CYTOKINE-INDUCED BETA-GALACTOSIDE ALPHA-2,6-SIALYLTRANSFERASE IN HUMAN ENDOTHELIAL-CELLS MEDIATES ALPHA-2,6-SIALYLATION OF ADHESION MOLECULES AND CD22 LIGANDS

Sialic acids decorating blood and cell surface proteins can play impor tant roles in various biological processes. The inflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-1, as well as bacterial lipopolysaccharide, can activate vascular endothelium, incr easing expression of several surface glycoproteins. Here we show that treatment of cultured human endothelial cells (HEC) with TNF-alpha, in terleukin-1, or lipopolysaccharide causes increased expression of the enzyme beta-galactoside alpha-2,6-sialyltransferase (alpha 2-6STN). TN F-alpha was most effective, inducing a 3.5-fold enhancement of cell-as sociated sialyltransferase activity by 72 h. In addition, activated HE C secreted a large portion of the induced sialyltransferase activity i nto the medium. Analysis of labeled HEC showed both a relative and an absolute increase of alpha 2,6-linked sialic acid on N-linked oligosac charides after TNF-alpha stimulation. This coincided with increased ex pression of endothelial glycoproteins bearing N-linked glycans with al pha 2,6-linked sialic acid detected by the lectin Sambucus nigra agglu tinin. The cytokine-inducible endothelial cell adhesion molecules E-se lectin, ICAM-1, and VCAM-1 are among these glycoprotein substrates for alpha 2-6STN. These changes also correlated with a substantial increa se in binding sites for CD22 beta, a mammalian lectin known to recogni ze oligosaccharides carrying multiple copies of alpha 2,6-linked siali c acid. Northern analysis revealed increased levels of mRNA encoding a lpha 2-6STN. Thus, activation of endothelial cells during in flammator y and immunological processes may induce alpha 2-6STN, which can parti cipate in sialylation of other activation-dependent molecules.