Molecular mechanisms of expression of Lewis b antigen and other type I Lewis antigens in human colorectal cancer

Helicobacter pylori Infection: Current Status and Future Prospects on Diagnostic, Therapeutic and Control Challenges

Helicobacter pylori (H. pylori) infection, which affects approximately half of the world's population, remains a serious public health problem. As H. pylori infection leads to a number of gastric pathologies, including inflammation, gastroduodenal ulcers, and malignancies, early detection and treatment are crucial to preventing the spread of the infection. Multiple extragastric complications, such as iron deficiency anaemia, immune thrombocytopenic purpura, vitamin B12 deficiency, diabetes mellitus, cardiovascular diseases, and certain neurological disorders, have also been linked to H. pylori infection. An awareness of H. pylori and associated health hazards is necessary to minimize or even eradicate the infection. Therefore, there is an urgent need to raise the standards for the currently employed diagnostic, eradication, alternative treatment strategies. In addition, a brief overview of traditional and cutting-edge approaches that have proven effective in identifying and managing H. pylori is needed. Based on the test and laboratory equipment available and patient clinical characteristics, the optimal diagnostic approach requires weighing several factors. The pathophysiology and pathogenic mechanisms of H. pylori should also be studied, focusing more on the infection-causing virulence factors of this bacterium. Accordingly, this review aims to demonstrate the various diagnostic, pathophysiological, therapeutic, and eradication tactics available for H. pylori, emphasizing both their advantages and disadvantages. Invasive methods (such as quick urease testing, biopsy, or culture) or noninvasive methods (such as breath tests, stool investigations, or serological tests) can be used. We also present the most recent worldwide recommendations along with scientific evidence for treating H. pylori. In addition to the current antibiotic regimens, alternative therapies may also be considered. It is imperative to eradicate the infections caused by H. pylori as soon as possible to prevent problems and the development of stomach cancer. In conclusion, significant advances have been made in identifying and treating H. pylori. To improve eradication rates, peptide mass fingerprinting can be used as a diagnostic tool, and vaccines can also eliminate the infection.

Bisimidazolium Salt Glycosyltransferase Inhibitors Suppress Hepatocellular Carcinoma Progression In Vitro and In Vivo

Hepatocellular carcinoma is a leading cause of cancer death, and the disease progression has been related to glycophenotype modifications. Previously synthesized bisimidazolium salts (C20 and C22) have been shown to selectively inhibit the activity of glycosyltransferases in cultured cancer cell homogenates. The current study investigated the anticancer effects of C20/C22 and the possible pathways through which these effects are achieved. The therapeutic value of C20/C22 in terms of inhibiting cancer cell proliferation, metastasis, and angiogenesis, as well as inducing apoptosis, were examined with hepatic cancer cell line HepG2 and a xenograft mouse model. C20/C22 treatment downregulated the synthesis of SLex and Ley sugar epitopes and suppressed selectin-mediated cancer cell metastasis. C20/C22 inhibited HepG2 proliferation, induced cell-cycle arrest, increased intracellular ROS level, led to ER stress, and eventually induced apoptosis through the intrinsic pathway. Furthermore, C20/C22 upregulated the expressions of death receptors DR4 and DR5, substantially increasing the sensitivity of HepG2 to TRAIL-triggered apoptosis. In vivo, C20/C22 effectively inhibited tumor growth and angiogenesis in the xenograft mouse model without adverse effects on major organs. In summary, C20 and C22 are new promising anti-hepatic cancer agents with multiple mechanisms in controlling cancer cell growth, metastasis, and apoptosis, and they merit further development into anticancer drugs.

Structural Insights in Mammalian Sialyltransferases and Fucosyltransferases: We Have Come a Long Way, but It Is Still a Long Way Down

Mammalian cell surfaces are modified with complex arrays of glycans that play major roles in health and disease. Abnormal glycosylation is a hallmark of cancer; terminal sialic acid and fucose in particular have high levels in tumor cells, with positive implications for malignancy. Increased sialylation and fucosylation are due to the upregulation of a set of sialyltransferases (STs) and fucosyltransferases (FUTs), which are potential drug targets in cancer. In the past, several advances in glycostructural biology have been made with the determination of crystal structures of several important STs and FUTs in mammals. Additionally, how the independent evolution of STs and FUTs occurred with a limited set of global folds and the diverse modular ability of catalytic domains toward substrates has been elucidated. This review highlights advances in the understanding of the structural architecture, substrate binding interactions, and catalysis of STs and FUTs in mammals. While this general understanding is emerging, use of this information to design inhibitors of STs and FUTs will be helpful in providing further insights into their role in the manifestation of cancer and developing targeted therapeutics in cancer.

Complementary Use of Carbohydrate Antigens Lewis a, Lewis b, and Sialyl-Lewis a (CA19.9 Epitope) in Gastrointestinal Cancers: Biological Rationale Towards A Personalized Clinical Application

Carbohydrate antigen 19.9 (CA19.9) is used as a tumor marker for clinical and research purposes assuming that it is abundantly produced by gastrointestinal cancer cells due to a cancer-associated aberrant glycosylation favoring its synthesis. Recent data has instead suggested a different picture, where immunodetection on tissue sections matches biochemical and molecular data. In addition to CA19.9, structurally related carbohydrate antigens Lewis a and Lewis b are, in fact, undetectable in colon cancer, due to the down-regulation of a galactosyltransferase necessary for their synthesis. In the pancreas, no differential expression of CA19.9 or cognate glycosyltransferases occurs in cancer. Ductal cells only express such Lewis antigens in a pattern affected by the relative levels of each glycosyltransferase, which are genetically and epigenetically determined. The elevation of circulating antigens seems to depend on the obstruction of neoplastic ducts and loss of polarity occurring in malignant ductal cells. Circulating Lewis a and Lewis b are indeed promising candidates for monitoring pancreatic cancer patients that are negative for CA19.9, but not for improving the low diagnostic performance of such an antigen. Insufficient biological data are available for gastric and bile duct cancer. Studying each patient in a personalized manner determining all Lewis antigens in the surgical specimens and in the blood, together with the status of the tissue-specific glycosylation machinery, promises fruitful advances in translational research and clinical practice.

Glycointeractome of Neisseria gonorrhoeae: Identification of Host Glycans Targeted by the Gonococcus To Facilitate Adherence to Cervical and Urethral Epithelial Cells

Multidrug-resistant strains of Neisseria gonorrhoeae are emerging worldwide, and novel treatment and prevention strategies are needed. Glycans are ubiquitously expressed by all human cells and can be specifically targeted by pathogens to facilitate association with host cells. Here we identify and characterize the N. gonorrhoeae host-glycan binding profile (glycointeractome), which revealed numerous interactions, including high-affinity binding to mannosyl glycans. We identify gonococcal potential mannose-binding proteins and show that N. gonorrhoeae uses mannosyl glycans expressed on the surface of cervical and urethral epithelia to facilitate adherence. Furthermore, a mannose-binding lectin or a mannoside compound was able to reduce this adherence. By characterizing the glycointeractome of N. gonorrhoeae, we were able to elucidate a novel mechanism used by this important pathogen to interact with human cells, and this interaction could be exploited to develop novel therapeutics to treat antibiotic-resistant gonorrhea.

Neisseria gonorrhoeae is a significant threat to global health for which a vaccine and novel treatment options are urgently needed. Glycans expressed by human cells are commonly targeted by pathogens to facilitate interactions with the host, and thus characterization of these interactions can aid identification of bacterial receptors that can be exploited as vaccine and/or drug targets. Using glycan array analysis, we identified 247 specific interactions between N. gonorrhoeae and glycans representative of those found on human cells. Interactions included those with mannosylated, fucosylated, and sialylated glycans, glycosaminoglycans (GAGs), and glycans terminating with galactose (Gal), N-acetylgalactosamine (GalNAc), and N-acetylglucosamine (GlcNAc). By investigating the kinetics of interactions with selected glycans, we demonstrate that whole-cell N. gonorrhoeae has a high affinity for mannosylated glycans (dissociation constant [K_D], 0.14 to 0.59 μM), which are expressed on the surface of cervical and urethral epithelial cells. Using chromatography coupled with mass spectrometric (MS) analysis, we identified potential mannose-binding proteins in N. gonorrhoeae. Pretreatment of cells with mannose-specific lectin (concanavalin A) or free mannose competitor (α-methyl-d-mannopyranoside) substantially reduced gonococcal adherence to epithelial cells. This suggests that N. gonorrhoeae targets mannosyl glycans to facilitate adherence to host cells and that mannosides or similar compounds have the potential to be used as a novel treatment option for N. gonorrhoeae.

Blood Group Antigen Recognition via the Group A Streptococcal M Protein Mediates Host Colonization

Streptococcus pyogenes (group A streptococcus [GAS]) is responsible for over 500,000 deaths worldwide each year. The highly virulent M1T1 GAS clone is one of the most frequently isolated serotypes from streptococcal pharyngitis and invasive disease. The oral epithelial tract is a niche highly abundant in glycosylated structures, particularly those of the ABO(H) blood group antigen family. Using a high-throughput approach, we determined that a strain representative of the globally disseminated M1T1 GAS clone 5448 interacts with numerous, structurally diverse glycans. Preeminent among GAS virulence factors is the surface-expressed M protein. M1 protein showed high affinity for several terminal galactose blood group antigen structures. Deletion mutagenesis shows that M1 protein mediates glycan binding via its B repeat domains. Association of M1T1 GAS with oral epithelial cells varied significantly as a result of phenotypic differences in blood group antigen expression, with significantly higher adherence to those cells expressing H antigen structures compared to cells expressing A, B, or AB antigen structures. These data suggest a novel mechanism for GAS attachment to host cells and propose a link between host blood group antigen expression and M1T1 GAS colonization.

IMPORTANCE

There has been a resurgence in group A streptococcal (GAS) invasive disease, which has been paralleled by the emergence of the highly virulent M1T1 GAS clone. Intensive research has focused on mechanisms that contribute to the invasive nature of this serotype, while the mechanisms that contribute to host susceptibility to disease and bacterial colonization and persistence are still poorly understood. The M1T1 GAS clone is frequently isolated from the throat, an environment highly abundant in blood group antigen structures. This work examined the interaction of the M1 protein, the preeminent GAS surface protein, against a wide range of host-expressed glycan structures. Our data suggest that susceptibility to infection by GAS in the oral tract may correlate with phenotypic differences in host blood group antigen expression. Thus, variations in host blood group antigen expression may serve as a selective pressure contributing to the dissemination and overrepresentation of M1T1 GAS.

Aberrant glycosylation as biomarker for cancer: focus on CD43

Glycosylation is a posttranslational modification of proteins playing a major role in cell signalling, immune recognition, and cell-cell interaction because of their glycan branches conferring structure variability and binding specificity to lectin ligands. Aberrant expression of glycan structures as well as occurrence of truncated structures, precursors, or novel structures of glycan may affect ligand-receptor interactions and thus interfere with regulation of cell adhesion, migration, and proliferation. Indeed, aberrant glycosylation represents a hallmark of cancer, reflecting cancer-specific changes in glycan biosynthesis pathways such as the altered expression of glycosyltransferases and glycosidases. Most studies have been carried out to identify changes in serum glycan structures. In most cancers, fucosylation and sialylation are significantly modified. Thus, aberrations in glycan structures can be used as targets to improve existing serum cancer biomarkers. The ability to distinguish differences in the glycosylation of proteins between cancer and control patients emphasizes glycobiology as a promising field for potential biomarker identification. In this review, we discuss the aberrant protein glycosylation associated with human cancer and the identification of protein glycoforms as cancer biomarkers. In particular, we will focus on the aberrant CD43 glycosylation as cancer biomarker and the potential to exploit the UN1 monoclonal antibody (UN1 mAb) to identify aberrant CD43 glycoforms.

Structural basis for the recognition of Lewis antigens by genogroup I norovirus

Noroviruses (NoVs) bind to histo-blood group antigens, namely, ABH antigens and Lewis antigens. We previously showed the NoVs GI/2, GI/3, GI/4, and GI/8 were able to strongly bind to Lewis a (Le(a)) antigen, which is expressed by individuals who are nonsecretors. In this study, to investigate how Lewis antigens interact with GI NoV virion protein 1 (VP1), we determined the crystal structures of the P domain of the VP1 protein from the Funabashi 258 (FUV258) strain (GI/2) in complexes with Le(a), Le(b), H type 1, or A type 1 antigens. The structures were compared with those of the NV/68 strain (GI/1), which does not bind to the Le(a) antigen. The four loop structures, loop P, loop S, loop A, and loop B, continuously deviated by more than 2 Å in length between the Cα atoms of the corresponding residues of the FUV258 and NV/68 P domains. The most pronounced differences between the two VP1 proteins were observed in the structures of loop P. In the FUV258 P domain, loop P protruded toward the next protomer, forming a Le(a) antigen-binding site. The Gln389 residue make a significant contribution to the binding of the Le(a) antigen through the stabilization of loop P as well as through direct interactions with the α4-fucosyl residue (α4Fuc) of the Le(a) antigen. Mutation of the Gln389 residue dramatically affected the degree of binding of the Lewis antigens. Collectively, these results suggest that loop P and the amino acid residue at position 389 affect Lewis antigen binding.

α(1,2)fucosylation in human colorectal carcinoma

Lewis(b) and Lewis(y) (Le) antigens are known to be elevated in colorectal tumours. Alterations in the catalytic behaviour of GDP-L-fucose:β-D-galactoside α(1,2)fucosyltransferase [α(1,2)FT, EC: 2.4.1.69], the key enzyme in their synthesis, have been suggested as being responsible for these changes. In particular, an aberrant tumour-specific α(1,2)FT activity that converts Le(a) and Le(x) to Le(b) and Le(y) determinants, respectively, has been reported in colorectal cancer tissues. To clarify the catalytic function of this enzyme during colorectal tumorigenesis, we analyzed α(1,2)FT activity levels in healthy and tumour colon specimens using different acceptor substrates and determined the kinetic properties of the enzyme. To complete the study, the aberrant Le(a)/Le(x) α(1,2)fucosylation was determined in healthy and tumour colorectal tissues. A correlation analysis between the activity levels and various standard clinicopathological features, such as tumour stage, was also carried out to elucidate the role of these activities in tumour progression. The results obtained confirm the enhanced α(1,2)fucosylation in colorectal neoplastic tissues and the importance of the aberrant Le(a)/Le(x) α(1,2)FT activity in this increase. However, taking into account the high levels of Le(a)/Le(x) fucosylation observed in healthy control tissues, we must rule out the idea of a colorectal tumour-specific α(1,2)FT. On the other hand, no significant association was observed between α(1,2)FT activity levels and the clinicopathological characteristics. Overall, our results suggest that α(1,2)FT activity plays a critical role in the accumulation of Le(b) and Le(y) antigens in human colorectal carcinoma.

Alpha1,2fucosylation is a superior predictor of postoperative prognosis for colorectal cancer compared with blood group A, B, or sialyl Lewis X antigen generated within colorectal tumor tissues

BACKGROUND

We have previously demonstrated tumor-specific alpha1,2fucosylation, which is associated with resistance of tumor cells to anticancer treatment in human colorectal tumor tissues. By using the YB-2 monoclonal antibody, the resulting products have been identified as Y, Le(b), and H type 2 antigens in colorectal tumor tissues.

METHODS

Immunohistochemical analyses of colorectal cancer tissues (74 specimens) were performed with a newly established mouse monoclonal antibody, YB-3 specifically recognizing H disaccharide (Fucalpha1,2Galbeta) structures, and anti-A, anti-B, YB-2, and anti-sialyl Lewis X (SLX) antibodies, together with the analyses of glycosyltransferases involved in the synthesis of ABH antigens in the same tissues.

RESULTS

The YB-3 antibody enabled us to detect colorectal tumors, particularly tumors in the distal large intestine and the rectum, with high sensitivity (74.3%) and specificity (100%). From immunohistochemical and enzymatic analyses of colorectal tissues, we found that once alpha1,2fucosylation had proceeded in tumor tissues, blood group A or B antigen was also synthesized in approximately half of the tissues of A or B blood type, but not in their normal tissues. A correlation of survival rate with immunostaining of tissues was found only by YB-3 antibody and not by anti-A, anti-B, or anti-SLX antibody.

CONCLUSIONS

As a predictor of postoperative prognosis of patients with colorectal cancer, immunodetection of alpha1,2fucosylated antigens with the YB-3 antibody seemed to be superior to blood groups A, B, or SLX antigen in colorectal tumor tissues.

Mucin-type O-glycans in human colon and breast cancer: glycodynamics and functions

The glycoproteins of tumour cells are often abnormal, both in structure and in quantity. In particular, the mucin-type O-glycans have several cancer-associated structures, including the T and Tn antigens, and certain Lewis antigens. These structural changes can alter the function of the cell, and its antigenic and adhesive properties, as well as its potential to invade and metastasize. Cancer-associated mucin antigens can be exploited in diagnosis and prognosis, and in the development of cancer vaccines. The activities and Golgi localization of glycosyltransferases are the basis for the glycodynamics of cancer cells, and determine the ranges and amounts of specific O-glycans produced. This review focuses on the glycosyltransferases of colon and breast cancer cells that determine the pathways of mucin-type O-glycosylation, and the proposed functional and pathological consequences of altered O-glycans.

Glycosyltransferases involved in type 1 chain and Lewis antigen biosynthesis exhibit glycan and core chain specificity

Sialyl Lewis A (SLe(a)), Lewis A (Le(a)), and Lewis B (Le(b)) have been studied in many different biological contexts, for example in microbial adhesion and cancer. Their biosynthesis is complex and involves beta1,3-galactosyltransferases (beta3Gal-Ts) and a combined action of alpha2- and/or alpha4-fucosyltransferases (Fuc-Ts). Further, O-glycans with different core structures have been identified, and the ability of beta3Gal-Ts and Fuc-Ts to use these as substrates has not been resolved. Therefore, to examine the in vivo specificity of enzymes involved in SLe(a), Le(a), and Le(b) synthesis, we have transiently transfected CHO-K1 cells with relevant human glycosyltransferases and, on secreted reporter proteins, detected the resulting Lewis antigens on N- and O-linked glycans using western blotting and Le-specific antibodies. beta3Gal-T1, -T2, and -T5 could synthesize type 1 chains on N-linked glycans, but only beta3Gal-T5 worked on O-linked glycans. The latter enzyme could use both core 2 and core 3 precursor structures. Furthermore, the specificity of FUT5 and FUT3 in Le(a) and Le(b) synthesis was different, with FUT5 fucosylating H type 1 only on core 2, but FUT3 fucosylating H type 1 much more efficient on core 3 than on core 2. Finally, FUT1 and FUT2 were both found to direct alpha2-fucosylation on type 1 chains on both N- and O-linked structures. This knowledge enables us to engineer recombinant glycoproteins with glycan- and core chain-specific Lewis antigen substitution. Such tools will be important for investigations on the fine carbohydrate specificity of Le(b)-binding lectins, such as Helicobacter pylori adhesins and DC-SIGN, and may also prove useful as therapeutics.

Glycodynamics of Mucin Biosynthesis in Gastrointestinal Tumor Cells

Glycoproteins found in the secretions and on the surfaces of cancer cells include mucins and mucin-like glycoproteins. These molecules have been shown to carry antigens that are characteristically expressed on cancer cells, including Tn and T antigens and Lewis epitopes. The structures of O-glycans are often abnormal in gastrointestinal tumors, or else are present in abnormal amounts, and these structures greatly contribute to the phenotype and biology of cancer cells. It has been shown that glycans of cancer cells have functional importance in cell adhesion, invasion and metastasis. The possible mechanisms leading to these cancer-specific changes in carbohydrate structures (termed glycodynamics) involve altered mRNA expression and catalytic activities of glycosyltransferases and sulfotransferases found in tissues and cells of gastrointestinal tumors. In a number of cases it has been possible to correlate enzyme changes with oligosaccharide structures. Different mechanisms have been suggested leading to the synthesis of cancer-specific Lewis, T and Tn antigens, but the regulation of cancer mucin antigens generally appears to be very complex and is poorly understood. The expression levels of specific mucin antigens and enzymes in gastro-intestinal tumors have diagnostic as well as prognostic value. These antigens also have potential for cancer immunotherapy. However, we first need to unravel the complexity of the control of glycosylation in cancer cells. Most importantly, studies of the functional implications of the glycodynamics in cancer cells, as related to cell adhesion and impact on the immune system will provide promising directions for future research.

Expression of histo-blood group A antigen increases resistance to apoptosis and facilitates escape from immune control of rat colon carcinoma cells

A and B histo-blood group antigens are present on carcinoma cells at the early stages of cancerogenesis and tend to disappear at later stages, but it is not yet clear whether they take part to the process of tumor progression. To gain some insight into this issue, we used a rat colon carcinoma experimental model. To obtain expression of the A antigen, REG cells were cotransfected with the rat A enzyme cDNA and a rat alpha1,2fucosyltransferase cDNA, either FTA or FTB, whereas PRO cells that spontaneously have alpha1,2fucosyltransferase activity were only transfected with the A enzyme cDNA. All A antigen-expressing transfected cells derived from either REG FTA, REG FTB, or PRO parental cells were more resistant to apoptosis induced by either serum deprivation or heat shock than were their respective controls. When injected to syngeneic immunocompetent rats, A enzyme-transfected PRO cells formed tumors that grew faster than those formed by mock-transfected PRO cells. However, in immunodeficient SCID mice, no difference in growth could be observed between the two types of tumors, indicating that the faster tumor growth of the A antigen-positive cells in immunocompetent animals was due to their higher ability to escape immune control and that this was associated with their higher degree of resistance to apoptosis. These results might explain the slightly augmented incidence of carcinomas observed in A and B blood group individuals compared to O individuals.

Biosynthesis of the carbohydrate antigenic determinants, Globo H, blood group H, and Lewis b: a role for prostate cancer cell alpha1,2-L-fucosyltransferase

Prostate carcinoma LNCaP cells were unique among several human cancer cell lines which include two other prostate cancer cell lines, PC-3 and DU-145, in expressing alpha1,2-L-fucosyltransferase (FT) as an exclusive FT activity. Affinity gel-GDP and Sephacryl S100 HR columns were used for a partial purification of this enzyme from 3.9 x 10(9) LNCaP cells (approximately 200-fold; 40% yield). The K(m) value (2.7 mM) for the LacNAc type 2 acceptor was quite similar to the one reported for the cloned blood group H gene-specified alpha1,2-FT [Chandrasekaran et al. (1996) Biochemistry 35, 8914-8924]. N-Ethylmaleimide was a potent inhibitor (K(i ) 12.5 microM). The enzyme showed four-fold acceptor preference for the LacNAc type 2 unit in comparison to the T-hapten in mucin core 2 structure. Its main features were similar to those of the cloned enzyme: (1) C-6 sulfation of terminal Gal in the LacNAc unit increased the acceptor efficiency, whereas C-6 sialylation abolished acceptor ability; (2) C-6 sulfation of GlcNAc in LacNAc type 2 decreased by 80% the acceptor ability, whereas LacNAc type 1 was unaffected; (3) Lewis x did not serve as an acceptor; (4) the C-4 hydroxyl rather than the C-6 hydroxyl group of the GlcNAc moiety in LacNAc type1 was essential for activity; and (5) the acrylamide copolymer of Galbeta1,3GlcNAcbeta-O-Al was the best acceptor among the acrylamide copolymers. Additionally, highly significant biological features of alpha1,2FT were identified in the present study. The synthesis of Globo H and Lewis b determinants became evident from the fact that Galbeta1,3GalNAcbeta1,3Galalpha-O-Me and Galbeta1,3(Fucalpha1,4)Glc-NAcbeta1,3Galbeta-O-Me served as high-affinity acceptors for this enzyme. Further, D-Fucbeta1,3Gal-NAcbeta1,3Galalpha-O-Me was a very efficient acceptor, indicating that the C-6 hydroxyl group of the terminal Gal moiety in Globo H is not essential for the enzyme activity. Thus, the present study was able to demonstrate three different catalytic roles of LNCaP alpha1,2-FT, namely, the expressions of blood group H, Lewis b from Lewis a, and Globo H.

Linear synthesis of a protected H-type II pentasaccharide using glycosyl phosphate building blocks

A linear synthesis of a fully protected H-type II blood group determinant pentasaccharide utilizing glycosyl phosphate and glycosyl trichloroacetimidate building blocks is reported. Envisioning an automated solid-phase synthesis of blood group determinants, the utility of glycosyl phosphates in the stepwise construction of complex oligosaccharides, such as the H-type II antigen, is demonstrated. Installation of the central glucosamine building block required the screening of a variety of nitrogen protecting groups to ensure good glucosamine donor reactivity and protecting group compatibility. The challenge to differentiate C2 of the terminal galactose in the presence of other hydroxyl and amine protecting groups prompted us to introduce the 2-(azidomethyl)benzoyl group as a novel mode of protection for carbohydrate synthesis. The compatibility of this group with traditionally employed protecting groups was examined, as well as its use as a C2 stereodirecting group in glycosylations. The application of the 2-(azidomethyl)benzoyl group along with a systematic evaluation of glycosyl donors allowed for the completion of the pentasaccharide and provides a synthetic strategy that is expected to be generally amenable to the solid support synthesis of blood group determinants.

Subsite-specific incidence rate and stage of disease in colorectal cancer by race, gender, and age group in the United States, 1992-1997

BACKGROUND

Subsite specific incidence rates of colorectal cancer vary considerably by age, gender, and race. This variation may be related not only to distinctions in exposure to genetic and environment factors but also to current strategies of early detection screening. Patterns of stage of disease in anatomic subsite may reflect the effect of screening. This study used the largest aggregation of cancer incidence data in the U.S. to examine subsite specific incidence rates of colorectal cancer and the relation of stage of disease to anatomic subsites by race, gender, and age group.

METHODS

Data on the incidence of invasive colorectal cancer were obtained from 28 population-based central cancer registries. Age-specific and age-adjusted rates and stage distributions were analyzed by subsite, race, and gender.

RESULTS

The impact of screening can be observed in the percentage of localized disease, which increased from 31.9% among cancers in the proximal colon to 37.0% in the descending colon to 41.5% in the distal colorectum. Within the same subsite, blacks were less likely than whites to receive a diagnosis of localized disease and more likely to receive a diagnosis of distant disease whereas stage distributions were approximately the same for males and females. Blacks were more likely than whites to receive a diagnosis of proximal colon cancer than distal colorectal cancer. The male-to-female rate ratios progressively increased from the proximal colon to the distal colorectum. The ratios of proximal-to-distal colorectal cancer gradually increased with advancing age.

CONCLUSIONS

Differentials in stage of disease by subsites indicate a need for a targeted effort at early detection of cancer in the proximal colon. Risk factors and higher risk populations for colorectal cancers in each subsite need to be studied further to guide actions for improving the efficacy of screening.

Human airway mucin glycosylation: a combinatory of carbohydrate determinants which vary in cystic fibrosis

Human airway mucins represent a very broad family of polydisperse high molecular mass glycoproteins, which are part of the airway innate immunity. Apomucins, which correspond to their peptide part, are encoded by at least 6 different mucin genes (MUC1, MUC2, MUC4, MUC5B, MUC5AC and MUC7). The expression of some of these genes (at least MUC2 and MUC5AC) is induced by bacterial products, tobacco smoke and different cytokines. Human airway mucins are highly glycosylated (70-80% per weight). They contain from one single to several hundred carbohydrate chains. The carbohydrate chains that cover the apomucins are extremely diverse, adding to the complexity of these molecules. Structural information is available for more than 150 different O-glycan chains corresponding to the shortest chains (less than 12 sugars). The biosynthesis of these carbohydrate chains is a stepwise process involving many glycosyl- or sulfo-transferases. The only structural element shared by all mucin O-glycan chains is a GalNAc residue linked to a serine or threonine residue of the apomucin. There is growing evidence that the apomucin sequences influence the first glycosylation reactions. The elongation of the chains leads to various linear or branched extensions. Their non-reducing end, which corresponds to the termination of the chains, may bear different carbohydrate structures, such as histo-blood groups A or B determinants, H and sulfated H determinants, Lewis a, Lewis b, Lewis x or Lewis y epitopes, as well as sialyl- or sulfo- (sometimes sialyl- and sulfo-) Lewis a or Lewis x determinants. The synthesis of these different terminal determinants involves three different pathways with a whole set of glycosyl- and sulfo-transferases. Due to their wide structural diversity forming a combinatory of carbohydrate determinants as well as their location at the surface of the airways, mucins are involved in multiple interactions with microorganisms and are very important in the protection of the underlying airway mucosa. Airway mucins are oversulfated in cystic fibrosis and this feature has been considered as being linked to a primary defect of the disease. However, a similar pattern is observed in mucins from patients suffering from chronic bronchitis when they are severely infected. Airway mucins from severely infected patients suffering either from cystic fibrosis or from chronic bronchitis are also highly sialylated, and highly express sialylated and sulfated Lewis x determinants, a feature which may reflect severe mucosal inflammation or infection. These determinants are potential sites of attachment for Pseudomonas aeruginosa, the pathogen responsible for most of the morbidity and mortality in cystic fibrosis, and the expression of the sulfo- and glycosyl-transferases involved in their biosynthesis is increased by TNFalpha. In summary, airway inflammation may simultaneously induce the expression of mucin genes (MUC2 and MUC5AC) and the expression of several glycosyl- and sulfo-transferases, therefore modifying the combinatory glycosylation of these molecules.

CD15 expression in mature granulocytes is determined by alpha 1,3-fucosyltransferase IX, but in promyelocytes and monocytes by alpha 1,3-fucosyltransferase IV

The CD15 carbohydrate epitope is expressed in mature human neutrophils, monocytes, and promyelocytes. We aimed to determine the alpha1,3-fucosyltransferase responsible for the expression of CD15 in each subpopulation of leukocytes. Three alpha1,3-fucosyltransferases, FUT4, FUT7, and FUT9, are expressed in human leukocytes. We demonstrated that FUT9 exhibits 20-fold stronger activity for CD15 synthesis than FUT4, whereas FUT4 exhibits 4.5-fold stronger activity for CDw65 synthesis than FUT9. By competitive reverse transcriptase-polymerase chain reaction, FUT9 was found to be strongly expressed in mature granulocytes and peripheral blood mononuclear cell, but not in monocytes. CD34(+) and CD15(+) cells in cord blood and myeloid cell lines (HL-60 and U937) did not express FUT9 at all. FUT4 transcripts were ubiquitously expressed in all blood cells and all cultured cell lines, with HL-60 and U937 cells in particular expressing a number of FUT4 transcripts. Transfection of the FUT9 gene into Jurkat and U937 cells demonstrated that FUT9 has the potential to express CD15 in myeloid and lymphoid cells. These findings suggest that the expression of CD15 in mature granulocytes is directed by FUT9, whereas it is determined in promyelocytes and monocytes by FUT4. Measurement of CD15 synthesizing activity in cell homogenates of each cell population using the polylactosamine acceptor further supported these conclusions.

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.

ABH and Lewis histo-blood group antigens in cancer

Antigens of the ABH and Lewis histo-blood group family can be found on many normal cells, mainly of epithelial type. In carcinomas, altered expression of the various carbohydrate epitopes of this family occur, and are often strongly associated with either a good or bad prognosis. A review of the available data on these tumor-associated markers, their biosynthesis and their prognostic value is proposed here. For a long time it has been unclear whether their presence could affect the behavior of carcinoma cells. Recent data, however, indicate that they play biological roles in the course of tumor progression. The presence of sialyl-Le(a) or sialyl-Le(x), which are ligands for selectins, promotes the metastatic process by facilitating interaction with the endothelium of distant organs. The loss of A and B antigens increases cellular motility, while the presence of H epitopes increases resistance to apoptosis by mechanisms that remain to be defined. The Le(y) antigen has procoagulant and angiogenic activities. All these observations are used to present a model that may account for the described associations between the presence or loss of these markers and the outcome of disease. Finally, their potential clinical applications as tumor-associated markers or as targets of immunotherapy are reviewed.

alpha1,2Fucosyltransferase increases resistance to apoptosis of rat colon carcinoma cells

Accumulation of histo-blood group antigens such as Lewis b, Lewis Y and H in colon cancer is indicative of poor prognosis. It is accompanied by increase in alpha1,2fucosyl-transferase activity, a key enzyme for synthesis of these antigens. Using a model of colon carcinoma, we previously showed that alpha1,2fucosylation increases tumorigenicity. We now show that tumorigenicity inversely correlates with the cells' sensitivity to apoptosis. In addition, poorly tumorigenic REG cells independently transfected with three different alpha1,2fucosyltransferase cDNAs, the human FUT1, the rat FTA and FTB were more resistant than control cells to apoptosis induced in vitro by serum deprivation. Inversely, PRO cells, spontaneously tumorigenic in immunocompetent syngeneic animals and able to synthesize alpha1,2fucosylated glycans, became more sensitive to apoptosis after transfection with a fragment of the FTA cDNA in the antisense orientation. Expression of alpha1,2fucosyl-transferase in poorly tumorigenic REG cells dramatically enhanced their tumorigenicity in syngeneic rats. However, in immunodeficient animals, both control and alpha1,2fuco-syltransferase transfected REG cells were fully tumorigenic and metastatic, indicating that the presence of alpha1,2fucosylated antigens allowed REG tumor cells to escape immune control. Taken together, the results show that increased tumorigenicity mediated by alpha1,2fucosyl-ation is associated to increased resistance to apoptosis and to escape from immune control.

Activation and routing of membrane-tethered prohormone convertases 1 and 2

Many peptide hormones and neuropeptides are processed by members of the subtilisin-like family of prohormone convertases (PCs), which are either soluble or integral membrane proteins. PC1 and PC2 are soluble PCs that are primarily localized to large dense core vesicles in neurons and endocrine cells. We examined whether PC1 and PC2 were active when expressed as membrane-tethered proteins, and how tethering to membranes alters the biosynthesis, enzymatic activity, and intracellular routing of these PCs. PC1 and PC2 chimeras were constructed using the transmembrane domain and cytoplasmic domain of the amidating enzyme, peptidylglycine alpha-amidating monooxygenase (PAM). The membrane-tethered PCs were rerouted from large dense core vesicles to the Golgi region. In addition, the chimeras were transiently expressed at the cell surface and rapidly internalized to the Golgi region in a fashion similar to PAM. Membrane-tethered PC1 and PC2 exhibited changes in pro-domain maturation rates, N-glycosylation, and in the pH and calcium optima required for maximal enzymatic activity against a fluorogenic substrate. In addition, the PC chimeras efficiently cleaved endogenous pro-opiomelanocortin to the correct bioactive peptides. The PAM transmembrane domain/cytoplasmic domain also prevented stimulated secretion of pro-opiomelanocortin products in AtT-20 cells.