Galectin-3 Mediates IL-4-Induced Survival and Differentiation of B Cells: Functional Cross-Talk and Implications during Trypanosoma cruzi Infection

The role of transcription factors in B cell survival and differentiation has been delineated during the last years. However, little is known about the intermediate signals and the intracellular pathways that control these events. In this study, we provide evidence both in vitro and in vivo, showing that galectin-3 (Gal-3), a beta-galactoside-binding protein, is a critical mediator of B cell differentiation and survival. Although Gal-3 is not expressed in resting B cells from normal mice, its expression is markedly induced after activation with stimuli such as IL-4 and CD40 cross-linking. These signals promote survival and block the final differentiation of these cells, thus allowing the rising of a memory B cell phenotype. In addition, Gal-3 is expressed in B cells from Trypanosoma cruzi-infected mice, which received signals for activation and differentiation in vivo. By using an antisense strategy, we determined that Gal-3 is a critical signal mediating the effects of IL-4 on B cell fate. Blockade of intracellular Gal-3 in vitro abrogated IL-4-induced survival of activated B cells, favoring the differentiation toward a plasma cell pathway. Moreover, B cells with restrained endogenous Gal-3 expression failed to down-regulate the Blimp-1 transcription factor after IL-4 stimulation. Finally, inhibition of Gal-3 in vivo skewed the balance toward plasma cell differentiation, which resulted in increased Ig production and parasite clearance during T. cruzi infection. Thus, the present study provides evidence of a novel role for Gal-3 as an intracellular mediator of B cell survival and a checkpoint in IL-4-induced B cell commitment toward a memory phenotype.

Homodimeric galectin-7 (p53-induced gene 1) is a negative growth regulator for human neuroblastoma cells

The extracellular functions of galectin-7 (p53-induced gene 1) are largely unknown. On the surface of neuroblastoma cells (SK-N-MC), the increased GM1 density, a result of upregulated ganglioside sialidase activity, is a key factor for the switch from proliferation to differentiation. We show by solid-phase and cell assays that the sugar chain of this ganglioside is a ligand for galectin-7. In serum-supplemented proliferation assays, galectin-7 reduced neuroblastoma cell growth without the appearance of features characteristic for classical apoptosis. The presence of galectin-3 blocked this effect, which mechanistically resembles that of galectin-1. By virtue of carbohydrate binding, galectin-7 thus exerts neuroblastoma growth control similar to galectin-1 despite their structural differences. In addition to p53-linked proapoptotic activity intracellularly, galectin-7, acting as a lectin on the cell surface, appears to be capable of reducing cancer cell proliferation in susceptible systems.

Evidence that IgE molecules mediate a spectrum of effects on mast cell survival and activation via aggregation of the FcepsilonRI

We demonstrate that binding of different IgE molecules (IgEs) to their receptor, FcepsilonRI, induces a spectrum of activation events in the absence of a specific antigen and provide evidence that such activation reflects aggregation of FcepsilonRI. Highly cytokinergic IgEs can efficiently induce production of cytokines and render mast cells resistant to apoptosis in an autocrine fashion, whereas poorly cytokinergic IgEs induce these effects inefficiently. Highly cytokinergic IgEs seem to induce more extensive FcepsilonRI aggregation than do poorly cytokinergic IgEs, which leads to stronger mast cell activation and survival effects. These effects of both types of IgEs require Syk tyrosine kinase and can be inhibited by FcepsilonRI disaggregation with monovalent hapten. In hybridoma-transplanted mice, mucosal mast cell numbers correlate with serum IgE levels. Therefore, survival effects of IgE could contribute to the pathogenesis of allergic disease.

Galectin 3 and its binding protein in rheumatoid arthritis

OBJECTIVE

To characterize the expression pattern and role of galectin 3 and galectin 3 binding protein (G3BP) in rheumatoid arthritis (RA), in comparison with galectin 1, and to explore whether soluble galectin 3 and G3BP, investigated in serum, synovial fluid, or cell culture supernatant, are associated with disease.

METHODS

Synovial tissues from patients with RA or osteoarthritis (OA), as well as from healthy controls, were analyzed for galectins 1 and 3 and G3BP by in situ hybridization and immunohistochemistry. Levels of galectin 3 and G3BP in serum and synovial fluid from patients with RA and OA and controls, as well as in cell culture supernatants, were determined by enzyme-linked immunosorbent assay (ELISA). In vitro, the intracellular expression of galectin 3 in RA and OA synovial fibroblasts after modulation with tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and anti-CD40 monoclonal antibodies was measured by flow cytometry.

RESULTS

In RA, galectin 3 messenger RNA and protein stained throughout the synovial membrane, whereas G3BP was particularly expressed at sites of bone destruction. In contrast, the expression of galectin 1 was not uniform in different RA specimens, and was never found at sites of invasion. In OA and normal synovial tissues, only a small number of cells were positive for galectins and/or G3BP. Galectin 3 was elevated in RA sera and synovial fluids, whereas G3BP was increased in RA synovial fluids only. In RA, serum galectin 3 correlated with C-reactive protein levels, whereas G3BP was associated with joint destruction and/or synovial cell activation as measured by the levels of cartilage oligomeric matrix protein. In vitro, RA synovial fibroblasts showed an increased release of galectin 3 into culture medium, as measured by ELISA, but decreased secretion of G3BP. In RA synovial fibroblasts with low basal expression of galectin 3, TNFalpha increased its intracellular level in a dose-dependent manner. In contrast, IL-1beta or anti-CD40 monoclonal antibodies showed no effect.

CONCLUSION

Our data indicate that galectin 3 and G3BP are not only involved in inflammation, but also contribute to the activation of synovial fibroblasts. The intracellular accumulation of galectin 3 can be enhanced by TNFalpha. Thus, galectin 3 and G3BP represent novel markers of disease activity in RA.

Critical role of galectin-3 in phagocytosis by macrophages

Galectin-3 is a member of a large family of animal lectins. This protein is expressed abundantly by macrophages, but its function in this cell type is not well understood. We have studied the effect of galectin-3 gene targeting on phagocytosis, a major function of macrophages. Compared with wild-type macrophages, galectin-3-deficient (gal3-/-) cells exhibited reduced phagocytosis of IgG-opsonized erythrocytes and apoptotic thymocytes in vitro. In addition, gal3-/- mice showed attenuated phagocytic clearance of apoptotic thymocytes by peritoneal macrophages in vivo. These mice also exhibited reduced IgG-mediated phagocytosis of erythrocytes by Kupffer cells in a murine model of autoimmune hemolytic anemia. Additional experiments indicate that extracellular galectin-3 does not contribute appreciably to the phagocytosis-promoting function of this protein. Confocal microscopic analysis of macrophages containing phagocytosed erythrocytes revealed localization of galectin-3 in phagocytic cups and phagosomes. Furthermore, gal3-/- macrophages exhibited a lower degree of actin rearrangement upon Fcgamma receptor crosslinkage. These results indicate that galectin-3 contributes to macrophage phagocytosis through an intracellular mechanism. Thus, galectin-3 may play an important role in both innate and adaptive immunity by contributing to phagocytic clearance of microorganisms and apoptotic cells.

Analysis of selected blood and immune cell responses to carbohydrate-dependent surface binding of proto- and chimera-type galectins

Cell surface glycans present docking sites to endogenous lectins. With growing insight into the diversity of lectin families it becomes important to answer the question on the activity profiles of individual family members. Focusing on galectins (beta-galactoside-binding proteins without Ca(2+)-requirement sharing the jelly-roll-like folding pattern), this study was performed to assess the potency of proto-type galectins (galectins-1 and -7 and CG-16) and the chimera-type galectin-3 to elicit selected cell responses by carbohydrate-dependent surface binding and compare the results. The galectins, except for galectin-1, were found to enhance detergent (SDS)-induced hemolysis of human erythrocytes to different degrees. Their ability to confer increased membrane osmofragility thus differs. Aggregation of neutrophils, thymocytes and platelets was induced by the proto-type galectin-1 but not -7, by CG-16 and also galectin-3. Cell-type-specific quantitative differences and the importance of the fine-specificity of the galectin were clearly apparent. In order to detect cellular responses based on galectin binding and bridging of cells the formation of haptenic-sugar-resistant (HSR) intercellular contacts (an indicator of post-binding signaling) was monitored. It was elicited by CG-16 and galectin-1 but not galectin-3, revealing another level at which activities of individual galectins can differ. Acting as potent elicitor of neutrophil aggregation, CG-16-dependent post-binding effects were further analyzed. Carbohydrate-dependent binding to the neutrophils' surface led to a sustained increase of cytoplasmic Ca2+ concentration in a dose-dependent manner. The ability of CG-16 to activate H2O2 generation by human peripheral blood neutrophils was primed by the Ca(2+)-ionophor ionomycin and by cytochalasin B. In a general context, these results emphasize that--besides plant lectins as laboratory tools--animal lectins can trigger cell reaction cascades, implying potential in vivo relevance for the measured activities. Within the family of galectins, the activity profiles depend on the target cell type and the individual galectin. Notably, proto-type galectins do not necessarily share a uniform capacity as elicitor.

Involvement of protein tyrosine kinase in Toll-like receptor 4-mediated NF-kappa B activation in human peripheral blood monocytes

Bacterial lipopolysaccharide (LPS) is a powerful activator of the innate immune system. Exposure to LPS induces an inflammatory reaction in the lung mediated primarily by human blood monocytes and alveolar macrophages, which release an array of inflammatory chemokines and cytokines including IL-8, TNF-alpha, IL-1beta, and IL-6. The signaling mechanisms utilized by LPS to stimulate the release of cytokines and chemokines are still incompletely understood. Pretreatment with the protein tyrosine kinase-specific inhibitors genistein and herbimycin A effectively blocked LPS-induced NF-kappaB activation as well as IL-8 gene expression in human peripheral blood monocytes. However, when genistein was added 2 min after the addition of LPS, no inhibition was observed. Utilizing a coimmunoprecipitation assay, we further showed that LPS-stimulated tyrosine phosphorylation of Toll-like receptor 4 (TLR4) may be involved in downstream signaling events induced by LPS. These findings provide evidence that LPS-induced NF-kappaB activation and IL-8 gene expression use a signaling pathway requiring protein tyrosine kinase and that such regulation may occur through tyrosine phosphorylation of TLR4.

Nuclear localization of Galectin-3 in transformed thyroid cells: a role in transcriptional regulation

The differential proteomic approach (2D gel analysis coupled to MALDI-MS analysis) of nuclear proteins can provide an extremely useful tool to understand control of cell proliferation and differentiation. In order to identify possible markers of dedifferentiation between normal and cancerous thyroid cells, we used a differential proteomics approach by comparing nuclear extracts from the normal rat thyroid cell line FRTL-5 and the completely undifferentiated Ki-mol cell line, obtained by transformation with the Ki-ras oncogene. Galectin-3 (Gal-3) was identified as highly expressed, in the nuclear compartment, only in the transformed cell line. By using different human cancer cell lines, we showed that Gal-3 is maximally expressed in nuclei of papillary cancer cells. We focused on the functional relationship existing between Gal-3 and the thyroid-specific transcription factor TTF-1, whose expression is maintained in papillary cancer where it can contribute to the proliferating status. By using gel-retardation and transient tranfection assays, we demonstrate that Gal-3 upregulates the TTF-1 transcriptional activity. GST-pulldown experiments demonstrate the occurrence of interaction between Gal-3 and TTF-1 homeodomain. Since several lines of evidence suggest a role for Gal-3 in controlling proliferation and tumor progression in thyroid cancer, the stimulatory activity played by Gal-3 over TTF-1 would account for a possible molecular mechanism through which the galectin controls proliferation in thyroid cells.

Galectin-7 as a potential mediator of corneal epithelial cell migration

OBJECTIVE

To assess the role of a carbohydrate-binding protein, galectin-7, in reepithelialization of corneal wounds.

METHODS

Transepithelial excimer laser ablations were performed on mouse corneas, and the wounds were allowed to partially heal in vivo for 18 to 22 hours. At the end of the healing period, expression levels of galectin-7 messenger RNA and protein were analyzed using semiquantitative reverse transcriptase-polymerase chain reaction, Western blot analysis, and immunohistochemical localization studies. To determine the effect of exogenous galectin-7 on reepithelialization of corneal wounds, corneas with 2-mm alkali burn wounds were allowed to partially heal in vitro for 20 to 24 hours in serum-free media in the presence or absence of recombinant galectin-7. At the end of the healing period, the wound areas were photographed and quantified.

RESULTS

Expression of galectin-7 messenger RNA and protein was markedly up-regulated in the corneal epithelium after injury. Exogenous galectin-7 stimulated reepithelialization of corneal wounds. The stimulatory effect of galectin-7 on corneal epithelial wound closure was specifically inhibited by a competing sugar, beta-lactose, but not by an irrelevant disaccharide, sucrose.

CONCLUSIONS

Galectin-7 has the potential to mediate corneal epithelial cell migration and reepithelialization of wounds.

CLINICAL RELEVANCE

These findings have broad implications for developing novel, galectin-based, therapeutic strategies for treatment of nonhealing corneal epithelial defects.

Changes in galectin-7 and cytokeratin-19 expression during the progression of malignancy in thyroid tumors: diagnostic and biological implications

Galectin-7 is associated with p53-dependent onset of apoptosis and proliferation control/differentiation in keratinocyte development. It is also up-regulated in chemically induced rat mammary carcinogenesis. Because the levels of expression of galectin-7 have never been investigated in thyroid tumors (in contrast to those of galectin-1 and -3 associated with malignancy), we initiated analysis of the expression of galectin-7 in benign and malignant thyroid lesions together with that of cytokeratin-19 (CK19), a marker already demonstrated to be useful in diagnosing this kind of lesion. The immunohistochemical expression levels were quantitatively determined by means of computer-assisted microscopy on a series of 84 thyroid lesions including 10 multinodular goiters, 32 adenomas, and 42 carcinomas. Our data clearly indicate a marked down-regulation of galectin-7 expression in a large proportion of adenomas (including the normomacrofollicular, microfollicular, and trabecular variants) if compared with carcinomas. In accordance with results of previous studies, a marked up-regulation of CK19 expression was observed in the thyroid carcinomas, and this contrasted in particular with the low CK19 expression observed in the microfollicular adenomas. Of importance for diagnostic implications, the combination of these two markers enabled our series of microfollicular adenomas (characterized by low galectin-7 and CK19 expression) to be efficiently distinguished from the encapsulated follicular variant of papillary thyroid carcinomas (high galectin-7 and CK19 expression).

IL-1 receptor-associated kinase and low molecular weight GTPase RhoA signal molecules are required for bacterial lipopolysaccharide-induced cytokine gene transcription

Proinflammatory cytokines such as IL-1, TNF, IL-6, and IL-8 are produced by leukocytes in response to bacteria or bacterial components. A great deal has been learned during the past few years about the synthesis and release of proinflammatory cytokines by leukocytes; however, relatively little is known about the intracellular events that lead to leukocyte proinflammatory cytokine gene transcription. This study examined the signal transduction pathway of IL-8 induction by bacterial LPS. Stimulation of monocytes with LPS rapidly activated RhoA, and pretreatment of monocytes with a RhoA inhibitor, C3 transferase exoenzyme, effectively blocked LPS-induced IL-8 gene expression. Overexpression of dominant negative RhoA (T19N) or IL-1R-associated kinase completely inhibited LPS-stimulated reporter gene expression. Induction of IL-8 was also inhibited by dominant negative IkappaB kinase and myeloid differentiation protein (MyD88). These results indicate that RhoA and IL-1R-associated kinase are novel signal transducers for LPS-induced Toll-like receptor 4-mediated proinflammatory cytokine synthesis in human monocytes.

Galectins-3 and -7, but not galectin-1, play a role in re-epithelialization of wounds

Disorders of wound healing characterized by impaired or delayed re-epithelialization are a serious medical problem. These conditions affect many tissues, are painful, and are difficult to treat. In this study, using cornea as a model, we demonstrate for the first time the importance of carbohydrate-binding proteins galectins-3 and -7 in re-epithelialization of wounds. In two different models of corneal wound healing, re-epithelialization of wounds was significantly slower in galectin-3-deficient (gal3(-/-)) mice compared with wild-type (gal3(+/+)) mice. In contrast, there was no difference in corneal epithelial wound closure rates between galectin-1-deficient and wild-type mice. Quantitation of the bromodeoxyuridine-labeled cells in gal3(+/+) and gal3(-/-) corneas revealed that corneal epithelial cell proliferation rate is not perturbed in gal3(-/-) corneas. Exogenous galectin-3 accelerated re-epithelialization of wounds in gal3(+/+) mice but, surprisingly, not in the gal3(-/-) mice. Gene expression analysis using cDNA microarrays revealed that healing corneas of gal3(-/-) mice contain markedly reduced levels of galectin-7 compared with those of gal3(+/+) mice. More importantly, unlike galectin-3, galectin-7 accelerated re-epithelialization of wounds in both gal3(-/-) and gal3(+/+) mice. In corresponding experiments, recombinant galectin-1 did not stimulate the corneal epithelial wound closure rate. The extent of acceleration of re-epithelialization of wounds with both galectin-3 and galectin-7 was greater than that observed in most of the published studies using growth factors. These findings have broad implications for developing novel therapeutic strategies for treating nonhealing wounds.

Intracellular functions of galectins

Many galectin family members are detected primarily intracellularly in most of the systems studied, although certain members can be found both inside and outside of cells. Specific functions that are consistent with their intracellular localization have now been documented for some of the galectins. Galectin-1 and -3 have been identified as redundant pre-mRNA splicing factors. Galectin-3, -7, and -12 have been shown to regulate cell growth and apoptosis, being either anti-apoptotic or pro-apoptotic. Galectin-3 and -12 have been shown to regulate the cell cycle. In some cases, the mechanisms by which galectins exert their functions have been partially delineated in relation to known intracellular pathways associated with these processes. In addition, a number of intracellular proteins involved in these processes have been identified as the interacting ligands of certain galectins. This review summarizes the intracellular activities displayed by several galectins and discusses the possible underlying mechanisms.

Optimized conjugation ratios lead to allergen immunostimulatory oligodeoxynucleotide conjugates with retained immunogenicity and minimal anaphylactogenicity

BACKGROUND

Immunotherapy has gradually fallen out of favor for the treatment of many allergic diseases because of the overall convenience, safety, and efficacy of medications. However, investigations suggest that allergen/immunostimulatory sequence oligodeoxynucleotide (ISS-ODN) conjugates (AICs) might have improved safety and efficacy compared with allergen extracts.

OBJECTIVE

We determined whether changes in the ISS-ODN conjugation ratio would effect the immunogenicity and allergenicity of AIC.

METHODS

Immunogenicity was determined by means of AIC vaccination of mice, followed by analysis of antigen-specific antibody and cytokine responses. The allergenicity of AIC was determined in mast cell release studies and in murine models of anaphylaxis and the Arthus reaction.

RESULTS

AIC induced a stronger immune response than allergen alone or allergen mixed with ISS-ODN, but higher-level ISS-ODN conjugation reduced its immunogenicity modestly. In mast cell degranulation studies AIC was approximately 100-fold less allergenic than native allergen, with stepwise increases in the ODN conjugation ratio leading to stepwise decreases in allergenicity. In anaphylaxis studies death rates were reduced from 100% with native allergen challenge to as low as 0% with high-ratio ISS-ODN AIC challenge. Similar results were obtained in an Arthus reaction model.

CONCLUSION

These investigations establish that AIC is both significantly more immunogenic and less allergenic than native allergens and the techniques used might have further utility for the standardization and optimization of AIC formulations for use in allergic patients.

IgE-dependent mast cell activation potentiates airway responses in murine asthma models

We have studied murine models of asthma using FcepsilonRIalpha-chain-deficient (FcepsilonRIalpha(-/-)) mice to investigate the role of IgE-dependent mast cell activation in these models. When mice were either 1) immunized once with OVA in alum i.p. and then challenged with OVA intranasally, or 2) repeatedly immunized with OVA in the absence of adjuvant and subsequently challenged with nebulized OVA, FcepsilonRalpha(-/-) mice had significantly fewer eosinophils and lower IL-4 levels in their bronchoalveolar lavage fluid compared with wild-type mice. When mice were given anti-IL-5 antibody before OVA challenge in protocol 1, eosinophilic infiltration into the airways was significantly suppressed in both genotypes, but only FcepsilonRIalpha(-/-) mice showed significantly reduced airway hyperresponsiveness (AHR). In addition, when mice immunized and challenged with OVA also received a late OVA provocation at a higher concentration and were then exposed to methacholine, only wild-type mice developed a substantial increase in AHR. Since FcepsilonRI is expressed mainly on mast cells in mouse airways, we conclude that IgE-dependent activation of this cell type plays an important role in the development of allergic airway inflammation and AHR in mice. The models used may be of value for testing inhibitors of IgE or mast cells for development of therapeutic agents for human asthma.

Thermodynamic binding studies of cell surface carbohydrate epitopes to galectins-1, -3, and -7: Evidence for differential binding specificities

Binding of a series of sialylated and non-sialylated cell surface carbohydrates to bovine heart galectin-1, recombinant murine galectin-3, and recombinant human galectin-7 was investigated by isothermal titration microcalori metry (ITC) and hemagglutination inhibition measurements. Galectin-7 shows nearly equal affinities for lactose and Galbeta(1–4)GlcNAc (LacNAc-II). Galectin-7, however, displays six- and 11-fold weaker affinity for LacNAc-II compared with galectins-1 and -3, respectively. The affinity of galectin-7 for LacNAc-II containing oligosaccharides is also weaker than the other two galectins. ITC measurements show that all three galectins bind to di- and trimeric oligomers of LacNAc-II, which are epitopes found in poly-N-acetyllactosamine chains of glycoprotein receptors, with affinity constants similar to that of LacNAc-II. The binding valencies of the di- and trimeric LacNAc-II oligomers were observed to be one from ITC measurements, indicating formation of 1:1 complexes with all three galectins. Thus, galectins-1, -3, and -7 all possess binding sites that primarily accommodate one LacNAc-II moiety per monomer of protein. Sialylated oligosaccharides show different specificities for the three galectins. While 2,3-sialyl LacNAc-II binds to all three galectins, 2,6-sialyl LacNAc-II fails to bind to any of the galectins; 2,6-sialylated diLacNAc binds well to galectin-3 and galectin-7, but only weakly to galectin-1. Similar results are obtained with 2,6-sialyl lacto-N-neo-tetraose, which has a reducing end lactose moiety. Thus, unlike galectin-1, which predominantly recognizes non-reducing terminal LacNAc-II residues in oligosaccharides, galectins-3 and -7 recognize both non-reducing terminal LacNAc-II residues as well as internal LacNAc-II and lactose residues in sialylated and non-sialylated oligosaccharides.Key words: isothermal titration microcalorimetry, galectins, binding specificities, lectins, carbohydrates.

Monoclonal antibodies against the C(epsilon)mX domain of human membrane-bound IgE and their potential use for targeting IgE-expressing B cells

BACKGROUND

IgE mediates immediate-type hypersensitivity reactions responsible for various allergic symptoms. It is secreted by IgE-producing plasma cells, which differentiate from B cells expressing membrane-bound IgE (mIgE) on their surface. The epsilon-chain of human mIgE contains a membrane-anchoring peptide and an extra 52-amino-acid (a.a.)-long domain (referred to as C(epsilon)mX) between the membrane anchor and the CH4 domain.

OBJECTIVE

The study was designed to evaluate the effects of C(epsilon)mX-specific monoclonal antibodies (mAbs) to target IgE-expressing B cells and decrease IgE production.

METHODS

A C(epsilon)mX-containing IgG1.Fc fusion protein was produced in CHO cells and used to immunize mice; five hybridoma clones secreting C(epsilon)mX-specific mAbs were obtained.

RESULTS

Characterization of the mAbs using ELISA, immunoprecipitation, and immunoblotting methods showed that they could bind to both native and denatured forms of C(epsilon)mX. The mAbs exhibited mutual inhibition of binding to mIgE. Epitope mapping using synthetic peptides revealed that all five mAbs recognize the same epitope, RADWPGPP, located near the C-terminus of C(epsilon)mX. Binding of one of the mAbs to mIgE on SKO-007 cells induced the cross-linking of mIgE molecules on the cell surface, resulting in their patching and capping. In vitro functional analysis revealed that mAbs are able to cause complement-mediated cytotoxicity on transfectants expressing the Fc portion of mIgE.

CONCLUSION

We have prepared several human mIgE-specific mAbs. The potential of the mAbs on targeting mIgE+ B cells was demonstrated by CDC analysis.

New alternatively spliced form of galectin-3, a member of the beta-galactoside-binding animal lectin family, contains a predicted transmembrane-spanning domain and a leucine zipper motif

Osteoclasts or their precursors interact with the glycoprotein-enriched matrix of bone during extravasation from the vasculature, and upon attachment prior to resorption. Reverse transcriptase-PCR studies showed that two new alternatively spliced forms of chicken galectin-3, termed Gal-3TM1 and Gal-3TR1, were enriched and preferentially expressed in highly purified chicken osteoclast-like cells. Gal-3TM1 and Gal-3TR1 mRNA were also detected in chicken intestinal tissue, but not in kidney, liver, or lung. Gal-3TM1 and Gal-3TR1 messages both contain an open reading frame encoding a predicted 70-amino acid TM1 sequence inserted between the N-terminal Gly/Pro repeat domain and the carbohydrate recognition domain (exons 3 and 4). Gal-3TR1 mRNA contains an additional 241-bp sequence, which encodes a truncated open reading frame between the 4th and 5th exons, and, whose translation is expected to terminate within the carbohydrate recognition domain encompassing exons 4, 5, and 6. Immunoblotting and affinity chromatography showed that purified osteoclast preparations and intestinal homogenates contained a 36-kDa lactose-binding galectin. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analyses on chymotryptic peptides from the 36-kDa lectin confirmed its identity as Gal-3TM1. The TM1 insert contains a single transmembrane-spanning region and a leucine zipper-like stalk domain that is predicted to position the intact carbohydrate recognition domain of Gal-3TM1 on the exterior surface of the plasma membrane. Immunofluorescent staining of chicken osteoclasts confirmed the expression of Gal-3TM1 at the plasma membrane. Gal-3TM1 is the first example of a galectin superfamily member capable of being expressed as a soluble protein and as a transmembrane protein.

Craniopharyngioma: a case report and comparative galectin histochemical analysis

Craniopharyngioma is a rare benign tumour originating from Rathke's pouch. This paper reports a tumour case studied with a set of markers defining protein-carbohydrate recognition. Expression of endogenous lectins and their reactive glycoligands is under differentiation-dependent control in many cell types. These parameters can be related to the degree of cell differentiation in tumours. Therefore, the expression patterns of endogenous lectins, namely galectins-1, -3, and -7, in the craniopharyngioma case were determined. Galectins-1 and -3 were also used to reveal glycoconjugates in cells and extracellular matrices, an approach that has heretofore relied largely on plant lectins. The staining pattern of craniopharyngioma is compared with that of two other types of ectodermally derived tumours, namely basal and squamous cell carcinomas. Clusters of polygonal and flattened cells with morphological characteristics of differentiated cells in the craniopharyngioma and the majority of poorly differentiated cells in squamous cell carcinomas were reactive with galectin-3. No binding of this probe was observed in cells of basal cell carcinomas and the majority of craniopharyngioma cells. In view of the lack of accessible binding in the basal layer of normal squamous epithelia where proliferative cells (including stem cells) are located, galectin-3 binding could be used to distinguish basal from suprabasal cells of squamous epithelial cells.