A Transfected Sialyltransferase That Is Elevated in Breast Cancer and Localizes to the medial/trans-Golgi Apparatus Inhibits the Development of core-2–based O-Glycans

Whitehouse, Caroline; Burchell, Joy; Gschmeissner, Stephen; Brockhausen, Inka; Lloyd, Kenneth O.; Taylor-Papadimitriou, Joyce

With the exception of the study of Roth et al. (1994) , who used an antibody to map the position of a GalNAc T to the cis-Golgi apparatus, the positioning of enzymes involved in mucin-type O-glycosylation has relied mainly on sucrose density gradient centrifugation (Chaney et al., 1989) or on following the glycosylation of marker proteins (Locker et al., 1992) . The work presented here represents the first fine mapping of a sialyltransferase active specifically in O-glycosylation. Previous work by Locker and colleagues following the acquisition of oligosaccharides onto the M protein of Coronavirus and the effects of brefeldin A suggested that ␣2,3 SAT (O) is in an earlier compartment than the TGN (Locker et al., 1992; Lippincott-Schwartz et al., 1990) . The results presented here support their interpretation of the data, as we place the ␣2,3 sialyltransferase in the trans and medial cisternae but also in the TGN. However, with the cloning of genes encoding the glycosyltransferases (Joziasse, 1992; Clausen and Bennett, 1996) , it is becoming apparent that this group of enzymes is extremely complex and that there is a large family of sialyltransferases (Tsuji, 1996) that may be resident in different Golgi cisternae. Thus, it becomes imperative to localize each specific enzyme directly, which can be achieved using tagged cDNA as described here, or by developing antibodies to the expressed recombinant enzymes.