Expression and Regulation of Glycosyltransferases for N-Glycosyl Oligosaccharides in Fresh Human Surgical and Murine Tissues and Cultured Cell Lines

Abstract

1. Mammalian membrane and serum proteins are glycosylated by the addition of heterogeneous N-linked oligosaccharides. It has been widely speculated that oligosaccharide diversity is achieved by corresponding heterogeneity of expression of the glycosyltransferases that are responsible for oligosaccharide synthesis. 2. We surveyed mRNA levels of three sequentially acting glycosyltransferases, N-acetylglucosaminyl-transferase I, beta 1,4-galactosyltransferase and alpha 2,6-sialyltransferase, in 11 human tissues and confirmed the expected variations. 3. The size heterogeneity of alpha 2,6-sialytransferase transcripts reported in rat tissues was evident neither in the human tissue survey nor in a panel of murine RNAs. Tissue distributions of alternative terminal sialyltransferases, alpha 2,6-sialyltransferase and alpha 2,3-sialyltransferase, were distinct. 4. Relative glycosyltransferase mRNA levels in four transformed human cell lines cultured in vitro did not fully reflect levels in the corresponding human tissues. 5. Expression of alpha 2,6-sialyltransferase mRNA was approximately 2.6-fold greater in adenocarcinomatous than in normal human colon, and beta 1,4-galactosyltransferase expression was approximately 1.8-fold greater in normal than in adenocarcinomatous colon. 6. n-Butyrate (0.003-0.005 mol/l), a short-chain fatty acid that is produced by colonic bacterial fermentation, caused approximately 80% inhibition of alpha 2,6-sialyltransferase, approximately 2.5-fold induction of beta 1,4-galactosyltransferase and approximately 6-fold induction of N-acetylglucosaminyltransferase mRNAs in T84 (colonic) cells. The effects on alpha 2,6-sialyltransferase and beta 1,4-galactosyltransferase were near maximal by 6h, but induction of N-acetylglucosaminyltransferase was fully apparent only after exposure for 24 h.

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