Cytokine-induced β-galactoside α-2,6-sialyltransferase in human endothelial cells mediates α2,6-sialylation of adhesion molecules and CD22 ligands

Sialic acids decorating blood and cell surface proteins can play important roles in various biological processes. The inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1, as well as bacterial lipopolysaccharide, can activate vascular endothelium, increasing expression of several surface glycoproteins. Here we show that treatment of cultured human endothelial cells (HEC) with TNF-α, interleukin-1, or lipopolysaccharide causes increased expression of the enzyme β-galactoside α-2,6-sialyltransferase (α2-6STN). TNF-α was most effective, inducing a 3.5-fold enhancement of cell-associated sialyltransferase activity by 72 h. In addition, activated HEC secreted a large portion of the induced sialyltransferase activity into the medium. Analysis of labeled HEC showed both a relative and an absolute increase of α2,6-linked sialic acid on N- linked oligosaccharides after TNF-α stimulation. This coincided with increased expression of endothelial glycoproteins bearing N-linked glycans with α2,6-linked sialic acid detected by the lectin Sambucus nigra agglutinin. The cytokine-inducible endothelial cell adhesion molecules E- selectin, ICAM-1, and VCAM-1 are among these glycoprotein substrates for α2- 6STN. These changes also correlated with a substantial increase in binding sites for CD22β, a mammalian lectin known to recognize oligosaccharides carrying multiple copies of α2,6-linked sialic acid. Northern analysis revealed increased levels of mRNA encoding α2-6STN. Thus, activation of endothelial cells during inflammatory and immunological processes may induce α2-6STN, which can participate in sialylation of other activation-dependent molecules.