1,6FUCOSYLTRANSFERASE IS HIGHLY AND SPECIFICALLY EXPRESSED IN HUMAN OVARIAN SEROUS ADENOCARCINOMAS Tomoaki TAKAHASHI 1,2 , Yoshitaka IKEDA 1 , Eiji MIYOSHI 1 , Yuji YAGINUMA 2 , Mutsuo ISHIKAWA 2 and Naoyuki TANIGUCHI 1 * 1 Department of Biochemistry, Osaka University Medical School, Osaka, Japan 2 Department of Obstetrics and Gynecology, Asahikawa Medical College, Asahikawa, Japan An elevated level of 1,6fucosylation in N-glycans repre- sents one of the cancer-related alterations of oligosaccha- rides and is associated with the metastatic potential of hep- atoma cells. However, expression of 1,6fucosyltransferase (1,6FucT), which is involved in this aberrant glycosylation, has not been intensively explored in other malignant tumors. We report on a study of the expression of 1,6FucT in various types of epithelial ovarian carcinoma tissue, as well as normal ovary, benign and borderline ovarian tumors. The activity assay showed that 1,6FucT is highly and specifically elevated in serous adenocarcinomas but not in normal and other ovarian tumor tissues. This elevation was due to en- hancement of mRNA expression, as evidenced by Northern blot analysis. Furthermore, we have shown immunohisto- chemically that 1,6FucT expression is localized predomi- nantly in cancer cells. Lectin blot analysis using Lens culinaris agglutinin, which preferentially recognizes 1,6fucose resi- due, suggested that several glycoproteins were likely targets for modification by 1,6fucosylation in serous adenocarci- noma tissues. These findings suggest that the elevated ex- pression of 1,6FucT and the resulting modification of N- glycans are distinctive features of this type of ovarian cancer and may be related to the progression of this malignancy. Int. J. Cancer 88:914 –919, 2000. © 2000 Wiley-Liss, Inc. A variety of structural alterations of cell-surface sugar chains of complex carbohydrates are associated with development, differen- tiation and malignant transformation (Hakomori, 1989). It has been proposed that alterations in the oligosaccharide structures of glycoproteins from malignant cells are associated with invasion and metastasis since cell-surface glycoproteins and their oligosac- charide moieties play an important role in cell adhesion and cell– cell interactions (Asada et al., 1997; Dennis et al.,1984; Glick et al., 1973; Taniguchi et al., 1996). N-Acetylglucosaminyltrans- ferases (GmTs), which are involved in the biosynthesis of com- plex-type N-glycans, play significant roles in the potential for malignancy via alteration of N-glycan structures (Demetriou et al., 1995; Dennis et al., 1987; Taniguchi et al., 1996; Yoshimura et al., 1995). Thus, a significant body of evidence suggests that alter- ations of cell-surface oligosaccharides are of critical importance in the progression of cancer. An elevated level of fucose content in glycoproteins is one of the cancer-related alterations of oligosaccharides, as found in patients with malignant diseases (Tatsumura et al., 1977). The change in fucosylation levels in an oligosaccharide structure has been intensively investigated in the case of -fetoprotein (AFP), an oncofetal protein. The level of AFP in serum is frequently in- creased in hepatoma patients, and, because of this, AFP is widely used as a tumor marker for the serum diagnosis of hepatoma. In other acute or chronic liver diseases, however, serum levels of AFP are also increased. Therefore, an increase in the level of fucosylation of AFP is more specifically observed in sera of hepatoma patients, as judged by lectin-affinoelectrophoresis using Lens culinaris agglutinin (LCA), a useful tumor marker since the lectin preferentially binds to an 1,6fucose residue in N-glycan (Aoyagi et al., 1985; Yamashita et al., 1993; Taketa et al., 1993). 1,6Fucosyltransferase (1,6FucT) catalyzes the transfer of fu- cose to the innermost GlcNAc residue of complex N-glycans via an 1,6 linkage (Fig. 1a) and was originally identified in porcine liver (Longmore and Schachter, 1982). The enzymatic basis for the change in oligosaccharide structures in hepatoma has been ex- plored by Hutchinson et al. (1991), who showed that 1,6FucT activity is consistently elevated in hepatoma tissues whereas it is decreased in uninvolved adjacent tissues. In addition, the activity is elevated in plasma of hepatoma patients. We have reported the purification of 1,6FucTs from porcine brain and a human gastric cancer cell line, obtaining their cDNAs with the goal of elucidating the molecular basis of the cancer-related alteration of oligosaccha- ride structures (Uozumi et al., 1996b; Yanagidani et al., 1997). 1,6FucT activity is strongly enhanced from an early stage of hepatocarcinogenesis in Long-Evans cinnamon (LEC) rats, which spontaneously develop hereditary hepatoma, and this enhancement is due to the increased expression levels of its mRNA (Noda et al., 1998a). Thus, it has been suggested that increases in the level of expression and the activity of 1,6FucT underlie the increased levels of 1,6fucosylation in glycoproteins, including AFP (Noda et al., 1998b) during hepatocarcinogenesis (Miyoshi et al., 2000). In contrast to hepatomas, the detailed enzymatic basis for struc- tural changes in N-glycans has not been investigated in ovarian carcinomas, the most lethal gynecological malignancy, and the extent of alteration of oligosaccharide structure with respect to this disease has not been examined in detail. However, while non- glycosylated proteins have been reported to be useful as tumor markers for the diagnosis of ovarian carcinomas (Ishikawa et al., 1990; Nakata et al., 1992), glycoproteins have also been used as markers on the basis of alterations in their oligosaccharide struc- tures. These structural changes are consistent with the aberrant glycosylation of glycoproteins, possibly as a result of malignant transformation (Hakomori, 1985). CA19-9 (sLe a ) and SLX (sLe x ) are oligosaccharide antigens used as markers for the diagnosis of ovarian cancer, which is consistent with the expression of glyco- syltransferases in ovarian carcinomas. Although these markers and their utility in the diagnosis of ovarian carcinomas have been investigated, the biological significance of such an alteration of oligosaccharide structures is not fully understood. It has also been suggested that CA125, which is one of the most widely used markers for ovarian cancer, is a mucin-type glycoprotein (Bast et al., 1983; Lloyd, et al., 1997). However, it is uncertain whether carbohydrate moieties of CA125 are altered in conjunction with carcinogenesis. It has been suggested that addition of an 1,6fucose residue to the innermost GlcNAc of the N-linked oligosaccharide leads to an unusual extended conformation (Stubbs et al., 1996). Therefore, it is possible that 1,6fucosylation leads to modifications of the functions of glycoproteins, such as growth factor receptors, adhe- sion molecules and extracellular matrices, by inducing conforma- tional changes in the N-glycan structure. This reasoning suggests that an 1,6fucose residue may be associated with the potential for the development of malignancy and that the enzyme involved in Grant sponsor: Ministry of Education, Science, Sports and Culture of Japan; Grant number: 10178104. *Correspondence to: Department of Biochemistry, Osaka University Medical School, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. Fax: +81-6-6879-3429. E-mail: proftani@biochem.med.osaka-u.ac.jp Received 13 June 2000; Revised 14 August 2000; Accepted 23 August 2000 Int. J. Cancer: 88, 914 –919 (2000) © 2000 Wiley-Liss, Inc. Publication of the International Union Against Cancer