Lectin-resistant variants and revertants of mouse melanoma cells: differential expression of a fucosylated cell-surface antigen and altered metastasizing capacity

Carbohydrate recognition in neuronal development: structure and expression of surface oligosaccharides and beta-galactoside-binding lectins

The differentiation and development of vertebrate neurons is controlled in part by interactions with cell surface and extracellular matrix molecules, many of which are glycoproteins that mediate their developmental actions by homophilic or heterophilic binding to other glycoproteins. In addition there is increasing evidence that cell recognition and adhesion in some embryonic cell types involve interactions between cell surface oligosaccharides and complementary carbohydrate-binding proteins. Although a role for carbohydrate recognition in neuronal development has been proposed, the precise function of complex carbohydrate structures on neural cells has not been defined. To approach this problem, we have examined the structure and expression of cell surface oligosaccharides and carbohydrate-binding proteins by primary sensory neurons in the rat dorsal root ganglion (DRG). There are several functionally distinct subsets of DRG neurons, each of which conveys a different sensory modality to distinct target domains in the spinal cord. Monoclonal antibodies against defined oligosaccharide structures identify each of the major subsets of DRG neurons on the basis of their expression of a distinct set of complex oligosaccharides, derived from lacto-, globo- and ganglioseries backbone structures. In particular, small diameter DRG neurons involved in pain processing express beta-galactoside-based lactoseries oligosaccharides. DRG and spinal cord neurons also express two soluble beta-galactoside-binding proteins of relative molecular masses 14,500 and 29,000, termed RL-14.5 and RL-29, which represent potential ligands for lactoseries oligosaccharides. RL-14.5 is expressed by the majority of DRG neurons whereas RL-29 is restricted to the subset of small DRG neurons that express surface N-acetyllactosamine structures. RL-14.5 and RL-29 are expressed soon after the differentiation of DRG neurons and appear to be released from cultured DRG neurons. Rat brain cDNA clones encoding RL-14.5 have been isolated. The nucleotide and predicted amino acid sequence of RL-14.5 has confirmed that this lectin is highly homologous to soluble beta-galactoside-binding proteins in other vertebrate species. Northern blot analysis and in situ hybridization indicate that RL-14.5 mRNA is selectively expressed in sensory and motor neurons in the rat nervous system. The selective expression of lactoseries oligosaccharides and complementary beta-galactoside-binding lectins may contribute to the differentiation and/or development of these two classes of neurons.

Down-regulation of N-acetylglucosaminyltransferase V by tumorigenesis- or metastasis-suppressor gene and its relation to metastatic potential of human hepatocarcinoma cells

The effects of transfection of the metastasis suppressor gene nm23-H1 and cell-cycle related tumor-suppressor gene p16 on the activity of N-acetylglucosaminyltransferase V (GnT-V) and their relations to cancer metastatic potential were investigated. After transfection of nm23-H1 into 7721 human hepatocarcinoma cells and A549 human lung cancer cells, the activities of GnT-V were decreased by 28%-42% in the cells. In contrast, when p16 was transfected into these two cell lines, the decrease of GnT-V activity was only observed in A549 cells. This was probably to be due to the obvious expression of p16 gene in parental 7721 cells and the deletion of p16 in A549 cells. The decrease of GnT-V mRNA was only observed in nm23-H1-transfected cells, but not in p16-transfected A549 cells, suggesting that these two genes regulated GnT-V via different mechanisms. Horseradish peroxidase (HRP)-lectin staining showed that the 7721 cells transfected with nm23-H1 or the A549 cells transfected with p16 displayed a decreased intensity with HRP-leucoagglutinating phytohemagglutinin and increased intensity with HRP-concanavalin A, indicating the decline of beta1,6 N-acetylglucosamine branching structure on the asparagine-linked glycans of cell-surface and intracellular glycoproteins. The nm23-H1 transfected 7721 cells also displayed some changes in metastasis-related phenotypes, including the increase in cell adhesion to fibronectin (Fn), the decline in cell adhesion to laminin (Ln), and the decreased cell migration and invasion through matrigel. Transfection of antisense GnT-V cDNA into 7721 cells resulted in a decrease of GnT-V activity, an increase of cell adhesion to Fn or Ln, and a decrease in cell migration and invasion through matrigel. These phenotypes bore similarity to those of the 7721 cells transfected with nm23-H1. Our findings indicate that the down-regulation of GnT-V by nm23-H1 contributes to the alterations in metastasis-related phenotypes, and is an important molecular mechanism of metastasis suppression mediated by nm23-H1.

Regulation of the GnT-V promoter by transcription factor Ets-1 in various cancer cell lines

Although the precise role of oligosaccharides in metastasis is presently unknown, numerous studies suggest that the beta1-6 branching structure of N-linked oligosaccharides plays a role in tumor metastasis. N-Acetylglucosaminyltransferase V (GnT-V), which catalyzes the formation of the beta1-6 branch, therefore appears to play a crucial role in tumor metastasis. Recently, we demonstrated that the expression of the GnT-V gene is regulated by a transcriptional factor, Ets-1 (Kang, R., Saito, H., Ihara, Y., Miyoshi, E., Koyama, N., Sheng, Y., and Taniguchi, N. (1996) J. Biol. Chem. 271, 26706-26712). In this study, we report an investigation of the general requirement for Ets-1 in the expression of GnT-V in cancer cell lines. In 16 cancer cell lines, the levels of GnT-V mRNA were closely correlated with ets-1 expression (r = 0.97; p < 0.0001). An increase in ets-1 levels by transfection of its cDNA led to an enhancement in GnT-V expression in cells that normally expressed low levels of ets-1. In contrast, the transfection of dominant negative ets-1 into cells that express high levels of ets-1 resulted in a decrease in GnT-V expression. Although Ets-1 cooperates with c-Jun in certain gene expressions, this was not the case in the regulation of the GnT-V gene. These results suggest that Ets-1 plays a significant role in regulating the expression of GnT-V in a variety of cancers and might be involved in the potential for malignancy via the action of GnT-V.

Transcriptional regulation of N-acetylglucosaminyltransferase V by the src oncogene

Transformation of baby hamster kidney fibroblasts by the Rous sarcoma virus causes a significant increase in the GlcNAcbeta(1, 6)Man-branched oligosaccharides by elevating the activity and mRNA transcript levels encoding N-acetylglucosaminyltransferase V (GlcNAc-T V). Elevated activity and mRNA levels could be inhibited by blocking cell proliferation with herbimycin A, demonstrating that Src kinase activity can regulate GlcNAc-T V expression. 5' RACE analysis was used to identify a 3-kilobase 5'-untranslated region from GlcNAc-T V mRNA and locate a transcriptional start site in a 25-kilobase pair GlcNAc-T V human genomic clone. A 6-kilobase pair fragment of the 5' region of the gene contained AP-1 and PEA3/Ets binding elements and, when co-transfected with a src expression plasmid into HepG2 cells, conferred src-stimulated transcriptional enhancement upon a luciferase reporter gene. This stimulation by src could be antagonized by co-transfection with a dominant-negative mutant of the Raf kinase, suggesting the involvement of Ets transcription factors in the regulation of GlcNAc-T V gene expression. The src-responsive element was localized by 5' deletion analysis to a 250-base pair region containing two overlapping Ets sites. src stimulation of transcription from this region was inhibited by co-transfection with a dominant-negative mutant of Ets-2, demonstrating that the effects of the src kinase on GlcNAc-T V expression are dependent on Ets.

Helix pomatia agglutinin binding in human tumour cell lines: correlation with pulmonary metastases in nude mice

The extent of lectin binding by three human melanoma (LOX, FEMX-1 and SESX) and two sarcoma lines (MHMX and OHSX) was related to their potential for experimental metastasis formation in athymic nude mice. The Helix pomatia agglutinin (HPA), which recognises the N-acetyl-D-galactosamine ligand, showed differential binding to the cell lines in a manner that correlated with their ability to give lung colonies after i.v. injection in the mice (P < 0.005). The degree of HPA binding and lung colony formation of the cell lines studied was ranked in the following order, LOX > MHMX > OHSX > SESX > FEMX-I. Similar patterns were not observed with the other lectins used in this study (WGA, Con A, PNA and UEA-I). The high HPA reacting LOX melanoma line shows extensive pulmonary metastatic formation with no extrapulmonary colonies, whereas the low HPA reacting FEMX-I cells give only extrapulmonary metastases with no detectable colonies in the lungs. Precoating of tumour cells with HPA prior to injection did not reduce the ability of cells to give pulmonary metastases, suggesting that the HPA epitope was not functionally associated with the pulmonary metastatic potential observed in nude mice. These findings support recent human studies of a correlation between HPA binding and incidence of metastasis, however, our data indicate that there is no causal relationship. Further analyses are required to identify the specific HPA-binding glycoconjugates that may be involved.

Antimetabolite-induced increases in the invasive capacity of murine leukaemia L1210 cells

Pretreatment of murine leukaemia L1210 cells with non-lethal concentrations of various antimetabolites increased the in vitro invasive capacity of these cells into monolayers of rat embryo fibroblasts. The increase in invasive capacity was partly correlated with the induced cell cycle arrest. The concomitant increase in cell surface fucosylation and inhibition of invasion with sulphate indicate a role for glycoproteins in this process. Our results suggest that treatment with antimetabolites may lead to a more aggressive phenotype by altering cell surface properties.

The identification of glioblastoma-associated, fucose-containing glycoproteins induced by retinoic acid

We have used a tumorigenic glioblastoma cell line, SNB-19, as a model system to identify fucose-containing glycoprotein candidates for tumor suppressor function. Glycoproteins were analyzed after treatment with a variety of chemical differentiating agents by two-dimensional SDS-PAGE, followed by electroblotting and visualization using the fucose-specific lectin, Ulex europeaus I. Approximately 25 fucose-containing glycoproteins (FUCGLAPs) were routinely visualized in control extracts using 60-70 micrograms of protein per gel and staining with Vectastain ABC kits. Retinoic acid induced the most marked change in FUCGLAP expression, causing a fivefold increase in one FUCGLAP (M(r) = 125 kDa, pI = 6.6). Neither butyric acid, dibutyryl cAMP, nor combinations of these compounds gave a similar result. Using this model system and analytical approach, it should be possible to identify, isolate, and evaluate glycoprotein oligosaccharides for their tumor modulating capability.

A, B, H, and Lewis-a and Lewis-b blood group antigens in human breast cancer: correlation with steroid hormone receptor and disease status

Estrogen (ER) and progesterone (PR) hormone receptor status and levels were correlated with blood group antigen (A, B, H, Lewis-a and Lewis-b) expression in 48 cases of human breast cancer. Reduced expression of all the blood group antigens was observed with statistically significant reductions for H, Lewis-a and Lewis-b (P < 0.05). The proportions of ER- and PR-positive breast cancers staining for Lewis-b were greater than in hormone-receptor-negative cancers but the differences were not significant. The loss of Lewis-b antigen in breast cancer increased with tumor grade but did not correlate with axillary lymph node metastases. Loss of Lewis-b antigen is probably not a predictor of local recurrence and survival in the short period of observation. We conclude that the loss of H, Lewis-a and, especially, Lewis-b in breast cancer reflects the invasiveness of breast cancer and that Lewis-a and b expression is probably only marginally and not significantly affected by steroid hormone receptor status and levels.

Analysis of factors associated with the tumorigenic potential of 12 tumor clones derived from a single rat colon adenocarcinoma

We analyzed several factors which could influence the immunogenicity of colon tumor cells, using a series of clones derived from a single chemically induced rat adenocarcinoma cell line. These clones display variable tumorigenic potential in syngeneic immunocompetent animals, and it has been established that in this model the tumorigenicity of the cells depends on their ability to escape immune surveillance. The results show an absence of relationship between tumorigenicity and expression of MHC-class-I antigens, cell adhesion to rat fibroblasts or fibroblast extracellular matrix. The secretion of latent and active TGF beta I appeared to be quite variable from one clone to the other, but was unrelated to tumorigenicity. Unexpectedly, some regressive clones produced elevated levels of this cytokine, suggesting that in this model, spontaneous secretion of TGF beta I is not sufficient to impair the immune system of the host. In contrast, the more tumorigenic clones were more resistant than less tumorigenic ones to cytotoxicity mediated by NK or LAK cells. They also showed arrest of cell proliferation after reaching confluence, something not observed in the less tumorigenic clones. Finally, the strongest relationship with tumorigenicity was found for expression of blood-group carbohydrate antigens. Increased expression of blood-group-H antigen and, conversely, decreased expression of beta-galactoside precursors of this antigen correlated with increased tumorigenicity.

Monoclonal antibodies against a human gastric cancer cell line with lung metastatic potential in nude mice define antigens with different expression between the primary and metastatic liver lesions

SCK-29 is a tumor cell line derived from human gastric adenocarcinoma with the feature of producing lung metastases when xenografted in nude mice. Monoclonal antibodies were produced against SCK-29 tumor cells or their glycoproteins prepared by affinity chromatography on a lectin-agarose column. Five antigens defined by the monoclonal antibodies MG-1 to MG-5 were expressed in a large number of gastric or colonic adenocarcinomas. Among the antigens, MG-1 and MG-3 proved to be tumor-associated, since they were detected only occasionally in normal tissues. MG-5 antigen was often detected in normal gastric mucosa but not in other tissues. The degree of expression of MG-1. MG-3 and MG-5 antigens differed considerably in metastatic lesions. In metastatic liver lesions of gastric adenocarcinoma, expression of these MG antigens was less marked than in primary tumors. MG-1 and MG-3 antigens were abolished by neuraminidase digestion and periodate oxidation. MG-5 antigen was likely to be a protein antigen, since it was resistant to neuraminidase digestion and to periodate oxidation but was sensitive to protease digestion.