Functional role of glycosphingolipids in contact inhibition of growth in a human mammary epithelial cell line.

We have demonstrated previously the involvement of certain glycosphingolipids (GSLs) in 'contact inhibition' (dependent on cell-to-cell contact) of cell growth. Here, we examined the roles of specific GSLs in contact inhibition of the human epithelial cell line MCF10A. Contact-inhibited cells show increased expression of the ganglioside GD3 and the globo-series GSL Gb3, and of the mRNAs for the corresponding sialyltransferases ST8SIA1 (GD3 synthase) and galactosyltransferase A4GALT (Gb3 synthase). siRNA knockdown (KD) of ST8SIA1 and/or A4GALT significantly suppresses contact inhibition. Exogenous addition of GD3 or Gb3 inhibits proliferation of low-density cells. Our findings suggest that GSLs play functional roles in contact inhibition of these cells and that Merlin/NF2, a tumor suppressor protein, is involved in the GSL function.