The j31-6 structure of N-linked oligosaccharides, formed by j8-1,6-N-acetylglucosaminyltransferase (GnT-V), is associated with metastatic potential. We established a highly metastatic subclone, B16-hm, from low metastatic B16-F1 murine melanoma cells. The gene encoding 18-1,4-N-acetylglucosaminyltransferase (GnT-III) was introduced into the B16-hm cells, and three clones that stably expressed high GnT-III activity were obtained. In these transfectants, the affinity to leukoagglutinating phytohemagglutinin was reduced, whereas the binding to erythroagglutinating phytohemagglutinin was increased, indicating that the level of 31-6 structure was decreased due to competition for substrate between intrinsic GnT-V and ectopically expressed GnT-III.Lung metastasis after intravenous injection of the transfectants into syngeneic and nude mice was significantly suppressed, suggesting that the decrease in 81-6 structure suppressed metastasis via a mechanism independent of the murine system. These transfectants also displayed decreased invasiveness into Matrigel and inhibited cell attachment to collagen and laminin. Cell growth was not affected. Our results demonstrate a causative role for p1-6 branches in invasion and cell attachment in the extravasation stage of metastasis.Malignant transformation is highly associated with alterations of N-linked oligosaccharides. The extensive and persistent changes in the population of protein-bound oligosaccharides in malignant cells have been proposed to disturb cell division, decrease intercellular adhesiveness, and mask immunogenicity (1). The glycopeptides in polyoma-transformed baby hamster kidney cells have unusually high molecular weights due to the presence of external sialic acid as well as galactose and GlcNAc (2). The predominant surface glycopeptide of baby hamster kidney cells transformed by Rous sarcoma virus was determined to be a triantennary, completely sialylated, complex glycopeptide containing a core region of Man, GlcNAc, and Fuc (3). Synthesis of these elongated branches is initiated by 13-1,6-N-acetylglucosaminyltransferase (GnT-V; EC 2.4.1.155), which catalyzes the formation of the (31-6 branch (4). GnT-V activity correlated well with the metastatic potential of rastransformed Rat2 fibroblasts, SP1 mammary carcinoma cells, the MDAY-D2 lymphoma cell line (5, 6), and human colon cancer cells (7). Rat2 fibroblasts transfected with H-ras or v-frs exhibited metastatic potential and had elevated GnT-V activity and increased (1-6 branches (8), whereas a mutant with decreased GnT-V activity from a highly metastatic tumor cell line had a decreased potential for metastasis in mice (6). These observations have suggested a positive correlation between ,B1-6 branching and metastatic capacity.One approach to analyzing the role of GnT-V and its product, (31-6 branches, in metastasis is to reduce GnT-V activity in malignant cells with a high tendency to metastasize. As shown in Fig. 1, both 1-1,4-N-acetylglucosaminyltransferase (GnT-III; EC 2.4.1.144) and GnT-V use the t...

No abstract

A beta 1-6N-acetylglucosaminyltransferase (GnT-V) [EC 2.4.1.155] which catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to alpha-D-6-mannoside has been purified up to 20,000-fold from the cultured supernatant of the QG small lung cancer cell line with a 37% yield. The isolation procedure included chromatography on phenyl-Sepharose, hydroxylapatite, UDP-hexanolamine Sepharose, and a biantennary sugar substrate (GnGn-bi-Asn) coupled to activated CH-Sepharose 4B. Sodium dodecyl sulfate gel electrophoresis under non-reducing conditions showed a single band of 73 kDa. Under reducing conditions, however, an additional component of 60 kDa was seen. Peptide mapping analysis indicated that both of these proteins were essentially identical, indicating that the 60-kDa component is probably a proteolytically cleaved form of the 73-kDa protein. Studies on the activity of the enzyme toward a variety of pyridylaminated sugars showed that the enzyme is most active toward triantennary (GnGnGn-tri-PA) and biantennary (GnGn-bi-PA) sugars. The Km values for GnGn-bi-PA and UDP-GlcNAc were 133 microM and 3.5 mM, respectively. These studies represent the first report of the enzymatic properties of a highly purified human GnT-V.

No abstract

Clostridium botulinum type C 16S progenitor toxin consists of a neurotoxin (NTX), a non-toxic non-HA (NTNH), and a haemagglutinin (HA). The HA acts as an adhesin, allowing the 16S toxin to bind to intestinal epithelial cells and erythrocytes. In type C, these bindings are dependent on sialic acid. The HA consists of four distinct subcomponents designated HA1, HA2, HA3a and HA3b. To identify the binding subcomponent(s) of HA of type C 16S toxin, all of the HA-subcomponents and some of their precursor forms were produced as recombinant proteins fused to glutathione S-transferase (GST). These proteins were evaluated for their capacity to adhere to intestinal epithelial cells of guinea pig and human erythrocytes. GST-HA1, GST-HA3b and GST-HA3 (a precursor form of HA3a and HA3b) bound intestinal epithelial cells and erythrocytes, whereas GST alone, GST-HA2 and GST-HA3a did not. GST-HA3b and GST-HA3 showed neuraminidase-sensitive binding to the intestinal epithelial cells and erythrocytes, whereas GST-HA1 showed neuraminidase-insensitive binding. TLC binding assay revealed that GST-HA3b and GST-HA3 recognized sialosylparagloboside (SPG) and GM3 in the ganglioside fraction of the erythrocytes, like native type C 16S toxin [Inoue, K. et al. (1999). Microbiology 145, 2533–2542]. On the other hand, GST-HA1 recognized paragloboside (PG; an asialo- derivative of SPG) in addition to SPG and GM3. Deletion mutant analyses of GST-HA3b showed that the C-terminal region of HA3b is important for its binding activity. Based on these data, it is concluded that the HA component contains two distinct carbohydrate-binding subcomponents, HA1 and HA3b, which recognize carbohydrates in different specificities.