Sialoglycosphingolipids (gangliosides) are synthesized in the Golgi complex before being moved via vesicular transport to the plasma membrane (PM), becoming components of the external leaflet. Glycosphingolipid catabolic enzymes (glycohydrolases) have been found to be associated with the PM, where they display activity on the membrane components. By biochemical and cell biology techniques, we explored the expression and activity of ganglioside glycosyltransferases at the PM of epithelial and melanoma cells. Both ectopically and endogenously expressed CMP-NeuAc:GM3 sialyltransferase (Sial-T2, GD3 synthase) were found to be able to sialylate GM3 at the PM (cis activity) using both the exogenous and endogenous donor (CMP-NeuAc) and acceptor (GM3) substrates. Next, we investigated whether ecto-Sial-T2 is capable to display a trans activity in living cells. It was demonstrated that ecto-Sial-T2 sialylates GM3 both absorbed into the plastic surface of microwells and expressed at the PM of neighbor cells. Thus, the relative interplay between glycohydrolases as well as cis and trans ecto-Sial-T2 activities emerges as a potential level of regulation of the local glycosphingolipid composition in response to different external and internal stimuli.
