GANGLIOSIDE SYNTHESIS BY PLASMA MEMBRANE-ASSOCIATED ECTOSIALYLTRANSFERASE IN MACROPHAGES

A. ALEJANDRO VILCAES; VANINA TORRES DEMICHELIS; JOSE L. DANIOTTI

Puerto Iguazu

Congreso; 56th International Conference on the Bioscience of lipids; 2015

International Conference on the Bioscience of lipids

Gangliosides, a particular class of glycolipids, contain sialic acid residues and are expressed in nearly all vertebrate cells. They are synthesized at the Golgi complex by a combination of glycosyltransferases enzymes and then travel to the plasma membrane (PM) through vesicular transport, where they participate in a variety of physiological as well as pathological processes. Recently, a number of enzymes of ganglioside metabolism have been shown to be associated with the PM. In particular, it was observed that CMP-NeuAc:GM3 ectosialyltransferase (ecto-ST8Sia-I) synthetize GD3 at the PM (cis-catalytic activity). Then, it was demonstrated in epithelial and melanoma cells that ecto-ST8Sia-I displayed enzymatic activity towards GM3 substrate exposed in PM of neighboring cells (trans-catalytic activity) which did not express endogenous ST8Sia-I. In the present work, we extended these investigations to macrophage cells and found that endogenous ecto-ST8Sia-I is present in Golgi-complex as well as in the cell-surface. In addition, LPS-stimulated macrophages reduced the ST8Sia-I levels at the PM. It is worth mentioning that ecto-ST8Sia-I enzymatic activity was performed in cells previously treated with a specific inhibitor of glycolipid biosynthesis. Interestingly, this pharmacological treatment also decreased the ecto-ST8Sia-I expression. Despite this variation, ecto-ST8Sia-I displayed cis-catalytic activity both in unstimulated and stimulated conditions. The diminution in the enzyme levels correlated with a reduction of GD3 and GM1 and with an increment of GD1a at the PM. Moreover, the levels of NO from LPS-stimulated macrophages were higher in cells previously treated than in cells untreated with the glycolipid inhibitor, suggesting a possible participation of these molecules in the macrophages activation. Taken together, the data further support the presence and activity of ecto-sialyltransferases at the PM. In addition, the variations of ecto-ST8Sia-I and gangliosides in stimulated macrophages provide a promissory information to further explore the role of this and others ganglioside metabolism-related enzymes at the PM.