Effect of dipeptidyl peptidase-4 inhibitors on complement activation

BACKGROUND

Adverse activation of the complement cascade in the innate immune system appears to be involved in development of vascular complications in diabetes. Dipeptidyl peptidase-4 (DPP-4) is a cell surface serine protease expressed in a variety of tissues. DPP-4 inhibitors are widely used in treatment of type 2 diabetes and appear to yield beneficial pleiotropic effects beyond their glucose-lowering action, for example, renoprotective and anti-inflammatory properties, but the exact mechanisms remain unknown. We hypothesised that DPP-4 inhibitors block adverse complement activation by inhibiting complement-activating serine proteases.

MATERIALS AND METHODS

We analysed the effects of 7 different DPP-4 inhibitors on the lectin and classical pathway of the complement system in vitro by quantifying complement factor C4b deposition onto mannan or IgG coated surfaces, respectively. Furthermore, plasma concentrations of mannan-binding lectin (MBL), soluble membrane attack complex (sMAC), and C4b deposition were quantified in 71 patients with a recent acute coronary syndrome and glucose disturbances, randomly assigned to sitagliptin 100 mg (n = 34) or placebo (n = 37) for 12 weeks.

RESULTS

All the 7 DPP-4 inhibitors tested in the study directly inhibited functional activity of the lectin pathway in a dose-dependent manner with varying potency in vitro. In vivo, MBL, sMAC, and C4b declined significantly during follow-up in both groups without significant effect of sitagliptin.

CONCLUSIONS

We demonstrated an inhibitory effect of DPP-4 inhibitors on the lectin pathway in vitro. The clinical relevance of this effect of DPP-4 inhibitors remains to be fully elucidated.

Changes in hemocytes of Biomphalaria glabrata infected with Echinostoma paraensei and exposed to glyphosate-based herbicide

The immune system of snails is highly sensitive to pollutants, which can suppress its immune response. We investigated the effects of exposure to the glyphosate-based herbicide Roundup® Original on the snail Biomphalaria glabrata infected by the platyhelminth Echinostoma paraensei by evaluating changes in the snail's internal defense system. Four cohorts were studied: control group, infected snails, snails treated with Roundup®, and snails infected and treated with Roundup®. The hemocyte viability was assessed, morphological differentiation of cells was observed and flow cytometry was performed to determine the morphology, viability and the lectin expression profiles. The frequencies of dead hemocytes were lower in the infected group and higher in both pesticide treated groups. Three cell types were identified: blast-like cells, hyalinocytes and granulocytes. The highest number of all types of hemocytes, as well as the highest number of dead cells, were observed in the infected, pesticide-treated group. The association between infection and herbicide exposure greatly increased the frequency of dead hemocytes, suggesting that this condition impairs the internal defense system of B. glabrata making the snails more vulnerable to parasitic infections.

Inhibition of streptococcal biofilm by hydrogen water

OBJECTIVES

The accumulation of oral bacterial biofilm is the main etiological factor of oral diseases. Recently, electrolyzed hydrogen-rich water (H-water) has been shown to act as an effective antioxidant by reducing oxidative stress. In addition to this general health benefit, H-water has antibacterial activity for disease-associated oral bacteria. However, little is known about the effect of H-water on oral bacterial biofilm. The objective of this study was to confirm the effect of H-water on streptococcal biofilm formation.

METHODS

In vitro streptococcal biofilm was quantified using crystal violet staining after culture on a polystyrene plate. The effect of H-water on the expression of genes involved in insoluble glucan synthesis and glucan binding, which are critical steps for oral biofilm formation, was evaluated in MS. In addition, we compared the number of salivary streptococci after oral rinse with H-water and that with control tap water. Salivary streptococci were quantified by counting viable colonies on Mitis Salivarius agar-bacitracin.

RESULTS

Our data showed that H-water caused a significant decrease in in vitro streptococcal biofilm formation. The expression level of the mRNA of glucosyltransferases (gtfB, gtfc, and gtfI) and glucan-binding proteins (gbpC, dblB) were decreased remarkably in MS after H-water exposure for 60s. Furthermore, oral rinse with H-water for 1 week led to significantly fewer salivary streptococci than did that with control tap water.

CONCLUSIONS

Our data suggest that oral rinse with H-water would be helpful in treating dental biofilm-dependent diseases with ease and efficiency.

PtLGBP, a pattern recognition receptor in Portunus trituberculatus involved in the immune response against different challenges

Lipopolysaccharide and b-1,3-glucan binding protein (LGBP) is a pattern recognition receptor that can recognize and bind LPS and b-1,3-glucan. LGBP has crucial roles in innate immune defense against Gram-negative bacteria and fungi. In this study, LGBP functions in Portunus trituberculatus innate immunity were analyzed. First, the mRNA expression of PtLGBP in hemocytes, hepatopancreas, and muscle toward three typical pathogen-associated molecular patterns (PAMPs) stimulations were examined using real-time PCR. Results show that the overall trend of relative expressions of the LGBP gene in three tissues is consistent, showing up-down trend. In each group, the highest expression of the LGBP gene was at 3 and 12 h post-injection. The LGBP gene is also expressed significantly higher in the hemocytes and hepatopancreas than in the muscle. The highest level of LGBP was in the lipopolysaccharides (LPS) and glucan-injected group, whereas the lowest level was in the PGN-injected group. Furthermore, bacterial agglutination assay with polyclonal antibody specifically for PtLGBP proved that the recombinant PtLGBP (designated as rPtLGBP) could exhibit obvious agglutination activity toward Gram-negative bacteria Escherichia coli, Vibrio parahaemolyticus, and V. alginolyticus; Gram-positive bacteria Bacillus subtilis; and fungi Saccharomyces cerevisiae. LGBP in Portunus trituberculatus possibly served as a multi-functional PRR. In addition, LGBP is not only involved in the immune response against Gram-negative and fungi, as manifested in other invertebrates, but also has a significant role in anti-Gram-positive bacteria infection.

Ficolin-B marks apoptotic and necrotic cells

Ficolins are a group of proteins consisting of a fibrinogen-like and a collagen-like domain. They play a role in innate immunity by activating the complement system via the lectin pathway upon binding to carbohydrate patterns on pathogens. Two types of ficolins have been identified in mice, ficolin A and ficolin B (FcnB). We show in this article that recombinant FcnB binds to late apoptotic cells and to apoptotic bodies as well as to necrotic cells but not to early apoptotic cells. This binding was calcium-dependent and could be competitively inhibited by acetylated BSA, a classical binding substrate of FcnB. In addition, DNA inhibited binding of FcnB to apoptotic and necrotic cells, indicating that DNA exposed by dying cells could also be a ligand for FcnB. Thus, FcnB may play a role in the removal of damaged host cells and maintenance of tissue homeostasis.

Metformin treatment may increase omentin-1 levels in women with polycystic ovary syndrome

OBJECTIVE

Polycystic ovary syndrome (PCOS) is associated with the metabolic syndrome. Decreased omentin-1 levels are associated with obesity and diabetes. To study the effects of metformin treatment on omentin-1 levels in PCOS subjects and effects of omentin-1 on in vitro migration and angiogenesis.

RESEARCH DESIGN AND METHODS

Serum omentin-1 was measured by ELISA. Angiogenesis was assessed by studying capillary tube formation in human microvascular endothelial cells (HMEC-1) on growth factor reduced Matrigel. Endothelial cell migration assay was performed in a modified Boyden chamber. Nuclear factor-κB (NF-κB) was studied by stably transfecting HMEC-1 cells with a cis-reporter plasmid containing luciferase reporter gene linked to five repeats of NF-κB binding sites. Akt phosphorylation was assessed by Western blotting.

RESULTS

Serum omentin-1 was significantly lower in PCOS women (P < 0.05). After 6 months of metformin treatment, there was a significant increase in serum omentin-1 (P < 0.01). Importantly, changes in hs-CRP were significantly negatively correlated with changes in serum omentin-1 (P = 0.036). In vitro migration and angiogenesis were significantly increased in serum from PCOS women (P < 0.01) compared with matched control subjects; these effects were significantly attenuated by metformin treatment (P < 0.01) plausibly through the regulation of omentin-1 levels via NF-κB and Akt pathways. CRP and VEGF induced in vitro migration, and angiogenesis was significantly decreased by omentin-1.

CONCLUSIONS

Increases in omentin-1 levels may play a role but are not sufficient to explain the decreased inflammatory and angiogenic effects of sera from metformin-treated PCOS women.

Reversal of neurochemical changes and pain-related behavior in a model of neuropathic pain using modified lentiviral vectors expressing GDNF

In this study, we evaluated the possible use of lentiviral vectors in the treatment of neuropathic pain. We chose to administer GDNF-expressing vectors because of the known beneficial effect of this trophic factor in alleviation of neuropathic pain in adult rodents. Lentiviral vectors expressing either GDNF or control, green fluorescent protein or beta-galactosidase, were injected unilaterally into the spinal dorsal horn 5 weeks before a spinal nerve ligation was induced (or sham surgery for the controls). We observed that intraspinally administered lentiviral vectors resulted in a large and sustained expression of transgenes in both neurons and glial cells. Injection of GDNF-expressing viral vectors induced a significant reduction of ATF-3 up-regulation and IB4 down-regulation in damaged DRG neurons. In addition, it produced a partial but significant reversal of thermal and mechanical hyperalgesia observed following the spinal nerve ligation. In conclusion, our study suggests that lentiviral vectors are efficient tools to induce a marked and sustained expression of trophic factors in specific areas of the CNS and can, even if with some limitations, be efficient in the treatment of neuropathic pain.

A novel approach to study adhesion mechanisms by isolation of the interacting system

For decades most investigations into mechanisms of adhesive interactions have examined whole organisms or single cells. Results using whole organisms are often unclear because it may not be known if a probe used in an experiment is directly affecting the cellular interaction under study or if it is an indirect effect resulting from action on some other structure or pathway. Here we develop a novel approach to isolate the structural components of a cellular interaction by dissecting them out of the organism to study them in a pristine environment away from all confounding factors. We used the adhesion between the archenteron and blastocoel roof of the sea urchin gastrula stage embryo as a model that can be replicated in many other developmental and pathological systems. The isolated components of the cellular interaction and those in the whole organism possessed identical cell surface receptors and adhesive affinities.

Mouse Siglec-F and human Siglec-8 are functionally convergent paralogs that are selectively expressed on eosinophils and recognize 6′-sulfo-sialyl Lewis X as a preferred glycan ligand

Mouse sialic acid-binding immunoglobulin-like lectin F (Siglec-F) is an eosinophil surface receptor, which contains an immunoreceptor tyrosine-based inhibitory motif (ITIM) in its cytoplasmic domain, implicating it as a regulator of cell signaling as documented for other siglecs. Here, we show that the sialoside sequence 6'-sulfo-sLe(X) (Neu5Acalpha2-3[6-SO4] Galbeta1-4[Fucalpha1-3]GlcNAc) is a preferred ligand for Siglec-F. In glycan array analysis of 172 glycans, recombinant Siglec-F-Fc chimeras bound with the highest avidity to 6'-sulfo-sLe X. Secondary analysis showed that related structures, sialyl-Lewis X (sLe X) and 6-sulfo-sLe X containing 6-GlcNAc-SO4 showed much lower binding avidity, indicating significant contribution of 6-Gal-SO4 on Siglec-F binding to 6'-sulfo-sLe x. The lectin activity of Siglec-F on mouse eosinophils was "masked" by endogenous cis ligands and could be unmasked by treatment with sialidase. Unmasked Siglec-F mediated mouse eosinophil binding and adhesion to multivalent 6'-sulfo-sLe X structure, and these interactions were inhibited by anti-Siglec-F monoclonal antibody (mAb). Although there is no clear-cut human ortholog of Siglec-F, Siglec-8 is encoded by a paralogous gene that is expressed selectively by human eosinophils and has recently been found to recognize 6'-sulfo-sLe X. These observations suggest that mouse Siglec-F and human Siglec-8 have undergone functional convergence during evolution and implicate a role for the interaction of these siglecs with their preferred 6'-sulfo-sLe X ligand in eosinophil biology.

Jasmonic acid methyl ester induces the synthesis of a cytoplasmic/nuclear chito-oligosaccharide binding lectin in tobacco leaves

In contrast to animal lectins, no evidence has indicated the occurrence of plant lectins, which recognize and bind "endogenous" receptors and accordingly are involved in recognition mechanisms within the organism itself. Here we show that the plant hormone jasmonic acid methyl ester (JAME) induces in leaves of Nicotiana tabacum (var. Samsun NN) the expression of a lectin that is absent from untreated plants. The lectin specifically binds to oligomers of N-acetylglucosamine and is detected exclusively in the cytoplasm and the nucleus. Both the subcellular location and specificity indicate that the Nicotiana tabacum agglutinin (called Nictaba) may be involved in the regulation of gene expression in stressed plants through specific protein-carbohydrate interactions with regulatory cytoplasmic/nuclear glycoproteins. Searches in the databases revealed that many flowering plants contain sequences encoding putative homologues of the tobacco lectin, which suggest that Nictaba is the prototype of a widespread or possibly ubiquitous family of lectins with a specific endogenous role.

The metal ion binding properties of calreticulin modulate its conformational flexibility and thermal stability

Calreticulin (CRT) is a soluble chaperone involved in the conformational maturation of glycoproteins in the endoplasmic reticulum. Using biochemical and biophysical techniques including circular dichroism, proteolysis, and analytical ultracentrifugation, we have determined the effects of calcium and zinc ions on the structural properties of human CRT. Circular dichroism analysis has shown that the binding of calcium and zinc ions to CRT induces no significant changes in the secondary structure of the protein but affects in very distinct ways the local tertiary packing of these elements. More specifically, these studies have revealed that CRT adopts a more rigid and thermally stable structure upon binding calcium ions and a more loosely packed and thermally destabilized structure upon binding zinc ions. Consistent with these results, proteolysis experiments demonstrated that the intrinsic conformational flexibility of CRT can be modulated toward either a decrease or an increase in susceptibility to cleavage by chymotrypsin upon binding calcium or zinc ions, respectively. Results from sedimentation analysis indicated that the global three-dimensional structure of CRT is essentially unchanged upon binding calcium ions. In marked contrast, CRT self-associates reversibly to form dimers upon binding zinc ions. Collectively, our results provide evidence that calcium and zinc ions induce strikingly different changes in the biochemical and structural properties of CRT.

Increase of Candida cell virulence by anticancer drugs and irradiation

The influence of anticancer drugs and irradiation on Candida cell proliferation, adherence to HeLa cells and susceptibility to antifungal drugs (amphotericin B and miconazole) and neutrophils were examined using two Candida albicans strains. After treatment with 5-fluorouracil (25 microg/ml to 250 microg/ml), cis-diammine-dichloroplatinum (10 microg/ml to 100 microg/ml), peplomycin (0.5 microg/ml to 5 microg/ml) or 137Cs (20 Gy to 40 Gy) for 3 days or more, surviving Candida cells proliferated more rapidly than did untreated control cells. Anticancer agent-pretreated Candida cells revealed an increased adhesion to HeLa cells corresponding to an increase of binding to the lectins. The concentration of half limited colony formation (IC50) of amphotericin B and miconazole was increased to near two-fold that of the control by pretreatment of Candida cells with the anticancer agents, except peplomycin, which only weakly increased IC50. In addition, the enolase and Candida acid proteinase activities in the culture supernatants were increased by pretreatment with the drugs and irradiation. Correspondingly, surviving Candida cells after these treatments were resistant to neutrophils, with a reduction to half of the killing. These results indicate that anti-cancer drugs and irradiation potentiate the virulence of Candida cells, or they eliminate Candida cells with low virulence, thereby enhancing the risk of oral and systemic candidiasis.

Enamel matrix derivative induces matrix synthesis by cultured human periodontal fibroblast cells

BACKGROUND

Periodontal wound healing and regeneration require that new matrix be synthesized, creating an environment into which cells can migrate. One agent which has been described as promoting periodontal regeneration is an enamel matrix protein derivative (EMD). Since no specific growth factors have been identified in EMD preparations, it is postulated that EMD acts as a matrix enhancement factor. This study was designed to investigate the effect of EMD in vitro on matrix synthesis by cultured periodontal fibroblasts.

METHODS

The matrix response of the cells was evaluated by determination of the total proteoglycan synthesis, glycosaminoglycan profile, and hyaluronan synthesis by the uptake of radiolabeled precursors. The response of the individual proteoglycans, versican, decorin, and biglycan were examined at the mRNA level by Northern blot analysis. Hyaluronan synthesis was probed by identifying the isotypes of hyaluronan synthase (HAS) expressed in periodontal fibroblasts as HAS-2 and HAS-3 and the effect of EMD on the levels of mRNA for each enzyme was monitored by reverse transcription polymerase chain reaction (RTPCR). Comparisons were made between gingival fibroblast (GF) cells and periodontal ligament (PDLF) cells.

RESULTS

EMD was found to significantly affect the synthesis of the mRNAs for the matrix proteoglycans versican, biglycan, and decorin, producing a response similar to, but potentially greater than, mitogenic cytokines. EMD also stimulated hyaluronan synthesis in both GF and PDLF cells. Although mRNA for HAS-2 was elevated in GF after exposure to EMD, the PDLF did not show a similar response. Therefore, the point at which the stimulation of hyaluronan becomes effective may not be at the level of stimulation of the mRNA for hyaluronan synthase, but, rather, at a later point in the pathway of regulation of hyaluronan synthesis. In all cases, GF cells appeared to be more responsive to EMD than PDLF cells in vitro.

CONCLUSIONS

EMD has the potential to significantly modulate matrix synthesis in a manner consistent with early regenerative events.

Specific pancreatic enzymes activate macrophages to produce tumor necrosis factor-alpha: role of nuclear factor kappa B and inhibitory kappa B proteins

The triggering events by which mononuclear cells throughout the body are induced to produce large amounts of cytokines during acute pancreatitis are unclear. However, recent work in our laboratory demonstrated that three specific pancreatic enzymes (elastase, carboxypeptidase A, and lipase) induced dramatic tumor necrosis factor-alpha (TNF-alpha) protein production from macrophages, whereas all others could not. This series of experiments was designed to examine the second messenger system by which this occurs. The rat macrophage cell line NR8383 was incubated for 3 hours with elastase, carboxypeptidase A, lipase, trypsin, or lipopolysaccharide (positive control). Activation of nuclear factor kappa B (NF-kappa B) was demonstrated by electrophoretic mobility shift assay, presence of inhibitory kappa B alpha and beta (I kappa B-alpha and I kappa B-beta) by Western blot analysis, and TNF-alpha protein production by enzyme-linked immunosorbent assay. Elastase, carboxypeptidase A, and lipase induced degradation of I kappa B-beta (but not I kappa B-alpha), activation of NF-kappa B, and production of TNF-alpha protein, whereas inhibition of I kappa B with pyrrolidine dithiocarbamate attenuated this response. Trypsin was unable to elicit any of these responses. Macrophages can be induced by specific activated pancreatic enzymes-elastase, carboxypeptidase A, and lipase-to produce TNF-alpha. This process is dependent on I kappa B-beta degradation and NF- kappa B activation, suggesting that these enzymes trigger this second messenger system through specific membrane-bound receptors.

Epitope mapping of monoclonal antibodies specific for a macrophage lectin: a calcium-dependent epitope is in the carbohydrate recognition domain

Mouse macrophage galactose/N-acetylgalactosamine-specific calcium-type lectin (mMGL) has a calcium-dependent conformational epitope which is a ligand-induced binding site. A monoclonal antibody (mAb) specific for this epitope (LOM-11) stabilize lectin activity. We performed mapping for this conformational epitope using trypsin fragments that contain a carbohydrate recognition domain (CRD) and chimeric recombinant proteins between mMGL and a human counterpart of this molecule. Binding site for the mAb LOM-11 was mapped within the C-terminal 59 amino acids of CRD. Binding sites for all four mAbs that block carbohydrate ligand binding were also mapped in the C-terminal half of CRD. These results indicated that the calcium-dependent site potentially involved in protein-protein interaction, regulatory or for coordinated binding, is mapped within CRD in addition to the independent carbohydrate binding site, and that both of the distinct sites may have spatial proximity.

Parallel solution synthesis of a "Carbohybrid" library designed to inhibit galactose-binding proteins

Parallel solution S-alkylations of a 1-thio-beta-D-galactopyranoside derivative with Michael acceptors and alpha-chloroketones, followed by ketone reductions, reductive aminations, and acylations were developed to yield a library of 1-thio-beta-D-galactopyranosides carrying small and diverse polar-neutral, hydrophobic, aromatic, cationic, or anionic non-carbohydrate aglycon structures. Screening of the library against a panel of galactose recognizing plant lectins revealed microM inhibitors of toxin A of A. precatorius superior to the reference ligands lactose and N-acetyl lactosamine. Such small, monosaccharide based inhibitors are attractive lead-molecules for therapeutic development, since they are low-molecular, hydrolytically stable and more hydrophobic than natural oligosaccharides.

Trypanosoma cruzi calreticulin is a lectin that binds monoglucosylated oligosaccharides but not protein moieties of glycoproteins

Trypanosoma cruzi is a protozoan parasite that belongs to an early branch in evolution. Although it lacks several features of the pathway of protein N-glycosylation and oligosaccharide processing present in the endoplasmic reticulum of higher eukaryotes, it displays UDP-Glc:glycoprotein glucosyltransferase and glucosidase II activities. It is herewith reported that this protozoan also expresses a calreticulin-like molecule, the third component of the quality control of glycoprotein folding. No calnexin-encoding gene was detected. Recombinant T. cruzi calreticulin specifically recognized free monoglucosylated high-mannose-type oligosaccharides. Addition of anti-calreticulin serum to extracts obtained from cells pulse-chased with [35S]Met plus [35S]Cys immunoprecipitated two proteins that were identified as calreticulin and the lysosomal proteinase cruzipain (a major soluble glycoprotein). The latter but not the former protein disappeared from immunoprecipitates upon chasing cells. Contrary to what happens in mammalian cells, addition of the glucosidase II inhibitor 1-deoxynojirimycin promoted calreticulin-cruzipain interaction. This result is consistent with the known pathway of protein N-glycosylation and oligosaccharide processing occurring in T. cruzi. A treatment of the calreticulin-cruzipain complexes with endo-beta-N-acetylglucosaminidase H either before or after addition of anti-calreticulin serum completely disrupted calreticulin-cruzipain interaction. In addition, mature monoglucosylated but not unglucosylated cruzipain isolated from lysosomes was found to interact with recombinant calreticulin. It was concluded that the quality control of glycoprotein folding appeared early in evolution, and that T. cruzi calreticulin binds monoglucosylated oligosaccharides but not the protein moiety of cruzipain. Furthermore, evidence is presented indicating that glucosyltransferase glucosylated cruzipain at its last folding stages.

Keratan sulfate glycosaminoglycans in murine eosinophil-specific granules

We examined the presence of sialyl glycoconjugates in specific granules from murine bone marrow eosinophils. Lectin cytochemistry using Maackia amurensis lectin II (MAL II) specific for sialyl alpha-2,3 galactose residues demonstrated positive labeling in both immature and mature specific granules. Pretreatment with Clostridium neuraminidase or keratanase II eliminated the positive labeling of MAL II in the specific granules. High iron diamine-thiocarbohydrazide-silver proteinate physical development (HID-TCH-SP-PD) staining, which is specific for sulfated glycoconjugates, also positively labeled immature specific granules lacking crystalloids but not mature granules with crystalloids. Pretreatment with a combination of chondroitinase ABC and keratanase, or a combination of chondroitinase ABC and keratanase II, eliminated the positive labeling obtained with HID-TCH-SP-PD. These results indicate that the sialyl residues detected by MAL II are expressed as terminal sugar residues of keratan sulfate proteoglycan, which appears to be of the corneal type in view of its sensitivity to keratanase and keratanase II. (J Histochem Cytochem 47:481-488, 1999)

A method to differentiate between thyroglobulin derived from normal thyroid tissue and from thyroid carcinoma based on analysis of reactivity to lectins

OBJECTIVE

The composition of sugar chains on thyroglobulin (Tg) produced in thyroid carcinoma cells (C-Tg) is different from Tg produced in normal thyroid tissues (N-Tg). In this study, we designed a new method for detecting Tg derived from thyroid carcinoma based on the differences between C-Tg and N-Tg in the reactivity with lectins.

MATERIALS AND METHODS

Thyroglobulin preparations obtained from various thyroid tissues were incubated with lectins, and the amount of lectin-unbound Tg (ub-Tg) in the supernatant relative to Tg untreated with lectin was determined by enzyme-linked immunosorbent assay and expressed as ub-Tg(%). In addition, to study further the differences in glycosylation between C-Tg and N-Tg, concanavalin A binding to Tg digested with Staphylococcus aureus V8 protease was analyzed on nitrocellulose membrane after Western blotting.

RESULTS

The ub-Tg(%) in C-Tg from papillary carcinoma was significantly higher than in Tg from Graves' disease, benign goiter, and normal thyroid tissue for both concanavalin A and ricinus communis agglutinin-120. Concanavalin A did not appear to bind to Tg from papillary carcinoma after V8 treatment by Western blot analysis. The ub-Tg(%) in Tg from follicular adenoma was significantly higher than C-Tg from follicular carcinoma, whereas there were no differences in ub-Tg(%) between follicular carcinoma and normal thyroid tissue in concanavalin A treatment.

CONCLUSIONS

These results suggest our new methods can distinguish both between C-Tg from papillary carcinoma and N-Tg, and between follicular carcinoma and follicular adenoma in thyroid tissue specimens. Thus, this type of analysis may be applicable to differentiate C-Tg from N-Tg in thyroid aspirates for the adjunctive cytodiagnosis of thyroid carcinoma.

Stabilization of the glucan-binding lectin of Streptococcus sobrinus by specific ligand

Cell suspensions of Streptococcus sobrinus can be aggregated by high molecular-weight alpha-1,6 glucans. The aggregation depends on the fidelity of a cell wall-bound, glucan-binding lectin (GBL). It is thought that the lectin may play a part in the sucrose-dependent accretion of streptococci in dental plaques. Results showed that the anionic detergent, sodium dodecyl sulphate (SDS) was a potent inhibitor of the lectin. When cells were incubated in SDS and washed to remove the detergent, lectin activity was diminished. Following incubation of the cells with SDS in the presence of glucan T-10, a low molecular-weight alpha-1,6 glucan, the loss of activity was less pronounced, suggesting that the glucan afforded partial protection against denaturation. Urea and guanidine hydrochloride were good inhibitors of the lectin, but, unlike SDS, were not able to inhibit it irreversibly, except at very high concentrations. Cationic detergents, such as cetylpyridinium bromide (and chloride), also irreversibly denatured the streptococcal lectin, but were not as effective as SDS in abolishing its activity. The results suggest that alpha-1,6 glucan stabilizes the GBL of S. sobrinus, rendering it more resistant to the effect of chaotropes. This may be one reason why dental plaques tend to resist detergents in dentrifices.

Effect of substituents on the thermodynamics of D-galactopyranoside binding to winged bean (Psophocarpus tetragonolobus) basic lectin

Isothermal titration calorimetric measurements of the binding of deoxy, fluorodeoxy, and methoxy derivatives of D-galactopyranoside (alpha-D-Gal) to the basic lectin from winged bean Psophocarpus tetragonolobus, WBA I, have been carried out. Each of the ligands binding to WBA I displayed the same stoichiometry of one per subunit (29 kDa) of WBA I. The binding enthalpies for various derivatives are essentially independent of temperature and show complementary changes with respect to binding entropies. Replacement of the hydroxyl group by fluorine or hydrogen on C3 and C4 of the galactopyranoside eliminates binding to the lectin, consistent with C3-OH and C4-OH acting as hydrogen bond donors. The affinity for C2 derivatives of galactose decreases in the order GalNAc > 2MeOGal > 2FGal congruent with Gal > 2HGal, which suggests that both polar and nonpolar residues surround the C2 locus of galactose, consistent with the observed high affinity of WBA I toward GalNAc where the acetamido group at C2 position is probably stabilized by both nonpolar interactions with the methyl group and polar interactions with the carbonyl group. The binding of C6 derivatives follows the order Gal > 6FGal > D-Fuc >> 6MeOGal congruent with L-Ara, indicating the presence of favourable polar interactions with a hydrogen bond donor in the vicinity. On the basis of these results the hydrogen bond donor-acceptor relationship of the complexation of methyl-alpha-D-galactopyranoside with the primary combining site of WBA I is proposed.

Natural human anti-Gal alpha(1,3)Gal antibodies react with human mucin peptides

We have recently demonstrated that both antibodies to Gal alpha(1,3)Gal, and the Gal alpha(1,3)Gal binding lectin (IB4), bind a synthetic peptide (DAHWESWL), there being a similar recognition of carbohydrate and peptide structures. We now report that the anti-Gal alpha(1,3)Gal antibodies and IB4 lectin also react with peptides encoded by mucin genes (MUC 1, 3, 4)-sequences known to be rich in serine, threonine and proline. This activity was demonstrated (1) by the ability of mucin derived peptides to block the reaction of anti-Gal alpha(1,3)Gal antibodies and IB4 lectin with a Gal alpha(1,3)Gal+ pig endothelial cell line; the reactions were specific and did not occur with a random peptide containing the same sequences or with other mucin peptides; (2) by the fact that anti-mucin1 antibodies could react with the Gal alpha(1,3)Gal expressed after transfection of COS cells (Gal alpha(1,3)Gal-,Muc1-) with cDNA encoding the pig alpha, 3galactosyltransferase; and (3) that the IB4 lectin and anti-Gal alpha(1,3)Gal antibodies could react with mucin 1 found on the surface of human breast cancer cells. Thus natural occurring anti-Gal alpha(1,3)Gal antibodies found in all human serum can react with self (Muc1) peptides expressed in large amounts on the surface of tumour cells but not on normal cells. The findings are of interest and serve to explain the previously reported findings that human cells can, at times, express Gal alpha(1,3)Gal; such expression is an artefact, the reaction is due to the phenomenon described herein, i.e. that anti-Gal alpha(1,3)Gal antibodies react with mucin peptides.

A multispecific saline-soluble lectin from the parasitic fungus Arthrobotrys oligospora. Similarities in the binding specificities compared with a lectin from the mushroom agaricus bisporus

Several fungi can express high levels of saline-soluble and low-molecular-mass lectins that bind to glycoproteins such as fetuin and different mucins but not bind to any monosaccharides. In this paper, we report the binding specificities of such a lectin (designated AOL) isolated from the nematophagous fungus Arthrobotrys oligospora. The results show that AOL is a multispecific lectin that interacts with the following ligands: (a) Several sulfated glycoconjugates including sulfatide, dextran sulfate, and fucoidan. The specificity of this binding was indicated by experiments showing that none of the tested neutral- and sialic-acid-containing glycolipids, chondroitin sulfates B and C, heparin, and polyvinyl sulfate bound to AOL; (b) Phosphatidic acid and phospatidylglycerol, two out of several tested phospholipids. (c) N-linked and O-linked sugar chains bound to intact fetuin. The involvement of such sugar structures was demonstrated by analyzing the binding of AOL to chemically deglycosylated (trifluoromethanesulfonic acid) fetuin. Treating fetuin with O-glycosidase and N-glycosidase indicated that AOL bound to Gal beta GaLNAc alpha-Ser/Thr and to some N-linked complex sugars, respectively. Further assays demonstrated that AOL could interact with several other glycoproteins containing O-linked and/or N-linked sugar chains. The observations that AOL did not bind to free N-linked sugars isolated from fetuin, or to fetuin treated with trypsin or pronase, or to any of the tested neoglycoproteins and glycolipids with neutral- or sialic acid-containing sugars, indicated that the sugar chains need to be bound to an intact peptide backbone to interact with AOL. We have recently shown that the deduced primary structure of AOL has a high similarity to the sequence of a saline-soluble lectin isolated from the mushroom Agaricus bisporus (ABL) (Rosén, S., Kata, M., Persson, Y., Lipniunas, P. H., Wikström, M., van den Hondel, C. A. M. J. J., van den Brink, J. M., Rask, L., Hedén L.-O. and Tunlid, A., see companion paper). It is well known that ABL binds to Gal beta 3GaLNAc alpha-Ser/Thr, and in this paper we demonstrate that ABL binds to sulfatide, phosphatidic acid, phospatidylglycerol, and possibly also to the same N-linked complex sugars as AOL. The above data indicate that AOL and ABL are members of a novel family of fungal lectins sharing similar primary structure and binding properties.

Calcium-dependent conformation of a mouse macrophage calcium-type lectin. Carbohydrate binding activity is stabilized by an antibody specific for a calcium-dependent epitope

We established monoclonal antibodies (mAbs) against the mouse macrophage galactose/N-acetylgalactosamine-specific lectin (MMGL) that is a 42-kDa calcium-dependent lectin, using a solid phase carbohydrate binding assay as a novel strategy for screening mAbs. The specificity of six mAbs were investigated by antibody binding to native or recombinant forms (rML) of MMGL, flow cytometry, and immunoprecipitation using a macrophage cell line RAW264.7. Four of these mAbs strongly inhibited the binding of fluorescein 5-isothiocyanate-labeled galactosylated polylysine to immobilized rML, one inhibited moderately, and one did not inhibit binding. The competitive binding study revealed that the binding sites of these four blocking mAbs were closely related to each other but were different from the rest of these mAbs. A non-blocking mAb having a unique binding specificity (LOM-11) exhibited calcium-dependent binding to rML, suggesting that calcium-dependent epitope was not situated in the vicinity of the ligand binding site. Furthermore, pretreatment of rML with the mAb LOM-11 preserved ligand binding activity, especially in a low calcium environment. The four blocking mAbs mentioned above facilitated the binding of the mAb LOM-11 to rML. These results indicate that there is a positive cooperativity between the lectin's ligand binding site and its physically distinct calcium-dependent epitope.

Midgut lectin activity and sugar specificity in teneral and fed tsetse

Midgut infection rates of Trypanosoma congolense in Glossina palpalis palpalis and of Trypanosoma brucei rhodesiense in Glossina pallidipes are potentiated by the addition of D+ glucosamine to the infective feed, but not to the levels of super-infection reported for G.m.morsitans, G.p.palpalis and G.pallidipes are shown to possess two trypanocidal molecules: a glucosyl lectin which can be inhibited by D+ glucosamine and a galactosyl molecule inhibited by D+ galactose. Addition of both D+ glucosamine and D+ galactose to the teneral infective feed promotes super-infection of the midguts of G.p.palpalis. The glucosyl lectin is specific for rabbit erythrocytes and is present in guts of fed G.m.morsitans and G.p.palpalis, titres of lectin activity do not increase substantially after the second bloodmeal. The galactosyl specific molecule does not show any erythrocyte specificity, although haemolytic activity is observed only in G.p.palpalis and not in G.m.morsitans. The presence of two trypanocidal molecules in some species of tsetse may account for the innate refractoriness of these flies to trypanosome infection. As D+ glucosamine also inhibits the killing of procyclic trypanosomes taken as an infective feed, it is suggested that the midgut lectin is normally responsible for the agglutination of trypanosomes in the fly midgut by binding to the procyclic surface coat, prior to establishment in the ecto-peritrophic space.

Role of intramolecular high-mannose chains in the folding and assembly of soybean (Glycine max) lectin polypeptides: studies by the combined use of spectroscopy and gel-filtration size analysis

It was previously reported [Nagai, K. & Yamaguchi, H. (1993) J. Biochem. 113, 123-125] that intramolecular high-mannose chains are essential for reconstitution of soybean lectin from denatured subunits. To obtain more detailed information on the role of the intramolecular high-mannose chains in the folding and assembly of soybean lectin polypeptides, the effects of asparagine-linked oligosaccharides, Man9GlcNAc2Asn (M9-Asn) and Glc1-3Man9GlcNAc2Asn (GM9-Asn), on the reconstitution of soybean lectin from denatured subunits were examined by comparison with the denaturation features of the lectin with varying concentrations of guanidine hydrochloride. The combined use of spectroscopy and size-analysis by gel filtration revealed that both the folding and assembly of denatured subunit polypeptides were completely prevented in the presence of 300 microM M9-Asn, whereas the same concentration of GM9-Asn only interfered with the polypeptide assembly, exhibiting no significant effect on the polypeptide folding. These results, considered together with those in the previous report, indicate that the sugar branch Man alpha 1-2Man-alpha 1-2Man linked to the 3 position of the beta-mannosyl residue of the high-mannose chains functions in the folding of the subunit polypeptides, and that other branches participate in the subunit assembly.

Isolation and characterization of a hemagglutinin with affinity for lipopolysaccharides from plasma of the crayfish Pacifastacus leniusculus

A hemagglutinin with a high specific activity against trypsinized rabbit erythrocytes was identified in plasma of the freshwater crayfish Pacifastacus leniusculus. The activity of this crayfish hemagglutinin could be inhibited by sialoglycoproteins such as porcine stomach mucin, bovine submaxillary mucin, fetuin, and ovalbumin. However, the involvement of sialic acid in its binding specificity could not be unambiguously proven. Furthermore, the hemagglutinating activity in the crayfish plasma could be specifically inhibited by lipopolysaccharide from E. coli K-235, which might indicate a recognition role for this hemagglutinin. This hemagglutinin, which accounts for less than 0.01% of the total plasma protein, was purified to near homogeneity using affinity chromatography on a Fetuin-Sepharose 4B column. The molecular mass of the unreduced protein as revealed by sodium dodecyl sulphate electrophoresis in polyacrylamide gel was found to be 420,000 Da. Upon reduction with dithiothreitol the hemagglutinin dissociated to several subunits with masses ranging from 65,000 to 80,000 Da. Affinoblotting with peroxidase labelled lectins indicated that the hemagglutinin was likely to be a glycoprotein.

Yeast flocculation: lectin synthesis and activation

Yeast flocculation involves binding of surface lectins to carbohydrate receptors on neighbouring cell walls. Brewing strains of Saccharomyces cerevisiae normally become flocculent in the stationary phase of growth. This paper presents evidence that lectins are synthesized in exponential phase, inserted into the cell wall, and activated later at the time of flocculation onset. Cycloheximide failed to prevent flocculation unless it was added in early growth; with later additions progressively larger degrees of flocculation occurred. Flocculation onset was delayed by cycloheximide but was otherwise cycloheximide insensitive. Preflocculent cells could be artificially activated to full flocculation by heat. Artificial activation of samples from growing yeast cultures confirmed the progressive synthesis of lectins throughout exponential growth. Pronase E treatment of whole cells prior to heating prevented any activation of flocculation. It was concluded that lectins were synthesized continuously from an early stage of growth and rapidly inserted into the cell wall (accessible by pronase E), where they remained inactive for up to 14 h, before being activated at flocculation onset by an as-yet unknown mechanism. It was found that lectin synthesis and activation occurred in all brewing strains tested.

Isolation and characterization of pro-barley lectin expressed in Escherichia coli

Lectins are a class of proteins with specific carbohydrate-binding properties found in a wide variety of plants and animals. Gramineae lectins are presumably defense-related proteins in plants that exert their effect by binding to N-acetylglucosamine. Barley lectin is a vacuolar protein synthesized with an amino-terminal signal sequence for entering the secretory pathway and a carboxyl-terminal propeptide necessary for proper targeting to the vacuole. To analyze the three-dimensional structure of barley lectin with the carboxyl-terminal extension and to investigate whether the conversion of the prolectin into the mature molecule leads to a conformational change, the precursor and the mature forms of barley lectin were expressed in Escherichia coli. Both proteins accumulated in denatured form in inclusion bodies were solubilized in 8 M urea and renatured in a redox buffer system. Active pro- and mature barley lectins were purified to homogeneity by affinity chromatography.

Vegetable gums modify lectin hemagglutinability

Arabic gum enhances lectin hemagglutinability. The more glycosylated the lectin, the greater the stimulatory effect of the gum. Evidence presented suggests that the interaction between gum and lectin is of a carbohydrate-carbohydrate nature.