Glycobiology Advance Access originally published online on July 17, 2009
Glycobiology 2009 19(10):1082-1093; doi:10.1093/glycob/cwp094
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The second bovine β-galactoside-
2,6-sialyltransferase (ST6Gal II): genomic organization and stimulation of its in vitro expression by IL-6 in bovine mammary epithelial cells
UMR1061, Unité de Génétique Moléculaire Animale, Université de Limoges, INRA, IFR N° 145 GEIST, France
1 To whom correspondence should be addressed: Tel: +33-5-55-45-76-71; Fax: +33-5-55-45-76-53; e-mail: jean-michel.petit{at}unilim.fr
Received on April 29, 2009; revised on June 19, 2009; accepted on June 21, 2009
We have cloned a cDNA sequence encoding the second bovine β-galactoside-
2,6-sialyltransferase whose sequence shares more than 75% of identity with hST6Gal II cDNA coding sequence. The bovine gene, located on BTA 11, spans over 50 kbp with five exons (E1–E5) containing the 1488 bp open reading frame and a 5'-untranslated exon (E0). The gene expression pattern reveals a specific tissue distribution (brain, lungs, spleen, salivary, and mammary glands) compared to ST6Gal I which is ubiquitously expressed. We identified for bovine ST6Gal II three kinds of transcripts which differ by their 5'-untranslated regions. Among them, two transcripts are brain specific whereas the third one is found in all of the tissues expressing the gene. Two pFlag-bST6Gal II vector constructions were separately transfected in COS-1 cells in order to express either membrane-bound or soluble active forms of ST6Gal II. Enzymatic assays with these two forms indicated that the enzyme used the LacdiNAc structure (GalNAcβ1,4GlcNAc) as a better acceptor substrate than the Type II (Galβ1-4GlcNAc) disaccharide. Moreover, the enzyme's efficiency is improved when the acceptor substrate is provided as a free oligosaccharide rather than as a protein-bound oligosaccharide. In order to investigate the potential role of ST6Gal II during the acute phase of inflammation, we used primary cultures of bovine mammary epithelial cells which were stimulated with pro-inflammatory cytokines. It appears that the ST6Gal II gene was upregulated in cells stimulated by IL-6. This result suggested that
2,6-sialylation mediated by this gene could contribute to organism's response to infections.
Key words: bovine / inflammation / interleukine / mammary gland / sialyltransferases