Linkage-specific action of endogenous sialic acid O-acetyltransferase in Chinese hamster ovary cells.
9-O-Acetylation of sialic acids shows cell type-specific and developmentally regulated expression in various systems. In a given cell type, O-acetylation can also be specific to a particular type of glycoconjugate. It is assumed that this regulation is achieved by control of expression of specific 9-O-acetyltransferases. However, it has been difficult to test this hypothesis, as these enzymes have so far proven intractable to purification or molecular cloning. During a cloning attempt, we discovered that while polyoma T antigen-positive Chinese hamster ovary cells (CHO-Tag cells) do not normally express cell-surface 9-O-acetylation, they do so when transiently transfected with a cDNA encoding the lactosamine-specific alpha2-6-sialyltransferase (Galbeta1-4GlcNAc:alpha2-6-sialyltransferase (ST6Gal I); formerly ST6N). This phenomenon is reproducible by stable expression of ST6Gal I in parental CHO cells, but not upon transfection of the competing lactosamine-specific alpha2-3-sialyltransferase (Galbeta1-(3)4GlcNAc:alpha2-3-sialyltransferase; (ST6Gal III) formerly ST3N) into either cell type. Further analyses of stably transfected parental CHO-K1 cells indicated that expression of the ST6Gal I gene causes selective 9-O-acetylation of alpha2-6-linked sialic acid residues on N-linked oligosaccharides. In a similar manner, while the alpha2-3-linked sialic acid residue of the endogenous GM3 ganglioside of CHO cells is not O-acetylated, transfection of an alpha2-8-sialyltransferase (GM3:alpha2-8-sialyltransferase (ST8Sia I); formerly GD3 synthase) caused expression of 9-O-acetylation of the alpha2-8-linked sialic acid residues of newly synthesized GD3. These data indicate either that linkage-specific sialic acid O-acetyltransferase(s) are constitutively expressed in CHO cells or that expression of these enzymes is secondarily induced upon expression of certain sialyltransferases. The former explanation is supported by a low level of background 9-O-acetylation found in parental CHO-K1 cells and by the finding that O-acetylation is not induced when the ST6Gal I or ST8Sia I cDNAs are overexpressed in SV40 T antigen-expressing primate (COS) cells. Taken together, these results indicate that expression of sialic acid 9-O-acetylation can be regulated by the action of specific sialyltransferases that alter the predominant linkage of the terminal sialic acids found on specific classes of glycoconjugates.
Shi
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WX
University of California at San Diego Cancer Center, Division of Cellular and Molecular Medicine, University of California at San Diego, La Jolla, California 92093, USA.
Chammas
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R
Varki
A
A
D000123:Acetyltransferases / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D002240:Carbohydrate Sequence; D002460:Cell Line; D002522:Chlorocebus aethiops; D002851:Chromatography, High Pressure Liquid; D002854:Chromatography, Paper; D002855:Chromatography, Thin Layer; D006224:Cricetinae; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D005732:Gangliosides / Q000032:analysis / Q000378:metabolism; D006001:Glycoconjugates / Q000378:metabolism; D006801:Humans; D007074:Immunoglobulin G; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000378:metabolism; D012799:Sialyltransferases / Q000378:metabolism*; D013379:Substrate Specificity; D014162:Transfection; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase; D000094663:beta-Galactoside alpha-2,3-Sialyltransferase
D005732:Gangliosides; D006001:Glycoconjugates; D007074:Immunoglobulin G; D011994:Recombinant Proteins; D000123:Acetyltransferases; C099970:sialic acid O-acetyltransferase; D012799:Sialyltransferases; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase; D000094663:beta-Galactoside alpha-2,3-Sialyltransferase