Co-ordinate and restricted expression of the ProXaaArg/lys-specific GalNAc-transferase and the GalNAcβ1,4GlcNAcβ1,2Manα-4-sulfotransferase

Asn-linked oligosaccharides terminating with the sequence SO₄-4GalNAcβ1,4GlcNAcβ1,2Manα (84GGnM) are present on the glycoprotein hormones lutropin and thyrotropin, pro-opiomelanocortin, and tissue factor pathway inhibitor. The peptide motif ProXaaArg/Lys (PXR/K), which is recognized by a PXR/K-specific GalNAc-transferase, is present in each of these glycoproteins 6-9 residues NH₂-terminal to an Asn glycosylation site. Both the PXR/K-specific GalNAc-transferase and a GalNAcβ1,4GlcNAcβ1,2Manα (GGnM)-4-sulfotransferase are required for synthesis of the S4GGnM sequence. Glycoproteins which do not contain the PXR/K motif but bear Asn-linked oligosaccharides terminating with GGnM or sialic acidα2,3/ 6GGnM have also been described, suggesting a distinct GalNAc-transferase may be responsible for their synthesis. We have examined a number of tissues and cultured cell lines for the transfer of sulfate to the trisaccharide acceptor GGnM and transfer of GalNAc to oligosaccharide acceptors on protein which do, human chorionic gonadotropin (hCG), and do not, transferrin (Trf), contain the PXR/K motif. The PXR/K-specific GalNAc-transferase and the GGnM-4-sulfotransferase are expressed in salivary gland, pituitary, lacrimal gland, kidney, and brain, and in the cell lines AtT-20, 293, SHSY5Y, and αT3. In contrast Bowes, EL-4, and B16L6 cell extracts transferred GalNAc to oligosaccharides acceptors on Trf but not on hCG. A number of tissues and cell lines displayed transfer of GalNAc to both hCG and to Trf suggesting that two distinct GalNAc-transferases were present. The GGnM-4-sulfotransferase was expressed in tissues and cell lines which expressed the PXR/K-specific GalNAc-transferase but not in cell lines expressing exclusively the Trf-specific GalNAc-transferase. Thus, the PXR/ K-specific GalNAc-transferase and the GGnM-4-sulfotransferase are coordinately expressed in a number of tissues other than pituitary. The Trf-specific GalNAc-transferase may account for the presence of β1,4-linked GalNAc on glycoproteins which do not contain the PXR/K motif.