Carbohydrate structures of a normal counterpart of the carcinoembryonic antigen produced by colon epithelial cells of normal adults

The universe of galectin-binding partners and their functions in health and disease

Galectins, a family of evolutionarily conserved glycan-binding proteins, play key roles in diverse biological processes including tissue repair, adipogenesis, immune cell homeostasis, angiogenesis, and pathogen recognition. Dysregulation of galectins and their ligands has been observed in a wide range of pathologic conditions including cancer, autoimmune inflammation, infection, fibrosis, and metabolic disorders. Through protein-glycan or protein-protein interactions, these endogenous lectins can shape the initiation, perpetuation, and resolution of these processes, suggesting their potential roles in disease monitoring and treatment. However, despite considerable progress, a full understanding of the biology and therapeutic potential of galectins has not been reached due to their diversity, multiplicity of cell targets, and receptor promiscuity. In this article, we discuss the multiple galectin-binding partners present in different cell types, focusing on their contributions to selected physiologic and pathologic settings. Understanding the molecular bases of galectin-ligand interactions, particularly their glycan-dependency, the biochemical nature of selected receptors, and underlying signaling events, might contribute to designing rational therapeutic strategies to control a broad range of pathologic conditions.

A case of stercoral colitis with marked elevation of serum carcinoembryonic antigen

It should be noted that the serum CEA level can become elevated in severe stercoral colitis. Marked elevation of the serum CEA level in stercoral colitis may suggest the necessity of surgery in patients with stercoral colitis.

Distinct substrate specificities of human GlcNAc-6-sulfotransferases revealed by mass spectrometry-based sulfoglycomic analysis

Sulfated glycans are known to be involved in several glycan-mediated cell adhesion and recognition pathways. Our mRNA transcript analyses on the genes involved in synthesizing GlcNAc-6-O-sulfated glycans in human colon cancer tissues indicated that GlcNAc6ST-2 (CHST4) is preferentially expressed in cancer cells compared with nonmalignant epithelial cells among the three known major GlcNAc-6-O-sulfotransferases. On the contrary, GlcNAc6ST-3 (CHST5) was only expressed in nonmalignant epithelial cells, whereas GlcNAc6ST-1 (CHST2) was expressed equally in both cancerous and nonmalignant epithelial cells. These results suggest that 6-O-sulfated glycans that are synthesized only by GlcNAc6ST-2 may be highly colon cancer-specific, as supported by immunohistochemical staining of cancer cells using the MECA-79 antibody known to be relatively specific to the enzymatic reaction products of GlcNAc6ST-2. By more precise MS-based sulfoglycomic analyses, we sought to further infer the substrate specificities of GlcNAc6STs via a definitive mapping of various sulfo-glycotopes and O-glycan structures expressed in response to overexpression of transfected GlcNAc6STs in the SW480 colon cancer cell line. By detailed MS/MS sequencing, GlcNAc6ST-3 was shown to preferentially add sulfate onto core 2-based O-glycan structures, but it does not act on extended core 1 structures, whereas GlcNAc6ST-1 prefers core 2-based O-glycans to extended core 1 structures. In contrast, GlcNAc6ST-2 could efficiently add sulfate onto both extended core 1- and core 2-based O-glycans, leading to the production of unique sulfated extended core 1 structures such as R-GlcNAc(6-SO3-)β1-3Galβ1-4GlcNAc(6-SO3-)β1-3Galβ1-3GalNAcα, which are good candidates to be targeted as cancer-specific glycans.

Lectin-Based Assay for Glycoform-Specific Detection of α2,6-sialylated Transferrin and Carcinoembryonic Antigen in Tissue and Body Fluid

Antibodies are useful for detecting glycoprotein antigens, but a conventional antibody recognizes only a protein epitope rather than a glycan. Thus, glycan isoform detection generally requires time- and labor-consuming processes such as lectin affinity column chromatography followed by sandwich ELISA. We recently found antigen-antibody reactions that were inhibited by lectin binding to glycans on the glycoprotein antigen, leading to a convenient glycoform-specific assay. Indeed, Sambucus sieboldiana agglutinin (SSA) lectin, a binder to sialylα2,6galactose residue, inhibited antibody binding to α2,6-sialylated transferrin (Tf) (SSA inhibition). SSA inhibition was not observed with other glycoforms, such as periodate-treated, sialidase-treated and sialidase/galactosidase-treated Tf, suggesting that the assay was glycoform-specific. SSA inhibition was also applicable for visualizing localization of α2,6-sialylated-Tf in a liver section. This is the first immunohistochemical demonstration of glycoform localization in a tissue section. SSA inhibition was utilized for establishing ELISA to quantify α2,6-sialylated carcinoembryonic antigen (CEA), a marker for various cancers. In addition, α2,6-sialylated-CEA was visualized in a colonic adenocarcinoma section by SSA inhibition. The method would further be applicable to a simple and rapid estimation of other α2,6-sialylated glycoproteins and have a potential aid to histopathological diagnosis.

N-Glycan matrix-assisted laser desorption/ionization mass spectrometry imaging protocol for formalin-fixed paraffin-embedded tissues

RATIONALE

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) of the proteome of a tissue has been an established technique for the past decade. In the last few years, MALDI-MSI of the N-glycome has emerged as a novel MALDI-MSI technique. To assess the accuracy and clinical significance of the N-linked glycan spatial distribution, we have developed a method that utilises MALDI-MSI followed by liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS) in order to assign glycan structures to the differentiating MALDI-MSI glycan masses released from the tissue glycoproteins.

METHODS AND RESULTS

Our workflow presents a comprehensive list of instructions on how to (i) apply MALDI-MSI to spatially map the N-glycome across formalin-fixed paraffin-embedded (FFPE) clinical samples, (ii) structurally characterise N-glycans extracted from consecutive FFPE tissue sections by LC/MS/MS, and (iii) match relevant N-glycan masses from MALDI-MSI with confirmed N-glycan structures determined by LC/MS/MS.

CONCLUSIONS

Our protocol provides groups that are new to this technique with instructions how to establish N-glycan MALDI-MSI in their laboratory. Furthermore, the method assigns N-glycan structural detail to the masses obtained in the MALDI-MS image. Copyright © 2017 John Wiley & Sons, Ltd.

Lectin inhibits antigen-antibody reaction in a glycoform-specific manner: Application for detecting α2,6sialylated-carcinoembryonic antigen

Carcinoembryonic antigen (CEA) is a glycoprotein marker, which is widely used for diagnosing various cancers, especially colon adenocarcinoma. In addition, CEA mediates homotypic adhesion of colon adenocarcinoma cells, which appears to favor hematogenous metastasis. CEA carries α2,6sialyl residues on its N-glycans whereas a normal counterpart, normal fecal antigen-2, does α2,3sialyl residues, suggesting that cancer-specific  α2,6sialylation on CEA may play a role for cell invasion and metastasis. A simple and rapid estimation of α2,6sialyled CEA in detergent extracts from formalin-fixed colon adenocarcinoma by "lectin inhibition" is reported. In the lectin inhibition method, Sambucus sieboldiana Agglutinin (SSA) lectin, an α2,6sialic acid binder, was used as a glycoform-specific inhibitor for antigen-antibody reaction in ELISA. Detergent extracts from colon adenocarcinoma showed a fair amount of ELISA signal in the absence of SSA whereas the signal was markedly reduced (45≈74%) in the presence of SSA, suggesting that the extracts contains α2,6sialyled CEA. The presence of α2,6sialyled CEA in the extracts was confirmed by lectin microarray, in which SSA, Sambucus nigra agglutinin, and Trichosanthes japonica agglutinin I lectins were used as α2,6sialyl binders. Thus lectin inhibition is a simple and rapid method for detecting α2,6sialyled CEA even in crude detergent extracts from formalin-fixed adenocarcinoma tissue.

High-sensitivity immunoassay with surface plasmon field-enhanced fluorescence spectroscopy using a plastic sensor chip: application to quantitative analysis of total prostate-specific antigen and GalNAcβ1-4GlcNAc-linked prostate-specific antigen for prostate cancer diagnosis

A high-sensitivity immunoassay system with surface plasmon field-enhanced fluorescence spectrometry (SPFS) was constructed using a plastic sensor chip and then applied to the detection of total prostate-specific antigen (total PSA) and GalNAcβ1-4GlcNAc-linked prostate-specific antigen (LacdiNAc-PSA) in serum, to discriminate between prostate cancer (PC) and benign prostate hyperplasia (BPH). By using this automated SPFS immunoassay, the detection limit for total PSA in serum was as low as 0.04 pg/mL, and the dynamic range was estimated to be at least five digits. A two-step sandwich SPFS immunoassay for LacdiNAc-PSA was constructed using both the anti-PSA IgG antibody to capture PSA and Wisteria floribunda agglutinin (WFA) for the detection of LacdiNAc. The results of the LacdiNAc-PSA immunoassay with SPFS showed that the assay had a sensitivity of 20.0 pg/mL and permitted the specific distinction between PC and BPH within the PSA gray zone. These results suggested that high-sensitivity automated SPFS immunoassay systems might become a powerful tool for the diagnosis of PC and other diseases.

In situ visualization of a glycoform of transferrin: localization of α2,6-sialylated transferrin in the liver

We previously found that a lectin, Sambucus sieboldiana agglutinin (SSA), bound to α2,6-sialylated glycan epitopes on transferrin and inhibited anti-transferrin antibody binding to the antigen in ELISA (SSA inhibition). Here we report that SSA inhibition is applicable to immunohistochemistry, localizing α2,6-sialylated transferrin in the liver. Immunohistochemistry using anti-transferrin polyclonal antibody revealed that transferrin was detected in hepatocytes near interlobular veins. Addition of SSA lectin markedly attenuated the staining. Sialidase treatment of a liver section abolished SSA binding and concomitantly cancelled SSA inhibition, suggesting that SSA binding to glycan epitopes on the section was essential for the inhibition. To examine the importance of proximity between antigen epitopes and SSA-binding (glycosylation) sites, we prepared two anti-peptide antibodies against partial amino acid sequences of transferrin. One antibody (Tf-596Ab) is against a peptide sequence, Cys596-Ala614, which is proximal to N-glycosylation sites (Asn-432 and Asn-630). The other (Tf-120Ab) is against a peptide sequence, Val120-Cys137, distal to the sites. The staining signals of Tf-596Ab were reduced by the addition of SSA, whereas those of Tf-120Ab were reduced only a little. This result suggests that proximity of the antigen epitope to SSA binding sites is critical for SSA inhibition in immunohistochemistry.

CEA-Related CAMs

The carcinoembryonic antigen (CEA) family comprises a large number of cellular surface molecules, the CEA-related cell adhesion molecules (CEACAMs), which belong to the Ig superfamily. CEACAMs exhibit a complex expression pattern in normal and malignant tissues. The majority of the CEACAMs are cellular adhesion molecules that are involved in a great variety of distinct cellular processes, for example in the integration of cellular responses through homo- and heterophilic adhesion and interaction with a broad selection of signal regulatory proteins, i.e., integrins or cytoskeletal components and tyrosine kinases. Moreover, expression of CEACAMs affects tumor growth, angiogenesis, cellular differentiation, immune responses, and they serve as receptors for commensal and pathogenic microbes. Recently, new insights into CEACAM structure and function became available, providing further elucidation of their kaleidoscopic functions.

Golgi pH, its regulation and roles in human disease

Most organelles within the exocytic and endocytic pathways typically acidify their interiors, a phenomenon that is known to be crucial for their optimal functioning in eukaryotic cells. This review highlights recent advances in our understanding of how Golgi acidity is maintained and regulated, and how its misregulation contributes to organelle dysfunction and disease. Both its biosynthetic products (glycans) and protein-sorting events are highly sensitive to changes in Golgi luminal pH and are affected in certain human disease states such as cancers and cutis laxa. Other potential disease states that are caused by, or are associated with, Golgi pH misregulation will also be discussed.

Novel O-linked glycans containing 6'-sulfo-Gal/GalNAc of MUC1 secreted from human breast cancer YMB-S cells: possible carbohydrate epitopes of KL-6(MUC1) monoclonal antibody

Human serum Krebs von den Lugen-6 (KL-6) antigen is a MUC1 glycoprotein (KL-6/MUC1) recognized by anti-KL-6 monoclonal antibody (KL-6/mAb) and has been utilized as a diagnostic marker for interstitial pneumonia. KL-6/mAb is thought to recognize the specific glycopeptides sequence of MUC1, but the precise glycan structure of the epitope is unclear. In this study, we determined the carbohydrate structures of KL-6/MUC1 to search the carbohydrate epitopes for KL-6/mAb. KL-6/MUC1 was purified from the culture medium of human breast cancer YMB-S cells by KL-6/mAb-affinity chromatography; the O-linked glycan structures were determined in combination with paper electrophoresis, several lectin column chromatographies, sialidase digestion and methanolysis. KL-6/MUC1 contained core 1 and extended core 1 glycans modified with one or two sialic acid/sulfate residues. Based on these structures, several synthetic glycans binding to anti-KL-6/mAb were compared with one another by surface plasmon resonance. Sequentially, related radiolabeled oligosaccharides were enzymatically synthesized and analyzed for binding to a KL-6/mAb-conjugated affinity column. 3'-sialylated, 6'-sulfated LNnT [Neu5Acα2-3(SO(3)(-)-6)Galβ1-4GlcNAcβ1-3Galβ1-4Glc], 3'-sialylated, 6-sulfated core 1 [Neu5Acα2-3Galβ1-3(SO(3)(-)-6)GalNAc] and disulfated core 1 SO(3)(-)-3Galβ1-3(SO(3)(-)-6)GalNAc exhibited substantial affinity for KL-6/mAb, and 3'-sulfated core 1 derivatives [SO(3)(-)-3Galβ1-3(±Neu5Acα2-6)GalNAc] and 3'-sialylated core 1 weakly interacted with KL-6/mAb. These results indicated that the possible carbohydrate epitopes of KL-6/mAb involve not only 3'-sialylated core 1 but also novel core 1 and extended core 1 with sulfate and sialic acid residues. Epitope expressing changes with suppression or over-expression of the Gal6ST (Gal 6-O-sulfotransferase) gene, suggesting that Gal6ST is involved in the biosynthesis of the unique epitopes of KL-6/mAb.

Enrichment method of sulfated glycopeptides by a sulfate emerging and ion exchange chromatography

Sulfated glycoproteins are of growing importance for biomarker discovery, as well as for investigating molecular recognition processes. Mass spectrometry (MS) has become a powerful technique for the characterization of glycans and glycoproteins. However, characterization and detection of sulfated glycopeptides by MS is difficult because of the low abundance and low ionization efficiency of these molecules. To overcome this problem, we developed a novel enrichment procedure for sulfated glycopeptides. The procedure consists of anion exchange chromatography and a sulfate emerging (SE) method which controls the net charge of peptides by utilizing limited proteolyzes and modification with acetohydrazide. Using this procedure, we are able to enrich and characterize the sulfated glycopeptides of bovine luteinizing hormone (bLH). Furthermore, we demonstrate the enrichment and detection of sulfated glycopeptides from a complex mixture comprising human serum spiked with bLH at a concentration of 0.1%.

alpha1,2-Fucosylated and beta-N-acetylgalactosaminylated prostate-specific antigen as an efficient marker of prostatic cancer

A prostate-specific antigen (PSA) is widely used as a diagnostic marker for prostate cancer (PC) because of its high specificity. However, elevated serum PSA does not occur only in PC but also in benign prostatic hyperplasia (BPH). Since the structural changes of N-glycans during carcinogenesis are common phenomena, we investigated whether PC-specific N-glycans are linked to PSA. We first analyzed the carbohydrate structures of PSA derived from seminal fluid, serum of BPH and PC patients, and PC cell line, namely, LNCaP using eight lectin-immobilized columns and then with enzyme-linked immunosorbent assay (ELISA). The fraction of serum PSA from PC patients bound to both Fucalpha1-2Gal and betaGalNAc binding Trichosanthes japonica agglutinin-II (TJA-II) column, while that from BPH patients did not exhibit this binding ability, thereby implying that there is elevated expression of alpha1,2-fucosylation and beta-N-acetylgalactosaminylation of PSA during carcinogenesis. We then performed a real-time polymerase chain reaction (PCR) and confirmed that these structural changes were responsible for the elevated expression of fucosyltransferase I (FUT1) and beta-N-acetylgalactosaminyltransferase 4(B4GALNT4). Second, we measured TJA-II-bound PSA contents and the binding ratios of TJA-II column chromatography in serum PSA samples from 40 patients of both PC and BPH. The results indicated that both TJA-II-bound PSA content and TJA-II binding ratios (%) could be used to discriminate between PC and BPH with more than 95% probability, and TJA-II-bound PSA can be regarded as a potential marker of PC.

C-type lectins on dendritic cells: key modulators for the induction of immune responses

DCs (dendritic cells) are specialized in the recognition of pathogens and play a pivotal role in the control of immune responses. DCs are also important for homoeostatic control, recognizing self-antigens and tolerizing the tissue environment. The nature of the antigen recognized tilts the balance towards immunity or tolerance. CLRs (C-type lectin receptors) expressed by DC are involved in the recognition and capture of many glycosylated self-antigens and pathogens. It is now becoming clear that these CLRs may not only serve as antigen receptors allowing internalization and antigen presentation, but also function in the recognition of glycosylated self-antigens, and as adhesion and/or signalling molecules. The expression of C-type lectins is very sensitive to maturation stimuli, leading to down-regulation as DCs mature. CLRs such as DC-SIGN (DC-specific intracellular adhesion molecule-3 grabbing non-integrin) recognizes high-mannose-containing structures and Lewis antigens (Le(x), Le(y), Le(b) and Le(a)), whereas the CLR MGL (macrophage galactose/N-acetylgalactosamine-specific C-type lectin) recognizes GalNAc. Le(x), Le(y) and GalNAc glycan structures are often expressed on tumours. We have demonstrated that glycan modification of antigen can strongly enhance MHC class I responses and the induction of antigen-specific cytotoxic T-lymphocytes, indicating that glycosylated antigen targets C-type lectin to enhance antigen-specific T-cell responses. Moreover, these CLRs induce signalling processes in DCs and specific cytokine responses in combination with TLR (Toll-like receptor) triggering. This implies that specific C-type lectin-targeted antigens can regulate T-cell polarization. Understanding the diversity of C-type lectins being expressed on DCs as well as their carbohydrate-specific recognition profiles should promote understanding of pathogen recognition in many diseases, as well as the regulation of cellular interactions of DCs that are essential in the control of immunity.

Specificity in cancer immunotherapy

From the earliest days in the field of tumor immunology three questions have been asked: do cancer cells express tumor-specific antigens, does the immune system recognize these antigens and if so, what is their biochemical nature? We now know that truly tumor-specific antigens exist, that they are caused by somatic mutations, and that these antigens can induce both humoral and cell-mediated immune responses. Because tumor-specific antigens are exclusively expressed by the cancer cell and are often crucial for tumorigenicity, they are ideal targets for anti-cancer immunotherapy. Nevertheless, the antigens that are targeted today by anti-tumor immunotherapy are not tumor-specific antigens, but antigens that are normal molecules also expressed by normal tissues (so-called "tumor-associated" antigens). If tumor-specific antigens exist and are ideal targets for immunotherapy, why are they not being targeted? In this review, we summarize current knowledge of tumor-specific antigens: their identification, immunological relevance and clinical use. We discuss novel tumor-specific epitopes and propose new approaches that could improve the success of cancer immunotherapy, especially for the treatment of solid tumors.

Intercellular transfer of carcinoembryonic antigen from tumor cells to NK cells

The inhibition of NK cell killing is mainly mediated via the interaction of NK inhibitory receptors with MHC class I proteins. In addition, we have previously demonstrated that NK cells are inhibited in a class I MHC-independent manner via homophilic carcinoembryonic Ag (CEA) cell adhesion molecules (CEACAM1)-CEACAM1 and heterophilic CEACAM1-CEA interactions. However, the cross-talk between immune effector cells and their target cells is not limited to cell interactions per se, but also involves a specific exchange of proteins. The reasons for these molecular exchanges and the functional outcome of this phenomenon are still mostly unknown. In this study, we show that NK cells rapidly and specifically acquire CEA molecules from target cells. We evaluated the role of cytotoxicity in the acquisition of CEA and demonstrated it to be mostly killing independent. We further demonstrate that CEA transfer requires a specific interaction with an unknown putative NK cell receptor and that carbohydrates are probably involved in CEA recognition and acquisition by NK cells. Functionally, the killing of bulk NK cultures was inhibited by CEA-expressing cells, suggesting that this putative receptor is an inhibitory receptor.

Interactions of DC-SIGN with Mac-1 and CEACAM1 regulate contact between dendritic cells and neutrophils

Early during infection neutrophils are the most important immune cells that are involved in killing of pathogenic bacteria and regulation of innate immune responses at the site of infection. It has become clear that neutrophils also modulate adaptive immunity through interactions with dendritic cells (DCs) that are pivotal in the induction of T cell responses. Upon activation, neutrophils release TNF-alpha and induce maturation of DCs that enables these antigen-presenting cells to stimulate T cell proliferation and to induce T helper 1 polarization. DC maturation by neutrophils also requires cellular interactions that are mediated by binding of the DC-specific receptor DC-SIGN to Mac-1 on the neutrophil. Here, we demonstrate that also CEACAM1 is an important ligand for DC-SIGN on neutrophils. Binding of DC-SIGN to both CEACAM1 and Mac-1 is required to establish cellular interactions with neutrophils. DC-SIGN is a C-type lectin that has specificity for Lewis(x), and we show that DC-SIGN mediates binding to CEACAM1 through Lewis(x) moieties that are specifically expressed on CEACAM1 derived from neutrophils. This indicates that glycosylation-driven binding of both Mac-1 and CEACAM1 to DC-SIGN is essential for interactions of neutrophils with DCs and enables neutrophils to modulate T cell responses through interactions with DCs.

Porcine, mouse and human galactose 3-O-sulphotransferase-2 enzymes have different substrate specificities; the porcine enzyme requires basic compounds for its catalytic activity

Sulphation of galactose at the C-3 position is one of the major post-translational modifications of colorectal mucin. Thus we partially purified a Gal 3-O-sulphotransferase from porcine colonic mucosa (pGal3ST) and studied its enzymatic characteristics. The enzyme was purified 48500-fold by sequential chromatographies on hydroxyapatite, Con A (concanavalin A)-Sepharose, porcine colonic mucin-Sepharose, Cu2+-chelating Sepharose and AMP-agarose. Interestingly, the purified pGal3ST required submillimolar concentrations of spermine or basic lipids, such as D-sphingosine and N,N-dimethylsphingosine, for enzymatic activity. pGal3ST recognized Galbeta1-->3GalNAc (core 1) as an optimal substrate, and had weaker activity for Galbeta1-->3GlcNAc (type 1) and Galbeta1-->4GlcNAc (type 2). Substrate competition experiments proved that a single enzyme catalyses sulphation of all three oligosaccharides. Among the four human Gal3STs cloned to date, the substrate specificity of pGal3ST is most similar to that of human Gal3ST-2, which is also strongly expressed in colonic mucosa, although the kinetics of pGal3ST and human Gal3ST-2 were rather different. To determine whether pGal3ST is the orthologue of human Gal3ST-2, a cDNA encoding porcine Gal3ST-2 was isolated and the enzyme was expressed in COS-7 cells for analysis of substrate specificity. This revealed that porcine Gal3ST-2 has the same specificity as pGal3ST, indicating that pGal3ST is indeed the porcine equivalent of Gal3ST-2. The substrate specificity of mouse Gal3ST-2 was also different from those of human and porcine Gal3ST-2 enzymes. Mouse Gal3ST-2 preferred core 1 and type 2 glycans to type 1, and the K(m) values were much higher than those of human Gal3ST-2. These results suggest that porcine Gal3ST-2 requires basic compounds for catalytic activity and that human, mouse and porcine Gal3ST-2 orthologues have diverse substrate specificities.

Altered glycosylation of proteins produced by malignant cells, and application for the diagnosis and immunotherapy of tumours

Most secretory and membrane-bound proteins produced by mammalian cells contain covalently linked sugar chains. Alterations of the sugar chain structures of glycoproteins have been found to occur in various tumours. Because the sugar chains of glycoproteins are essential for the maintenance of the ordered social behaviour of differentiated cells in multicellular organisms, alterations to the sugar chains are the molecular basis of abnormal social behaviours in tumour cells, such as invasion into the surrounding tissues and metastasis. In this review, the structure and enzymatic basis of typical alterations of the N-linked sugar chains, which are found in various tumours, are introduced. These data are useful for devising diagnostic methods and immunotherapies for the clinical treatment of tumours. Three beta-N-acetylglucosaminyltransferases, GnT-III, -IV and -V, play roles in the structural alteration of the complex-type sugar chains in various tumours. In addition, transcriptional changes in various glycosyltransferases, together with the transporters of sugar nucleotides and sulfate, which are responsible for the formation of the outer chain moieties of complex-type sugar chains, are the keys to inducing the alterations.

Dendritic cells recognize tumor-specific glycosylation of carcinoembryonic antigen on colorectal cancer cells through dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin

Dendritic cells play a pivotal role in the induction of antitumor immune responses. Immature dendritic cells are located intratumorally within colorectal cancer and intimately interact with tumor cells, whereas mature dendritic cells are present peripheral to the tumor. The majority of colorectal cancers overexpress carcinoembryonic antigen (CEA), and malignant transformation changes the glycosylation of CEA on colon epithelial cells, resulting in higher levels of Lewis(x) and de novo expression of Lewis(y) on tumor-associated CEA. Dendritic cells express the C-type lectin dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) that has high affinity for nonsialylated Lewis antigens, so we hypothesized that DC-SIGN is involved in recognition of colorectal cancer cells by dendritic cells. We show that immature dendritic cells within colorectal cancer express DC-SIGN and that immature dendritic cells but not mature dendritic cells interact with tumor cells. DC-SIGN mediates these interactions through binding of Lewis(x) and Lewis(y) carbohydrates on CEA of colorectal cancer cells. In contrast, DC-SIGN does not bind CEA expressed on normal colon epithelium that contains low levels of Lewis antigens. This indicates that dendritic cells may recognize colorectal cancer cells through binding of DC-SIGN to tumor-specific glycosylation on CEA. Similar to pathogens that target DC-SIGN to escape immunosurveillance, tumor cells may interact with DC-SIGN to suppress dendritic cell functions.

Galectin-4 Binds to Sulfated Glycosphingolipids and Carcinoembryonic Antigen in Patches on the Cell Surface of Human Colon Adenocarcinoma Cells

Galectin-4, a member of the galectin family, is expressed in the epithelium of the alimentary tract. It has two tandemly repeated carbohydrate recognition domains and specifically binds to an SO3- -->3Galbeta1-->3GalNAc pyranoside with high affinity (Ideo, H., Seko, A., Ohkura, T., Matta, K. L., and Yamashita, K. (2002) Glycobiology 12, 199-208). In this study, we found that galectin-4 binds to glycosphingolipids carrying 3-O-sulfated Gal residues, such as SB1a, SM3, SM4s, SB2, SM2a, and GM1, but not to glycosphingolipids with 3-O-sialylated Gal, such as sLc4Cer, snLc4Cer, GM3, GM2, and GM4, using both an enzyme-linked immunosorbent assay and a surface plasmon resonance assay. A confocal immunocytochemical assay showed that galectin-4 was colocalized with SB1a, GM1, and carcinoembryonic antigen (CEA) in the patches on the cell surface of human colon adenocarcinoma CCK-81 and LS174T cells. This localization was distinct from caveolin/VIP21 localization. Furthermore, immobilized galectin-4 promoted adhesion of CCK-81 cells through the sulfated glycosphingolipid, SB1a. CEA also bound to galectin-4 with KD value of 2 x 10(-8) m by surface plasmon resonance and coimmunoprecipitated with galectin-4 in LS174T cell lysates. These findings suggest that SB1a and CEA in the patches on the cell surface of human colon adenocarcinoma cells could be biologically important ligands for galectin-4.

Suppression of beta 1,3galactosyltransferase beta 3Gal-T5 in cancer cells reduces sialyl-Lewis a and enhances poly N-acetyllactosamines and sialyl-Lewis x on O-glycans

We investigated the role of beta 3 Gal-T5, a member of the beta 1,3galactosyltransferase (beta 1,3Gal-T) family, in cancer-associated glycosylation, focusing on the expression of sialyl-Lewis a (sLea, the epitope of CA19.9 antigen), poly N-acetyllactosamines, and sialyl-Lewis x (sLex) antigen. A clone permanently expressing an antisense fragment of beta 3Gal-T5 was obtained from the human pancreas adenocarcinoma cell line BxPC3 and characterized. Both beta 1,3Gal-T activity and sLea expression are dramatically impaired in the clone. Analysis of the oligosaccharides synthesized in cells metabolically labelled with tritiated galactose shows that a relevant amount of radioactivity is associated to large O-glycans. Endo-beta-galactosidase mostly releases NeuAc alpha 2-3Gal beta 1-3[Fuc alpha 1-4]GlcNAc beta 1-3Gal and NeuAc alpha 2-3Gal beta 1-3GlcNAc beta 1-3Gal from such O-glycans of BxPC3 membranes, but GlcNAc beta 1-3Gal and type 2 chain oligosaccharides, including NeuAc alpha 2-3Gal beta 1-4[Fuc alpha 1-3]GlcNAc beta 1-3Gal, from those of the antisense clone. Furthermore, BxPC3 cells secrete sLea in the culture media but not sLex, while antisense clone secretes mostly sLex, and accumulation of both antigens is prevented by benzyl-alpha-GalNAc. These data indicate that beta 3Gal-T5 suppression turns synthesis of type 1 chain O-glycans to poly N-acetyllactosamine elongation and termination by sLex. In other cell lines and clones, beta 3Gal-T5 transcript, beta 1,3Gal-T activity, and sLea antigen are also correlated, but quantitatively the relative expression ratios are very different from cell type to cell type. We suggest that beta 3Gal-T5 plays a relevant role in gastrointestinal and pancreatic tissues counteracting the glycosylation pattern associated to malignancy, and is necessary for the synthesis and secretion of CA19.9 antigen, whose expression still depends on multiple interacting factors.

Beta 1,4-galactosyltransferase (beta 4GalT)-IV is specific for GlcNAc 6-O-sulfate. Beta 4GalT-IV acts on keratan sulfate-related glycans and a precursor glycan of 6-sulfosialyl-Lewis X

The Galbeta1-->4(SO(3)(-)-->6)GlcNAc moiety is present in various N-linked and O-linked glycans including keratan sulfate and 6-sulfosialyl-Lewis X, an L-selectin ligand. We previously found beta1,4-galactosyltransferase (beta4GalT) activity in human colonic mucosa, which prefers GlcNAc 6-O-sulfate (6SGN) as an acceptor to non-substituted GlcNAc (Seko, A., Hara-Kuge, S., Nagata, K., Yonezawa, S., and Yamashita, K. (1998) FEBS Lett. 440, 307-310). To identify the gene for this enzyme, we purified the enzyme from porcine colonic mucosa. The purified enzyme had the characteristic requirement of basic lipids for catalytic activity. Analysis of the partial amino acid sequence of the enzyme revealed that the purified beta4GalT has a similar sequence to human beta4GalT-IV. To confirm this result, we prepared cDNA for each of the seven beta4GalTs cloned to date and examined substrate specificities using the membrane fractions derived from beta4GalT-transfected COS-7 cells. When using several N-linked and O-linked glycans with or without 6SGN residues as acceptor substrates, only beta4GalT-IV efficiently recognized 6SGN, keratan sulfate-related oligosaccharides, and Galbeta1-->3(SO(3)(-)-->6GlcNAcbeta1-->6) GalNAcalpha1-O-pNP, a precursor for 6-sulfosialyl-Lewis X. These results suggested that beta4GalT-IV is a 6SGN-specific beta4GalT and may be involved in the biosynthesis of various glycoproteins carrying a 6-O-sulfated N-acetyllactosamine moiety.

Ectopic expression of a GlcNAc 6-O-sulfotransferase, GlcNAc6ST-2, in colonic mucinous adenocarcinoma

The content of sulfated glycans having 6-O-sulfated GlcNAc residues alters in the course of colonic carcinogenesis. We previously characterized two GlcNAc 6-O-sulfotransferases (SulTs), SulT-a and -b, expressed in colonic normal tissues and adenocarcinomas [Seko et al. (2000) Glycobiology, 10, 919-929]. Levels of the enzymatic activities of SulT-a in normal colonic mucosa are higher than those in colonic adenocarcinomas, and the enzymatic activities of SulT-b are detected only in mucinous adenocarcinomas. To determine which GlcNAc 6-O-SulTs cloned so far correspond to SulT-a and -b, we expressed seven enzymes of a Gal/GalNAc/GlcNAc 6-O-SulT family in COS-7 cells and examined their substrate specificities in comparison with those of SulT-a and -b. GlcNAc6ST-2 (HEC-GlcNAc6ST, LSST, or GST-3) can recognize GlcNAcbeta1-->3GalNAcalpha1-O-pNP as a good acceptor as well as other O-linked- and N-linked-type oligosaccharides, and its substrate specificity was similar to that of SulT-b. GlcNAc6ST-3(I-GlcNAc6ST or GST-4alpha) preferred Galbeta1-->3(GlcNAcbeta1-->6)GalNAcalpha1-O-pNP as an acceptor to the other oligosaccharides examined, and its specificity was similar to that of SulT-a. To confirm these correspondences, we further performed quantitative analyses of transcripts for GlcNAc6ST-2 and -3 genes by competitive RT-PCR. As a result, GlcNAc6ST-2 gene was expressed in almost all the mucinous adenocarcinomas examined and hardly expressed in normal colonic mucosa and nonmucinous adenocarcinoma. Expression levels of transcript for GlcNAc6ST-3 in normal mucosa were significantly higher than those in adenocarcinomas. From these results, it was indicated that GlcNAc6ST-2 corresponds to mucinous adenocarcinoma-specific SulT-b and that expression of GlcNAc6ST-3 is down-regulated in colonic adenocarcinomas.

Studies on selectin blocker. 9. SARs of non-sugar selectin blocker against E-, P-, L-selectin bindings

As a part of study of selectin blockers, we have already reported that a non-sugar selectin antagonist (3) was successfully discovered using a computational screening (Hiramatsu, Y.; Tsukida, T.; Nakai, Y.; Inoue, Y.; Kondo, H. J. Med. Chem. 2000, 43, 1476). To investigate the SARs of compound 3 against E-, P-, and L-selectins, we synthesized the derivatives of compound 3 and evaluated their inhibitory activities toward selectin bindings. The structural diversity of compound 3 contained the following: (1) a modification of the spacer unit (4--7), (2) a modification of the tail unit (8--11), (3) a modification of the head unit (12--18). As a result, it was found that a non-sugar based selectin blocker (3) could be a potential lead compound for E-, P-, and L-selectin blockers and some of the derivatives showed broad and/or selective inhibitory activities toward the E-, P-, and L-selectins. In addition, it was found that the experimental evidence well supported that the computational screening using 3D-pharmacophore model could be useful methodology to find out a new lead for the several type of selectin blockers, which included a broad and/or a selective inhibitor.

beta 1,3-Galactosyltransferase beta 3Gal-T5 acts on the GlcNAcbeta 1-->3Galbeta 1-->4GlcNAcbeta 1-->R sugar chains of carcinoembryonic antigen and other N-linked glycoproteins and is down-regulated in colon adenocarcinomas

We attempted to determine whether beta1,3-galactosyltransferase beta3Gal-T5 is involved in the biosynthesis of a specific subset of type 1 chain carbohydrates and expressed in a cancer-associated manner. We transfected Chinese hamster ovary (CHO) cells expressing Fuc-TIII with beta3Gal-T cDNAs and studied the relevant glycoconjugates formed. beta3Gal-T5 directs synthesis of Lewis type 1 antigens in CHO cells more efficiently than beta3Gal-T1, whereas beta3Gal-T2, -T3, and -T4 are almost unable to direct synthesis. In the clone expressing Fuc-TIII and beta3Gal-T5 (CHO-FT-T5), sialyl-Lewis a synthesis is strongly inhibited by swainsonine but not by benzyl-alpha-GalNAc, and sialyl-Lewis x is absent, although it is detected in the clones expressing Fuc-TIII and beta3Gal-T1 (CHO-FT-T1) or Fuc-TIII and beta3Gal-T2 (CHO-FT-T2). Endo-beta-galactosidase treatment of N- glycans prepared from clone CHO-FT-T5 releases (+/-NeuAcalpha2-->3)Galbeta1-->3[Fucalpha1-->4]GlcNAcbeta1-->3Gal but not GlcNAcbeta1-->3Gal or type 2 chain oligosaccharides, which are found in CHO-FT-T1 cells. This result indicates that beta3Gal-T5 expression prevents poly-N-acetyllactosamine and sialyl-Lewis x synthesis on N-glycans. Kinetic studies confirm that beta3Gal-T5 prefers acceptors having the GlcNAcbeta1-->3Gal end, including lactotriosylceramide. Competitive reverse transcriptase mediated-polymerase chain reaction shows that the beta3Gal-T5 transcript is expressed in normal colon mucosa but not or poorly in adenocarcinomas. Moreover, recombinant carcinoembryonic antigen purified from a CHO clone expressing Fuc-TIII and beta3Gal-T5 reacts with anti-sialyl-Lewis a and carries type 1 chains on oligosaccharides released by endo-beta-galactosidase. We conclude that beta3Gal-T5 down-regulation plays a relevant role in determining the cancer-associated glycosylation pattern of N-glycans.

Biochemical differences between two types of N-acetylglucosamine:-->6sulfotransferases in human colonic adenocarcinomas and the adjacent normal mucosa: specific expression of a GlcNAc:-->6sulfotransferase in mucinous adenocarcinoma

6-O-Sulfation of beta-GlcNAc is an initial step in the biosynthesis of N-linked and O-linked sulfated glycans, which are widely distributed in colonic tissues. However, the biochemical mechanism of this sulfation in human colonic carcinogenesis was still unclear. In this study, we found two types of GlcNAc:-->6sulfotransferases (SulT) in human colonic adenocarcinomas and the adjacent normal mucosa, and we determined their enzymatic characteristics. One SulT, named SulT-a, was present in the adjacent normal mucosa and in non-mucinous adenocarcinomas, whereas the other SulT, named SulT-b, was present only in mucinous adenocarcinomas and adenocarcinomas with a mucinous component. SulT-a preferentially acted on Galbeta1-->3(GlcNAcbeta1-->6)GalNAc(alpha1)-p-nitrophenyl (pNP) and GlcNAcbeta1-->2Man, whereas SulT-b could act not only on these two glycans, but also on GlcNAcbeta1-->3GalNAc(alpha1)-pNP and GlcNAcbeta1-->3Galbeta1-->4Glc. The levels of SulT-a activity were significantly lower in non-mucinous adenocarcinomas than in the adjacent mucosa. In contrast, SulT-b was expressed in mucinous adenocarcinomas and in adenocarcinomas with a mucinous component. These results indicate that there are at least two types of GlcNAc:-->6SulT, SulT-a and -b, in colonic mucosa and adenocarcinomas, and that the occurrence of these enzymes is closely correlated with colonic cancer and the presence of areas of mucin accumulation.

Study on selectin blocker. 8. Lead discovery of a non-sugar antagonist using a 3D-pharmacophore model

We have developed a pharmacophore model of a ligand/E-selectin complex to screen drug candidates for selectin blockers. In a series of sugar mimetic studies of the E-selectin ligand, sialyl Lewis X (sLe(x)), we have already found a potent compound, a sulfated Le(x) analogue (1), and also have proposed how compound 1 binds to E-selectin (Tsujishita, H.; Hiramatsu, Y.; Kondo, N.; Ohmoto, H.; Kondo, H.; Kiso, M.; Hasegawa, A. J. Med. Chem. 1997, 40, 362-369). To find drug candidates that fit into the binding pocket of E-selectin, we constructed an original 3D-pharmacophore model from structural information of a compound 1/E-selectin complex model and screened lead compounds for selectin blockers using a commercially available database ACD-3D. As a result, we discovered a lead compound (2) containing good selectin inhibitory activity, and in addition, we succeeded to preliminarily optimize it to a more active lead compound (3) with micromolar IC(50) values, based on the 3D-pharmacophore model investigation. This methodology using the 3D-pharmacophore model could be applicable as a pre-screen system for selectin blockers.

Intracellular lectins associated with N-linked glycoprotein traffic

The vectorial intracellular transport of N-glycan-linked glycoproteins is indispensable for biological functions. In order to sort these glycoproteins to the correct destination, animal intracellular lectins play important roles as sorting receptors. The roles of such lectins in the biosynthetic pathway from the endoplasmic reticulum (ER) to the cell surface are addressed in this review. Calnexin and calreticulin function via specific carbohydrates in quality control of newly synthesized glycoproteins in the ER, and ERGIC-53 seems to function in the transport of glycoproteins from ER to the Golgi complex. In addition to the well-understood role of mannose 6-phosphate receptor in lysosomal protein sorting, the vesicular integral protein of 36 kDa (VIP36) functions as a sorting receptor by recognizing high-mannose type glycans containing alpha1-->2Man residues for transport from Golgi to the cell surface in polarized epithelial cells.

Differential expression of beta1,3galactosyltransferases in human colon cells derived from adenocarcinomas or normal mucosa

Two beta1,3galactosyltransferases are detected in human colon cells: one corresponds to beta3GalT1, the other (beta3GalTx) is found to be different from any cloned beta3GalT since in vitro it utilizes GlcNAc very efficiently under specific reaction conditions. Expression of beta3GalT1 transcript is high in normal colon mucosa and control neuroectodermal cells, which do not express sialyl-Lewis a antigen, and low in colon adenocarcinoma cells, as assessed by competitive RT-PCR. beta3GalTx activity is high in adenocarcinoma cells expressing sialyl-Lewis a and undetectable in all other cells, suggesting differential involvement and opposite regulation of such enzymes during carcinogenesis.

Synthesis of a sialyl-alpha-(2-->6)-lactosamine trisaccharide with a 5-amino-3-oxapentyl spacer group at C-1I

As part of a continuing study aimed to achieve improved monoclonal antibodies against carcinoembryonic antigen (CEA) carbohydrate fragments, the synthesis of a sialyl-(2-->6)-lactosamine trisaccharide with a 5-amino-3-oxapentyl spacer group at C-1I has been developed. Two different routes to access this target are described. For this purpose 5-azido-3-oxapentyl 6-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside (4) was selectively beta-galactosylated in 81% yield using the crystalline 2,3-di-O-acetyl-4,6-O-benzylidene-alpha-D-galactopyranosyl trichloroacetimidate as the donor, taking advantage of the bulky phthalimido group at C-2 of 4. On the other hand, galactosylation of the suitable protected acceptor 5-azido-3-oxapentyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside with the crystalline 2,3-di-O-acetyl-4,6-O-benzylidene-alpha-D-galactosyl bromide renders the corresponding disaccharide in a moderate 58% yield. Despite the fact that the first strategy, unlike the second one, requires a hydrazinolysis-acetylation reaction at the disaccharide stage, it was found to be more convenient to access the disaccharide acceptor. Sialylation was performed using a thiophenyl donor under an NIS-TfOH activation procedure in acetonitrile to give a mixture of alpha and beta trisaccharides in 49 and 16% yields, respectively.

Synthesis of oligosaccharides containing beta-D-Gal-(1-->3)-O-(6-O-sulfo-beta-D-GlcNAc) as a terminal unit

The chemical synthesis of beta-D-Gal-(1-->3)-6-O-SO3Na-beta-D-GlcNAc-(1-->6)-alpha-D-Man-O-+ ++C6H4NO2 (1) and beta-D-Gal-(1-->3)-6-O-SO3Na-beta-D-GlcNAc-(1-->2)-alpha-D-Man-OMe (2) is reported using a key glycosyl donor, phenyl O-(2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl)-(1-->3)-4,6-di-O- chloroacetyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside (3).

CD66 receptor specificity exhibited by neisserial Opa variants is controlled by protein determinants in CD66 N-domains

Neisseria gonorrhoeae strain MS11 is able to express 11 different opacity (Opa) proteins on its outer surface. A number of these Opa proteins have been shown to function as adhesins through binding of CD66 receptors present on human cells. CD66 antigens, or carcinoembryonic antigen family members, constitute a family of glycoproteins belonging to the immunoglobulin superfamily. Opa variants recognize this class of receptors in a differential manner such that certain Opa variants recognize up to four different CD66 receptors (CD66a, -c, -d, and -e), whereas others recognize only two (CD66a and -e) or none. We explored the basis for this receptor tropism in the present study. Our data show that glycoforms of CD66e and deglycosylated CD66e are recognized by gonococci in an Opa-specific manner. Binding by Opa variants of recombinant N-terminal domains of CD66 receptors expressed in Escherichia coli reflected the adherence specificities of Opa variants to HeLa cells expressing native CD66 molecules. These data indicate that recognition of CD66 receptors by Opa variants is mediated by the protein backbone of the CD66 N-domains. Furthermore, by using chimeric constructs between different CD66 N-domains we identified distinct binding regions on the CD66e N-domain for specific groups of Opa variants, suggesting that the differential recognition of CD66 receptors by Opa variants is dictated by the presence of specific binding regions on the N-domain of the receptor.

Studies on selectin blockers. 6. Discovery of homologous fucose sugar unit necessary for E-selectin binding

We describe a mimic of the sugar unit of the E-selectin ligand, sialyl Lewis X (sLeX). Carbohydrates are entering the realm of rational drug design, aided by the growing understanding of the structure-function relationships. We investigated a new methodology of preparing sLeX mimetics and developed a potent E-selectin blocker characterized by beta-turn dipeptides. Another characteristic point of this E-selectin blocker is that the six-membered fucose ring was replaced with a five-membered fucose ring. Interestingly, it was found that the five-membered fucose ring could also bind to a calcium ion on the E-selectin, which could be an important role of the six-membered fucose ring. Especially, the L-Ser-D-Glu and D-Ser-L-Glu derivatives 3a,b showed 65-90-fold more potent inhibitory activities than the sulfated LeX analogue 1. In addition, molecular dynamics (MD) studies indicated that the 2- and 3-OH groups of the six-membered fucose ring, which were necessary for the calcium binding, overlapped well with the 2- and 3-OH groups of the five-membered fucose ring. These new findings could be useful for the design of new types of selectin blockers.

GalNAc-alpha-O-benzyl inhibits NeuAcalpha2-3 glycosylation and blocks the intracellular transport of apical glycoproteins and mucus in differentiated HT-29 cells

Exposure for 24 h of mucus-secreting HT-29 cells to the sugar analogue GalNAc-alpha-O-benzyl results in inhibition of Galbeta1-3GalNAc:alpha2,3-sialyltransferase, reduced mucin sialylation, and inhibition of their secretion (Huet, G., I. Kim, C. de Bolos, J.M. Loguidice, O. Moreau, B. Hémon, C. Richet, P. Delannoy, F.X. Real., and P. Degand. 1995. J. Cell Sci. 108:1275-1285). To determine the effects of prolonged inhibition of sialylation, differentiated HT-29 populations were grown under permanent exposure to GalNAc-alpha-O-benzyl. This results in not only inhibition of mucus secretion, but also in a dramatic swelling of the cells and the accumulation in intracytoplasmic vesicles of brush border-associated glycoproteins like dipeptidylpeptidase-IV, the mucin-like glycoprotein MUC1, and carcinoembryonic antigen which are no longer expressed at the apical membrane. The block occurs beyond the cis-Golgi as substantiated by endoglycosidase treatment and biosynthesis analysis. In contrast, the polarized expression of the basolateral glycoprotein GP 120 is not modified. Underlying these effects we found that (a) like in mucins, NeuAcalpha2-3Gal-R is expressed in the terminal position of the oligosaccharide species associated with the apical, but not the basolateral glycoproteins of the cells, and (b) treatment with GalNAc-alpha-O-benzyl results in an impairment of their sialylation. These effects are reversible upon removal of the drug. It is suggested that alpha2-3 sialylation is involved in apical targeting of brush border membrane glycoproteins and mucus secretion in HT-29 cells.

Targeting strategy for gene delivery to carcinoembryonic antigen-producing cancer cells by retrovirus displaying a single-chain variable fragment antibody

Cancer-specific antigens are promising targets for the specific delivery of certain drugs or genes to cancer cells in cancer therapy. Carcinoembryonic antigen (CEA) is one of the cancer-associated antigens predominantly detected in the gastrointestinal cancer of the colon and stomach. Targeting strategies for CEA-producing cancer cells have been thoroughly developed mainly by the production of monoclonal antibodies to CEA and further single-chain variable fragment (scFv) antibodies. Here, we have generated Moloney murine leukemia virus-derived retroviral vectors co-displaying an anti-CEA scFv-envelope chimeric protein and an unmodified envelope protein to deliver a gene for herpes simplex virus thymidine kinase (HSV-tk) or Escherichia coli beta-galactosidase. The harvested viruses successfully incorporated the chimeric envelope protein as well as the unmodified envelope into the viral particles, and specifically bound to and infected human CEA-producing cancer cells via recognition of CEA, depending on the CEA-producing phenotype of the target cells. These results may have significant implications for the use of scFv directed against tumor-specific antigens for targeting specific antigen-producing cancer cells, a potential step toward in vivo cancer therapy.

Characterization of a rat liver Golgi sulphotransferase responsible for the 6-O-sulphation of N-acetylglucosamine residues in beta-linkage to mannose: role in assembly of sialyl-galactosyl-N-acetylglucosamine 6-sulphate sequence of N-linked oligosaccharides

Rat liver Golgi membranes were found to contain an enzyme that can transfer sulphate from 3'-phosphoadenosine 5'-phosphosulphate (PAPS) to C-6 of the terminal GlcNAc in beta-linkage to mannose and has properties indicating that it is involved in the synthesis of the NeuAc alpha 2-3(6)Gal beta 1-4GlcNAc(6-SO4) sequences observed in the N-linked carbohydrate units of various glycoproteins. Assays performed with [35S]PAPS (Km 0.67 microM) and GlcNAc beta 1-6Man alpha 1-O-Me (GnMaMe) acceptor (Km 0.71 mM) indicated that the sulphotransferase had a pH optimum of approx. 7.0 and is markedly stimulated by Mn2+ ions (maximum approx. 15 mM) and Triton X-100 (0.05-0.1%). Hydrazine/nitrous acid/NaBH4 treatment of the 35S-labelled product yielded radiolabelled 2,5-anhydromannitol(6-SO4). The sulphated GnMaMc product of the GlcNAc-6-O-sulphotransferase could be galactosylated by a rat liver Golgi enzyme that was shown to have the same properties as the UDP-Gal:GlcNAc beta-1,4-galactosyltransferase from bovine milk. Competition studies performed with GlcNAc and GlcNAc-6-SO4 furthermore indicated that the same liver enzyme acted on both acceptors to produce Gal beta 1-4GlcNAc and Gal beta 1-4GlcNAc(6-SO4) with Km values of 1.04 and 1.68 mM respectively. Because the sulphated N-acetyl-lactosaminc could in turn serve as an acceptor for rat liver sialyltransferase, it seems that this enzyme, together with the Golgi galactosyltransferase and the GlcNAc-6-O-sulphotransferase, could act in concert in assembling the NeuAc alpha 2-3(6)Gal beta 1-4GlcNAc(6-SO4) branches of complex N-linked oligosaccharides.