Occurrence of the human tumor-specific antigen structure Galß1-3GalNAcα- (Thomsen-Friedenreich) and related structures on gut bacteria: prevalence, immunochemical analysis and structural confirmation.

The Thomsen-Friedenreich antigen (TF; CD176, Galß1-3GalNAcα-) is a tumor-specific carbohydrate antigen and a promising therapeutic target. Antibodies that react with this antigen are frequently found in the sera of healthy adults and are assumed to play a role in cancer immunosurveillance. In this study, we examined the occurrence of α-anomeric TF (TFα) on a large variety of gastrointestinal bacteria using a novel panel of well-characterized monoclonal antibodies. Reactivity with at least one anti-TF antibody was found in 13% (16 of 122) of strains analyzed. A more in-depth analysis, using monoclonal antibodies specific for α- and ß-anomeric TF in combination with periodate oxidation, revealed that only two novel Bacteroides ovatus strains (D-6 and F-1), isolated from the faeces of healthy persons by TF-immunoaffinity enrichment, possessed structures that are immunochemically identical to the true TFα antigen. The TF-positive capsular polysaccharide structure of strain D-6 was characterized by mass spectrometry, monosaccharide composition analysis, glycosidase treatments and immunoblot staining with TFα- and TFß-specific antibodies. The active antigen was identified as Galß1-3GalNAc-, which was α-anomerically linked as a branching structure within a heptasaccharide repeating unit. We conclude that structures immunochemically identical to TFα are extremely rare on the surface of human intestinal bacteria and may only be identifiable by binding of both antibodies, NM-TF1 and NM-TF2, which recognize a complete immunomolecular imprint of the TFα structure. The two novel B. ovatus strains isolated in this study may provide a basis for the development of TF-based anti-tumor vaccines.

Invasion of Trypanosoma cruzi into host cells is impaired by N-propionylmannosamine and other N-acylmannosamines.

The etiologic agent of Chagas' disease, Trypanosoma cruzi, is widely distributed in South America, affecting millions of people with thousands of deaths every year. Adherence of the infectious trypomastigote to host cells is mediated by sialic acid. T. cruzi cannot synthesize sialic acids on their own but cleave them from the host cells and link them to glycans on the surface of the parasites using the trans-sialidase, a GPI-anchored enzyme. The infectivity of the protozoan parasites strongly depends on the activity of this enzyme. In this report, we investigated whether the transfer of sialic acids from the host to the parasites can be attenuated using novel sialic acid precursors. The cell line 86-HG-39 was infected with T. cruzi and treated with defined N-acylmannosamine analogues bearing an elongated N-acyl side-chain. By treatment of these cells the number of T. cruzi infected cell was reduced up to 60%. We also showed that the activity of the bacterial sialidase C was reduced with N-glycan substrates with elongated N-acyl side chains of the terminal sialic acids. The affinity of this sialidase decreased with the length of the N-acyl side-chain. The data presented suggest that N-acyl modified sialic acid precursors can change the transfer of sialic acids leading to modification of infection. Since the chemotherapy of this disease is inefficient and afflicted by side effects, the need of effective drugs is lasting. These findings propose a new path to prevent the dissemination of T. cruzi in the human hosts. These compounds or further modified analogues might be a basis for the search of new agents against Chagas' disease.

Liver-specific increase of UTP and UDP-sugar concentrations in rats induced by dietary vitamin B6-deficiency and its relation to complex N-glycan structures of liver membrane-proteins.

This is the first known report on the influence of vitamin B6-deficiency on the concentration of UDP-sugars and other uracil nucleotides in rats. Animals aged 3 weeks or 2 months were fed a vitamin B6-free diet for periods varying from 3 days to 7 weeks. Nucleotides were quantified by enzymatic-photometry and by SAX-high precision liquid chromatography. In 3 week-old rats, vitamin B6-deficiency resulted in an up to 6.3-fold increase in the concentrations of UTP, UDP, UMP and UDP-sugars and less of CTP in rat liver, while no changes were observed in older rats. In young rats, the concentration of uracil nucleotides started to increase after 1 week diet, with a maximum after 2 weeks. After 5 weeks, the concentrations returned to normal values. In heart, lungs, kidney and brain, concentrations were measured after 2 weeks diet in young rats. In contrast to liver, the heart muscle uracil nucleotide concentrations were decreased by 40%. In kidney, the sum of UTP, UDP and UMP showed a decrease of 40%, whereas UDP-sugars were increased 1.4-fold. In the lungs, nucleotide concentrations were mostly unaffected by vitamin B6-deficiency, despite a 70% increase of UDP-GA. In brain, UDP-Glc, UDP-Gal and the sum of CTP and CDP showed an increase of 30-50%. We became surprised that the increased UDP-sugar concentrations did not influence the structure of liver plasma membrane-N-glycans. Despite the 4 to 6-fold increase of UTP and UDP-sugars, no changes in the complexity or sialylation of these N-glycans could be detected. This study demonstrates that, especially in liver, pyridoxal phosphate is closely involved in the control of uracil nucleotides during a defined period of development. In contrast to in vitro experiments, in vivo N-glycan biosynthesis in liver is regulated by a more complex or higher mechanism than substrate concentrations.

Engineering the sialic acid in organs of mice using N-propanoylmannosamine.

Sialic acids play an important role during development, regeneration and pathogenesis. The precursor of most physiological sialic acids, such as N-acetylneuraminic acid is N-acetyl-D-mannosamine. Application of the novel N-propanoylmannosamine leads to the incorporation of the new sialic acid N-propanoylneuraminic acid into cell surface glycoconjugates. Here we analyzed the modified sialylation of several organs with N-propanoylneuraminic acid in mice. By using peracetylated N-propanoylmannosamine, we were able to replace in vivo between 1% (brain) and 68% (heart) of physiological sialic acids by N-propanoylneuraminic acid. The possibility to modify cell surfaces with engineered sialic acids in vivo offers the opportunity to target therapeutic agents to sites of high sialic acid concentration in a variety of tumors. Furthermore, we demonstrated that application of N-propanoylmannosamine leads to a decrease in the polysialylation of the neural cell adhesion molecule in vivo, which is a marker of poor prognosis for some tumors with high metastatic potential.

The ether lipid inositol-C2-PAF is a potent inhibitor of cell proliferation in HaCaT cells.

The search for specific anticancer drugs that do not interfere with DNA synthesis or influence the cytoskeleton has led to the development of modified phospholipids with antiproliferative properties. These compounds cause remodeling of the structure and function of plasma membranes. Recently, we described novel compounds, the glycosidated phospholipids, that surprisingly inhibit cell proliferation. These compounds contain alpha-D-glucose in the sn-2 position of the glycerol backbone of phosphatidylcholine (PC) and platelet-activating factor (PAF), which gives rise to 2-glucophosphatidylcholine (Glc-PC) and 1-O-octadecyl-2-O-alpha-d-glucopyranosyl-sn-2-glycero-3-phosphatidylcholine (Glc-PAF), respectively. Glc-PC and Glc-PAF inhibit the growth of HaCaT cells at nontoxic concentrations. Here we report the introduction of myo-inositol, in place of alpha-D-glucose, in the sn-2 position of the glycerol backbone; this leads to two diastereomeric 1-O-octadecyl-2-O-(2-(myo-inositolyl)-ethyl)-sn-glycero-3-(R/S)-phosphatidylcholines (Ino-C2-PAF). The inositol-containing PAF enhances the antiproliferative capacity (IC(50)=1.8 microM) and reduces the cytotoxicity relative to Glc-PAF (LC(50)=15 microM). Through biological assays, we showed that, in HaCaT cells, Ino-C2-PAF causes upregulation of the keratinocyte-specific differentiation marker involucrin, increases the activity of the differentiation marker transglutaminase, and induces apoptosis at nontoxic concentrations. Ino-C2-PAF therefore seems to be a promising candidate for development as an antiproliferative drug for the treatment of hyperproliferative diseases of the skin.

Selective inhibition of polysialyltransferase ST8SiaII by unnatural sialic acids.

Polysialic acid (polySia) is a unique and highly regulated posttranslational modification of the neural cell adhesion molecule (NCAM). The presence of polySia affects NCAM-dependent cell adhesion and plays an important role during brain development, neural regeneration and plastic processes including learning and memory. Polysialylated NCAM is expressed on several neuroendocrine tumors of high malignancy and correlates with poor prognosis. Two closely related enzymes, the polysialyltransferases ST8SiaII and ST8SiaIV, catalyze the biosynthesis of polySia. However, the impact of each enzyme in NCAM polysialylation is not understood. Here, we describe the selective cell-based in vitro inhibition of ST8SiaII using synthetic sialic acid precursors. We provide evidence for different substrate affinities of ST8SiaII and ST8SiaIV. These data open the possibility to study the individual role of the two enzymes during various aspects of brain development and function and in tumorigenesis.

Expression, purification, and characterization of human dipeptidyl peptidase IV/CD26 in Sf9 insect cells.

The human dipeptidyl peptidase IV/CD26 (DPPIV/CD26) is a multifunctional type-II membrane bound glycoprotein. As a receptor of collagen I and fibronectin it mediates cell-cell and cell-matrix adhesion, and by interacting with extracellular adenosine deaminase and CD45 it is involved in regulatory and costimulatory events in the immune system. DPPIV/CD26 has a very distinct substrate specificity, and is potentially capable of truncating many cytokines, chemokines, and peptide hormones. In this study, we describe the overexpression, purification, and characterization of human DPPIV/CD26 in Spodoptera frugiperda (Sf9) cells, using the baculovirus system. Overexpression of DPPIV/CD26 was confirmed by measurement of its peptidase specificity, SDS-PAGE, and Western blot analyses. Expression rates were between 6.4 and 17.6 mg protein per liter suspension culture (1.5 x 10(9)cells). The N-linked oligosaccharide composition was examined and compared with that of mammalian cell-expressed DPPIV/CD26. Two-step purification by immunoaffinity chromatography and size-exclusion fast protein liquid chromatography (SE-FPLC) led to highly stable protein with significant peptidase activity. A subsequent gel filtration step on a Superdex 200 column yielded 2mg homogeneous dimeric DPPIV/CD26 (per liter insect cell culture) for crystallographic studies. Protein homogeneity was confirmed by silver staining of non-denaturating PAGE gels and by MALDI-TOF analysis of tryptic peptides.

Purification and characterization of N-acetylneuraminic acid-9-phosphate synthase from rat liver.

Sialic acids are a group of carboxylated amino sugars important for a variety of cellular functions. N-Acetylneuraminic acid (Neu5Ac) is the predominant sialic acid in nature. Neu5Ac-9-phosphate synthase catalyzes the formation of Neu5Ac-9-phosphate from N-acetylmannosamine-6-phosphate and phosphoenolpyruvate. Neu5Ac-9-phosphate synthase was purified 11,700-fold from rat liver cytosol to apparent homogeneity by ammonium sulfate precipitation, chromatography on hydroxylapatite, phenyl-Sepharose, MonoQ, and finally gel filtration. SDS-PAGE and gel filtration chromatography indicated that the enzyme is a dimer composed of 37-kDa subunits. Analysis of trypic peptides by MALDI-TOF MS verified a high sequence similarity to the corresponding murine enzyme. The K(m) values of Neu5Ac-9-phosphate synthase were 35 microM for N-acetylmannosamine-6-phosphate and 100 microM for phosphoenolpyruvate. The enzyme displayed an absolute requirement for divalent cations, Mn(2+), Fe(2+), and Mg(2+) being the most effective. In contrast to human Neu5Ac-9-phosphate synthase, the rat enzyme did not utilize mannose-6-phosphate in the synthesis of 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid 9-phosphate. Neu5Ac-9-phosphate synthase was inactivated by the sulfhydryl modifying reagents, 5,5'-dithio-bis (2-nitrobenzoic acid) and N-ethylmaleimide, and protected from inactivation by the presence of the substrate phosphoenolpyruvate, but not by the presence of N-acetylmannosamine-6-phosphate, showing that at least one cysteine residue is located in the active site of the enzyme.