GnT-V, macrophage and cancer metastasis: a common link

The lectin DrfL inhibits cell migration, adhesion and triggers autophagy-dependent cell death in glioma cells

Glioblastoma multiforme (GBM) is the most aggressive type of glioma, displaying atypical glycosylation pattern that may modulate signaling pathways involved in tumorigenesis. Lectins are glycan binding proteins with antitumor properties. The present study was designed to evaluate the antitumor capacity of the Dioclea reflexa lectin (DrfL) on glioma cell cultures. Our results demonstrated that DrfL induced morphological changes and cytotoxic effects in glioma cell cultures of C6, U-87MG and GBM1 cell lines. The action of DrfL was dependent upon interaction with glycans, and required a carbohydrate recognition domain (CRD), and the cytotoxic effect was apparently selective for tumor cells, not altering viability and morphology of primary astrocytes. DrfL inhibited tumor cell migration, adhesion, proliferation and survival, and these effects were accompanied by activation of p38^MAPK and JNK (p46/54), along with inhibition of Akt and ERK1/2. DrfL also upregulated pro-apoptotic (BNIP3 and PUMA) and autophagic proteins (Atg5 and LC3 cleavage) in GBM cells. Noteworthy, inhibition of autophagy and caspase-8 were both able to attenuate cell death in GBM cells treated with DrfL. Our results indicate that DrfL cytotoxicity against GBM involves modulation of cell pathways, including MAPKs and Akt, which are associated with autophagy and caspase-8 dependent cell death.

Glycan array analysis of Pholiota squarrosa lectin and other fucose-oriented lectins

The α(1,6)fucose residue attached to the N-glycoprotein core is suspected to play an essential role in the progression of several types of cancer. Lectins remain the first choice for probing glycan modifications, although they may lack specificity. Thus, efforts have been made to identify new lectins with a narrower core fucose (CF) detection profile. Here, we present a comparison of the classical Aleuria aurantia lectin (AAL), Lens culinaris agglutinin (LCA) and Aspergillus oryzae lectin (AOL) with the newer Pholiota squarrosa lectin (PhoSL), which has been described as being specific for core fucosylated N-glycans. To this end, we studied the binding profiles of the four lectins using mammalian glycan arrays from the Consortium of Functional Glycomics. To validate their glycan specificity, we probed AOL, LCA and PhoSL in western-blot assays using protein extracts from eight common colorectal cancer (CRC) lines and colorectal biopsies from a small cohort of patients with CRC. The results showed that (i) LCA and PhoSL were the most specific lectins for detecting the presence of CF in a concentration-dependent manner; (ii) PhoSL exhibited the highest N-glycan sequence restriction, with preferential binding to core fucosylated paucimannosidic-type N-glycans, (iii) the recognition ability of PhoSL was highly influenced by the presence of terminal N-acetyl-lactosamine; (iv) LCA bound to paucimannosidic, bi-antennary and tri-antennary core fucosylated N-glycans and (v) AOL and AAL exhibited broader specificity towards fucosylation. Together, our results support the choice of LCA as the most appropriate lectin for CF detection, as validated in protein extracts from CRC cell lines and tissue specimens from patients with CRC.

The Role of MGAT5 in Human Umbilical Vein Endothelial Cells

Preeclampsia (PE) is associated with shallow invasion of the trophoblast and insufficient remodeling of the uterine spiral artery. Glycosylation reactions are catalyzed by glycosyltransferases including N-acetylglucosaminyltransferase V (MGAT5) and accumulating evidence suggests that MGAT5 is correlated with the migration, proliferation, and survival of various cell types. Our previous study confirmed that MGAT5 is a negative regulator of trophoblast migration and invasion via the direct or indirect inhibition of matrix metalloproteinase 2/9 activity. The primary purpose of this study is to investigate the role of MGAT5 in the function of human umbilical vein endothelial cells (HUVECs) during the development of PE. We observed that MGAT5 was specifically localized within the decidual cells and endothelial cells in maternal decidual tissues. The expression of MGAT5 was elevated in PE placentas compared with the normal control placentas. Moreover, the expression of MGAT5 was increased in hypoxia-reoxygenation (H/R)-treated HUVECs. The knockdown of MGAT5 and PD98059 treatment significantly enhanced cell migration in vitro, promoted tube formation capacity, and inhibited apoptosis in H/R-exposed HUVECs. Our data suggest that oxidative stress induces the overexpression of MGAT5 via the regulation of the focal adhesion kinase-extracellular signal-regulated kinase signaling pathway, which, in turn, affects the function of endothelial cells, which then participates in the pathogenesis of PE.

Effect of GnT-V knockdown on the proliferation, migration and invasion of the SMMC7721/R human hepatocellular carcinoma drug-resistant cell line

Hepatocellular carcinoma (HCC) is a commonly occurring malignant tumor, with a high incidence rate. The present study aimed to investigate the effect of knocking down the N‑glycosyltransferase‑V (GnT‑V) protein on the proliferation, migration and invasion of the human HCC drug‑resistant cell line, SMMC7721/R. SMMC7721/R cells with GnT‑V‑knockdown (SMMC‑7721/R‑GnT‑V) were constructed using the method of lentiviral transfection. The expression of GnT‑V was assessed using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blotting. Cell proliferation was determined using an MTT assay, and the extent of cellular apoptosis was assessed using flow cytometric analysis. Additionally, the metastatic ability of the cells in vitro was analyzed using cell adhesion and invasion assays. Western blotting was used to investigate the protein expression levels of caspase‑3, caspase‑9, Bcl‑2, Bax, matrix metalloproteinase (MMP)‑2 and MMP‑9, and RT‑qPCR was used to determine the mRNA expression levels of the genes for the breast cancer resistance protein and P‑glycoprotein in the SMMC‑7721/R cells. Taken together, the results of the present study revealed that the knockdown of GnT‑V significantly suppressed the proliferation, migration and invasion (P<0.05) of the SMMC‑7721/R cells. Furthermore, the possible mechanism underlying these phenomena may be associated with the induction of mitochondria‑mediated apoptosis, inhibition of the degradation of the extracellular matrix and an enhancement of the drug-sensitivity. GnT‑V‑knockdown may therefore be used to treat drug‑resistant HCC in the future.

Binding of N-acetylglucosamine (GlcNAc) β1-6-branched oligosaccharide acceptors to β4-galactosyltransferase I reveals a new ligand binding mode

N-Acetyllactosamine is the most prevalent disaccharide moiety in the glycans on the surface of mammalian cells and often found as repeat units in the linear and branched polylactosamines, known as i- and I-antigen, respectively. The β1–4-galactosyltransferase-I (β4Gal-T1) enzyme is responsible for the synthesis of the N-acetyllactosamine moiety. To understand its oligosaccharide acceptor specificity, we have previously investigated the binding of tri- and pentasaccharides of N-glycan with a GlcNAc at their nonreducing end and found that the extended sugar moiety in these acceptor substrates binds to the crevice present at the acceptor substrate binding site of the β4Gal-T1 molecule. Here we report seven crystal structures of β4Gal-T1 in complex with an oligosaccharide acceptor with a nonreducing end GlcNAc that has a β1–6-glycosidic link and that are analogous to either N-glycan or i/I-antigen. In the crystal structure of the complex of β4Gal-T1 with I-antigen analog pentasaccharide, the β1–6-branched GlcNAc moiety is bound to the sugar acceptor binding site of the β4Gal-T1 molecule in a way similar to the crystal structures described previously; however, the extended linear tetrasaccharide moiety does not interact with the previously found extended sugar binding site on the β4Gal-T1 molecule. Instead, it interacts with the different hydrophobic surface of the protein molecule formed by the residues Tyr-276, Trp-310, and Phe-356. Results from the present and previous studies suggest that β4Gal-T1 molecule has two different oligosaccharide binding regions for the binding of the extended oligosaccharide moiety of the acceptor substrate.

Global gene expression profiles of canine macrophages and canine mammary cancer cells grown as a co-culture in vitro

Background

Solid tumours comprise various cells, including cancer cells, resident stromal cells, migratory haemopoietic cells and other. These cells regulate tumour growth and metastasis. Macrophages constitute probably the most important element of all interactions within the tumour microenvironment. However, the molecular mechanism, that guides tumour environment, still remains unknown. Exploring the underlying molecular mechanisms that orchestrate these phenomena has been the aim of our study.

A co-culture of canine mammary cancer cells and macrophages was established and maintained for 72 hrs. Having sorted the cells, gene expression in cancer cells and macrophages, using DNA microarrays, was examined. The results were confirmed using real-time qPCR and confocal microscopy. Moreover, their ability for migration and invasion has been assessed.

Results

Microarray analysis showed that the up-regulated genes in the cancer cell lines are involved in 15 highly over-manifested pathways. The pathways that drew our diligent attention included: the inflammation pathway mediated by chemokine and cytokine, the Toll receptor signalling pathway and the B cell activation. The up-regulated genes in the macrophages were involved in only 18 significantly over-manifested pathways: the angiogenesis, the p53 pathway feedback loops2 and the Wnt signalling pathway. The microarray analysis revealed that co-culturing of cancer cells with macrophages initiated the myeloid-specific antigen expression in cancer cells, as well as cytokine/chemokine genes expression. This finding was confirmed at mRNA and protein level. Moreover, we showed that macrophages increase cancer migration and invasion.

Conclusions

The presence of macrophages in the cancer environment induces acquisition of the macrophage phenotype (specific antigens and chemokines/cytokines expression) in cancer cells. We presumed that cancer cells also acquire other myeloid features, such as: capabilities of cell rolling, spreading, migration and matrix invasion (what has also been confirmed by our results). It may, perhaps, be the result of myeloid-cancer cell hybrid formation, or cancer cells mimicking macrophages phenotype, owing to various proteins secreted by macrophages.

MS-based glycomic strategies for probing the structural details of polylactosaminoglycan chain on N-glycans and glycoproteomic identification of its protein carriers

Most MS-based glycomic and glycoproteomic analyses focus on identifying changes in terminal glyco-epitopes represented by sialylation and fucosylation at specific positions of the terminal N-acetyllactosamine units. Much less attention was accorded to the underlying linear or branched poly-N-acetyllactosamine extension from the N-glycan trimannosyl core other than a simple inference of its presence due to mass data and hence glycosyl compositional assignment. Using the EA.hy926 cell line derived from human umbilical vein endothelial cells (HUVEC), we have systematically investigated the MALDI- and ESI-MS-based methodologies for probing the structural details of endothelial polylactosaminoglycans at both MS and MS(2) levels in conjunction with the use of endo-β-galactosidase to identify branching motifs and initiation sites. We showed that the polylactosaminoglycan chains on the N-glycans of EA.hy926 were less sialylated and fucosylated but more extended and branched than those of human umbilical vein endothelial cells, thus demonstrating a fundamental glycomic difference. For EA.hy926 that was investigated in more details, its polylactosaminoglycan chains were shown to be not restricted to extending from a specific antenna including the biologically important 6-arm position. Finally, experimental conditions for glycopeptide enrichment by tomato lectin were further optimized, which led to identification of over 40 candidate endothelial membrane protein carriers of polylactosaminoglycans by proteomic analysis.

The glycobiology of brain tumors: disease relevance and therapeutic potential

The oligosaccharides that decorate cell surface glycoconjugates play important roles in intercellular recognition and cell-extracellular matrix interactions, and thus the regulation of cellular migration, metastasis and invasivity. Virtually all tumor cells display aberrant cell-surface glycosylation patterns brought about by alterations in their biosynthetic machinery. This holds true for highly invasive, malignant brain tumors as well as tumor cells that metastasize to the brain. The field of glycobiology is well established with essentially all of the biochemical pathways for oligosaccharide metabolism characterized and all of the 'glycogenes' involved in these pathways cloned. Yet there has been a paucity of progress toward the development of therapeutics. However, recent studies aimed at controlled glycosylation of therapeutic antibodies and mucins with anticancer vaccine potential, the emergence of new and highly sensitive tools for the identification of tumor-associated biomarkers and the manipulation of the expression of glycogenes that inhibit brain tumor invasivity have emerged. The opportunity now exists to answer questions as to how glycogenes are regulated at the genomic and transcriptomic level and how altered glycogene expression patterns lead to altered cell surface glycoconjugates. These studies should lead to the development of ways to directly regulate tumor cell glycogene expression, which should have significant therapeutic potential.

Expression of the macrophage antigen CD163 in rectal cancer cells is associated with early local recurrence and reduced survival time

Expression of the macrophage antigen CD163 in breast cancer cells is recently shown to be related to early distant recurrence and shortened survival. In this study, 163 patients with rectal cancer, included in the Swedish rectal cancer trial and followed up for a median of 71 months, were examined for the expression of CD163 in the primary tumors. The cancer cells expressed CD163 in the primary tumors in 23% (n = 32) of the patients. In pretreatment biopsies from 101 patients, 10 had CD163-positive cancers and these patients had earlier local recurrence (p < 0.044) and reduced survival time (p < 0.045) compared with those with CD163-negative tumors. When studying surgical specimens from 61 patients randomized to preoperative irradiation (5 x 5 Gy delivered in 1 week), it was found that 31% were CD163 positive whereas the corresponding figure was only 17% for 78 patients who were nonirradiated (p < 0.044), which tentatively may be consistent with X-rays inducing fusion. In CD163-positive tumors there was a reduced apoptotic activity as measured with the Termina deoxynucleotidyl Transferase Biotin-dUTP Nick End Labeling (TUNEL) technique (p = 0.018). There tended also to be an increased proliferation activity measured as an expression of Ki-67 non significant (NS). It is concluded that primary rectal cancers may express CD-163, and this phenotypic macrophage trait is related to early local recurrence, shorter survival time and reduced apoptosis. Furthermore, the expression of CD163 is more common after irradiation.

The cancer cell--leukocyte fusion theory of metastasis

The cause of metastasis remains elusive despite vast information on cancer cells. We posit that cancer cell fusion with macrophages or other migratory bone marrow-derived cells (BMDCs) provides an explanation. BMDCs fused with tumor cells were present in animal tumor xenografts where they were associated with metastases. In myeloma patients, transcriptionally active myeloma nuclei were incorporated into osteoclasts through fusion. In patients with renal cell carcinoma arising poststem cell transplant, donor genes were incorporated in recipient cancer cell nuclei, most likely through fusion, and showed tumor distribution patterns characteristic of cancer stem cells. Melanoma-macrophage hybrids generated in vitro contained chromosomes from both parental partners, showed increased ploidy, and transcribed and translated genes from both parents. They exhibited chemotactic migration in vitro toward fibronectin and exhibited high frequencies of metastasis when implanted in mice. They produced macromolecules that are characteristic of macrophages and known indicators of metastasis (c-Met, SPARC, MCR1, GnT-V, and the integrin subunits alpha(3), alpha(5), alpha(6), alpha(v), beta(1), beta(3)). They also produced high levels of beta1,6-branched oligosaccharides-predictors of poor survival in patients with melanoma or carcinomas of the breast, lung, and colon. We thus hypothesize that such gene expression patterns in cancer are generated through fusion. Tumor hybrids also showed active autophagy, a characteristic of both metastatic cancers and macrophages. BMDC-tumor cell fusion explains epidermal-mesenchymal transition in cancer since BMDCs express mesodermal traits and epithelial-mesenchymal transition regulators (Twist, SPARC, and others). If BMDC-tumor cell fusion underlies invasion and metastasis in human cancer, new approaches for therapeutic intervention would be mandated.

Evidence for tyrosinase as a beta1,6 branch containing glycoprotein: substrate of GnT-V

Tyrosinase is a rate-limiting enzyme in mammalian melanogenesis, and is known as a glycoprotein. Post-translational processing of mammalian tyrosinase is required for its folding, sorting, and for enzymatic activity. Here we show for the first time that the mammalian tyrosinase has beta1,6-branched N-glycan structure that can be recognized by binding with specific lectin Leukoagglutinating phytohematoagglutinin (L-PHA). Further, this specific glycoconjugate structure has been shown to have a function relationship in melanin synthesis.

Fusion of tumour cells with bone marrow-derived cells: a unifying explanation for metastasis

The causes of metastasis remain elusive despite vast information on cancer cells. We posit that cancer cell fusion with macrophages or other migratory bone marrow-derived cells (BMDCs) provides an explanation. BMDC-tumour hybrids have been detected in numerous animal models and recently in human cancer. Molecular studies indicate that gene expression in such hybrids reflects a metastatic phenotype. Should BMDC-tumour fusion be found to underlie invasion and metastasis in human cancer, new approaches for therapy would surely follow.

Beta1,6-branched oligosaccharides regulate melanin content and motility in macrophage-melanoma fusion hybrids

In previous studies, fusion of peritoneal macrophages or blood monocytes with mouse melanoma cells produced hybrids with upregulated expression of the glycosyltransferase beta1,6-N-acetylglucosaminyltransferase V (GnT-V) and its enzymatic product, beta1,6-branched oligosaccharides. This correlated with marked increases in motility, metastatic potential and, surprisingly, melanin content. This study was designed to establish direct roles for beta1,6-branched oligosaccharides in melanogenesis and motility. The levels of beta1,6-branched oligosaccharides were lowered by transfecting beta1,4-N-acetylglucosaminyltransferase III, a competitive inhibitor of GnT-V. beta1,4-N-acetylglucosaminyltransferase III transfection virtually eliminated melanin production and markedly decreased chemotactic motility. This implied that the metastatic and melanogenic phenotypes in hybrids were each upregulated by beta1,6-branched oligosaccharides. Although roles for beta1,6-branched oligosaccharides in motility and metastasis have been reported previously, this is the first study to directly implicate these structures in melanogenesis. Although drawn from experimental models, the findings might explain the well known hypermelanotic regions of human cutaneous malignant melanoma as hypermelanotic cutaneous malignant melanoma cells are rich in beta1,6-branched oligosaccharides. They might also explain why melanogenesis pathways differ between malignant and normal melanocytes as GnT-V is a myeloid-associated enzyme that is aberrantly expressed in melanoma cells but not in normal melanocytes.

Novel carbohydrate-binding activity of bovine liver β-glucuronidase toward lactose/N-acetyllactosamine sequences

Beta-glucuronidase is a lysosomal enzyme that plays an essential role in normal turnover of glycosaminoglycans and remodeling of the extracellular matrix components in both physiological and inflammatory states. The regulation mechanisms of enzyme activity and protein targeting of beta-glucuronidase have implications for the development of a variety of therapeutics. In this study, the effectiveness of various carbohydrate-immobilized adsorbents for the isolation of bovine liver beta-glucuronidase (BLG) from other glycosidases was tested. Beta-glucuronidase and contaminating glycosidases in commercial BLG preparations bound to and were coeluted from adsorbents immobilized with the substrate or an inhibitor of beta-glucuronidase, whereas beta-glucuronidase was found to bind exclusively with lactamyl-Sepharose among the adsorbents tested and to be effectively separated from other enzymes. Binding and elution studies demonstrated that the interaction of beta-glucuronidase with lactamyl-Sepharose is pH dependent and carbohydrate specific. BLG was purified to homogeneity by lactamyl affinity chromatography and subsequent anion-exchange high-performance liquid chromatography (HPLC). Lactose was found to activate beta-glucuronidase noncompetitively, indicating that the lactose-binding site is different from the substrate-binding site. Binding studies with biotinyl glycoproteins, lipids, and synthetic sugar probes revealed that beta-glucuronidase binds to N-acetyllactosamine/lactose-containing glycoconjugates at neutral pH. The results indicated the presence of N-acetyllactosamine/lactose-binding activity in BLG and provided an effective purification method utilizing the novel carbohydrate binding activity. The biological significance of the carbohydrate-specific interaction of beta-glucuronidase, which is different from the substrate recognition, is discussed.

Does glycosylation of melanoma cells influence their interactions with fibronectin?

Cell surface integrins, especially those binding to fibronectin (FN), participate in processes of tumor cell invasion and metastasis. Changes in glycosylation of cell surface adhesion proteins are often associated with malignant transformation of cells. In this study we examined the influence of swainsonine (SW) on adhesion, wound healing and haptotactic migration on FN, comparing the responses of different human melanoma cell lines: primary WM35 and metastatic WM9, WM239 and A375. We also examined the role of alpha subunits in adhesion to FN. All of the antibodies inhibited adhesion to FN but with different efficiencies depending on the cell line. Adhesion was mediated mainly by integrin alpha(5)beta(1) (WM9, A375), alpha(3)beta(1) (WM35, A375, WM239). Scratch wound repair was significantly faster on FN-coated wells than on plastic for all cells except for WM9. A375 and WM9 had the greatest migration ability, both expressing the highest level of alpha(5)beta(1) integrin. It seems very likely that adhesion to FN can be accomplished by many different integrins, but for effective migration alpha(5)beta(1) integrin is responsible. Only A375 and WM239 cell lines reacted to SW treatment. In the presence of SW WM239 and A375 cells had 70% and 40% increased adhesion to FN, and their migration was decreased 40% and 50%, respectively. Interestingly, although most of the cell lines share a common profile of integrins, each line interacted with FN differently. They differed mainly in the repertoire of integrins used for adhesion, and in the manner in which glycosylation affected these processes. The influence of SW was observed in two metastatic cell lines indicating the contribution of glycosylation status to the progression of melanoma. The lack of reaction to SW in WM9 cells may suggest that there is a threshold in the expression level of the highly branched N-glycans that may influence the adhesion and migration properties of the cell.

GnT-V expression and metastatic phenotypes in macrophage-melanoma fusion hybrids is down-regulated by 5-Aza-dC: evidence for methylation sensitive, extragenic regulation of GnT-V transcription

Beta1,6-acetylglucosaminyltransferase V (GnT-V) forms beta1,6 branching on the trimannosyl terminus of N-glycans, allowing for the production of beta1,6Glc-NAc-bearing oligosaccharides. These are used by healthy myeloid cells and cancer cells alike for systemic migration. GnT-V has multiple glycoprotein substrates and thereby exerts global effects on cancer progression, characteristic of a master regulator of metastasis. Yet little is known of the regulation of GnT-V expression by tumor cells. It was previously reported that fusion of macrophages with Cloudman S91 mouse melanoma cells produced macrophage-melanoma hybrids with up-regulated GnT-V expression regarding mRNA and enzymatic activity. Majority of these hybrids showed increased chemotactic motility in vitro and elevated metastatic potential in vivo. Here we attempted to understand this at the molecular genetic level focusing on DNA hypermethylation as a potentially key step. Treatment of cells with 5-Aza-dC, an inhibitor of DNA methylation, resulted in decreased expression of GnT-V mRNA and beta1,6-branched oligosaccharides along with reduced glycosylation of LAMP-1, a major substrate for GnT-V. This was accompanied by reduced chemotactic motility of the cells. The results suggested that DNA hypermethylation in some fashion stimulated GnT-V expression. We thus investigated the promoter region of the GnT-V gene for hypermethylation of CpG islands, comparing macrophage-melanoma hybrids of low and high metastatic potential with the parental melanoma cell line. Genomic DNA after bisulfite modification amplified from this region showed identical sequences between the cell lines. The findings indicated that differential methylation of the promoter region of GnT-V gene was not responsible for its transcriptional control, rather, appeared to be controlled through a negative regulator, nm23, whose own expression was regulated by hypermethylation. Although our studies involved a highly experimental system, the results further suggest that by whatever mechanism, reduction of GnT-V activity through 5-Aza-dC treatment might provide a new approach towards prevention of metastatic progression.

The cell clone ecology hypothesis and the cell fusion model of cancer progression and metastasis: History and experimental support

The two-stage initiation-progression model of cancer is widely accepted. Although mutations explain initiation of neoplasia, the assumption that mutations are responsible for progression of neoplasia to cancer appears to have little experimental support. The "cell clone ecology hypothesis" explains why neoplasia evolve and the "cell fusion model of cancer progression and metastasis" describes how they evolve into clinically significant tumors. A brief history of important concepts and experiments is provided. Clinically significant cancers are effectively new parasite species that live, expand and evolve within the host. It is hypothesized that survival and fate of the parasite clones called "cancer" are governed by the principles of ecology. It is argued that while mutations or aneuploidy (asexual reproduction) can result in transient/self-limiting neoplasia, neither of these asexual modes of forming new karyotypes can maintain the ecologically fit parasites that develop into clinically significant cancer. Mutations and/or unstable genomes (aneuploidy) progressively degrade cell lines and if only these mechanisms were at work, neoplasia would spontaneously become extinct or benign (enfeebled) before reaching clinical significance (an example of "Muller's ratchet"). In the cell fusion model of (clinically significant) cancer progression and metastasis, cell-cell fusion is the essential element allowing normal cells or (transient) neoplasia to evolve into clinically significant cancers. Cell-cell fusion is required for producing and sustaining clinically significant cancer because it provides a sex-like mode of reproduction essential for an ecologically fit parasite organism. Cell-cell fusion provides the opportunity needed for tumors to rejuvenate cell lines containing abnormal genomes and rapidly evolve to acquire dramatically aggressive traits such as metastasis. Indeed, metastasis appears to require cell-cell fusion. Cell-cell fusion also partially overcomes erosion of teleomeres during clone expansion and allows the essential elements of a tumorigenic genome to hide from chemotherapy as recessive traits in cells with normal phenotypes and re-emerge (by cell-cell fusion) as a new cancer after the phenotypically cancerous cells have been eradicated by classical chemotherapy. Eradication of the cancer parasite cannot be routinely achieved by classical toxic chemotherapy alone or even by chemotherapy augmented with techniques needed to overcome anti-apoptotic traits of cancer cells. Direct chemical intervention against cell-cell fusion concurrent with classical toxic chemotherapy holds a promise of preventing re-lapse of the disease. Intervention against cell-cell fusion may also directly suppress metastasis based on the model presented here. The paper also summarizes work on the cell surface glycoprotein CD44 that implicates it as a key element in cell-cell fusion and hence cancer.

Recognition of tumor glycans by antigen-presenting cells

C-type lectin receptors on antigen-presenting cells are potent antigen-uptake receptors with specificity for glycan structures. Glycosylation changes during malignant transformation create tumor-specific carbohydrate structures that interact with C-type lectins on dendritic cells. Recent findings revealed that tumor glycoproteins, such as carcinoembryonic antigen and MUC-1, indeed interact with the C-type lectins DC-SIGN and macrophage galactose-type lectin on antigen-presenting cells. The consequences for anti-cancer immunity or tolerance induction can be extrapolated from the function of C-type lectins in pathogen recognition and antigen presentation. In addition, in vivo studies in mice recently demonstrated the potency of targeting antigens to C-type lectins on antigen-presenting cells for anti-tumor vaccination strategies.

Co-localization of beta1,6-branched oligosaccharides and coarse melanin in macrophage-melanoma fusion hybrids and human melanoma cells in vitro

Fusion hybrids between normal macrophages and Cloudman S91 melanoma cells were shown earlier to have increased metastatic potential, along with high expression of beta1,6-N-acetylglucosaminyltransferase V and beta1,6-branched oligosaccharides. Curiously, hybrids, but not parental melanoma cells, also produced 'coarse melanin'- autophagic vesicles with multiple melanosomes. As beta1,6-branched oligosaccharides were known to be associated with metastasis, and coarse melanin had been described in invasive human melanomas, we looked for potential relationships between the two. Using lectin- and immunohistochemistry, we analyzed cell lines producing coarse melanin for beta1,6-branched oligosaccharides: gp100/pmel-17 (a melanosomal structural component) and CD63 (a late endosome/lysosome component associated with melanoma and certain other human cancers). Cell lines used in this study were (i) hybrid 94-H48, a highly metastatic, macrophage-melanoma experimental fusion hybrid; (ii) 6(neo) mouse melanoma cells, the weakly metastatic, parental fusion partner; and (iii) SKmel-23, a human melanoma cell line derived from a metastasis. Coarse melanin granules were prominent both in hybrids and in SKmel-23 cells, and co-localized with stains for beta1,6-branched oligosaccharides, gp100/pmel 17, and CD63. This is the first report of this phenotype being expressed in vitro, although co-expression of beta1,6-branched oligosaccharides and coarse melanin was recently shown to be a common and pervasive characteristic in archival specimens of human melanomas, and was most prominent in metastases. The results suggest that pathways of melanogenesis in melanoma may differ significantly from those in normal melanocytes. In vitro expression of this phenotype provides new biological systems for more detailed analyses of its genesis and regulation at the molecular genetic level.

Relationship between expression of chemokines and tumor-associated macrophage counting in pancreatic cancer

AIM: To investigate the relationship among the expression of IL-8, MCP-1, MIP-1a and tumor-associated macrophage (TAM) counting in pancreatic cancer.

METHODS: Paraffin section of pancreatic cancer specimen was made using routine method. TAM was counted after staining. The expression of IL-8, MCP-1, MIP-1a was detected by immunohistochemical method

RESULTS: The positive rates of IL-8, MCP-1 and MIP-1a were 62.7%, 66.7% and 66.7%, and their scores were 2.9±1.9, 2.6±1.8 and 2.4±1.7, respectively. Mean counting of TAM was 18.0±6.0 in each pancreatic cancer specimen. The scores of IL-8 and TAM counting were significantly less in well-differentiated cancer than those in poorly-differentiated cancer (IL-8:2.7±1.7 vs 3.2±1.2, P <0.05; TAM:15.9±6.4 vs 21.2±5.2, P <0.05). The positive rates and levels of IL-8, MCP-1, MIP-1a expression as well as TAM counting were significantly higher in metastatic cancer than those in the cancer without metastasis (P <0.05 or P <0.01). TAM counting was significantly higher in IL-8, MCP-1 and MIP-1a positive cancer than that in the negative one. The levels of IL-8, MCP-1, MIP-1a expression positively related to TAM counting (r_IL-8 = 0.52, P <0.01; r_MCP-1 = 0.50, P <0.01; r_MIP-1a = 0.46, P <0.01). At the same time, positive relationship existed between expression of IL-8 and MCP-1a (r = 0.52, P <0.01), IL-8 and MCP-1 (r = 0.54, P <0.01), MCP-1 and MCP-1a (r = 0.64, P <0.01).

CONCLUSION: The expression of IL-8, MCP-1, MIP-1a and TAM counting may relate to the progression, angiogenesis, metastasis and prognosis of pancreatic cancer. Positive expression of IL-8, MCP-1, MIP-1a and high TAM counting may indicate rapid progression and poor prognosis of pancreatic cancer.

Links between CD147 function, glycosylation, and caveolin-1

Cell surface CD147 shows remarkable variations in size (31-65 kDa) because of heterogeneous N-glycosylation, with the most highly glycosylated forms functioning to induce matrix metalloproteinase (MMP) production. Here we show that all three CD147 N-glycosylation sites make similar contributions to both high and low glycoforms (HG- and LG-CD147). l-Phytohemagglutinin lectin binding and swainsonine inhibition experiments indicated that HG-CD147 contains N-acetylglucosaminyltransferase V-catalyzed, beta1,6-branched, polylactosamine-type sugars, which account for its excess size. Therefore, CD147, which is itself elevated on invasive tumor cells, may make a major contribution to the abundance of beta1,6-branched polylactosamine sugars that appear on invasive tumor cells. It was shown previously that caveolin-1 associates with CD147, thus inhibiting CD147 self-aggregation and MMP induction; now we show that caveolin-1 associates with LG-CD147 and restricts the biosynthetic conversion of LG-CD147 to HG-CD147. In addition, HG-CD147 (but not LG-CD147) was preferentially captured as a multimer after treatment of cells with a homobifunctional cross-linking agent and was exclusively recognized by monoclonal antibody AAA6, a reagent that selectively recognizes self-associated CD147 and inhibits CD147-mediated MMP induction. In conclusion, we have 1) determined the biochemical basis for the unusual size variation in CD147, 2) established that CD147 is a major carrier of beta1,6-branched polylactosamine sugars on tumor cells, and 3) determined that caveolin-1 can inhibit the conversion of LG-CD147 to HG-CD147. Because it is HG-CD147 that self-aggregates and stimulates MMP induction, we now have a mechanism to explain how caveolin-1 inhibits these processes. These results help explain the previously established tumor suppressor functions of caveolin-1.