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 alpha 2-6-sialyltransferase (Gal beta 1-4Glc-NAc:alpha 2-6 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 (alpha 2-3-sialyltransferase (Gal beta 1-(3)4GlcNAc:alpha 23-sialyltransferase (ST6Gal III) formerly ST3N) into either cell type, Further analyses of stably transfected parental CHO-K1 cells indicated that expression of the STGGa1 I gene causes selective 9-O-acetylation of alpha 2-6-linked sialic acid residues on N-linked oligosaccharides, In a similar manner, while the alpha 2-3 linked sialic acid residue of the endogenous G(M3) ganglioside of CHO cells is not O-acetylated, transfection of an alpha 2-8-sialyltransferase (G(M3):alpha 2-8-sialyltransferase (ST8Sia I); formerly G(D3) synthase) caused expression of 9-O-acetylation of the alpha 2-8-linked sialic acid residues of newly synthesized G(D3). 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.