Identification of asparagine-linked oligosaccharides involved in tumor cell adhesion to laminin and type IV collagen

Glycosylation Changes in Brain Cancer

Protein glycosylation is a posttranslational modification that affects more than half of all known proteins. Glycans covalently bound to biomolecules modulate their functions by both direct interactions, such as the recognition of glycan structures by binding partners, and indirect mechanisms that contribute to the control of protein conformation, stability, and turnover. The focus of this Review is the discussion of aberrant glycosylation related to brain cancer. Altered sialylation and fucosylation of N- and O-glycans play a role in the development and progression of brain cancer. Additionally, aberrant O-glycan expression has been implicated in brain cancer. This Review also addresses the clinical potential and applications of aberrant glycosylation for the detection and treatment of brain cancer. The viable roles glycans may play in the development of brain cancer therapeutics are addressed as well as cancer-glycoproteomics and personalized medicine. Glycoprotein alterations are considered as a hallmark of cancer while high expression in body fluids represents an opportunity for cancer assessment.

Glycosylation alterations in lung and brain cancer

Alterations in glycosylation are common in cancer and are thought to contribute to disease. Lung cancer and primary malignant brain cancer, most commonly glioblastoma, are genetically heterogeneous diseases with extremely poor prognoses. In this review, we summarize the data demonstrating that glycosylation is altered in lung and brain cancer. We then use specific examples to highlight the diverse roles of glycosylation in these two deadly diseases and illustrate shared mechanisms of oncogenesis. In addition to alterations in glycoconjugate biosynthesis, we also discuss mechanisms of postsynthetic glycan modification in cancer. We suggest that alterations in glycosylation in lung and brain cancer provide novel tumor biomarkers and therapeutic targets.

Leukocyte-cancer cell fusion: initiator of the warburg effect in malignancy?

The causes of metastasis remain unknown, however it has been proposed for nearly a century that metastatic cells are generated by fusion of tumor cells with tumor-associated leukocytes such as macrophages. Indeed, regardless of cell or tissue origin, when cancer cells in the original in situ tumor transform to malignant, invasive cells, they generally become aneuploid and begin to express molecules and traits characteristic of activated macrophages. This includes two key features of malignancy: chemotactic motility and the use of aerobic glycolysis as a metabolic energy source (the Warburg effect). Here we review evidence that these phenomena can be well-explained by macrophage-cancer cell fusion, as evidenced by studies of experimental macrophage-melanoma hybrids generated in vitro and spontaneous host-tumor hybrids in animals and more recently humans. A key finding to emerge is that experimental and spontaneous cancer cell hybrids alike displayed a high degree of constitutive autophagy, a macrophage trait that is expressed under hypoxia and nutrient deprivation as part of the Warburg effect. Subsequent surveys of 21 different human cancers from nearly 2,000 cases recently revealed that the vast majority (~85%) exhibited autophagy and that this was associated with tumor proliferation and metastasis. While much work needs to be done, we posit that these findings with human cancers could be a reflection of widespread leukocyte-cancer cell fusion as an initiator of metastasis. Such fusions would generate hybrids that express the macrophage capabilities for motility and survival under adverse conditions of hypoxia and nutrient deprivation, while at the same time maintaining the deregulated mitotic cycle of the cancer cell fusion partner.

In vivo expression of the 25-kDa laminin-binding protein ofHelicobacter pylori

The gastroduodenal pathogen Helicobacter pylori has been shown to inhibit the interaction between the extracellular matrix protein laminin and its receptor on gastric epithelial cells, potentially contributing to a loss of mucosal integrity. As a 25-kDa outer membrane protein of H. pylori in association with the bacterial lipopolysaccharides (LPS) mediates attachment to laminin, the aim of this study was to determine whether the 25-kDa protein is produced by H. pylori in infected hosts. We examined the immune response to the 25-kDa laminin binding protein in 12 paediatric patients; samples from a H. pylori-negative healthy adult were used as controls. In immunoblotting, antibodies to a 25-kDa protein were found in the serum and saliva of H. pylori-positive individuals only, and using the positive sera and saliva, laminin binding to the 25-kDa protein was inhibited. Thus, the 25-kDa laminin-binding protein is produced by H. pylori in infected hosts.

The Autoantigen of Anti-p200 Pemphigoid Is an Acidic Noncollagenous N-Linked Glycoprotein of the Cutaneous Basement Membrane

Anti-p200 pemphigoid is an autoimmune subepidermal blistering disease characterized by autoantibodies to a 200-kDa protein (p200) of the dermal-epidermal junction (DEJ). p200 has been demonstrated to be distinct from all major DEJ autoantigens and is thought to be important for cell-matrix adhesion. This study provides the first biochemical characterization of p200. Differential extraction experiments demonstrated that efficient recovery of p200 from the dermis was strongly dependent on the presence of reducing agents, suggesting that it forms highly insoluble oligomers and/or is extensively cross-linked to other extracellular matrix components by disulfide bonding. p200 was resistant to digestion with bacterial collagenase, whereas this treatment did degrade major collagenous proteins of the dermis, including type I, VI, and VII collagen. This finding firmly established the noncollagenous nature of p200. N-Glycosidase F reduced the molecular size of the p200 autoantigen from 200 to 190 kDa without decreasing its immunoreactivity. In contrast, digestion of p200 with neuraminidase, O-glycosidase, chondroitinase ABC, and heparitinase I had no effect on its electrophoretic mobility. These data suggest that the p200 molecule contains N-glycans but lacks O-linked oligosaccharides and chondroitin/heparan sulfate side chains. Two-dimensional gel electrophoresis demonstrated that p200 is an acidic protein with an isoelectric point of 5.4 to 5.6. Six different p200-specific sera recognized an identical protein spot of two-dimensionally separated dermal extracts, confirming that patients with this novel autoimmune disease indeed form a single pathobiochemical entity.

alpha1,6fucosyltransferase is highly and specifically expressed in human ovarian serous adenocarcinomas

An elevated level of alpha1,6fucosylation in N-glycans represents one of the cancer-related alterations of oligosaccharides and is associated with the metastatic potential of hepatoma cells. However, expression of alpha1,6fucosyltransferase (alpha1,6FucT), 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 alpha1,6FucT in various types of epithelial ovarian carcinoma tissue, as well as normal ovary, benign and borderline ovarian tumors. The activity assay showed that alpha1,6FucT is highly and specifically elevated in serous adenocarcinomas but not in normal and other ovarian tumor tissues. This elevation was due to enhancement of mRNA expression, as evidenced by Northern blot analysis. Furthermore, we have shown immunohistochemically that alpha1,6FucT expression is localized predominantly in cancer cells. Lectin blot analysis using Lens culinaris agglutinin, which preferentially recognizes alpha1,6fucose residue, suggested that several glycoproteins were likely targets for modification by alpha1, 6fucosylation in serous adenocarcinoma tissues. These findings suggest that the elevated expression of alpha1,6FucT 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.

Prior culture with concanavalin A increases intramuscular migration of transplanted myoblast

The effect was studied of pretreatment with concanavalin A (ConA) of primary myoblast cultures on their migration when transplanted into muscles. As donors, transgenic CD1 mice in which the beta-galactosidase gene is under the control of a CMV promoter (CMVLacZ.9) were used. The myoblasts were grown with 20 microg/mL ConA during the 2 days before injecting them in the right tibialis anterior (TA) muscles of BALB/c mice and mdx mice. As a control, myoblasts from the same primary cultures were grown without ConA and injected in the left TA muscles. The host muscles were not previously irradiated or damaged by notexin injection. The recipient mice were immunosuppressed with FK506. Four days after myoblast transplantation, the area occupied by donor cells was significantly greater (more than threefold) following culture with ConA than without ConA. This result indicates that culture of myoblasts with ConA permits them to migrate farther following their transplantation in host muscles not previously damaged by notexin injection or irradiation. This suggests that pretreatment with ConA may be helpful for myoblast transplantation in humans. The mechanism of this effect still remains to be investigated.

Identification of the N-acetylneuraminyllactose-specific laminin-binding protein of Helicobacter pylori

The interaction of the gastroduodenal pathogen Helicobacter pylori with the glycoprotein laminin was investigated. Binding of 125I-radiolabelled laminin in a liquid-phase assay by both hemagglutinating and poorly hemagglutinating strains was rapid, saturable, specific, partially reversible, of high affinity, and insensitive to pH. Inhibition of laminin binding by fetuin, but not asialofetuin, and reduced bacterial binding to periodate- or sialidase-treated laminin indicated that glycosylation, particularly sialylation, was important for laminin binding by H. pylori. Inhibition experiments with monosaccharides, disaccharides, and trisaccharides showed that the strains bound to a region spanning a trisaccharide. In particular, inhibition and displacement studies showed that binding to the trisaccharide N-acetylneuraminyl-alpha(2-3)-lactose [NeuAc(2-3)Lac] was preferential to that to the NeuAc(2-6)Lac isomer. Complete inhibition of laminin binding by both hemagglutinating and poorly hemagglutinating strains was achieved only when isolated lipopolysaccharide (LPS) was used as an inhibitor in combination with heat or protease treatment of H. pylori cells, thereby confirming the involvement of both LPS and a protein adhesin in laminin binding. Further inhibition experiments indicated that the protein receptor, rather than LPS, on H. pylori bound NeuAc(2-3)Lac. By using a Western blotting procedure, a 25-kDa outer membrane protein was identified as mediating laminin binding by both hemagglutinating and poorly hemagglutinating H. pylori strains. The specificity of binding was confirmed by complete inhibition of laminin binding by the 25-kDa protein with NeuAc(2-3)Lac. The data collectively suggest that a 25-kDa outer membrane protein acts in a lectin-like manner with LPS to mediate attachment of H. pylori to laminin.

The antimetabolite Tiazofurin (TR) inhibits glycoconjugate biosynthesis and invasiveness of tumour cells

We investigated the effect of Tiazofurin (TR-2-beta-D-furanosylthiazole-4-carbamide) on tumour cell invasion using metastatic 3LL-HH murine lung carcinoma and HT168-M1 human melanoma as experimental models. TR pretreatment of 3LL-HH cells, in a dose range of 15-60 microM, caused inhibition of cell proliferation, adhesion to plastic and extracellular matrix proteins. The TR-induced altered matrix interactions of 3LL-HH cells were reflected in decreased migration through matrix-covered filters. Analysis of the expression of certain invasion markers indicated that TR suppressed the expression of alpha v beta 3 integrin and MMP2 metalloproteinase. Biochemical studies indicated that 24 h 60 microM TR treatment of 3LL-HH cells inhibited glycosylation of a wide range of glycoproteins with the most pronounced effect on proteoglycans. TR pretreatment of 3LL-HH tumour cells resulted in the loss of lung colonisation potential in vivo. Furthermore, in vivo TR treatment inhibited the formation of liver metastases of 3LL-HH murine carcinoma. TR treatment also induced inhibition of integrin and MMP2 expression, migration and liver colonisation of the human melanoma HT168-M1 cell line. Since the TR concentration which inhibited various cellular functions was much lower for cell adhesion and lung colonisation than for cell proliferation, we suggest that the predominant effect of TR is the inhibition of metastasis in these model systems. We also suggest that both the effect of TR on tumour cell proliferation and on extracellular matrix interaction contribute to its remarkable antimetastatic potential in vivo.

Monoclonal antibody recognizing a determinant on type 2 chain blood group A and B oligosaccharides detects oncodevelopmental changes in azoxymethane-induced rat colon tumors and human colon cancer cell lines

Altered expression of ABH blood group substances is a common feature of human colorectal carcinoma, yet it remains unclear how these structural changes influence the biological properties of tumor cells. Azoxymethane-induced rat colon tumors display many features of the human disease, thereby providing a potentially useful model to study the role of blood group substances in colon cancer progression. We have prepared monoclonal antibodies to a microsomal fraction isolated from an azoxymethane-induced rat colon tumor and selected an antibody that detects cancer-associated changes. Monoclonal antibody (mAb) 3A7 recognizes a determinant on type 2 chain blood group A (GalNAc alpha 1-3[Fuc alpha 1-2]Gal beta 1-4GlcNAc-R) and B (Gal alpha 1-3[Fuc alpha 1-2]Gal beta 1-4GlcNAc-R) oligosaccharides. Expression of the epitope detected by this antibody was developmentally regulated in rat colon, with maximal expression from day 4-21 after birth. Immunohistochemical staining and Western blotting analyses of azoxymethane-induced colon tumors revealed increased expression of the epitope in all of the 21 colonic tumors examined, including preneoplastic glands within transitional mucosa. Conventional and signet-ring adenocarcinomas that had invaded through the muscularis propria (Duke's B2) consistently showed the most intense staining with mAb 3A7, including regions depicting angioinvasion. Some of the lymph node metastases (Duke's C2) stained poorly with the antibody. The epitope was also expressed in blood group A positive human colon carcinoma cell lines, including HT29 and SW480 but not by SW620, a cell line derived from a lymph node metastasis isolated in vivo from the SW480 primary tumor, or in the blood group B cell line SW1417. The glycoproteins detected by mAb 3A7 in rat colon tumors and HT29 cells ranged in size between 50 and 200 kd, including a major species of 140 kd. Affinity chromatography of detergent lysates of normal rat colon on the blood group A specific lectin Dolichos biflorus (DBA)-agarose resulted in nearly quantitative binding of glycoprotein species detected by the antibody. By contrast, immunoreactive glycoproteins from rat colon tumors or HT29 cells bound poorly to DBA-agarose but were retained by another blood group A-binding lectin, Helix-pomatia (HPA)-agarose. These results indicate that colon carcinogenesis results in quantitative as well as qualitative changes in oligosaccharides detected by mAb 3A7 and suggest that the combined use of mAb 3A7 and blood group A-specific lectins may provide a useful tool for early detection of colon cancer.

Interaction of lipopolysaccharides of Helicobacter pylori with basement membrane protein laminin

The ability of hemagglutinating and poorly hemagglutinating strains of the gastroduodenal pathogen Helicobacter pylori to bind 125I-radiolabelled laminin was quantitated in a liquid phase assay. Although all strains bound laminin, some hemagglutinating strains were good binders of laminin (maximum of 31% binding), whereas poorly hemagglutinating strains bound intermediate to small amounts of laminin (minimum of 6% binding). Since a hydrophobic component of the bacterium has been reported to be involved in binding of laminin (T. J. Trust, P. Doig, L. Emödy, Z. Kienle, T. Wadström, and P. O'Toole, Infect. Immun. 59:4398-4404, 1991), we investigated the role of lipopolysaccharide (LPS) in the interaction of both types of strains with laminin. Although the extent of inhibition varied among strains, laminin binding to hemagglutinating and poorly hemagglutinating strains was inhibited with homologous and heterologous smooth-form LPS. The ability of heterologous rough-form LPS to produce inhibition comparable to that shown by smooth-form LPS indicated that the O side chain of H. pylori LPS was not involved in the interaction. Further inhibition experiments with dephosphorylated LPS, isolated core oligosaccharide, and free lipid A suggested that a phosphorylated structure in the core oligosaccharide mediates the interaction of a hemagglutinating strain of H. pylori with laminin, whereas a conserved nonphosphorylated structure in the core oligosaccharide mediates the interaction of a poorly hemagglutinating strain. Furthermore, we showed that the interaction of H. pylori LPS with 125I-radiolabelled laminin in a solid phase assay was saturable, specific, and inhibitable with unlabelled laminin. It was postulated that the initial recognition and binding of laminin by H. pylori may occur through LPS and that subsequently a more specific interaction with a lectin-like adhesin on the bacterial surface occurs.

High-affinity binding of laminin by Helicobacter pylori: evidence for a lectin-like interaction

Laminin, the major glycoprotein of basement membranes, was shown to be bound by the human gastric pathogen Helicobacter pylori. Binding of 125I-laminin by strain 17874 was time-dependent, specific and saturable. Scatchard analysis of specific binding indicated about 2000 binding sites per cell with a dissociation constant of 8.5 pM. Treatment of the cells by heat (80 degrees) and with proteolytic enzymes drastically reduced laminin binding, suggesting that the laminin receptors are surface proteins. Some highly glycosylated glycoproteins inhibited laminin binding by 50%. Furthermore, N-acetylneuraminyllactose decreased laminin binding by 70% and neuraminidase treatment of laminin by 50%, while a recombinant B1 chain of laminin, containing high-mannose type oligosaccharides, inhibited binding by only 25%. This suggests that terminal sialic acids on laminin compete for a specific sugar binding protein(s) on H. pylori cells.

Functionally distinct roles for glycosylation of alpha and beta integrin chains in cell-matrix interactions

Laminin interaction with gp120/140, a B16-F10 laminin-binding protein immunologically related to alpha 6 beta 1 integrin, has been shown to be dependent on oligosaccharides from both ligand and receptor. Lectin analysis of gp120/140 led to the conclusion that this integrin is a sialoglycoprotein bearing mainly complex antennary structures. By means of exoglycosidase treatment, it was possible to identify alpha-galactosyl residues on the integrin alpha chain as the laminin-binding determinants. These residues are involved in cell adhesion to laminin. On the other hand, beta-chain complex antennary structures, whose synthesis could be inhibited by swainsonine, were associated with cell spreading rather than cell adhesion. Thus, it was possible to modulate integrin-mediated cell adhesion and spreading through changes in the glycosylation state of integrin alpha and beta chains.

Role of laminin carbohydrates on cellular interactions

Laminins, a family of large multidomain glycoproteins of the basal lamina, have been implicated in the development and maintenance of cellular and tissue organization. Considerable interest has arisen concerning the ways in which laminin carries out its biological functions. Previously these biologic responses have been primarily attributed to the peptide sequences of laminin, however, newer studies suggest that laminin carbohydrates may also participate in such cellular activities. Recently, a subpopulation of laminin molecules purified from EHS sarcoma by lectin affinity chromatography has been shown to contain about 25 to 30% carbohydrate. Most of the carbohydrates present are complex-type asparagine-linked oligosaccharides encompassing many different structures, some of which are unique to laminin. To date, the biological function of the carbohydrates of laminin remains somewhat unclear. They do not appear to be needed for heparin binding or to enhance proteinase stability, however, current evidence suggests they are important in cellular spreading and neurite outgrowth. It is our hypothesis that in the covalently-linked carbohydrate moieties of laminin will ultimately prove to be involved in information transfer to responsive cells. It is the purpose of this review to delineate current concepts of the structure and function of this unique glycoprotein's sugar chains.

Laminins and other strange proteins

Laminins are large multidomain proteins of the extracellular matrix (ECM) with important functions in the development and maintenance of cellular organization and supramolecular structure, in particular in basement membranes. Each molecule is composed of three polypeptide chains, A (300-400 kDa) and B1 and B2 (180-200 kDa), which together form the characteristic cross-shaped laminin structure with three short arms and one long arm. Many different domains have been identified in laminin by sequence analysis, structural investigations, and functional studies. Each short arm is formed by homologous N-terminal portions of one of the three chains. Structurally, each short arm contains two or three globular domains which are connected by rows of manyfold-repeated Cys-rich "EGF-like" domains. In all three chains this region is followed by a long heptad repeat region similar to those found in many alpha-helical coiled-coil proteins. These parts of the three laminin chains constitute a triple-stranded coiled-coil domain, which forms the extended rodlike structure of the long arm. This is the only domain in the protein which is made up of more than one chain and consequently serves the function of chain assembly. The two B chains are terminated by the coiled-coil domain, but the A chain contains an additional C-terminal segment which accounts for five globular domains located at the tip of the long arm. Several important functions of laminin have been assigned to individual domains in either the short arms or terminal regions of the long arm.(ABSTRACT TRUNCATED AT 250 WORDS)

A truncated laminin chain homologous to the B2 chain: structure, spatial expression, and chromosomal assignment

We describe the identification of a novel laminin chain. Overlapping clones were isolated from a human fibrosarcoma HT1080 cell cDNA library spanning a total of 5,200 bp. A second set of clones contained an alternative 3' end sequence giving a total of 4,316 bp. The longer sequence contained an open reading frame for a 1,193-residue-long polypeptide. The alternative sequence was shortened at the carboxyl-terminal end coding for a 1,111-residue-long polypeptide. The amino acid sequence contained 21 amino acids of a putative signal peptide and 1,172 residues or alternatively 1,090 residues of a sequence with five distinct domains homologous to domains I-V in laminin chains. Comparison of the amino acid sequences showed that the novel laminin chain is homologous to the laminin B2 chain. However, the structure of the novel laminin chain isolated here differs significantly from that of the B2 chain in that it has no domain VI and domains V, IV, and III are shorter, resulting in a truncated laminin chain. The alternative sequence had a shortened domain I/II. In accordance with the current nomenclature, the chain characterized here is termed B2t. Calculation of possible chain interactions of laminin chains with the B2t chain domain I/II indicated that the B2t chain can replace the B2 chain in some laminin molecules. The gene for the laminin B2t chain (LAMB2T) was localized to chromosome 1q25-q31 in close proximity to the laminin B2 chain gene. Northern analysis showed that the B2t chain is expressed in several human fetal tissues but differently from the laminin B1 and B2 chains. By in situ hybridization expression of the B2t chain was localized to specific epithelial cells in skin, lung, and kidney as opposed to a general epithelial and endothelial cell expression of the laminin B2 chain in the same tissues.

Identification of a 14-kDa laminin binding protein (HLBP14) in human melanoma cells that is identical to the 14-kDa galactoside binding lectin

The carbohydrate moieties present on laminin play a crucial role in the multiple biological activities of this basement membrane glycoprotein. We report the identification of a human laminin binding protein with an apparent molecular mass of 14 kDa on sodium dodecyl sulfate-polyacrylamide gels that was found, after purification and amino acid microsequencing, to be identical to the previously described 14-kDa galactoside binding soluble L-14 lectin. We have designated this human laminin binding protein as HLBP14. HLBP14 was purified from human melanoma cells in culture by laminin affinity chromatography and gel electroelution. We demonstrate that HLBP14 binds specifically to the poly-N-acetyllactosamine residues of murine laminin and does not bind to other glycoproteins that do not contain such structures, such as fibronectin. HLBP14 was eluted from a murine laminin column by lactose, N-acetyllactosamine, and galactose but not by other control saccharides, including glucose, fucose, mannose, and melibiose. It did not bind to laminin treated with endo-beta-galactosidase. Lactose also eluted HLBP14 off a human laminin affinity column, implying that human laminin also contains poly-N-acetyllactosamine residues. On immunoblots, polyclonal antibodies raised against HLBP14 recognized HLBP14 as well as 31- and 67-kDa molecules that are also laminin binding proteins, indicating that these proteins share common epitopes. L-14, a dimeric lactose binding lectin, is expressed in a wide variety of tissues. Although the expression of this molecule has been linked to a variety of biological events, the elucidation of its specific functions has been elusive. The observation that HLBP14, a human cancer cell laminin binding protein, is identical to L-14 strongly suggests that the functions attributed to this lectin could be mediated, at least in part, through its ability to interact with the poly-N-acetyllactosamine residues of laminin. HLBP14 could potentially play a role during tumor invasion and metastasis by modulating the interactions between cancer cells and laminin.

Characterization of a family of structurally related glycoproteins expressing beta 1-6-branched asparagine-linked oligosaccharides in human colon carcinoma cells

Previous studies have established that metastatic tumour cells express high levels of beta 1-6-branched Asn-linked oligosaccharides which can be detected with the lectin leucoagglutinin (L-PHA) [Dennis, Laferté, Waghorne, Breitman & Kerbel (1987) Science 236, 582-585]. In order to identify L-PHA-binding glycoproteins which may play a role specifically in colon cancer, we have prepared monoclonal antibodies (MAbs) to the moderately well-differentiated human colon carcinoma cell line HT29. In this paper we present the initial characterization of a family of structurally related L-PHA-binding glycoproteins detected by MAb 1H9 which are differentially expressed and processed by HT29 cells and by two other human colon carcinoma cell lines, SW480 and SW620. In contrast to HT29, the SW480 and SW620 cell lines were established from a poorly differentiated grade III/IV primary tumour and one of its lymph node metastases respectively. MAb 1H9 detects in HT29 cells a conformational determinant present on three L-PHA-binding glycoproteins of 100, 70 and 25kDa, as well as a 74 kDa glycoprotein with high-mannose-type Asn-linked oligosaccharides. Pulse-chase experiments and peptide mapping analyses revealed that the 74 kDa and 100 kDa species are related by carbohydrate processing and are probably derived from a common 76 kDa precursor. On the other hand, the 70 kDa glycoprotein is synthesized from an endoglycosidase H-sensitive precursor of 56 kDa which is structurally related to, but distinct from, the aforementioned 76 kDa precursor. In addition, the 100 kDa species is secreted into the culture medium, whereas the 70 kDa glycoprotein is retained intracellularly. SW480 and SW620 cells showed qualitative and quantitative differences from HT29 cells, including increased secretion of a smaller L-PHA-binding glycoprotein of 92 kDa into the culture medium, as well as apparent differences in glycosylation of the intracellular 66 kDa glycoprotein. These results suggested that the expression, glycosylation and subcellular localization of this family of L-PHA-binding glycoproteins may correlate with the differentiation status of colon cancer cells and/or reflect biochemical changes. characteristic of more progressive metastatic tumours.

Alterations in cell surface carbohydrate composition of a human colon carcinoma cell line affect adhesion to extracellular matrix components

The adhesion of HT29 human colon adenocarcinoma cells to different extracellular matrix components was studied. While treatment of the cells with sialidase had no detectable effect on binding to laminin and fibronectin, attachment to collagen IV was decreased. However, additional removal of beta-(1-4)-bound galactose led to significantly reduced binding to all of the substrates, including fibronectin and laminin. Tunicamycin treatment, monitored by lectin-induced aggregation, drastically diminished cell adhesion to laminin and fibronectin, whereas cell binding to collagen IV was not affected. Arg-Gly-Asp (RGD)-related peptides were used to study the adhesion to collagen IV. The results show that a serine-containing RGD-related peptide GRGDSP has virtually no effect on colon carcinoma cell adhesion to type IV collagen. In contrast, when serine was substituted for threonine (GRGDTP) adhesion to collagen IV was strongly inhibited. After incubation of sialidase-treated cells with the threonine-containing peptide adhesion was almost totally blocked. These results demonstrate the existence of both RGD-dependent and carbohydrate-based mechanisms for metastatic human HT29 cell binding to collagen IV.

Increase of sialylated tetraantennary sugar chains in parallel to the higher lung-colonizing abilities of mouse melanoma clones

The N-linked sugar chains of melanoma cell membrane from five murine B16 melanoma clones (F1, F10, BL6, W1-4, and C4-1) with different degrees of metastatic abilities after intravenous and intrafootpad injections were released quantitatively as oligosaccharides by hydrazinolysis, and their structures were analyzed by serial lectin column chromatography, Bio-Gel P-4 column chromatography, and sequential glycosidase digestion. Sugar chain structures of each clone have shown to consist of the same elemental oligosaccharides, but to differ in their percent compositions. More than 84% of the neutral oligosaccharides were high mannose-type sugar chains. Most complex-type sugar chains were sialylated, of which the major structure was tetraantennary sugar chain. Highly lung-colonizing F10 cells had 1.4 and 1.7 times more non-repeated tetraantennary sugar chains than moderately colonizing F1 and C4-1 cells, respectively, and 2.5 times more than poorly colonizing W1-4 cells. BL6 cells, which are also highly lung-colonizing, had 1.5 and 1.9 times more non-repeated tetraantennary sugar chains than F1 and C4-1 cells, respectively, and 2.8 times more than W1-4 cells. These results suggest that increase of sialylated tetraantennary complex-type sugar chains without N-acetyllactosamine repeating units of B16 melanoma cells might correlate with the higher lung-colonizing ability after intravenous injection.

Sialic acid dependent cell adhesion to collagen IV correlates with in vivo tumorigenicity of the human colon carcinoma sublines HCT116, HCT116a and HCT116b

Cell surface sialylation of three metastasizing sublines HCT116, HCT116a and HCT116b of a human colon carcinoma was shown to correlate with their in vivo tumorigenicity. Lectin binding studies revealed further differences in cell surface glycosylation between HCT116a and HCT116 sublines. Binding to collagen IV correlated with the in vivo aggressiveness of the cells, whereas binding to fibronectin did not. On a laminin substrate the most tumorigenic line adhered best, but binding of the other lines was similar. Sialidase treatment of the cells had no effect on cell binding to laminin and fibronectin, but resulted in a decrease of cell binding to collagen IV.

The S-type lectin from calf heart tissue binds selectively to the carbohydrate chains of laminin

We report that the S-type lectin in calf heart tissue, termed calf heart agglutinin (CHA), binds to immobilized mouse laminin in ligand blotting and solid-phase radioligand binding assays. When compared with other glycoproteins, radioiodinated CHA binds preferentially to immobilized laminin. The binding is saturable with a Kd of 9.2 x 10(-7) M and is competitively inhibited by nonradiolabeled CHA as well as a similar lectin from porcine heart tissue. Both lactose and N-acetyllactosamine are good inhibitors of binding to laminin but binding is not inhibited by heparin. Exoglycosidase treatments demonstrated that the binding of radioiodinated CHA to laminin is not dependent on terminal sialyl-, fucosyl-, beta- or alpha-linked galactosyl residues, whereas treatment of laminin with endo-beta-galactosidase significantly decreases the lectin binding. Thus, CHA binds selectively to the poly-N-acetyllactosamine chains on complex-type Asn-linked oligosaccharides in laminin.

Neutrophils show chemotaxis to type IV collagen and its 7S domain and contain a 67 kD type IV collagen binding protein with lectin properties

Neutrophils were found to demonstrate chemotactic responses to pepsinized human placental type IV collagen and its purified aminoterminal 7S domain. The maximal chemotactic responses occur at approximately 400 ng/ml and approximately 30 ng/ml of type IV collagen and 7S collagen, respectively, and are similar in magnitude to the chemotactic response of neutrophils to 10(-8) M FMLP. Human leukemic cells of the HL 60 line display chemotaxis to type IV collagen and 7S collagen only after they are differentiated along the neutrophilic pathway with dimethyl sulfoxide. When detergent extracts of neutrophils are applied to type IV collagen-Affi-Gel resin, a 67 kD protein is retained by the resin and is eluted with guanidine/octyl-beta-glucoside or lactose. This 67 kD polypeptide has an amino acid composition resembling the 67 kD component of the elastin receptor complex, displays immunologic cross-reactivity with antibody to the 67 kD component of the elastin receptor, and binds to elastin and laminin affinity resins. Neutrophil chemotaxis to type IV collagen and 7S collagen is selectively abolished by exposing the test neutrophils to lactose or elastin peptides. We conclude that neutrophils may migrate in vivo to proteolytic fragments of type IV collagen and that this response may be mediated by a lectin-like protein that is similar to the 67 kD component of the elastin receptor.

Evidence that beta 1-6 branched Asn-linked oligosaccharides on metastatic tumor cells facilitate invasion of basement membranes

In previous studies we have shown that the ability of murine tumor cells to metastasize in situ is directly linked to expression of -GlcNAc beta 1-6Man alpha 1-6Man beta 1-branched complex-type Asn-linked oligosaccharides in tumor-cell glycoproteins. Here we demonstrate that cell-surface expression of beta 1-6 branched oligosaccharides in metastatic tumor cells is specifically associated with increased invasion of human amnion basement membranes in vitro. Compared to nonmetastatic SP1 murine mammary carcinoma cells, 2 metastatic sublines expressed higher levels of beta 1-6 branched oligosaccharides and were found to be invasive but poorly adhesive on the amnion basement membrane. Swainsonine, a non-toxic inhibitor of Asn-linked oligosaccharide processing which blocks the pathway prior to initiation of the beta 1-6 linked antenna, blocked metastatic tumor-cell invasion and increased adhesiveness. Swainsonine and the metalloprotease inhibitor O-phenanthroline inhibited invasion, apparently via independent mechanisms. O-phenanthroline did not affect tumor-cell adhesion to the amnion basement membrane and swainsonine did not block secretion of metalloproteases, beta-hexosaminadase or tissue plasminogen activator activity by the tumor cells. These results suggest that tumor-cell invasion of basement membranes requires both secretion of hydrolase activities and expression of beta 1-6 branched complex-type oligosaccharides at the tumor cell surface, such oligosaccharides being associated with reduced tumor-cell adhesion to extracellular matrix.

Structure and biological activity of basement membrane proteins

Collagen type IV, laminin, heparan sulfate proteoglycans, nidogen (entactin) and BM-40 (osteonectin, SPARC) represent major structural proteins of basement membranes. They are well-characterized in their domain structures, amino acid sequences and potentials for molecular interactions. Such interactions include self-assembly processes and heterotypic binding between individual constituents, as well as binding of calcium (laminin, BM-40) and are likely to be used for basement membrane assembly. Laminin, collagen IV and nidogen also possess several cell-binding sites which interact with distinct cellular receptors. Some evidence exists that those interactions are involved in the control of cell behaviour. These observations have provided a more defined understanding of basement membrane function and the definition of new research goals in the future.

Structure and distribution of N-linked oligosaccharide chains on various domains of mouse tumour laminin

Asparagine-linked oligosaccharides were liberated from laminin and some of its fragments by hydrazinolysis, and after purification characterized by exoglycosidase digestions. This demonstrated the presence of nine forms of complex oligosaccharide chains, which differed in antennary and oligolactosamine structure, and of small amounts of high-mannose-type oligosaccharides. Additional variations were found with regard to substitutions by terminal alpha-galactose and sialic acid residues. Each of the various laminin fragments showed a unique but less complex repertoire of carbohydrate structures. These fragments also differed in mass, carbohydrate content, localization within the laminin molecule and functional activities such as cell-binding (fragments 1 and 6) and heparin- and collagen-binding (fragments 3 and 4). Fragment 7 with a particularly high carbohydrate content (72%) also showed the highest complexity of tri- and tetra-antennary structures. Further differences between the fragments were detected with human antibodies against the Gal alpha 1-3Gal epitope, which was expressed in either a high-affinity or a low-affinity form. Such differences in carbohydrate structure of topologically distinct laminin domains may have implications for their functions and in the regulation of post-translational modification events.

Structures, function, and transformational changes of the sugar chains of glycohormones

Human chorionic gonadotropin (hCG), human luteinizing hormone, human thyroid-stimulating hormone, and human follicle-stimulating hormone are closely related family of proteins which share a common alpha-subunit. However, their sugar moieties are quite different. hCG contains five acidic asparagine-linked sugar chains. These five sugar chains are derived by sialylation from three neutral oligosaccharides: two biantennary (N-1 and N-2) and one monoantennary (N-3) complex-type oligosaccharides. Although hCG purified from the urine of pregnant women is more enriched in sialylated sugar chains than that purified from placenta, the molar ratio of N-1, N-2, and N-3 of these two hCGs are the same (1:2:1). Comparative study of the sugar moieties of the alpha- and beta-subunits of hCG revealed that alpha contains 1 mol each of N-2 and N-3, while beta contains 1 mol each of N-1 and N-2. This specific distribution of oligosaccharides at the four asparagine loci of the hCG molecule is now helping us to consider the functional role of the sugar moiety of glycohormones. hCG is produced not only by the trophoblast but also by various trophoblastic diseases. The hCGs purified from the urine of patients with hydatidiform mole contain the same oligosaccharides as normal hCG. However, those from the urine of choriocarcinoma patients contain five additional neutral oligosaccharides. In contrast, hCGs from invasive-mole patients contain three of the five oligosaccharides, specifically found in choriocarcinoma hCGs. The malignant transformational change of the sugar moiety of hCG can be explained by an increase of a fucosyltransferase, which forms the Fuc alpha 1----6GlcNAc group and by ectopic expression and subsequent modification of N-acetylglucosaminyltransferase IV. The appearance of tumor-specific sugar chains of hCG has been used to develop a new diagnostic method for invasive mole and choriocarcinoma.

Molecular identification of lectin binding sites differentiating related low and high metastatic murine lymphomas

We have previously shown that differences in cell surface carbohydrates can be detected in related murine tumor lines of varying metastatic capacity using plant lectins such as soybean agglutinin (SBA) or Vicia villosa (VV) but not concanavalin A (ConA). Here we show that weakly metastatic Eb cells bind SBA via four glycoproteins and one GL2-like glycolipid. The major high-affinity SBA binding component of weakly metastatic ESb-MP cells was a glycoprotein of 210-220 kd. Highly metastatic ESb cells also expressed this protein but the oligosaccharide side chains were altered in such a way that SBA-binding was completely lost while ConA and peanut agglutinin (PNA) binding remained similar. Quantitative binding studies using iodinated lectins indicated that SBA binding of ESb cells could only be detected at lectin concentrations greater than 75 micrograms/ml. The role of altered carbohydrates in metastasis is discussed.

Structural basis for altered soybean agglutinin lectin binding between a murine metastatic lymphoma and an adhesive low malignant variant

By selection for plastic adhesiveness we have previously established a variant tumor line (ESb-MP) from the metastatic murine lymphoma ESb. In contrast to the parental line, the adhesion variant is significantly decreased in malignancy and is altered in the capacity to bind soybean agglutinin (SBA) lectin. Here we show biochemically that the major SBA-binding cell-surface component of ESb-MP cells is the T200 glycoprotein. In ESb cells, T200 antigens bind SBA only after sialidase treatment. Enzymatic studies suggested that glycans detected by the lectin with or without sialidase treatment are different. Inhibition of N-glycosylation by tunicamycin and biosynthetic labeling revealed two T200 chains for ESb-MP cells that were larger in size than the single chain detected in ESb cells. Studies on the biosynthesis revealed that ESb-MP cells expressed two precursor chains for T200 whereas ESb cells displayed only one. There was no size difference detectable in the mature T200 molecules of ESb and ESb-MP cells. Our data suggest that the molecules differ in expression of O-linked glycans that can be recognized by SBA. Additional O-linked sugars on ESb-MP T200 molecules seem to be expressed in particular after trimming of the second T200 precursor chain.

Endogenous galactoside-binding lectins: a new class of functional tumor cell surface molecules related to metastasis

The formation of secondary tumors by circulating cancer cells (blood-borne metastasis) correlates with an increased tendency of the cells to form emboli by aggregation with other tumor cells or with host cells. Although it is evident that cell-cell recognition and adhesion are mediated by cell surface components, the identity of these molecules is only now being unraveled. Over the last decade an increasing number of studies have demonstrated the presence of endogenous carbohydrate-binding proteins on the surface of various normal cells, and it has been proposed that such lectin-like molecules might be involved in intercellular adhesion. We have shown that various tumor cell lines contain endogenous galactose-specific lectins. Lectin activity was detected at the cell surface by the binding of asialofetuin. This glycoprotein also enhanced the aggregation of the tumor cells. After purification by affinity chromatography on immobilized asialofetuin the lectin activity was associated with two proteins of Mr 14,500 and 34,000. By using polyclonal and monoclonal antilectin antibodies in conjunction with various immunologic techniques we have demonstrated that the endogenous lectins are present on the surface of different tumor cells. Quantitation of cell surface lectins by flow cytometric analyses of antilectin antibody binding revealed that among related tumor cells those exhibiting a higher metastatic potential expressed more lectin on their surface. The binding of monoclonal antilectin antibodies to metastatic cells decreased asialofetuin-induced homotypic aggregation in vitro and suppressed the ability of the cells to form lung metastases after intravenous injection in the tail vein of syngeneic mice. These results strongly implicate the tumor cell surface lectins in cell adhesion and metastasis. We propose that such lectins can increase the ability of tumor cells that enter the blood stream to form aggregates with other tumor cells, or to adhere to host cells or the extracellular matrix and thereby increase their metastatic potential. Other contributing components to tumor cell-host cell interactions are cell surface carbohydrate-binding proteins that have been detected on lymphocytes, platelets, macrophages, hepatocytes, and endothelial cells. These lectin-like molecules might recognize and bind carbohydrates expressed on the surface of tumor cells and enhance emboli formation and organ colonization.

Poly-N-acetyllactosamine glycans of cellular glycoproteins: predominance of linear chains in mouse neuroblastoma and rat pheochromocytoma cell lines

To study the properties of protein-bound oligosaccharides in neuronally differentiating cells, two model systems were used: murine N1E-115 and N-18 neuroblastoma cells inducible by serum starvation and rat PC12 pheochromocytoma cells inducible by nerve growth factor. Glycopeptides were prepared from cells metabolically labeled with [3H]glucosamine and analyzed by gel filtration. The properties of the high-molecular-weight glycopeptides were studied using enzymatic digestion with neuraminidase and endo-beta-galactosidase. In contrast to other cell lines analyzed, the neuroblastoma and pheochromocytoma lines contained predominantly glycopeptides completely cleavable with endo-beta-galactosidase, which indicated that they were linear-type poly-N-acetyllactosamine glycans. The proportion of these linear chains in the high-molecular-weight fraction increased during neuronal differentiation in both cell systems. The linear nature of the glycans was also correlated with positive anti-i and negative anti-I reactivity of the cells in immunofluorescence microscopy. Specific cell surface labeling for poly-N-acetyllactosamine glycans and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed several glycoprotein components, some of which showed changes during neuronal differentiation. The high proportion of linear poly-N-acetyllactosamine chains in these neuronal cell lines and its increase during neuronal differentiation suggests that these glycans may be a characteristic feature of neuronal or neuronally differentiating cells.

Role of carbohydrates in cell-substrate interactions during newt epidermal cell migration

The effect of several solubilized monosaccharides on epidermal cell migration from skin explants of the adult newt was examined. The ability of epidermal cells to migrate on substrates coated with these same sugars or with wheat germ agglutinin (WGA) was also determined. Adding 0.05 M N-acetyl-glucosamine (GlcNAc) to the medium inhibited epidermal cell migration in dishes coated with either type I collagen or fibrinogen. The same concentration of fucose, galactose, or mannose had no effect. In contrast to type I collagen, which supported considerable migration when dried onto the bottom of plastic dishes, epidermal cells were unable to migrate on dishes coated similarly with WGA, mucin (a protein high in sialic acid residues), or bovine serum albumin (BSA) conjugated to galactose, mannose, or GlcNAc. Red blood cell (RBC) binding assays showed that drying WGA onto plastic did not destroy its GlcNAc binding sites--nor did it damage the GlcNAc residues of BSA-GlcNAc. The RBC assay also verified that for both these proteins, substrates with distinctly different cell binding capacities had been tested in the migration experiments. In dishes coated with either WGA or BSA-GlcNAc, red cells bound to dish bottoms in a GlcNAc-specific manner right up to the margins of explants. Other control experiments showed that the failure of migration in WGA- and BSA-GlcNAc-coated dishes could not be explained by competition between adsorbed and desorbing protein for cell surface receptors. This work shows that adhesive bonds between epidermal cell surface GlcNAc and a GlcNAC-specific lectin on the substrate are not by themselves adequate to support cell migration. Nor is GlcNAc, sialic acid, galactose, or mannose alone on the substrate sufficient. In conjunction with our earlier work (Donaldson and Mahan: J. Exp. Zool., 231:211-219, '84; Donaldson, Mahan, Hasty, McCarthy, and Furcht: J. Cell. Biol., 101: 73-78, '85), these observations suggest that factors other than carbohydrate content or capacity to act as a lectin determine whether a given extracellular protein will support migration.

Investigation of the antimetastatic effects of agents that inhibit cell adhesion or protein glycosylation

In this overview the authors describe their recent attempts to specifically interfere with the metastatic spread of B16-F10 melanoma cells. Using the experimental metastasis model system, inhibitory effects of (1) coinjection of cells with synthetic peptides derived from the glycoprotein fibronectin, which possess the ability to disrupt cell adhesion, and (2) treatment of cells with inhibitors of protein glycosylation and oligosaccharide processing have been examined.

Developmentally-related changes in surface membrane glycopeptides of murine haemopoietic cells

We have carried out a comparative study of mature murine granulocytes with two immature haemopoietic cell lines (multipotential cells, FDCP-Mix, and granulocyte progenitor cells, FDCP-2) with respect to the structure and composition of their surface membrane glycopeptides. The glycopeptides were labelled biosynthetically by incubation of the cells for 1-3 days with [3H]glucosamine. Cell-associated glycopeptides were released by treatment with trypsin and the trypsin extract was exhaustively digested with Pronase to remove most residual peptide. Radiolabelled materials were fractionated by chromatography on lectin affinity columns connected in the series: lentil lectin (LCA), concanavalin A (Con A) and wheat germ agglutinin (WGA). Lectin-binding glycopeptides were eluted with appropriate competing sugars and further analysed by gel filtration, base/borohydride elimination and susceptibility to degradation by glycosidases including endo-beta-galactosidase. Abundant quantities of N-linked polylactosamine-type glycopeptides, which bound only to the WGA columns, were identified on mature granulocytes but the molecules were highly-branched (i.e. resistant to endo-beta-galactosidase). In contrast, there seemed to be very little branching in the polylactosamine chains from FDCP-2 cells, whilst corresponding carbohydrates from multipotential FDCP-Mix cells gave evidence for both linear and branched domains in the same, large complex glycans. O-Linked tetrasaccharides of general structure: NeuAc-Gal-(NeuAc)-GalNAc were found in clusters on WGA-binding glycopeptides from all cell types, these components being especially prominent on mature granulocytes. FDCP-2 cells were distinguished by the presence of monosialylated and non-sialylated counterparts of the foregoing tetrasaccharides. The relative amount of LCA-binding glycopeptides was low on FDCP-Mix cells by comparison with FDCP-2 cells and mature granulocytes. Our findings therefore demonstrate that notable differences in gross composition and molecular fine structure of surface membrane glycopeptides are detectable in haemopoietic cells at different stages of development. The relationship of these differences to the biological properties of cell surfaces remains to be established.

Distinct patterns of glycosylation of colligin, a collagen-binding glycoprotein, and SPARC (osteonectin), a secreted Ca2+-binding glycoprotein. Evidence for the localisation of colligin in the endoplasmic reticulum

Mouse parietal endoderm PYS cells were labelled with [2-3H]mannose for 16-24 h. Colligin, an Mr-47000 collagen-binding protein, and SPARC, a Mr-43000 protein, highly homologous to the Ca2+-binding protein osteonectin, were isolated from labelled cell extracts and culture medium respectively. Glycopeptides obtained by exhaustive digestion with pronase were analysed by lectin-affinity, ion-exchange, and gel-filtration chromatography and by paper chromatography of high-mannose oligosaccharides after endo H release. The results show that the N-linked carbohydrate chains of colligin are exclusively the high-mannose type, of which (Man)8(GlcNAc)2 and (Man)9(GlcNAc)2 make up 77%. This carbohydrate structure provides strong evidence that colligin is a component of the endoplasmic reticulum, and argues against a role in cell-surface interactions. By contrast to colligin, SPARC secreted by PYS cells contains predominantly a diantennary complex type of chain containing a variable number of sialic acid and core-substituted fucose residues. Similar glycosylation patterns to those discussed above were seen in colligin isolated from primary mouse embryonic parietal endoderm cells and the murine 3T3 cell line, and in SPARC secreted by bovine corneal endothelial cells. Unlike the type-IV-collagen-binding glycoprotein studied by Dennis, J., Waller, C. and Schirrmacher, V. [J. Cell Biol. 99, 1416-1423 (1984)], removal of N-linked oligosaccharides from colligin had no effect on its binding to native type IV collagen.

Glycoprotein profiles of macrophages at different stages of activation as revealed by lectin binding after electrophoretic separation

Glycoprotein profiles of rat macrophages (M phi) at different stages of activation were studied by examining the reactivity of various lectins to the glycoproteins separated by polyacrylamide gel electrophoresis. Ricinus communis agglutinin 1 (RCA1) revealed several components including glycoproteins of Mr 160 kDa and 65 kDa prominent in resident M phi. A pokeweed mitogen (PWM) isolectin, Pa-4, recognizes branched poly(N-acetyllactosamine)-type carbohydrate chains, and revealed a significant increase in glycoproteins of Mr ranging from 70 kDa to 150 kDa on thioglycolate-elicited M phi. Increased reactivity of PWM to thioglycolate-elicited M phi was observed by direct binding of 125I-labeled Pa-4 to intact or glutaraldehyde-fixed M phi. Histochemical staining of formaldehyde-fixed M phi in vitro with biotinylated Pa-4 was consistent with the gel analysis, that is, resident M phi had no reactivity while thioglycolate-elicited M phi showed slight reactivity. Alveolar and intratumoral M phi bound more Pa-4 than resident or thioglycolate-elicited M phi. The PWM isolectin may therefore serve as a marker for an early stage of M phi activation.

Tumor cell surface carbohydrate and the metastatic phenotype

The synthesis and expression of cell surface carbohydrates is a developmentally regulated process that appears to affect a number of cell-cell interactions. To determine whether specific oligosaccharide structures present on highly malignant cells are required for expression of the metastatic phenotype, we have isolated lectin resistant tumor cell mutants with defects in the biosynthesis of oligosaccharides. The mutants selected from the highly aggressive lymphoreticular-like tumor line MDAY-D2 were grouped into genetic complementation classes, compared for metastatic ability and for changes in cell surface glycoconjugates. The Asn-linked oligosaccharides and glycolipids of class 1 mutants were deficient in both sialic acid and galactose and the cells showed a greatly attenuated metastatic phenotype compared to the parental cells. A revertant of the class 1 mutation selected in vitro regained the wild type glycoconjugate profile and the highly metastatic phenotype indicating a direct association between the mutation and the loss of metastatic potential. Class 2 mutants remained highly metastatic and had Asn-linked oligosaccharide structures very similar to those found in the wild type cells with N-glycolylneuraminic acid rather than the N-acetylneuraminic acid. Swainsonine, an inhibitor of golgi alpha-mannosidase II, blocks the synthesis of complex-type Asn-linked oligosaccharides resulting in the expression of hybrid-type oligosaccharides at the cell surface and the cells display a lectin resistant phenotype. Although swainsonine inhibited neither tumor cell growth in vitro nor solid tumor growth in situ, the drug dramatically reduced the incidence of lung colonies after i.v. inoculation of both MDAY-D2 and B16F10 melanoma cells. These results, taken together, indicate that certain sialylated Asn-linked oligosaccharides found on metastatic tumor cells are required for expression of the metastatic phenotype.

Functional differences in the interactions of glycosylation-deficient cell lines with fibronectin, laminin, and type IV collagen

Fibronectin isolated from the conditioned medium of monolayer cultures of baby hamster kidney (BHK) cells and several ricin-resistant (Ric) mutants derived from them express differences in N-glycosylation. The asparagine-linked oligosaccharides of BHK cell-derived fibronectin consist largely of complex chains, whereas hybrid and/or high-mannose chains are present in the fibronectins of mutant cell lines. The fibronectins exhibiting different glycosylation patterns are incorporated to similar extents into the cell-layer of human skin fibroblasts. In contrast, mutant cells retain significantly less endogenously produced fibronectin than BHK cells and also incorporate less human cellular fibronectin into a pericellular matrix. In vitro adhesion assays show that mutant cells attach to and spread relatively poorly on fibronectin-or type IV collagen-coated substrata but interact as well as do BHK cells with a laminin substratum. These results indicate that asparagine-linked oligosaccharides of fibronectin are not required for the binding and incorporation of the molecule into cell layers, but, as constituents of other cellular glycoproteins, they do modulate the ability of BHK cells to interact with some matrix components.

Structures of the asparagine-linked sugar chains of laminin

This investigation describes the isolation and characterization of oligosaccharides of the basement membrane glycoprotein, laminin. Pronase-released glycopeptides of isolated laminin, from a mouse Engelbreth-Holm-Swarm tumor, were fractionated using a combination of gel permeation chromatography and Con A-Sepharose affinity chromatography. The glycopeptides were analyzed for sugar linkage patterns by methylation analysis. Glycopeptides and hydrazine-released oligosaccharides were further analyzed using endo-beta-galactosidase, endo-beta-N-acetylglucosaminidase H and specific exoglycosidases in conjunction with calibrated gel permeation chromatography. Based on these experiments, murine tumor laminin was shown to contain asparagine-linked oligosaccharides with the following structures: bi-, tri- and tetraantennary complex-type oligosaccharides; polylactosaminyl side chains containing Gal(beta 1----4)GlcNAc(beta 1----3) repeating units attached to the trimannose core portion of the bi-, tri- and tetraantennary complex-type oligosaccharides; unusual complex-type oligosaccharides terminated at the nonreducing end with sialic acid, alpha-galactose, beta-galactose and beta-N-acetylglucosamine; alpha-galactosyl residues linked to N-acetyllactosamine sequences; high-mannose-type oligosaccharides. These results, in conjunction with analytical data, indicate that most of the carbohydrate of this laminin is N-linked to asparagine and that there are about 43 such N-linked oligosaccharides per laminin molecule.

Sporadic somatic fusion between MDAY-D2 murine tumor cells and DBA/2 host cells: role in metastasis

An ouabain- and 6-thioguanine-resistant mutant (K3T103) of the metastatic MDAY-D2 murine tumor cell line was transplanted s.c. into syngeneic DBA/2 mice in order to isolate K3T103 X host cell hybrids emerging in vivo, and examine their metastatic potential. Of 10 tumor-bearing animals that were analyzed at various time intervals, only 3 developed fusion products in the primary site, present at a frequency ranging between 10(-5) and 10(-4). These hybrids survived in HAT + ouabain medium, had a lymphoblastoid morphology and a hypo-tetraploid karyotype, were non-adherent, and were as rapidly metastatic as K3T103 cells when transplanted s.c. or i.v. into DBA/2 mice. All these characteristics were shared by cloned hybrids generated in vitro following polyethylene glycol (PEG)-mediated fusion of K3T103 cells with normal DBA/2 normal splenocytes. In marked contrast, the products of K3T103 X DBA/2 normal lung fibroblast fusion displayed a fibroblastic appearance, were adherent, progressively ceased to divide and remained dormant for several weeks in culture. These results indicate: that spontaneous fusion of K3T103 cells with host cells in the course of their expansion and subsequent dissemination is a stochastic and rare event, and that since the expression of their tumorigenic and metastatic potential is retained after fusion with splenocytes, host cells of lymphoreticular origin are most likely involved in that process.