We have recently established and characterized cellular clones deriving from MDA-MB-231 breast cancer cells that express the human G_D3 synthase (GD3S), the enzyme that controls the biosynthesis of b- and c-series gangliosides. The GD3S positive clones show a proliferative phenotype in the absence of serum or growth factors and an increased tumor growth in severe immunodeficient mice. This phenotype results from the constitutive activation of the receptor tyrosine kinase c-Met in spite of the absence of ligand and subsequent activation of mitogen-activated protein kinase/extracellular signal-regulated kinase and phosphoinositide 3-kinase/Akt pathways. Here, we show by mass spectrometry analysis of total glycosphingolipids that G_D3 and G_D2 are the main gangliosides expressed by the GD3S positive clones. Moreover, G_D2 colocalized with c-Met at the plasma membrane and small interfering RNA silencing of the G_M2/G_D2 synthase efficiently reduced the expression of G_D2 as well as c-Met phosphorylation and reversed the proliferative phenotype. Competition assays using anti-G_D2 monoclonal antibodies also inhibit proliferation and c-Met phosphorylation of GD3S positive clones in serum-free conditions. Altogether, these results demonstrate the involvement of the disialoganglioside G_D2 in MDA-MB-231 cell proliferation via the constitutive activation of c-Met. The accumulation of G_D2 in c-Met expressing cells could therefore reinforce the tumorigenicity and aggressiveness of breast cancer tumors.

written by written by Journal of Glycobiology