ENDOCYTOSIS AND RECYCLING OF GANGLIOSIDES IN A HUMAN-MELANOMA CELL-LINE - INHIBITORY EFFECT OF BREFELDIN-A AND MONENSIN

The internalization and recycling of glycosphingolipids (GLs), added e xogenously to cells, has been shown in a number of systems. In additio n, a portion of the internalized GLs becomes elongated by further glyc osylation, presumably by passage through the Golgi apparatus, and is r ecycled to the plasma membrane. We have previously shown (K. Furukawa, I. Thampoe, H. Yamaguchi, and K. O. Lloyd J. Immunol. 142, 848, 1989) that NeuGc-LacCer (G(M3)), added exogenously to cultured human melano ma cells, is converted to NeuAc-NeuGc-LacCer (G(D3)) and appears at th e cell surface where it can be recognized by a monoclonal antibody (32 -27M) specifically recognizing this structure. The mechanism of this p rocess has been investigated by analyzing the effect of monensin and B refeldin A (BFA), two drugs known to affect vesicular transport and Go lgi function, on the recycling of NeuGc-LacCer. Using two different se rological assays, BFA was shown to specifically inhibit the recycling process. BFA probably achieves this effect by inhibiting the transfer of endocytosed GL from endosomes and the trans Golgi network to the Go lgi stacks by a retrograde route and thus prevents its entry into the biosynthetic compartments. Monensin had a similar, but less clear-cut, effect on G(MS), recycling. These results have important implications for understanding the modulation of cell surface glycolipids. (C) 199 4 Academic Press, Inc.