α2,3-Sialyl and α1,3-fucosyltransferase-dependent synthesis of sialyl Lewis x, an essential oligosaccharide present on L-selectin counterreceptors, in cultured endothelial cells

Abstract

Sialyl Lewis x (sLex) oligosaccharides have been shown to be present in counterreceptors for L-selectin. We and others have previously shown that high endothelial cells in lymph nodes and at sites of inflammation express sLex. Here we show that also cultured human umbilical vein endothelial cells (HUVEC) express sLex on their cell surface. This oligosaccharide is formed by sequential action of α2,3-sialyl- (α2,3-ST) and α1,3-fucosyltransferases (α1,3-FT) on N-acetyllactosamine. At least two of the several α2,3-ST and four of the several α1,3-FT are present in HUVEC. In functional assays both α2,3-ST and α1,3-FT activities were observed in HUVEC lysates with exogenous lactosamine and sialyllactosamine acceptors, leading to the generation of the sialyllactosamine and sLex sequences, respectively. TNF stimulation increased the level of mRNA expression of FT VI, and the α1,3-FT activity in HUVEC. Taken together these data show that endothelial cells express sLex and that they possess mRNA as well as enzyme activities of several α2,3-ST and α1,3-FT necessary in the final steps of sLex synthesis. Furthermore, inflammatory cytokines such as TNF can enhance transferase activities relevant in generating putative L-selectin counterreceptors.