Galectins structure and function--a synopsis

"Outcome of non-surgical periodontal treatment on Gal-1 and Gal-3 GCF levels in periodontitis patients: a case-control study"

OBJECTIVES

This study aimed to explore the effect of nonsurgical periodontal treatment on Galectin-1 and -3 GCF levels in gingivitis and periodontitis stage III compared to periodontally healthy individuals, to determine whether they could serve as diagnostic markers / therapeutic targets for periodontitis and revealing their possible role in periodontal disease.

MATERIALS AND METHODS

Forty-five systemically healthy participants were included and equally subdivided into three groups: gingivitis, periodontitis (stage III), and a periodontally healthy control group. The clinical parameters were recorded. Galectin-1 and -3 GCF levels were evaluated (before and after non-surgical treatment for periodontitis) using an enzyme linked immune-sorbent assay (ELISA) kit. Receiver operating characteristic (ROC) curve was performed to reveal sensitivity, specificity, predictive value, and diagnostic accuracy of both markers.

RESULTS

The study showed statistical significance between different groups regarding Galectin-3 with higher values in periodontitis and the lowest values in healthy control. Also, Galectin-1 was significantly higher in the periodontitis/gingivitis groups than in the control group. Moreover, non-surgical periodontal treatment in periodontitis patients caused a statistical reduction in clinical parameters and biomarkers. ROC analysis revealed excellent diagnostic ability of both biomarkers in discriminating periodontitis/gingivitis against healthy individuals (100% diagnostic accuracy for Galectin-1 and 93% for Galectin-3, AUC > 0.9) and acceptable diagnostic ability between periodontitis participants against gingivitis (73% diagnostic accuracy for Gal-1 and 80% for Gal-3, AUC > 0.7).

CONCLUSIONS

Both Galectin-1 and Galectin-3 seem to have outstanding diagnostic accuracy for the identification of periodontal disease, an acceptable ability to measure periodontal disease activity and the severity of inflammatory status. Additionally, they could serve as therapeutic targets to monitor treatment efficiency.

CLINICALTRIAL

GOV REGISTRATION NUMBER: (NCT06038812).

Heterologous Interactions with Galectins and Chemokines and Their Functional Consequences

Extra- and intra-cellular activity occurs under the direction of numerous inter-molecular interactions, and in any tissue or cell, molecules are densely packed, thus promoting those molecular interactions. Galectins and chemokines, the focus of this review, are small, protein effector molecules that mediate various cellular functions-in particular, cell adhesion and migration-as well as cell signaling/activation. In the past, researchers have reported that combinations of these (and other) effector molecules act separately, yet sometimes in concert, but nevertheless physically apart and via their individual cell receptors. This view that each effector molecule functions independently of the other limits our thinking about functional versatility and cooperation, and, in turn, ignores the prospect of physiologically important inter-molecular interactions, especially when both molecules are present or co-expressed in the same cellular environment. This review is focused on such protein-protein interactions with chemokines and galectins, the homo- and hetero-oligomeric structures that they can form, and the functional consequences of those paired interactions.

Galectins: Important Regulators in Normal and Pathologic Pregnancies

Galectins (Gal) are characterized by their affinity for galactoside structures on glycoconjugates. This relationship is mediated by carbohydrate recognition domains, which are multifunctional regulators of basic cellular biological processes with high structural similarity among family members. They participate in both innate and adaptive immune responses, as well as in reproductive immunology. Recently, the discovery that galectins are highly expressed at the maternal–fetal interface has garnerd the interest of experts in human reproduction. Galectins are involved in a variety of functions such as maternal–fetal immune tolerance, angiogenesis, trophoblast invasion and placental development and are considered to be important mediators of successful embryo implantation and during pregnancy. Dysregulation of these galectins is associated with abnormal and pathological pregnancies (e.g., preeclampsia, gestational diabetes mellitus, fetal growth restriction, preterm birth). Our work reviews the regulatory mechanisms of galectins in normal and pathological pregnancies and has implications for clinicians in the prevention, diagnosis and treatment of pregnancy-related diseases.

Human galectin-1 and galectin-3 promote Tropheryma whipplei infection

Tropheryma whipplei, is an actinobacterium that causes different infections in humans, including Whipple's disease. The bacterium infects and replicates in macrophages, leading to a Th2-biased immune response. Previous studies have shown that T. whipplei harbors complex surface glycoproteins with evidence of sialylation. However, the exact contribution of these glycoproteins for infection and survival remains obscure. To address this, we characterized the bacterial glycoprofile and evaluated the involvement of human β-galactoside-binding lectins, Galectin-1 (Gal-1) and Galectin-3 (Gal-3) which are highly expressed by macrophages as receptors for bacterial glycans. Tropheryma whipplei glycoproteins harbor different sugars including glucose, mannose, fucose, β-galactose and sialic acid. Mass spectrometry identification revealed that these glycoproteins were membrane- and virulence-associated glycoproteins. Most of these glycoproteins are highly sialylated and N-glycosylated while some of them are rich in poly-N-acetyllactosamine (Poly-LAcNAc) and bind Gal-1 and Gal-3. In vitro, T. whipplei modulates the expression and cellular distribution of Gal-1 and Gal-3. Although both galectins promote T. whipplei infection by enhancing bacterial cell entry, only Gal-3 is required for optimal bacterial uptake. Finally, we found that serum levels of Gal-1 and Gal-3 were altered in patients with T. whipplei infections as compared to healthy individuals, suggesting that galectins are also involved in vivo. Among T. whipplei membrane-associated proteins, poly-LacNAc rich-glycoproteins promote infection through interaction with galectins. T. whipplei modulates the expression of Gal-1 and Gal-3 both in vitro and in vivo. Drugs interfering with galectin-glycan interactions may provide new avenues for the treatment and diagnosis of T. whipplei infections.

Galectin-3, Possible Role in Pathogenesis of Periodontal Diseases and Potential Therapeutic Target

Periodontal diseases are chronic inflammatory diseases that occur due to the imbalance between microbial communities in the oral cavity and the immune response of the host that lead to destruction of tooth supporting structures and finally to alveolar bone loss. Galectin-3 is a β-galactoside-binding lectin with important roles in numerous biological processes. By direct binding to microbes and modulation of their clearence, Galectin-3 can affect the composition of microbial community in the oral cavity. Galectin-3 also modulates the function of many immune cells in the gingiva and gingival sulcus and thus can affect immune homeostasis. Few clinical studies demonstrated increased expression of Galectin-3 in different forms of periodontal diseases. Therefore, the objective of this mini review is to discuss the possible effects of Galectin-3 on the process of immune homeostasis and the balance between oral microbial community and host response and to provide insights into the potential therapeutic targeting of Gal-3 in periodontal disease.

Utilization of Galectins by Pathogens for Infection

Galectins are glycan-binding proteins which are expressed by many different cell types and secreted extracellularly. These molecules are well-known regulators of immune responses and involved in a broad range of cellular and pathophysiological functions. During infections, host galectins can either avoid or facilitate infections by interacting with host cells- and/or pathogen-derived glycoconjugates and less commonly, with proteins. Some pathogens also express self-produced galectins to interfere with host immune responses. This review summarizes pathogens which take advantage of host- or pathogen-produced galectins to establish the infection.

Characterization and functional study of Galectin3 from Japanese flounder (Paralichthys olivaceus)

Galectins belong to the β-galactoside binding protein family and participate in both innate and acquired immunity. In this study, we described the molecular characteristics of Galectin3 gene from Japanese flounder (Paralichthys olivaceus), designed as PoGalectin3. Its open reading frame was 1128 bp, encoding a protein composed of 375 amino acids. PoGalectin3 belongs to chimeric galactose agglutinin, which contains a C-terminal carbohydrate recognition domain (CRD) (L₂₅₀-P₃₇₂), and its N-terminal is rich in proline (P) and glycine (G). Multiple sequence alignment and phylogenetic tree showed that PoGalectin3 was conservative in different aquatic animals. Tissue distribution confirmed that PoGalectin3 showed significantly highest expression in brain, moderate expression in liver, intestine and muscle. PoGalectin3 was significantly increased post infection with Edwardsiella tarda from intestine tissue of P. olivaceus. In order to investigate the binding ability of PoGalectin3 to pathogen-associated molecular patterns, the recombinant PoGalectin3 protein (rPoGalectin3) was successfully expressed and purified, and an Enzyme linked immunosorbent assay (ELISA) experiment was performed. ELISA refers to the qualitative and quantitative detection method of immune response by combining soluble antigen or antibody with solid-phase carrier. It was confirmed that rPoGalectin3 exhibited high affinity to lipopolysaccharide and peptidoglycan. The rPoGalectin3 also exhibited a concentration dependent binding capacity with Gram-positive bacteria (Bacillus pumilus, Bacillus subtilis, Bacillus cereus) and Gram-negative bacteria (Aeromonas salmonicida, E. tarda, Vibrio vulnificus). In addition, the results of microbial agglutination experiment showed that rPoGalectin3 could agglutinate Gram-positive bacteria (B. pumilus, B. subtilis) and Gram-negative bacteria (A. salmonicida, E. tarda) in the presence of Ca²⁺. In conclusion, this research laid an important foundation for the specific function analysis of PoGalectin3, which provide theoretical basis for the prevention and control of aquatic diseases.

Charcot-Leyden crystal protein/galectin-10 interacts with cationic ribonucleases and is required for eosinophil granulogenesis

BACKGROUND

The human eosinophil Charcot-Leyden crystal (CLC) protein is a member of the Galectin superfamily and is also known as galectin-10 (Gal-10). CLC/Gal-10 forms the distinctive hexagonal bipyramidal crystals that are considered hallmarks of eosinophil participation in allergic responses and related inflammatory reactions; however, the glycan-containing ligands of CLC/Gal-10, its cellular function(s), and its role(s) in allergic diseases are unknown.

OBJECTIVE

We sought to determine the binding partners of CLC/Gal-10 and elucidate its role in eosinophil biology.

METHODS

Intracellular binding partners were determined by ligand blotting with CLC/Gal-10, followed by coimmunoprecipitation and coaffinity purifications. The role of CLC/Gal-10 in eosinophil function was determined by using enzyme activity assays, confocal microscopy, and short hairpin RNA knockout of CLC/Gal-10 expression in human CD34⁺ cord blood hematopoietic progenitors differentiated to eosinophils.

RESULTS

CLC/Gal-10 interacts with both human eosinophil granule cationic ribonucleases (RNases), namely, eosinophil-derived neurotoxin (RNS2) and eosinophil cationic protein (RNS3), and with murine eosinophil-associated RNases. The interaction is independent of glycosylation and is not inhibitory toward endoRNase activity. Activation of eosinophils with INF-γ induces the rapid colocalization of CLC/Gal-10 with eosinophil-derived neurotoxin/RNS2 and CD63. Short hairpin RNA knockdown of CLC/Gal-10 in human cord blood-derived CD34⁺ progenitor cells impairs eosinophil granulogenesis.

CONCLUSIONS

CLC/Gal-10 functions as a carrier for the sequestration and vesicular transport of the potent eosinophil granule cationic RNases during both differentiation and degranulation, enabling their intracellular packaging and extracellular functions in allergic inflammation.

The Role of Galectins in Cervical Cancer Biology and Progression

Cervical cancer is one of the malignant tumors with high incidence and high mortality among women in developing countries. The main factors affecting the prognosis of cervical cancer are the late recurrence and metastasis and the effective adjuvant treatment, which is radiation and chemotherapy or combination therapy. Galectins, a family containing many carbohydrate binding proteins, are closely involved in the occurrence and development of tumor. They are involved in tumor cells transformation, angiogenesis, metastasis, immune escape, and sensitivity against radiation and chemotherapy. Therefore, galectins are deemed as the targets of multifunctional cancer treatment. In this review, we mainly focus on the role of galectins, especially galectin-1, galectin-3, galectin-7, and galectin-9 in cervical cancer, and provide theoretical basis for potential targeted treatment of cervical cancer.

Galectins as Molecular Targets for Therapeutic Intervention

Galectins are a family of small, highly conserved, molecular effectors that mediate various biological processes, including chemotaxis and angiogenesis, and that function by interacting with various cell surface glycoconjugates, usually targeting β-galactoside epitopes. Because of their significant involvement in various biological functions and pathologies, galectins have become a focus of therapeutic discovery for clinical intervention against cancer, among other pathological disorders. In this review, we focus on understanding galectin structure-function relationships, their mechanisms of action on the molecular level, and targeting them for therapeutic intervention against cancer.

Different expression patterns of LGALS1 and LGALS3 in polycythemia vera, essential thrombocythemia and primary myelofibrosis

Despite all the knowledge, the cellular and molecular mechanisms involved in myeloproliferative neoplasm (MPN) pathophysiology remain unclear. Authors have shown galectin-1 (Gal-1) and 3 playing roles in tumour angiogenesis and fibrosis, which were correlated with poor prognosis in patients with MPN. In the present study LGALS1 and LGALS3 were differently expressed between polycythemia vera, essential thrombocythemia (ET) and primary myelofibrosis (PMF) diseases. Increased LGALS3 expression was associated with a negative JAK2 V617F status mutation in leucocytes from PMF but not in patients with ET without this mutation. However, a positive Janus kinase 2 (JAK2) V617F cell line established from patients with ET (SET-2 cells) when treated with JAK inhibitor presented high levels of LGALS3. Additionally, high LGALS1 expression was found in CD34(+) cells but not in leucocytes from patients with PMF, in absence of JAK2 V617F mutation, and also in SET-2 cells treated with JAK inhibitor. Thus, our findings indicate that differential expression of LGALS1 and/or LGALS3 in patients with MPN is linked with JAK2 V617F status mutation in these diseases and state of cell differentiation.

The Differential Expression of Galectin-1 and Galectin-3 in Normal Lymphoid Tissue and Non-Hodgkin's and Hodgkin's Lymphomas

The WHO classification of lymphomas was established on the basis of clinical, morphological, immunohistochemical and genetic criteria. However, each entity displays its own spectrum of clinical aggressiveness. Treatment success varies widely and is not predictable. Since galectins are involved in oncogenesis and the physiology of immune cells, we investigated whether galectin-1 and galectin-3 immunohistochemical expression could differ in 25 normal lymphoid tissues, 42 non-Hodgkin's and 14 Hodgkin's lymphomas. Immunohistochemical galectin expression was submitted to semi-quantitative and quantitative (computer-assisted microscopy) evaluations. This study is completed by an analysis (by means of quantitative RT-PCR) of galectin-3 mRNA expression in 3 normal lymph nodes, 3 follicular lymphomas (FLs) and 3 diffuse large B-cell lymphomas (DLBCLs). The data show that in normal lymphoid tissue, lymphocytes do not express galectin-1 and rarely express galectin-3. In contrast, galectin-3 was expressed in 8 of the 16 DLBCL cases and in 1 of the 8 FL cases. Furthermore, galectin-3 mRNA was expressed 3-times more in the DLBCLs than in the FLs. While the blood vessel walls of the lymphomas expressed galectin-1, the vessel walls of normal lymphoid tissues did not. This expression of galectin-1 in blood vessel walls was correlated with vascular density. The present study thus shows that DLBCL can be distinguished from normal lymphoid tissue and other lymphomas on the basis of galectin-3 expression.

Platelets and galectins

A major function of platelets is keeping the vascular system intact. Platelet activation at sites of vascular injury leads to the formation of a hemostatic plug. Activation of platelets is therefore crucial for normal hemostasis; however, uncontrolled platelet activation may also lead to the formation of occlusive thrombi that can cause ischemic events. Although they are essential for proper hemostasis, platelet function extends to physiologic processes such as tissue repair, wound remodeling and antimicrobial host defense, or pathologic conditions such as thrombosis, atherosclerosis, chronic inflammatory diseases and cancer. Platelets can be activated by soluble molecules including thrombin, thromboxane A2 (TXA2), adenosine diphosphate (ADP), serotonin or by adhesive extracellular matrix (ECM) proteins such as von Willebrand factor (vWF) and collagen. Here we describe recent advances in the activation of platelets by non-canonical platelet agonists such as galectins. By acting either in soluble or immobilized form, these glycan-binding proteins trigger all platelet activation responses through modulation of discrete signaling pathways. We also offer new hypotheses and some speculations about the role of platelet-galectin interactions not only in hemostasis and thrombosis but also in inflammation and related diseases such as atherosclerosis and cancer.

Galectin-1 and Galectin-3 mRNA expression in renal cell carcinoma

Background

Galectins are known to regulate cell differentiation and growth as well as cell adhesion and apoptosis. Galectins have been discussed as possible prognosticators for survival in renal cell cancer (RCC) and other urological tumors. They might also play an emerging role as possible new marker-proteins for RCC. In this study, we analyzed the expression of galectin-1 and galectin-3 mRNA in order to further investigate their clinical significance in RCC.

Methods

Tissue samples were obtained from 106 patients undergoing surgery for RCC. The expression of galectin-1 and galectin-3 mRNA in normal kidney and corresponding cancer tissue was analyzed using quantitative real time PCR. Differences in expression levels of paired tissue samples were assessed using paired two-sample tests. Associations of relative mRNA expression levels in tumor tissues with clinical findings were analyzed using univariate logistic regression.

Results

The expression of galectin-1 (p < 0.001) and -3 (p < 0.001) mRNA were significantly higher in RCC when compared to the adjacent normal kidney tissue. For clear cell RCC, an association of male gender with higher galectin-1 and galectin-3 mRNA expression (p = 0.054, p = 0.034) was detected. For all RCCs, galectin-1 mRNA expression failed to show a significant association with advanced disease as well as a higher rate of lymph node metastases (p = 0.058, p = 0.059).

Conclusion

The mRNA expression of galectin-1 and galectin-3 is significantly increased in RCC cancer tissue. The higher mRNA expression in tumor tissue of male patients raises the question of a functional connection between galectins and the higher prevalence of RCC in men. Associations with advanced disease might lead to new ways of identifying patients at higher risk of recurrent disease and might even facilitate early metastasectomy with curative intent.

Vascular galectins: regulators of tumor progression and targets for cancer therapy

Galectins are a family of carbohydrate binding proteins with a broad range of cytokine and growth factor-like functions in multiple steps of cancer progression. They contribute to tumor cell transformation, promote tumor angiogenesis, hamper the anti-tumor immune response, and facilitate tumor metastasis. Consequently, galectins are considered as multifunctional targets for cancer therapy. Interestingly, many of the functions related to tumor progression can be linked to galectins expressed by endothelial cells in the tumor vascular bed. Since the tumor vasculature is an easily accessible target for cancer therapy, understanding how galectins in the tumor endothelium influence cancer progression is important for the translational development of galectin-targeting therapies.

Eosinophil-expressed galectin-3 regulates cell trafficking and migration

Galectin-3 (Gal-3), a β galactoside-binding lectin, is implicated in the pathogenesis of allergic airway inflammation and allergen-challenged mice deficient in Gal-3 (Gal-3(-/-)) exhibit decreased airway recruitment of eosinophils (Eos). Gal-3 is expressed and secreted by several cell types and can thus function extracellularly and intracellularly to regulate a variety of cellular responses. We sought to determine the role of Eos-expressed Gal-3 in promoting Eos trafficking and migration in the context of allergic airway inflammation using bone marrow (BM)-derived Eos from wild-type (WT) and Gal-3(-/-) mice. Airway recruitment of Eos in acute (4 weeks) and chronic (8-12 weeks) allergen-challenged WT mice correlated with Gal-3 expression in the lungs. BM-derived Eos were found to express Gal-3 on the cell surface and secrete soluble Gal-3 when exposed to eotaxin-1. Compared to WT Eos, Gal-3(-/-) Eos exhibited significantly reduced rolling on vascular cell adhesion molecule 1 (VCAM-1) and decreased stable adhesion on intercellular adhesion molecule 1 (ICAM-1) under conditions of flow in vitro. Evaluation of cytoskeletal rearrangement demonstrated that relatively fewer adherent Gal-3(-/-) Eos undergo cell spreading and formation of membrane protrusions. In addition, cell surface expression of integrin receptor αM (CD11b) was lower in Gal-3(-/-) Eos, which is likely to account for their altered adhesive interactions with VCAM-1 and ICAM-1. Gal-3(-/-) Eos also exhibited significantly decreased migration toward eotaxin-1 compared to WT Eos irrespective of similar levels of CCR3 expression. Further, eotaxin-induced migration of WT Eos remained unaffected in the presence of lactose, suggesting a role for intracellular Gal-3 in regulating Eos migration. Overall, our findings indicate that Gal-3 expression in the lungs correlates with Eos mobilization during allergic airway inflammation and signaling involving intracellular Gal-3 and/or secreted Gal-3 bound to the cell surface of Eos appears to be essential for Eos trafficking under flow as well as for migration.

Neural stem cells, adult neurogenesis, and galectin-1: from bench to bedside

Neural stem cells (NSCs) in the adult brain have been a consistent focus of biomedical research largely because of their potential clinical application. To fully exploit this potential, the molecular mechanisms that regulate NSCs must be clarified. Several lines of evidence show that a multifunctional protein, Galectin-1, is expressed and has a functional role in a subset of adult NSCs. Researchers, including our group, have explored the physiological role of Galectin-1 in NSCs and its application in the treatment of animal models of neurological disorders such as brain ischemia and spinal cord injury. Here, we summarize what is currently known regarding the role of Galectin-1 in adult NSCs. Furthermore, we discuss current issues in researching the role of Galectin-1 in adult NSCs under both physiological and pathological conditions.

Novel role for galectin-8 protein as mediator of coagulation factor V endocytosis by megakaryocytes

Galectin-8 (Gal8) interacts with β-galactoside-containing glycoproteins and has recently been implicated to play a role in platelet activation. It has been suggested that Gal8 may also interact with platelet coagulation factor V (FV). This indispensable cofactor is stored in α-granules of platelets via a poorly understood endocytic mechanism that only exists in megakaryocytes (platelet precursor cells). In this study, we now assessed the putative role of Gal8 for FV biology. Surface plasmon resonance analysis and a solid phase binding assay revealed that Gal8 binds FV. The data further show that β-galactosides block the interaction between FV and Gal8. These findings indicate that Gal8 specifically interacts with FV in a carbohydrate-dependent manner. Confocal microscopy studies and flow cytometry analysis demonstrated that megakaryocytic DAMI cells internalize FV. Flow cytometry showed that these cells express Gal8 on their cell surface. Reducing the functional presence of Gal8 on the cells either by an anti-Gal8 antibody or by siRNA technology markedly impaired the endocytic uptake of FV. Compatible with the apparent role of Gal8 for FV uptake, endocytosis of FV was also affected in the presence of β-galactosides. Strikingly, thrombopoietin-differentiated DAMI cells, which represent a more mature megakaryocytic state, not only lose the capacity to express cell-surface bound Gal8 but also lose the ability to internalize FV. Collectively, our data reveal a novel role for the tandem repeat Gal8 in promoting FV endocytosis.

Proteomic analyses of the Xiphophorus Gordon-Kosswig melanoma model

Interspecies hybridization between the platyfish X. maculatus Jp 163 A, and the swordtail X. helleri (Sarabia), generates F(1) hybrids with pronounced melanin pigmentation. Backcrossing of F(1) hybrids with the X. helleri parent results in 25% of progeny that will spontaneously develop melanoma. We have applied proteomic methods to this Gordon-Kosswig (G-K) melanoma model to identify candidate proteins that exhibit modulated expression in fin tissue due to interspecies hybridization and progression of hybrid tissues to spontaneous melanoma. Difference Gel Electrophoresis (DIGE) was used to minimize the variability commonly observed in quantitative analyses of comparative protein samples. Following identification of up- or down-regulated protein expression by DIGE, candidate protein spots were identified by mass spectrometric sequencing. Several protein expression differences displayed in interspecies hybrids were identified and compared to distinct differences that occur upon backcrossing and progression to melanoma. These studies are important for the identification of distinct biochemical pathways involved in the variety of Xiphophorus interspecies hybrid tumor models.

Galectin-1 and immunotherapy for brain cancer

The prognosis of patients diagnosed with high-grade glioma continues to be dismal in spite of multimodal treatment. Active specific immunotherapy by means of dendritic cell vaccination is considered to be a new promising concept that aims at generating an anti-tumoral immune response. However, it is now widely accepted that the success of immunotherapeutic strategies to promote tumor regression will rely not only on enhancing the effector arm of the immune response but also on downregulation of the counteracting tolerogenic signals. In this article, we summarize evidence that galectin-1, an evolutionarily conserved glycan-binding protein that is abundantly expressed in high-grade glioma, is an important player in glioma-mediated immune escape.

D-(+)-galactose-conjugated single-walled carbon nanotubes as new chemical probes for electrochemical biosensors for the cancer marker galectin-3

d-(+)-Galactose-conjugated single-walled carbon nanotubes (SWCNTs) were synthesized for use as biosensors to detect the cancer marker galectin-3. To investigate the binding of galectin-3 to the d-(+)-galactose-conjugated SWCNTs, an electrochemical biosensor was fabricated by using molybdenum electrodes. The binding affinities of the conjugated SWCNTs to galectin-3 were quantified using electrochemical sensitivity measurements based on the differences in resistance together with typical I-V characterization. The electrochemical sensitivity measurements of the d-(+)-galactose-conjugated SWCNTs differed significantly between the samples with and without galectin-3. This indicates that d-(+)-galactose-conjugated SWCNTs are potentially useful electrochemical biosensors for the detection of cancer marker galectin-3.

Human platelets express and are activated by galectin-8

Gals (galectins) are proteins with glycan affinity that are emerging as mediators of atherosclerosis. Despite the similarities in structure and sequence, different Gals exert distinct effects on their target cells. We have shown that Gal-1 triggers platelet activation, suggesting a role for Gals in thrombus formation. Since Gal-8 is expressed upon endothelial activation and also contributes to inflammation, to understand further the role of these lectins in haemostasis, we evaluated the effect of Gal-8 on human platelets. Gal-8 bound specific glycans in the platelet membrane and triggered spreading, calcium mobilization and fibrinogen binding. It also promoted aggregation, thromboxane generation, P-selectin expression and granule secretion. GP (glycoprotein) αIIb and Ib-V were identified as putative Gal-8 counter-receptors by MS. Studies performed using platelets from Glanzmann's thromboasthenia and Bernard-Soulier syndrome patients confirmed that GPIb is essential for transducing Gal-8 signalling. Accordingly, Src, PLC2γ (phospholipase C2γ), ERK (extracellular-signal-regulated kinase) and PI3K (phosphoinositide 3-kinase)/Akt downstream molecules were involved in the Gal-8 signalling pathway. Gal-8 fragments containing either the N- or C-terminal carbohydrate-recognition domains showed that activation is exerted through the N-terminus. Western blotting and cytometry showed that platelets not only contain Gal-8, but also expose Gal-8 after thrombin activation. These findings reveal Gal-8 as a potent platelet activator, supporting a role for this lectin in thrombosis and inflammation.

Human galectin-3 interacts with two anticancer drugs

Human galectin-3 (hGal-3) is a mammalian lectin involved in regulation of RNA splicing, apoptosis, cell differentiation, and proliferation. Multimerized extracellular hGal-3 is thought to crosslink cells by binding to glycoproteins and glycosylated cancer antigens on the cell surface or extracellular matrix. Fluorescence spectroscopy and circular dichroism were used to study the interaction of hGal-3 with two anticancer agents: bohemine and Zn porphyrin (ZnTPPS(4)). The dissociation constant (k(D)) for binding of bohemine with hGal-3 was k(D) 0.23+/-0.05 microM. The hyperbolic titration curve indicated the presence of a single bohemine binding site. The binding of ZnTPPS(4) to hGal-3 (with and without lactose) is of high affinity having k(D)=0.18-0.20 microM and is not inhibited by lactose, indicating that ZnTPPS(4) and carbohydrate bind different sites. Circular dichroism spectra of the hGal-3 complexes suggested that the binding of the hydrophobic compounds changed the hGal-3 secondary structure. In summary, we show that two compounds with anticancer activity, bohemine and ZnTPPS(4), have high affinity for hGal-3 at a site that is distinct from its carbohydrate site. Since hGal-3 binds to several carbohydrate cancer antigens, the results suggest that it may have utility in the targeted delivery of drugs for cancer.

[Galectin expression in urological cancer. Diagnostic, prognostic and therapeutic potential]

Galectins are a family of 15 proteins. They interact with glycoproteins in both the extracellular and intracellular milieu and regulate various biological cycles including cell growth, cell differentiation, cell adhesion and apoptosis. In biomolecular studies certain patterns of expression showed a correlation with metastasis and apoptosis. Therefore, galectins could be used as potential markers for early tumour recognition, long-term prognosis and a better-founded choice of therapy. Acknowledging these possibilities this review points out the standing of galectins with all currently available data in the development and progression of renal, bladder and prostatic tumours. The expression patterns of galectin-1 and -3 have been researched extensively. For example, several studies could show a decreased expression of galectin-3 in clear renal cell carcinoma, which correlated with a poor clinical prognosis. On the contrary, patients with a bladder tumour showed an elevated serum level of galectin-3. Furthermore, in analysis of prostatic tumour tissue galectin-1 was found to be an independent predictor of a PSA relapse. In addition, pathological patterns of galectin expression could be detected in non-urological malignancies such as breast cancer. Though all findings indicate a future significance of galectins as markers of urological malignancies with clinical relevance, more research will be necessary to particularly assess the evolutional-dependent function of galectins in the process of tumourigenesis.

Lactose binding to galectin-1 modulates structural dynamics, increases conformational entropy, and occurs with apparent negative cooperativity

Galectins are a family of lectins with a conserved carbohydrate recognition domain that interacts with beta-galactosides. By binding cell surface glycoconjugates, galectin-1 (gal-1) is involved in cell adhesion and migration processes and is an important regulator of tumor angiogenesis. Here, we used heteronuclear NMR spectroscopy and molecular modeling to investigate lactose binding to gal-1 and to derive solution NMR structures of gal-1 in the lactose-bound and unbound states. Structure analysis shows that the beta-strands and loops around the lactose binding site, which are more open and dynamic in the unbound state, fold in around the bound lactose molecule, dampening internal motions at that site and increasing motions elsewhere throughout the protein to contribute entropically to the binding free energy. CD data support the view of an overall more open structure in the lactose-bound state. Analysis of heteronuclear single quantum coherence titration binding data indicates that lactose binds the two carbohydrate recognition domains of the gal-1 dimer with negative cooperativity, in that the first lactose molecule binds more strongly (K(1)=21+/-6 x 10(3) M(-1)) than the second (K(2)=4+/-2 x 10(3) M(-1)). Isothermal calorimetry data fit using a sequential binding model present a similar picture, yielding K(1)=20+/-10 x 10(3) M(-1) and K(2)=1.67+/-0.07 x 10(3) M(-1). Molecular dynamics simulations provide insight into structural dynamics of the half-loaded lactose state and, together with NMR data, suggest that lactose binding at one site transmits a signal through the beta-sandwich and loops to the second binding site. Overall, our results provide new insight into gal-1 structure-function relationships and to protein-carbohydrate interactions in general.

Galectins and gliomas

Malignant gliomas, especially glioblastomas, are associated with a dismal prognosis. Despite advances in diagnosis and treatment, glioblastoma patients still have a median survival expectancy of only 14 months. This poor prognosis can be at least partly explained by the fact that glioma cells diffusely infiltrate the brain parenchyma and exhibit decreased levels of apoptosis, and thus resistance to cytotoxic drugs. Galectins are a family of mammalian beta-galactoside-binding proteins characterized by a shared characteristic amino acid sequence. They are expressed differentially in normal vs. neoplastic tissues and are known to play important roles in several biological processes such as cell proliferation, death and migration. This review focuses on the role played by galectins, especially galectin-1 and galectin-3, in glioma biology. The involvement of these galectins in different steps of glioma malignant progression such as migration, angiogenesis or chemoresistance makes them potentially good targets for the development of new drugs to combat these malignant tumors.

1H, 13C, and 15N backbone and side-chain chemical shift assignments for the 29 kDa human galectin-1 protein dimer

Galectin-1 is an important regulator of leukocyte function and tumor angiogenesis. Recently, this lectin has been identified as a molecular target for the potent angiogenesis inhibitor anginex. Here, we report (1)H, (13)C, and (15)N chemical shift assignments for human galectin-1 as determined by using heteronuclear triple resonance NMR spectroscopy.

Evaluation of galectin-8 expression in thyroid tumors

The expression of galectin-8 (gal-8) has been shown to be altered during neoplastic transformation of certain cell types. This is the first study aimed to analyze the expression of this protein in normal and pathological human thyroid tissue. A total of 41 archival thyroid tissue samples (5 follicular adenomas, 31 papillary carcinomas, 5 follicular carcinomas) together with 36 adjacent hyperplastic or normal thyroid tissues were analyzed by immunohistochemistry. Galectin-8 was expressed in the majority of papillary carcinomas (27/31; 87%). Positive but weaker staining was also found in some of the follicular thyroid carcinomas (2/5; 40%) and adenomas (2/5; 40%). This protein was not detectable in five normal thyroid tissue samples, whereas hyperplastic areas adjacent to tumor were weakly positive in 9 out of 31 cases (29%). High gal-8 immunostaining in papillary thyroid carcinoma indicates that gal-8 may potentially serve as a marker of papillary thyroid carcinoma. However, it does not seem to be helpful in the differential diagnostics of follicular carcinoma and adenoma. Further studies are required to determine biological functions and molecular mechanisms underlying the increased expression of gal-8 protein in thyroid lesions, particularly, in papillary thyroid carcinoma.

Galectins in the tumor endothelium: opportunities for combined cancer therapy

Galectins are emerging as a family of proteins that play an important role in several steps of tumorigenesis. Evidence is accumulating that galectins are expressed by the tumor endothelium, where they contribute to different steps of tumor progression such as immune escape and metastasis. Recent studies have identified an important role for galectins in tumor angiogenesis. Moreover, it has been shown that galectins in the endothelium can be targeted for therapeutic applications. This opens a window of opportunity for the development of tumor-type independent treatment strategies. This review focuses on the expression of galectins in the tumor endothelium, their contribution to tumor progression, and their application in tumor-type independent cancer therapy.

Human galectin-1, -2, and -4 induce surface exposure of phosphatidylserine in activated human neutrophils but not in activated T cells

Cellular turnover is associated with exposure of surface phosphatidylserine (PS) in apoptotic cells, leading to their phagocytic recognition and removal. But recent studies indicate that surface PS exposure is not always associated with apoptosis. Here we show that several members of the human galectin family of glycan binding proteins (galectins-1, -2, and -4) induce PS exposure in a carbohydrate-dependent fashion in activated, but not resting, human neutrophils and in several leukocyte cell lines. PS exposure is not associated with apoptosis in activated neutrophils. The exposure of PS in cell lines treated with these galectins is sustained and does not affect cell viability. Unexpectedly, these galectins bind well to activated T lymphocytes, but do not induce either PS exposure or apoptosis, indicating that galectin's effects are cell specific. These results suggest novel immunoregulatory contribution of galectins in regulating leukocyte turnover independently of apoptosis.

A carbohydrate-binding protein, Galectin-1, promotes proliferation of adult neural stem cells

In the subventricular zone of the adult mammalian forebrain, neural stem cells (NSCs) reside and proliferate to generate young neurons. We screened factors that promoted the proliferation of NSCs in vitro by a recently developed proteomics technique, the ProteinChip system. In this screen, we identified a soluble carbohydrate-binding protein, Galectin-1, as a candidate. We show herein that Galectin-1 is expressed in a subset of slowly dividing subventricular zone astrocytes, which includes the NSCs. Based on results from intraventricular infusion experiments and phenotypic analyses of knockout mice, we demonstrate that Galectin-1 is an endogenous factor that promotes the proliferation of NSCs in the adult brain.

Expanding the protein catalogue in the proteome reference map of human breast cancer cells

In this report we present a catalogue of 162 proteins (including isoforms and variants) identified in a prototype of proteomic map of breast cancer cells. This work represents the prosecution of previous studies describing the protein complement of breast cancer cells of the line 8701-BC, which has been well characterized for several parameters, providing to be a useful model for the study of breast cancer-associated candidate biomarkers. In particular, 110 spots were identified ex novo by PMF, or validated following previous gel matching identification method; 30 were identified by N-terminal microsequencing and the remaining by gel matching with maps available from our former work. As a consequence of the expanded number of proteins, we have updated our previous classification extending the number of protein groups from 4 to 13. In order to facilitate comparative proteome studies of different kinds of breast cancers, in this report we provide the whole complement of proteins so far identified and grouped into the new classification. A consistent number of them were not described before in other proteomic maps of breast cancer cells or tissues, and therefore they represent a valuable contribution for breast cancer protein databases and for future application in basic and clinical researches.

Galectin-3 expression in papillary thyroid carcinoma: relation to histomorphologic growth pattern, lymph node metastasis, extrathyroid invasion, and tumor size

BACKGROUND

Galectin-3 has been recently recognized as a promising presurgical marker of thyroid malignancy.

METHODS

Galectin-3 expression was examined immunohistochemically in 202 specimens of papillary thyroid carcinoma (PTC) in relation to histomorphologic subtypes and clinicopathologic data. RESULTS.: The sensitivity of galectin-3 immunostaining versus conventional histology was 98% (100 of 102) for classical PTC, 85.2% (46 of 54) for follicular variant, and 50% (23 of 46) for follicular/solid variant of PTC. All cases (n = 36) involving lymph node metastases and 42 of 45 cases with extrathyroid invasion expressed galectin-3. However, among the galectin-3-positive cases (n = 169), 133 were without lymph node metastases, and 127 were without extrathyroid invasion. Galectin-3 expression was not related to the size of intrathyroid PTC.

CONCLUSIONS

Galectin-3 immunohistochemical expression itself is not an indicator of local metastatic spread or extrathyroid invasion of PTC, thus being irrelevant clinically from this aspect. Galectin-3 is an excellent marker for classical PTC but must be used with caution in diagnosing unconventional variants of PTC because of the possibility of false-negative results.

Galectin-3 expression in papillary microcarcinoma of the thyroid

AIMS

Galectin-3 is a beta-galactoside binding protein, recently recognized as a promising molecular marker of thyroid malignancy. As reported in several studies, galectin-3 is highly expressed in papillary thyroid carcinoma, but its expression has not been investigated in papillary microcarcinoma, which is a variant of papillary thyroid carcinoma.

METHODS AND RESULTS

Using a monoclonal antibody to galectin-3 and the avidin-biotin-peroxidase complex (ABC) immunohistochemical technique, we analysed galectin-3 expression in 63 cases of papillary microcarcinoma. The results showed immunohistochemical reactivity for galectin-3 in 51 (80.9%) cases. Intensity of staining varied from strong or moderate to weak. Galectin-3 localization was mostly cytoplasmic, but also membranous or nuclear in some cells. Immunohistochemical expression of galectin-3 was not found in 12 (19.1%) cases. Most galectin-3 negative microcarcinomas (10/12) were of the non-classical type, i.e. without papillary architecture. Neither the frequency nor the intensity of a positive reaction was related to tumour size.

CONCLUSIONS

Galectin-3 gene is expressed at the protein level in most papillary microcarcinomas, although with slightly lower frequency than that reported for clinically evident papillary thyroid carcinoma. The presence of galectin-3 in clinically silent microcarcinomas may indicate that galectin-3 is not related to growth or aggressiveness of papillary thyroid microcarcinomas but rather plays some other role in thyroid tumour biology.

Galectins as markers of aggressiveness of mouse mammary carcinoma: towards a lectin target therapy of human breast cancer

Galectins, beta-galactoside binding proteins, expressed selectively in human breast carcinoma are attractive targets to employ lectin-aimed therapeutics. We examined beta-galactoside binding potency of neoplastic cells using fluorescein-labelled synthetic glycoconjugates as probes for flow cytometry. As a result, surface beta-galactoside binding proteins/galectins were discovered on mouse mammary carcinoma cells in vitro and in vivo unlike non-malignant cells from the several tissues; and asialo-GM1 ganglioside carbohydrate part--containing probe was the most specific one. However, in liver and lung metastatic cells galectins seem to be expressed within cytoplasm and/or nuclei. Galectin expression correlated directly with aggressive tumour potential in the A/Sn transplantable model similar to findings in several human breast carcinoma cell lines. However, galectin expression was reduced during tumour progression in more aggressive forms of spontaneous BLRB mammary carcinomas like it was shown for human breast carcinoma specimens. Analysis of the histopathological data led, however, to the conclusion that galectin expression hardly might be a suitable marker of aggressiveness of heterogeneous mammary carcinomas as the observed level of galectin expression is influenced by the amount of the stroma in a tumour sample and/or probably, galectin expression inversely correlates with tumour aggressiveness during the initial and advanced steps of mammary tumour progression. We conclude that surface beta-galactoside binding proteins/galectins that are selectively expressed during mouse mammary carcinoma progression, similarly to human breast carcinomas, seem to be proper targets for asialo-GM1-vectored cytotoxics and our mouse model system might be a relevant instrument to further test novel modes of anti-breast cancer therapy.

Ligand interactions of the Coprinopsis cinerea galectins

The basidiomycete Coprinopsis cinerea (Coprinus cinereus) expresses two fruiting body-specific isolectins (CGL1 and CGL2) that belong to the family of galectins. Understanding the role of these beta-galactoside binding lectins is still in the beginning. Even though the prerequisites for substrate binding are well understood, it is not known how discrimination between potential substrates is achieved and what kind of influence this has on the function in a distinct cellular context. Precise knowledge of the expression of galectins and their ligands will aid in elucidating their function. In Coprinopsis, the developmentally regulated ligands for galectins co-localise with galectin expression in the veil surrounding the developing primordium and the outer cells of the young stipe. In addition, galectin ligands are observed in the hymenium. The subcellular localisation of the galectin ligands suggests these to be present in cellular compartments distinct from galectin transport. The sensitivity of the in situ interactions with exogenous galectin towards detergents and organic solvents infers that these ligands are lipid-borne. Accordingly, lipid fractions from primordia are shown to contain galectin-binding compounds. Based on these results and the determined binding specificity towards substituted beta-galactosides we hypothesise that beta-galactoside-containing lipids (basidiolipids) found in mushrooms are physiological ligands for the galectins in C. cinerea.

Galectin genes: regulation of expression

In this review we have summarized the more recent studies on the expression of mammalian galectins. One interesting observation that can be made is that in most of microarrays and/or differential display analysis performed in recent years one or more galectins have been picked up. From a critical evaluation of the pertinent studies the main conclusion that can be drawn is that, although it is not yet clear whether the 14 galectins identified so far have functions in common, a striking common feature of all galectins is the strong modulation of their expression during development, differentiation stages and under different physiological or pathological conditions. This suggests that the expression of different galectins is finely tuned and possibly coordinated. In spite of these observations it is rather unexpected that very few studies have been performed on the molecular mechanisms governing the activity of galectin genes.

Phylogenetic analysis of the vertebrate galectin family

Galectins form a family of structurally related carbohydrate binding proteins (lectins) that have been identified in a large variety of metazoan phyla. They are involved in many biological processes such as morphogenesis, control of cell death, immunological response, and cancer. To elucidate the evolutionary history of galectins and galectin-like proteins in chordates, we have exploited three independent lines of evidence: (i) location of galectin encoding genes (LGALS) in the human genome; (ii) exon-intron organization of galectin encoding genes; and (iii) sequence comparison of carbohydrate recognition domains (CRDs) of chordate galectins. Our results suggest that a duplication of a mono-CRD galectin gene gave rise to an original bi-CRD galectin gene, before or early in chordate evolution. The N-terminal and C-terminal CRDs of this original galectin subsequently diverged into two different subtypes, defined by exon-intron structure (F4-CRD and F3-CRD). We show that all vertebrate mono-CRD galectins known to date belong to either the F3- or F4- subtype. A sequence of duplication and divergence events of the different galectins in chordates is proposed.

Involvement of the Galbeta1 - 3GalNAcbeta structure in the recognition of apoptotic bodies by THP-1 cells

A specific apoptotic glycosylation pattern may play an assistant or even a causative role in phagocytosis of apoptotic bodies. To elucidate the role of macrophages in lectin-mediated phagocytosis, an experimental system was used, where monocyte-derived THP-1 cells engulf the apoptotic bodies from the melanoma cell line MELJUSO. A flow cytometry assay was performed to reveal lectin expression and quantify the phagocytosis of apoptotic bodies. Taking into account that siglecs, a mannose receptor and galectins expressed on macrophages could be involved in engulfment of apoptotic bodies we studied their potential expression on THP-1 cells by means of polyacrylamide glycoconjugates. A strong binding of the cells to siglec ligands (3'SiaLac, 6'SiaLac, [Neu5Acalpha2-8]2) and galectin ligands (LacNAc, GalNAcbeta1 - 4GlcNAc, Galbeta1 - 3GalNAcbeta and asialoGM1) was observed. To reveal the corresponding targets on apoptotic bodies, the carbohydrate pattern of MELJUSO cells was analyzed. The apoptotic membrane was characterized by a high level of glycans terminated by galactose or sialic acid. To study lectin-mediated phagocytosis of apoptotic bodies by THP-1 cells, an inhibitory phagocytosis assay was performed. Binding of Galbeta1 - 3GalNAc- or LacNAc-specific reagents (lectins and antibodies) to apoptotic bodies abolished their engulfment by the THP-1 cells whereas blocking of Neu5Acalpha2 - 6 or Neu5Acalpha2 - 3 sites by the corresponding lectins was not effective. Furthermore, Galbeta1 - 3GalNAcbeta-PAA or asialoGM1-PAA binding to the THP-1 cells decreased phagocytosis, whereas two other potent THP-1-binding probes, LacNAc-PAA and GalNAcbeta1 - 4GlcNAc-PAA did not inhibit phagocytosis. Thus, Galbeta1 - 3GalNAcbeta-terminated chains represented on the apoptotic bodies but not the other tested galectin ligands appear to be a target for THP-1 cells.

Ah, sweet mystery of death! Galectins and control of cell fate

Control of cell death is critical in eukaryotic development, immune system homeostasis, and control of tumorigenesis. The galectin family of lectins is implicated in all of these processes. Other families of molecules function as death receptors or death effectors, but galectins are uniquely capable of acting both extracellularly and intracellularly to control cell death. Extracellularly, galectins cross-link glycan ligands to transduce signals that lead directly to death or that influence other signals regulating cell fate. Intracellular expression of galectins can modulate other signals controlling cell viability. Individual galectins can act on multiple cell types, and multiple galectins can act on the same cell. Understanding how galectins regulate cell viability and function will broaden our knowledge of the roles of galectins in basic biological processes and facilitate development of therapeutic applications for galectins in autoimmunity, transplant-related disease, and cancer.

Expression of galectin-1 and galectin-3 in human fetal thyroid gland

High levels of expression of galectin-1 and galectin-3, the beta-galactoside-binding proteins, have been recently described in malignant thyroid tumors but not in adenomas nor in normal thyroid tissue. However, there are no data about the expression of these galectins during fetal thyroid development. In this study we analyzed immunohistochemically the presence of galectin-1 and galectin-3 in human fetal thyroid glands (16-37 weeks of gestation). Weak to moderate cytoplasmic staining for galectin-1 was observed in follicular cells of all fetal thyroids. Galectin-3 could not be detected in thyroid follicular cells of any fetal thyroid investigated. Both galectins were detected in stromal tissue, but staining for galectin-1 was more intense. The absence of galectin-3 in thyroid cells during fetal development suggests that galectin-3 is expressed de novo during malignant transformation of thyroid epithelium, and that galectin-1 could be considered an oncofetal antigen. The results obtained indicated potential roles for galectin-1 and galectin-3 during the investigated period of human fetal thyroid gland development. Both galectins might participate in developmental processes regarding stromal fetal thyroid tissue organization, whereas galectin-1 might have a function in thyroid epithelium maturation.

Sialic acid capping of CD8beta core 1-O-glycans controls thymocyte-major histocompatibility complex class I interaction

Bidentate interaction of a T-cell receptor and CD8alphabeta heterodimer with a peptide-MHCI complex is required for the generation of cytotoxic T-lymphocytes. During thymic development, the modification of CD8beta glycans influences major histocompatibility complex class I binding to T-cell precursors called thymocytes. ES mass spectrometry (MS) and tandem MS/MS analysis were used to identify the changes occurring in the CD8beta-glycopeptides during T-cell development. Several threonine residues proximal to the CD8beta Ig headpiece are glycosylated with core-type 1 O-glycans. Non-sialylated glycoforms are present in immature thymocytes but are virtually absent in mature thymocytes. These results suggest how sialylation in a discrete segment of the CD8beta stalk by ST3Gal-1 sialyltransferase creates a molecular developmental switch that affects ligand binding.