Lineage- and differentiation-dependent alterations in the expression of receptors for glycoconjugates (lectins) in different human hematopoietic cell lines and low grade lymphomas

Unique sequence and expression profiles of rat galectins-5 and -9 as a result of species-specific gene divergence

Presence of species-specific gene divergence in a protein family prompts to thoroughly study structural aspects and expression profiles of the products. We herein focus on two members of an adhesion/growth-regulatory group of endogenous lectins, i.e. galectins-5 and -9. After first ascertaining species specificity of occurrence of galectin-5, constituted by a short section of rat galectin-9's N-terminal part and its C-terminal carbohydrate recognition domain, by database mining, we next detected and defined sequence differences in the proximal promoter region between the two genes. The ensuing hypothesis for distinct expression profiles was tested first by RT-PCR and then by immunohistochemistry. For the latter purpose, we employed antibodies rigorously controlled for absence of cross-reactivity including assays with various other galectins and, if necessary, refined by chromatographic removal of bi- or oligospecific activities. Indeed, the galectins have non-identical expression profiles, qualitative differences, e.g. seen for galectin-5-positive bone marrow and erythrocytes or for hitherto unknown expression in cells of the theca folliculi and galectin-9-positive skin epidermis and esophageal epithelium. Lack of hepatocyte or renal cortex staining separates these two expression profiles in rat from localization of galectin-9 in mouse. Interspecies extrapolation in a case of a galectin involved in unique gene divergence may thus not be valid. The presented results on galectin-5 relative to galectin-9 intimate distinct functions especially in erythropoiesis and imply currently unknown mechanisms to compensate its absence from the galectin network in other mammals.

Human Galectin-2: Novel Inducer of T Cell Apoptosis with Distinct Profile of Caspase Activation

Galectin-2 is structurally closely related to galectin-1, but has a distinct expression profile primarily confined to the gastrointestinal tract. Prominent differences in the proximal promoter regions between galectins-2 and -1 concern Sp1-, hepatocyte NF-3, and T cell-specific factor-1 binding sites. Of note, these sequence elements are positioned equally in the respective regions for human and rat galectins-2. Labeled galectin-2 binds to T cells in a beta-galactoside-specific manner. In contrast to galectin-1, the glycoproteins CD3 and CD7 are not ligands, while the shared affinity to beta1 integrin (or a closely associated glycoprotein) accounts for a substantial extent of cell surface binding. The carbohydrate-dependent binding of galectin-2 induces apoptosis in activated T cells. Fluorogenic substrate and inhibitor assays reveal involvement of caspases-3 and -9, in accordance with cleavage of the DNA fragmentation factor. Enhanced cytochrome c release, disruption of the mitochondrial membrane potential, and an increase of the Bax/Bcl-2 ratio by opposite regulation of expression of both proteins add to the evidence that the intrinsic apoptotic pathway is triggered. Cell cycle distribution and expression of regulatory proteins remained unaffected. Notably, galectins-1 and -7 reduce cyclin B1 expression, defining functional differences between the structurally closely related galectins. Cytokine secretion of activated T cells was significantly shifted to the Th2 profile. Our study thus classifies galectin-2 as proapoptotic effector for activated T cells, raising a therapeutic perspective. Of importance for understanding the complex galectin network, it teaches the lesson that selection of cell surface ligands, route of signaling, and effects on regulators of cell cycle progression are markedly different between structurally closely related galectins.

Visualization of carbohydrate-binding molecules expressed by myelomono- and erythropoietic cells derived from human bone marrow: an immunoenzymatic double-staining study

Interactions between human haematopoietic and bone marrow stromal cells are governed by complex carbohydrate-mediated adhesion processes. In order to evaluate corresponding carbohydrate-binding sites on human myelo- and erythropoietic cells which were able to react with mono- or oligosaccharides, we established an immunocytochemical double-staining assay. In a first step, cell lineages were visualized using Lewis(x) (CD15) or glycophorin C-specific monoclonal antibodies. The second step included polyacrylamide-conjugated carbohydrate structures. According to our results, the carbohydrate-binding potential of granulopoietic cells increased during the process of maturation, contrasting a reduction of carbohydrate-binding sites on erythroid precursor cells during differentiation. With respect to previous in vitro studies, these findings shed some light on certain aspects of bone marrow homing as well as on the trafficking of mature cellular elements into circulation. It is tempting to speculate that carbohydrate-mediated adhesion mechanisms may be involved in the various functional defects of progenitor cells in chronic myelogenic leukaemia, especially regarding their complex interactions with the marrow microenvironment.

Affinity purification and characterization of recombinant human galectin-1

Galectin-1, a polypeptidic factor that can have major effects on cell growth and apoptosis, was overexpressed in E. coli. This protein was purified to homogeneity by affinity chromatography on lactose coupled to divinylsulfone-activated agarose. The recombinant galectin-1 (rGAL1) was compared with the homologous protein purified from human brain tissue using two-dimensional electrophoresis on immobilized pH gradient (IPG-DALT). rGAL1 had a major isoelectric point of 5.4 (major pI of tissular galectin-1, 5.1) and its subunit molecular mass was 14500. Addition of rGAL1 to Jurkat T-lymphoblastoid cells induced cell death in a concentration-dependent manner.

Galectin-3 inhibits granulocyte-macrophage colony-stimulating factor (GM-CSF)-driven rat bone marrow cell proliferation and GM-CSF-induced gene transcription

The expression of galectin-3 (formerly known as IgE-binding protein or Mac-2) in rat bone marrow (BM) was investigated by FACS, immunocytochemical and immunoblot analysis. The functional significance of rat recombinant galectin-3 on mouse recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF)-driven proliferation of macrophage progenitors and gene transcription was further examined. Immunocytochemical analysis of in situ BM sections demonstrated galectin-3 in myelopoietic cells and surrounding stroma, whereas erythropoietic and lymphopoietic environments essentially lacked galectin-3 expression. FACS analysis demonstrated that incubation of freshly isolated BMC with lactose, a competing ligand for galectin-3 binding to glycoconjugates, decreased binding of antigalectin antibodies to cells primarily expressing the myeloid antigen recognized by mAb His-54. Similarly, lectin-mediated binding of exogenous galectin-3 to myeloid lineage cells was also demonstrated. Immunoblot analysis of BM eluates demonstrated galectin-3 both in the extracellular matrix and in a lactose elutable form, bound to the surface of BMC. [3H]Thymidine incorporation studies on BMC cultured in the presence of galectin-3 demonstrated suppression of GM-CSF-induced proliferation by galectin-3. In addition, differential display analysis of immediate early gene expression in BMC cultured in the presence of galectin-3 revealed a 76.2% inhibition of GM-CSF-induced gene transcription by galectin-3 assessed by the number of PCR-fragments generated. Our data suggest a role for galectin-3 in the organization of myelopoietic compartments in rat BM and regulation of the action of growth factors on myelopoietic precursor cells.

Cell calcium signalling induced by endogenous lectin carbohydrate interaction in the Jurkat T cell line

The effects of the beta-galactoside-binding lectin from human placenta (HPL14) on intracellular calcium concentration ([Ca2+]i) were examined in the human Jurkat T cell line. The lectin induces a concentration dependent increase in [Ca2+]i. This calcium signalling effect is clearly mediated through complementary cell surface galactoglycoconjugates because it can be blocked by beta-galactosides. The observed Ca2+ - response involves both the release of calcium from intracellular stores and a calcium influx from the extracellular space. It is sustained in the presence of 1 mM extracellular calcium whereas it becomes transient when the influx of extracellular calcium was blocked by calcium chelation to EGTA. Voltage-sensitive calcium channel blockers like verapamil and prenylamine were without effect on the action of HPL14. Protection of the sugar binding activity of HPL14 in the absence of a thiol-reducing reagent by carboxamidomethylation (CM-HPL14) or by substitution Cys2 with serine (C2S) results in lectin proteins with considerably decreased calcium signalling efficiency. The recombinant lectin (Rec H) and the mutant protein obtained by substitution of highly conservative Trp68 with tyrosine (W68Y) induce lower levels of [Ca2+]i compared to wild type lectin.

Carbohydrate-dependent binding of human myeloid leukemia cell lines to neoglycoenzymes, matrix-immobilized neoglycoproteins, and bone marrow stromal cell layers

The presence of sugar receptors on human myeloid leukemia cells was comparatively assessed by a highly sensitive binding assay, employing a panel of 14 types of neoglycoenzymes (chemically glycosylated Escherichia coli beta-galactosidase). The selected carbohydrate ligands mainly encompass common components of natural glycoconjugates as mono- or disaccharides. The monocytoid cells of the THP-1 line, the very young myeloblasts and the myeloblasts of the lines KG-1a and KG-1, the promyelocytes of the HL-60 line, and the early myeloblasts/erythroblasts of the K-562 line displayed a nonuniform pattern of specific binding with quantitative differences at a fixed, nonsaturating concentration of the probes. Scatchard analysis in four cases corroborated the indication of cell-type-related differences between the various cell lines. To test whether the detectable cellular sugar-binding sites can mediate adhesion to glycoligands, a rather simple model matrix of nitrocellulose-immobilized neoglycoproteins was first used. In comparison to the carbohydrate-free carrier protein significant cell adhesion was observed primarily with neoglycoproteins that exposed galactose, N-acetylgalactosamine, N-acetylglucosamine, mannose, and fucose moieties among the 11 tested types of carbohydrate residue. Subsequently, human bone marrow stromal cell layers were tested as a model matrix with increased levels of physiological relevance and complexity. Mixtures of carbohydrate and neoglycoprotein were employed as inhibitors of an interaction via lectins between the stromal and the tumor cells. The carbohydrate-dependent alterations of this parameter revealed cell-type-associated properties. Tumor cell binding was significantly decreased for not more than two lines with the effective sugars, namely N-acetylgalactosamine, mannose, fucose, and sialic acid.

Identification of endogenous sugar-binding proteins in the accessory sex glands of NMRI mice. A histochemical and biochemical study

In the present study we report on the histotopographical distribution of carbohydrate-binding proteins in the prostate and seminal vesicle of sexually mature NMRI mice using a panel of fluorescein-isothiocyanate labelled neoglycoproteins and asialoglycoproteins. Additionally, biochemical analysis using affinity chromatography and SDS-gel electrophoresis was performed to purify and characterize the respective proteins from the tissue. Our histochemical results clearly demonstrate the presence of endogenous receptors for the carbohydrate part of glycoconjugates in both glands. In the prostate a distinct staining was seen after incubation with melibiose-BSA-FTC, glucuronic acid-BSA-FTC and asialofetuin-FTC (only in the ventral prostate). In the epithelium of the seminal vesicle a weak staining occurred after incubation with asialofetuin-FTC and maltose-FTC. In the stroma of both accessory sex glands a distinct binding of several (neo)glycoproteins specific for beta-galactoside-binding proteins was observed which could be attributed to a beta-galactoside-binding lectin. Indeed biochemical analysis ascertained presence of such a histochemically detectable activity. We assume that the carbohydrate-binding proteins of the stroma, which were obviously linked to the elastic fibers, could play a role in the organisation of the extracellular matrix in the interstitium of the glands.

Lectin localization in human nerve by biochemically defined lectin-binding glycoproteins, neoglycoprotein and lectin-specific antibody

Molecular recognition can be mediated by protein (lectin)-carbohydrate interaction, explaining the interest in this topic. Plant lectins and, more recently, chemically glycosylated neoglycoproteins principally allow to map the occurrence of components of this putative recognition system. Labelled endogenous lectins and the lectin-binding ligands can add to the panel of glycohistochemical tools. They may be helpful to derive physiologically valid conclusions in this field for mammalian tissues. Consequently, experiments were prompted to employ the abundant beta-galactoside-specific lectin of human nerves in affinity chromatography and in histochemistry to purify and to localize its specific glycoprotein ligands. In comparison to the beta-galactoside-specific plant lectins from Ricinus communis and Erythrina cristagalli, notable similarities were especially detectable in the respective profiles of the mammalian and the Erythrina lectin. They appear to account for rather indistinguishable staining patterns in fixed tissue sections. Inhibitory controls within affinity chromatography, within solid-phase assays for each fraction of lectin-binding glycoproteins and within histochemistry as well as the demonstration of crossreactivity of the three fractions of lectin-binding glycoproteins with the biotinylated Erythrina lectin in blotting ascertained the specificity of the lectin-glycoprotein interaction. In addition to monitoring the accessible cellular ligand part by the endogenous lectin as probe, the comparison of immunohistochemical and glycohistochemical detection of the lectin in serial sections proved these methods for receptor analysis to be rather equally effective. The observation that the biotinylated lectin-binding glycoproteins are also appropriate ligands in glycohistochemical analysis warrants emphasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Sugar receptors of the stromal cell layer in human long-term bone marrow cultures: their presence, modulatory responses to changes in the microenvironment and potential role in cellular adhesion

Intimate cellular contacts and coordinated supply of regulatory factors are required to maintain the still inexplicable dynamic equilibrium of hemopoiesis. To infer the potential participation of protein-carbohydrate interaction in this complex process, human long-term bone marrow cultures were initiated from eleven donors, and the adherent cell layer was characterized enzyme- and immunohistochemically. Utilizing an array of carrier-immobilized carbohydrate ligands and sulfated polysaccharides as probes, specific binding of various constituents of the carbohydrate chains of cellular glycoconjugates to the stromal cells was unmistakably disclosed. Biochemical analysis, employing glycocytologically effective ligands in affinity chromatography, corroborated this result. The extent of binding was markedly lower in the two samples, derived from leukemia patients. Pronounced adaptive responses for this characteristic followed changes in the culture microenvironment that are known to influence qualitative and quantitative aspects of hemopoiesis in vitro, namely omission of hydrocortisone and horse serum or addition of cytokines. Similarly, such adaptive modulation occurred on the level of accessible cell surface receptors, monitored by neoglycoenzymes. These binding sites can be involved in mediation of cellular interactions, as revealed in a model system by the interference of N-acetyl-D-galactosamine in cell adhesion. Overall, the results support the idea that glycobiological recognition may contribute to the functional integrity of the stromal cell layer as well as provide the basis for further analysis.

Influence of type of linkage and spacer on the interaction of beta-galactoside-binding proteins with immobilized affinity ligands

Affinity chromatography provides a powerful tool for isolation of carbohydrate-binding proteins. However, the choice of the ligand and spacer has an important impact on effectiveness. The influence of several different ligands on qualitative and quantitative aspects of the purification of two beta-galactoside-specific lectins has been evaluated. Sepharose was modified by coupling four types of neoglycoproteins (galactosylated or lactosylated bovine serum albumin with increasing sugar content) and two naturally occurring asialoglycoproteins at similar densities. Carbohydrate ligands at essentially equal density were made accessible to the lectins by seven commonly used methods. The yield of mistletoe lectin was high when lactosylated neoglycoproteins were used for separation. For these resins the sugar incorporation exceeded 10 sugar groups per protein carrier molecule. The yield was similarly high with the asialoglycoproteins and with lactose; the sugar was coupled to the resin as a p-aminophenyl derivative or by means of divinyl sulfone activation. An epoxy group in linkages of galactose or lactose decreased the binding capacity. A quantitatively similar degree of protein yields was obtained for the beta-galactoside-binding protein of bovine heart, although different proteins were obtained when neoglycoproteins were used as ligand. The nature of the affinity ligand in lectin purification can increase the yield and may also influence the profile of the carbohydrate-binding proteins.

Spatial differences of endogenous lectin expression within the cellular organization of the human heart: a glycohistochemical, immunohistochemical, and glycobiochemical study

Protein-carbohydrate recognition may be involved in an array of molecular interactions on the cellular and subcellular levels. To gain insight into the role of proteins in this type of interaction, surgically removed specimens of human endomyocardial tissue were processed for histochemical and biochemical analysis. The inherent capacity of these sections to bind individual sugar moieties, which are constituents of the carbohydrate part of cellular glycoconjugates, was assessed using a panel of biotinylated neoglycoproteins according to a standardized procedure. Together with appropriate controls, it primarily allowed localization of endogenous lectins. Differences in lectin expression were observed between layers of endocardial tissue, myocardial cell constituents, connective-tissue elements, and vascular structures. The endocardium proved to be positive with beta-galactoside-bearing probes; with neoglycoproteins carrying beta-xylosides, alpha-fucosides, and galactose-6-phosphate moieties; and with probes containing a carboxyl group within the carbohydrate structure, namely sialic acid and glucuronic acid. In contrast, only fucose-and maltose-specific receptors were apparent in the elastic layers of the endocardium. Aside from ascertaining the specificity of the protein-carbohydrate interaction by controls, i.e., lack of binding of the probe in the presence of the unlabelled neoglycoprotein and lack of binding of the labelled sugar-free carrier protein, respective sugar receptors were isolated from heart extracts by using histochemically effective carbohydrates as immobilized affinity ligand. Moreover, affinity chromatography using immobilized lactose as affinity ligand as well as the use of polyclonal antibodies against the predominant beta-galactoside-specific lectin of heart demonstrated that the lactose-specific neoglycoprotein binding was due to this lectin. Remarkably, the labelled endogenous lectin, preferred to plant lectins for detecting ligands of the endogenous lectin, localized ligands in tissue parts where the lectin itself was detected glycohistochemically as well as immunohistologically. This demonstration of receptor-ligand presence in the same system is a further step toward functional assignment of the recorded protein-carbohydrate interaction. Overall, the observed patterns of lectin expression may serve as a guideline to elucidate the precise physiological relevance of lectins and to analyze pathological conditions comparatively.

Carrier-immobilized derivatized lysoganglioside GM1 is a ligand for specific binding sites in various human tumor cell types and peripheral blood lymphocytes and monocytes

Biotinylation of ganglioside-protein conjugates, derived from selective N-acylation of the sphingoid amino group of deacylated ganglioside GM1 or a ganglioside mixture, yielded probes to detect specific binding sites in fixed specimens. GM1-containing neoligandoprotein significantly bound to tumor cells in sections of 15 out of 16 cases of human lung cancer, while the probe, derived from the mixture, was ineffective under these conditions. The same graduation of staining was under identical conditions observed with these two probes on fixed human tumor cells and on peripheral blood lymphocytes and monocytes. Attempts of biochemical isolation of proteins, responsible for this binding capacity, from tumor cell extracts in the presence of the abundant endogenous ligands led to protein bands with apparent molecular weights of 44,000, 68,000 and 72,000 with yields of 0.1-0.24 micrograms/mg protein, after the detergent extracts had been passed over a resin, exposing gangliosides of the markedly less efficient mixture, to exclude binding by non-specific ionic or hydrophobic interactions.

Reduced expression of mannose-specific receptors on murine peripheral blood polymorphonuclear leukocytes following prolonged anaesthesia with different inhalation agents

Inhalation anaesthetic agents are known to depress phagocytic functions such as mobilization, attachment, chemotactic motility, engulfment and intracellular killing. Mannose-specific sugar receptors on the surface of leukocytes are involved in a series of phagocytosis-related activities. To investigate the effect of anaesthesia on the expression of this type of sugar receptor, mice were anaesthetized with halothane, enflurane and isoflurane. The presence of mannose-binding receptors on peripheral blood polymorphonuclear leukocytes was examined glycocytochemically using the biotinylated neoglycoprotein mannosylated bovine serum albumin. Prolonged administration of inhalation anaesthetic agents, especially halothane, markedly depressed expression of mannose-specific receptors. This reduction may possibly contribute to postoperative immunodepression, resulting from the impaired cellular interaction which is involved in the phagocytic function of granulocytes.

Regional differences in the distribution of endogenous receptors for carbohydrate constituents of cellular glycoconjugates, especially lectins, in cortex, hippocampus, basal ganglia and thalamus of adult human brain

Ten different types of labelled neoglycoproteins, exposing glycohistochemically pivotal carbohydrate moieties that mostly are constituents of naturally occurring glycoconjugates with an aromatic spacer, were synthesized. The panel was applied to fixed, paraffin-embedded sections of different cortical regions and white matter, of hippocampal gyrus, basal ganglia, thalamus nuclei and adjacent areas of adult human brain to comprehensively map the presence of respective binding sites in these parts. Compliance with accepted criteria for specificity of binding was routinely ascertained. Overall, not a uniform binding pattern, but a distinct distribution with regional differences on the level of specific cytoplasmic and nuclear staining in nerve cells was determined, fiber structures being generally labelled with medium or strong intensity. For example, among the neurons localized in the five cortical laminae the binding of N-acetyl-D-galactosamine varied from strong to undetectable. Biochemical analysis, employing carbohydrate residues as affinity ligands in chromatography, proved that the neuroanatomically different regions exhibited a pattern of receptors with notable similarities. These results on endogenous binding sites for glycoconjugates, especially lectins, are complementary to assessment of localization of cellular glycoconjugates by plant lectins and carbohydrate-specific monoclonal antibodies. They are thus a further obligatory step to substantiate the physiological roles of recognitive protein-carbohydrate interactions in the central nervous system.

Malignant and normally developing trophoblastic cells of human placenta display different characteristics defined by histochemical and biochemical mapping of endogenous lectins

Trophoblastic cells with their strictly controlled propensity for invasive growth hereby bear limited resemblance to malignant cells. Therefore, detailed description of molecular characteristics of this cell type in comparison to histologically related tumor cells may aid in defining physiologically relevant differences. In view of the potential importance of selective protein-carbohydrate interactions in recognitive processes, labelled neoglycoproteins were employed to evaluate systematically the presence and distribution of sugar receptors in tumor cells of chorionepithelioma and in trophoblastic cells of an early stage of gestation. Control reactions in glycohistochemistry, involving prolonged incubation, pH variation and use of nucleotides excluded the possibility that glycosidases or glycosyltransferases govern the sugar-specific binding to the tissue sections. Pronounced differences were detected in the expression of receptors (lectins) for alpha- and beta-glucosides as well as for N-acetylgalactosamine and N-acetylglucosamine. Further differences were revealed by probing both types of tissue with lactosylated, fucosylated, xylosylated and sialylated carrier protein. Upon developmental maturation of the normal cells in placenta the extent of binding of the neoglycoproteins decreased. The glycohistochemical differences between malignant and normally developing trophoblastic cells were found to be reflected in the alteration of expression of certain endogenous lectins, as ascertained by affinity chromatography and gel electrophoretic analysis. Consequently, we assume that the transient presence of certain endogenous lectins during early stages of gestation and their differential expression in relation to tumor cells of chorionepithelioma may be relevant for the special invasive and adhesive behavior of human trophoblastic cells.