence of growth factors (1) and culminating in enhanced cell mitogenesis and oncogenesis. Although the mechanism for this cross-talk is poorly understood, this cross-talk does not require cytoskeletal mobility or focal adhesion kinase (FAK) 1 activation (6), suggesting interaction at the membrane level, proximal to FAK and cytoskeletal activation. In fact, certain growth factor receptors have been shown to interact physically with specific integrins, suggesting that the formation of complexes at the membrane level is required for the convergence of signaling pathways (6 -11). EGFR, for example, forms a complex with ␤ 1 integrin after cells attach to fibronectin (6, 12), both platelet-derived growth factor receptor-␤ and vascular endothelial cell growth factor receptor 2 show association with ␣ v ␤ 3 integrin (13,14), and ErbB2 asso...

A crucial role of plasma membrane-associated sialidase in the survival of human cancer cells

“…For clarification, we tested whether NEU3 stimulates EGFR phosphorylation. As expected from the previous reports (Bremer et al, 1986;Wang et al, 2003) describing inhibition of EGFR tyrosine phosphorylation by GM3, siRNA3 introduction reduced phosphorylation of EGFR (Figure 5a, left panel) and in contrast, the overexpression promoted phosphorylation (Figure 5a, right panel) and the receptor dimerization ( Figure 5b) in response to EGF. It is interesting to note that using anti-phospho-EGF receptor antibodies to specific tyrosine residues, the level of EGFR phosphorylation at tyrosine (Tyr)-845 was the most highest among those at Tyr-992, 1045, 1068, 1148 and 1173 in NEU3 transfected HeLa cells (data not shown), raising the possibility that NEU3 may largely stimulate EGFR phosphorylation that Src kinase is involved in (Biscardi et al, 1999).…”

Caveolin-1 Regulates Matrix Metalloproteinases-1 Induction and CD147/EMMPRIN Cell Surface Clustering

“…It has not yet been determined whether CD147-caveolin-1 complexes reside at the periphery of caveolae. Whereas the bulk of plasma membrane-associated caveolin is typically resistant to non-ionic detergent solubilization, the presence of ganglioside GM3 can shift caveolin-1 to a more detergent soluble state (41,42). It remains to be determined whether CD147-caveolin-1 complexes are enriched for GM3, thus perhaps helping to explain the atypical solubility of caveolin-1 that is associated with CD147.…”

Ganglioside GM3 promotes cell migration by regulating MAPK and c-Fos/AP-1

“…Signal transduction through MAPK Previous reports suggested that GM3 might interfere with MAPK signal transduction in numeral types of mammalian cells (Garofalo et al, 2002;Wang et al, 2003). Therefore, we considered that loss of GM3 expression would be predicted to induce activation of MAPK pathway and higher migration activities in MEFs.…”