Remodeling of cell surface glycoproteins by N-acetylglucosaminyltransferase III gene transfection: modulation of metastatic potentials and down regulation of hepatitis B virus replication.

Abstract

The biosynthesis of sugar chains in N-glycans is catalyzed by several glycosyltransferases. Among them, at least six kinds of N-acetylglucosaminyltransferase (GnT) occur in mammalian tissues (Gleeson and Schachter, 1983; Rademachter et ai, 1988). We have focused on two GnTs that are implicated in the branch formation of N-glycans such as GnT-III and GnT-V, (Taniguchi and Ihara, 1995). GnT-III and GnT-V use the same biantennary structure as a substrate (Schachter, 1985). GnT-III catalyzes the formation of (31-4 GlcNAc branches (bisecting GlcNAc), while GnT-V catalyzes the formation of (31-6 branches as shown in Figure 1. The GnT-III product, bisecting GlcNAc, has been found in various glycoproteins such as IgG (Fujii et ai, 1990) and -y-glutamyltranspeptidases (Yamashita, 1983). On the other hand, (31-6 branches are found in various tumor cell lines with high metastatic potentials (Dennis et ai, 1987; Dennis and Laferte et ai, 1989; Saitoh et ai, 1992). We have purified GnT-V from a human lung cancer cell line (Gu et ai, 1993) and found that GnT-V is not able to form any further tri'-structure once a bisecting GlcNAc residue is added to the core mannose by GnT-III (Schachter, 1985). Therefore, we have investigated whether high activity of GnT-III, produced by the overexpression of GnT-III gene, will inhibit GnT-V activity in vivo. We showed that this occurs in melanoma cells with high metastatic potentials. Thus, the overexpression of GnT-III downregulates the GnT-V activity (Yoshimura et ai, 1995) as well as modulating various intracellular or cell surface glycoproteins such as E-cadherin and lysosomal associated membranous protein-1 (LAMP-1). Also, the metastasis to the lung was markedly suppressed in the experimental models for metastasis in mice (Yoshimura et al, 1996). We also obtained stably transfectants of GnT-III in the hepatitis B virus (HBV) transfected hepatoma cells and found that the transfection of GnT-III gene modifies glycoproteins on the cell surface and the virus replication is dramatically suppressed (Miyoshi et ai, 1995). The data suggest that remodeling of cell surface or intracellular glycoproteins by glycosyltransferase gene transfection may change the gene expression and cellular communications in the cells.