Ganglioside modulates ligand binding to the epidermal growth factor receptor

Whereas previous investigations have shown that pharmacologic addition of g angliosides inhibits keratinocyte proliferation by downregulating epidermal growth factor receptor phosphorylation, the underlying biochemical basis a nd physiologic relevance are unknown. Using Scatchard and displacement plot s, we have shown that supplemental purified gangliosides decrease the bindi ng of I-125-labeled epidermal growth factor to keratinocyte-derived SCC12 c ells. Conversely, SCC12 cells transfected with sialidase and thus depleted of gangliosides show increased ligand binding to the epidermal growth facto r receptor, which is consistent with their increased proliferation in respo nse to epidermal growth factor and transforming growth factor-alpha, and in creased phosphorylation of the epidermal growth factor receptor, and downst ream signal transduction pathway components. The mechanism of the altered b inding appears to involve primarily decreased numbers of available receptor s within the intact membrane, but not altered receptor protein expression. These studies provide evidence that the effect of gangliosides on keratinoc yte proliferation results, at least in part, from the direct binding of gan glioside to the receptor and disruption of the receptor-ligand interaction. Manipulation of membrane ganglioside content may be a powerful new means t o alter epidermal growth factor receptor-dependent cell proliferation.