Role of p56lck and ZAP70-mediated tyrosine phosphorylation in galectin-1-induced cell death

Galectin-1: A Traditionally Immunosuppressive Protein Displays Context-Dependent Capacities

Galectin–Carbohydrate interactions are indispensable to pathogen recognition and immune response. Galectin-1, a ubiquitously expressed 14-kDa protein with an evolutionarily conserved β-galactoside binding site, translates glycoconjugate recognition into function. That galectin-1 is demonstrated to induce T cell apoptosis has led to substantial attention to the immunosuppressive properties of this protein, such as inducing naive immune cells to suppressive phenotypes, promoting recruitment of immunosuppressing cells as well as impairing functions of cytotoxic leukocytes. However, only in recent years have studies shown that galectin-1 appears to perform a pro-inflammatory role in certain diseases. In this review, we describe the anti-inflammatory function of galectin-1 and its possible mechanisms and summarize the existing therapies and preclinical efficacy relating to these agents. In the meantime, we also discuss the potential causal factors by which galectin-1 promotes the progression of inflammation.

Therapeutic potential of galectin-1 and galectin-3 in autoimmune diseases

Galectins are a highly conserved protein family that binds to β-galactosides. Different members of this family play a variety of biological functions in physiological and pathological processes such as angiogenesis, regulation of immune cell activity, and cell adhesion. Galectins are widely distributed and play a vital role both inside and outside cells. It can regulate homeostasis and immune function in vivo through mechanisms such as apoptosis. Recent studies indicate that galectins exhibit pleiotropic roles in inflammation. Furthermore, emerging studies have found that galectins are involved in the occurrence and development of autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), type 1 diabetes (T1D) and systemic sclerosis (SSc) by regulating cell adhesion, apoptosis, and other mechanisms. This review will briefly discuss the biological characteristics of the two most widely expressed and extensively explored members of the galectin family, galectin-1 and galectin-3, as well as their pathogenetic and therapeutic roles in autoimmune diseases. These information may provide a novel and promising therapeutic target for autoimmune diseases.

Immunosuppressive Roles of Galectin-1 in the Tumor Microenvironment

Evasion of immune surveillance is an accepted hallmark of tumor progression. The production of immune suppressive mediators by tumor cells is one of the major mechanisms of tumor immune escape. Galectin-1 (Gal-1), a pivotal immunosuppressive molecule, is expressed by many types of cancer. Tumor-secreted Gal-1 can bind to glycosylated receptors on immune cells and trigger the suppression of immune cell function in the tumor microenvironment, contributing to the immune evasion of tumors. The aim of this review is to summarize the current literature on the expression and function of Gal-1 in the human tumor microenvironment, as well as therapeutics targeting Gal-1.

Altered Cell Surface N-Glycosylation of Resting and Activated T Cells in Systemic Lupus Erythematosus

Altered cell surface glycosylation in congenital and acquired diseases has been shown to affect cell differentiation and cellular responses to external signals. Hence, it may have an important role in immune regulation; however, T cell surface glycosylation has not been studied in systemic lupus erythematosus (SLE), a prototype of autoimmune diseases. Analysis of the glycosylation of T cells from patients suffering from SLE was performed by lectin-binding assay, flow cytometry, and quantitative real-time PCR. The results showed that resting SLE T cells presented an activated-like phenotype in terms of their glycosylation pattern. Additionally, activated SLE T cells bound significantly less galectin-1 (Gal-1), an important immunoregulatory lectin, while other lectins bound similarly to the controls. Differential lectin binding, specifically Gal-1, to SLE T cells was explained by the increased gene expression ratio of sialyltransferases and neuraminidase 1 (NEU1), particularly by elevated ST6 beta-galactosamide alpha-2,6-sialyltranferase 1 (ST6GAL1)/NEU1 and ST3 beta-galactoside alpha-2,3-sialyltransferase 6 (ST3GAL6)/NEU1 ratios. These findings indicated an increased terminal sialylation. Indeed, neuraminidase treatment of cells resulted in the increase of Gal-1 binding. Altered T cell surface glycosylation may predispose the cells to resistance to the immunoregulatory effects of Gal-1, and may thus contribute to the pathomechanism of SLE.

Systemic lupus erythematosus in the light of the regulatory effects of galectin-1 on T-cell function

Galectin-1 is an endogenous immunoregulatory lectin-type protein. Its most important effects are the inhibition of the differentiation and cytokine production of Th1 and Th17 cells, and the induction of apoptosis of activated T-cells. Galectin-1 has been identified as a key molecule in antitumor immune surveillance, and data are accumulating about the pathogenic role of its deficiency, and the beneficial effects of its administration in various autoimmune disease models. Initial animal and human studies strongly suggest deficiencies in both galectin-1 production and responsiveness in systemic lupus erythematosus (SLE) T-cells. Since lupus features widespread abnormalities in T-cell activation, differentiation and viability, in this review the authors wished to highlight potential points in T-cell signalling processes that may be influenced by galectin-1. These points include GM-1 ganglioside-mediated lipid raft aggregation, early activation signalling steps involving p56Lck, the exchange of the CD3 ζ-ZAP-70 to the FcRγ-Syk pathway, defective mitogen-activated protein kinase pathway activation, impaired regulatory T-cell function, the failure to suppress the activity of interleukin 17 (IL-17) producing T-cells, and decreased suppression of the PI3K-mTOR pathway by phosphatase and tensin homolog (PTEN). These findings place galectin-1 into the group of potential pathogenic molecules in SLE.

Molecular cloning and characterization of a galectin-1 homolog in orange-spotted grouper, Epinephelus coioides

As a member of animal lectin family, galectin has the functions of pathogen recognition, anti-bacteria and anti-virus. In the present study, a galectin-1 homolog (EcGel-1) from grouper (Epinephelus coioides) was cloned and its possible role in fish immunity was analyzed. The full length cDNA of EcGel-1 is 504 bp, including a 408 bp open reading frame (ORF) which encodes 135 amino acids with a molecular mass of 15.19 kDa. Quantitative real-time PCR analysis indicated that EcGel-1 was constitutively expressed in all analyzed tissues of healthy grouper. The expression of EcGel-1 in the spleen of grouper was differentially up-regulated challenged with Singapore grouper iridovirus (SGIV), poly (I:C), and LPS. EcGel-1 was abundantly distributed in the cytoplasm in GS cells. Recombinant EcGel-1(rEcGel-1) protein can make chicken erythrocyte aggregation, and combine with gram negative bacteria and gram positive bacteria in the presence of 2-Mercaptoethanol (β-ME). Taken together, the results showed that EcGel-1 may be an important molecule involved in pathogen recognition and pathogen elimination in the innate immunity of grouper.

Glycobiology of cell death: when glycans and lectins govern cell fate

Although one typically thinks of carbohydrates as associated with cell growth and viability, glycosylation also has an integral role in many processes leading to cell death. Glycans, either alone or complexed with glycan-binding proteins, can deliver intracellular signals or control extracellular processes that promote initiation, execution and resolution of cell death programs. Herein, we review the role of glycans and glycan-binding proteins as essential components of the cell death machinery during physiologic and pathologic settings.

Knockdown of core 1 beta 1, 3-galactosyltransferase prolongs skin allograft survival with induction of galectin-1 secretion and suppression of CD8+ T cells: T synthase knockdown effects on galectin-1 and CD8+ T cells

Core 1 beta 1,3-galactosyltransferase also known as T-antigen-synthase or T-synthase is a key enzyme for the synthesis of the common core 1 O-glycan structure (T-antigen). Although T-synthase is known to be important in human immune-related diseases, the effects of T-synthase and T-antigen on host immune responses remain poorly defined. In this study, a T-synthase-specific short hairpin RNA (shRNA) was transfected into murine colon carcinoma CT26 cells or mouse muscle tissues via intramuscular electroporation to assess the effects of T-synthase on T cells and cytokines. T-synthase knockdown significantly induced galectin-1 secretion both in vivo and in vitro and strongly enhanced Th2 cytokine (IL-10 and IL-4) production in vivo. Further, the increased production of galectin-1 induced by T-synthase knockdown promoted CD8(+) T-cell apoptosis, which, when combined with the increased production of CD4(+) T cell-derived Th2 cytokines prolonged the survival of skin allografts in mice. Our data suggest core 1 beta 1,3-galactosyltransferase-shRNA could serve not only as a useful tool in organ transplantation but also as a powerful tool for investigating O-glycans and glycoprotein synthesis and function.

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.

When galectins recognize glycans: from biochemistry to physiology and back again

In the past decade, increasing efforts have been devoted to the study of galectins, a family of evolutionarily conserved glycan-binding proteins with multifunctional properties. Galectins function, either intracellularly or extracellularly, as key biological mediators capable of monitoring changes occurring on the cell surface during fundamental biological processes such as cellular communication, inflammation, development, and differentiation. Their highly conserved structures, exquisite carbohydrate specificity, and ability to modulate a broad spectrum of biological processes have captivated a wide range of scientists from a wide spectrum of disciplines, including biochemistry, biophysics, cell biology, and physiology. However, in spite of enormous efforts to dissect the functions and properties of these glycan-binding proteins, limited information about how structural and biochemical aspects of these proteins can influence biological functions is available. In this review, we aim to integrate structural, biochemical, and functional aspects of this bewildering and ancient family of glycan-binding proteins and discuss their implications in physiologic and pathologic settings.

Role of the JNK/c-Jun/AP-1 signaling pathway in galectin-1-induced T-cell death

Galectin-1 (gal-1), an endogenous β-galactoside-binding protein, triggers T-cell death through several mechanisms including the death receptor and the mitochondrial apoptotic pathway. In this study we first show that gal-1 initiates the activation of c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase kinase 4 (MKK4), and MKK7 as upstream JNK activators in Jurkat T cells. Inhibition of JNK activation with sphingomyelinase inhibitors (20 μM desipramine, 20 μM imipramine), with the protein kinase C-δ (PKCδ) inhibitor rottlerin (10 μM), and with the specific PKCθ pseudosubstrate inhibitor (30 μM) indicates that ceramide and phosphorylation by PKCδ and PKCθ mediate gal-1-induced JNK activation. Downstream of JNK, we observed increased phosphorylation of c-Jun, enhanced activating protein-1 (AP-1) luciferase reporter, and AP-1/DNA-binding in response to gal-1. The pivotal role of the JNK/c-Jun/AP-1 pathway for gal-1-induced apoptosis was documented by reduction of DNA fragmentation after inhibition JNK by SP600125 (20 μM) or inhibition of AP-1 activation by curcumin (2 μM). Gal-1 failed to induce AP-1 activation and DNA fragmentation in CD3-deficient Jurkat 31-13 cells. In Jurkat E6.1 cells gal-1 induced a proapoptotic signal pattern as indicated by decreased antiapoptotic Bcl-2 expression, induction of proapoptotic Bad, and increased Bcl-2 phosphorylation. The results provide evidence that the JNK/c-Jun/AP-1 pathway plays a key role for T-cell death regulation in response to gal-1 stimulation.

How does it act when soluble? Critical evaluation of mechanism of galectin-1 induced T-cell apoptosis

Galectin-1 (Gal-1), a mammalian lectin induces apoptosis of T lymphocytes. Contradictory data have resulted in confusing knowledge regarding mechanism of Gal-1 induced T-cell apoptosis. In this paper we aimed to resolve this controversy by comparing cell death induced by low (1.8 μM, lowGal-1) and high (18 μM, highGal-1) concentration of soluble Gal-1. We show that lowGal-1 and highGal-1 trigger phosphatidylserine exposure, generation of rafts and mitochondrial membrane depolarization. In contrast, lowGal-1 but not highGal-1 is dependent on the presence of p56lck and ZAP70 and activates caspase cascade. The results allow the conclusion that the cell-death mechanism strictly depends on the concentration of Gal-1.

Dissecting the signal transduction pathways triggered by galectin-glycan interactions in physiological and pathological settings

Galectins are a family of evolutionarily conserved animal lectins with pleiotropic functions and widespread distribution. Fifteen members have been identified in a wide variety of cells and tissues. Through recognition of cell surface glycoproteins and glycolipids, these endogenous lectins can trigger a cascade of intracellular signaling pathways capable of modulating cell differentiation, proliferation, survival, and migration. These cellular events are critical in a variety of biological processes including embryogenesis, angiogenesis, neurogenesis, and immunity and are substantially altered during tumorigenesis, neurodegeneration, and inflammation. In addition, galectins can modulate intracellular functions and this effect involves direct interactions with distinct signaling pathways. In this review, we discuss current knowledge on the intracellular signaling pathways triggered by this multifunctional family of beta-galactoside-binding proteins in selected physiological and pathological settings. Understanding the "galectin signalosome" will be essential to delineate rational therapeutic strategies based on the specific control of galectin expression and function.

Mechanism of tumor cell-induced T-cell apoptosis mediated by galectin-1

Galectin-1 (Gal-1) has been implicated in tumor progression partly via the induction of T-cell apoptosis. However the mechanism of Gal-1 induced T-cell death was mostly studied using recombinant, soluble Gal-1 producing controversial results. To explore the true mechanism of Gal-1 and hence tumor cell-induced T-cell death, we applied co-cultures of tumor cells and T-cells thus avoiding artificial circumstances generated using recombinant protein. T-cells died when co-cultured with Gal-1-expressing but survived with Gal-1 non-expressing tumor cells. Removing tumor cell surface Gal-1 or knocking down Gal-1 expression resulted in diminution of T-cell apoptosis. Gal-1 transgenic or soluble Gal-1 treated HeLa cells became cytotoxic. Stimulation of apoptosis required interaction between the tumor and T-cells, presence of p56lck and ZAP70, decrease of mitochondrial membrane potential and caspase activation. Hence tumor cell-derived Gal-1 might efficiently contribute to tumor self-defense. Moreover this system resolves the discrepancies obtained using recombinant Gal-1 in T-cell apoptosis studies.

Conveying glycan information into T-cell homeostatic programs: a challenging role for galectin-1 in inflammatory and tumor microenvironments

The immune system has evolved sophisticated mechanisms composed of several checkpoints and fail-safe processes that enable it to orchestrate innate and adaptive immunity, while at the same time limiting aberrant or unfaithful T-cell function. These multiple regulatory pathways take place during the entire life-span of T cells including T-cell development, homing, activation, and differentiation. Galectin-1, an endogenous glycan-binding protein widely expressed at sites of inflammation and tumor growth, controls a diversity of immune cell processes, acting either extracellularly through specific binding to cell surface glycan structures or intracellularly through modulation of pathways that remain largely unexplored. In this review, we highlight the discoveries that have led to our current understanding of the role of galectin-1 in distinct immune cell process, particularly those associated with T-cell homeostasis. Also, we emphasize findings emerging from the study of experimental models of autoimmunity, chronic inflammation, fetomaternal tolerance, and tumor growth, which have provided fundamental insights into the critical role of galectin-1 and its specific saccharide ligands in immunoregulation. Challenges for the future will embrace the rational manipulation of galectin-1-glycan interactions both towards attenuating immune responses in autoimmune diseases, graft rejection, and recurrent fetal loss, while at the same overcoming immune tolerance in chronic infections and cancer.

Galectin-1 induced activation of the apoptotic death-receptor pathway in human Jurkat T lymphocytes

Galectin-1 (gal-1), a member of the family of beta-galactoside binding proteins, participates in several biological processes such as immunomodulation, cell adhesion, regulation of cell growth and apoptosis. The aim of this study was to investigate whether gal-1 interferes with the Fas (Apo-1/CD95)-associated apoptosis cascade in the T-cell lines Jurkat and MOLT-4. Gal-1 and an Apo-1 monoclonal antibody (mAb) induced DNA-fragmentation in Jurkat T-cells whereas MOLT-4 cells were resistant. Gal-1 stimulated DNA-fragmentation could be efficiently inhibited by caspase-8 inhibitor II (Z-IETD-FMK) and a neutralizing Fas mAb. Fas could be identified as a target for gal-1 recognition as demonstrated by immunofluorescence staining, binding of the receptor glycoprotein to immobilized gal-1 and analyses by immunoblotting as well as by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Gal-1 stimulates the activation and proteolytic processing of procaspase-8 and downstream procaspase-3 in Jurkat-T cells. Inhibition of gal-1 induced procaspase-8 activation by a neutralizing Fas mAb strongly suggests that gal-1 recognition of Fas is associated with caspase-8 activation. Our data provide the first experimental evidence for targeting of gal-1 to glycotopes on Fas and the subsequent activation of the apoptotic death-receptor pathway.

Galectins as modulators of tumor progression in head and neck squamous cell carcinomas

Head and neck squamous cell carcinomas (HNSCCs) remain a significant cause of morbidity worldwide. Biological therapies able to induce and/or upregulate antitumor immune responses could represent a complementary approach to conventional treatments for patients with HNSCC because, despite advances in surgery, radiotherapy, and chemotherapy, the overall survival rates for these patients have not changed over recent decades. Galectins are involved in the control of cell proliferation, cell death, and cell migration and in the modulation of various functions of the immune system. In this context, galectin-1 is known to protect HNSCCs from the immune system. The present review details the involvement of galectins in HNSCC biology and suggests a number of approaches to reduce the levels of expression of galectin-1 in HNSCCs, with the aim of improving the efficiency of HNSCC immunotherapy.

A novel anti-inflammatory function of human galectin-1: inhibition of hematopoietic progenitor cell mobilization

OBJECTIVE

The immunosuppressive and anti-inflammatory activity of mammalian galectin-1 (Gal-1) has been well established in experimental in vivo animal models and in vitro studies. Since the proliferation and migration of leukocytes represent a necessary and important step in response to the inflammatory insult, we have investigated whether Gal-1 affects the mobilization of hematopoietic progenitor cells (HPC) induced by cyclophosphamide (CY) and granulocyte colony-stimulating factor (G-CSF).

METHODS

Bone marrow HPCs were mobilized with CY/G-CSF or CY/G-CSF plus human recombinant Gal-1 in BDF1 mice. Bone marrow (BM) and blood cells were taken at different time points and analyzed for their in vivo repopulating ability in lethally irradiated syngeneic animals. The number of myeloid progenitor cells in BM and blood samples was determined by colony-forming cell assay. Expression of surface markers (Sca-1, CD3epsilon, CD45R/B220, Ter-119, GR-1, and CD11b) on nucleated marrow cells was measured by flow cytometry. The lymphocytes, granulocytes, and monocytes in blood samples were counted after Giemsa staining.

RESULTS

Gal-1 dramatically inhibited CY/G-CSF-induced HPC migration to the periphery as well as decreased peripheral neutrophilia and monocytosis in a dose- and time-dependent manner. In contrast, Gal-1 itself stimulated HPC expansion and accumulation within the BM. The presence of the lectin for inhibition of HPC mobilization was essential during the second half of the treatment. Moreover, Gal-1 inhbited transendothelial migration of BM-derived HPCs in response to SDF-1 in vitro.

CONCLUSION

Gal-1 blocked BM progenitor cell migration induced by CY/G-CSF treatment, indicating a novel anti-inflammatory function of the lectin. We suggest that the inhibition of HPC mobilization occurs mainly via obstructing the transendothelial migration of BM-derived cells including primitive hematopoietic and committed myeloid progenitor cells and mature granulocytes and monocytes.

An emerging role for galectins in tuning the immune response: lessons from experimental models of inflammatory disease, autoimmunity and cancer

Inflammation is a critical process for eliminating pathogens, but can lead to serious deleterious effects if left unchecked. Identifying the endogenous factors that control immune tolerance and inflammation is a key goal in the field of immunology. Galectins, a family of endogenous lectins with affinity for beta-galactoside-containing oligosaccharides, are expressed by several cells of the immune system and tissue-resident stromal cells. According to their architecture, this family of glycan-binding proteins is classified in those containing one-carbohydrate-recognition domain (CRD) (proto-type), those containing two-CRD joined by a linker non-lectin domain (tandem-repeat) and those that have one-CRD attached to an N-terminal peptide (chimera-type). Accumulating evidence indicates that galectins play critical regulatory roles in immune cell response and homeostasis. In this review, we summarize recent developments in our understanding of the galectins' roles within different immune cell compartments, and in the broader context of the inflammatory microenvironments. In particular we illustrate the immunoregulatory role of three representative members of each galectin subfamily: galectin-1, -3 and -9. This body of knowledge, documenting the coming of age of galectins as potential immunosuppressive agents or targets for anti-inflammatory drugs, represents a sound basis to further explore their potential as novel therapies for autoimmune diseases, chronic inflammation and cancer.

Dissecting the pathophysiologic role of endogenous lectins: Glycan-binding proteins with cytokine-like activity?

Several families of endogenous glycan-binding proteins have been implicated in a wide variety of immunological functions including first-line defence against pathogens, cell trafficking, and immune regulation. These include, among others, the C-type lectins (collectins, selectins, mannose receptor, and others), S-type lectins (galectins), I-type lectins (siglecs and others), P-type lectins (phosphomannosyl receptors), pentraxins, and tachylectins. This review will concentrate on the immunoregulatory roles of galectins (particularly galectin-1) and collectins (mannose-binding lectins and surfactant proteins) to illustrate the ability of endogenous glycan-binding proteins to act as cytokines, chemokines or growth factors, and thereby modulating innate and adaptive immune responses under physiological or pathological conditions. Understanding the pathophysiologic relevance of endogenous lectins in vivo will reveal novel targets for immunointervention during chronic infection, autoimmunity, transplantation and cancer.

Galectin-1: a small protein with major functions

Galectins are a family of carbohydrate-binding proteins with an affinity for beta-galactosides. Galectin-1 (Gal-1) is differentially expressed by various normal and pathological tissues and appears to be functionally polyvalent, with a wide range of biological activity. The intracellular and extracellular activity of Gal-1 has been described. Evidence points to Gal-1 and its ligands as one of the master regulators of such immune responses as T-cell homeostasis and survival, T-cell immune disorders, inflammation and allergies as well as host-pathogen interactions. Gal-1 expression or overexpression in tumors and/or the tissue surrounding them must be considered as a sign of the malignant tumor progression that is often related to the long-range dissemination of tumoral cells (metastasis), to their dissemination into the surrounding normal tissue, and to tumor immune-escape. Gal-1 in its oxidized form plays a number of important roles in the regeneration of the central nervous system after injury. The targeted overexpression (or delivery) of Gal-1 should be considered as a method of choice for the treatment of some kinds of inflammation-related diseases, neurodegenerative pathologies and muscular dystrophies. In contrast, the targeted inhibition of Gal-1 expression is what should be developed for therapeutic applications against cancer progression. Gal-1 is thus a promising molecular target for the development of new and original therapeutic tools.

Impact of protein–glycan interactions in the regulation of autoimmunity and chronic inflammation

Protein-glycan interactions control essential immunological processes, including T-cell activation, differentiation and survival. Galectins, carbohydrate-binding proteins, defined by shared consensus amino acid sequences and affinity for beta-galactose-containing oligosaccharides, participate in a wide spectrum of immunological processes. These carbohydrate-binding proteins regulate the development of pathogenic T-cell responses by influencing T-cell survival, activation and cytokine secretion. Administration of recombinant galectins or their genetic delivery modulate the development and severity of chronic inflammatory responses in experimental models of autoimmunity by triggering different and potentially overlapping immunoregulatory mechanisms. Given the potential use of galectins as novel anti-inflammatory agents or targets for immunosuppressive drugs, we will summarize here recent findings on the influence of these carbohydrate-binding proteins in autoimmune and chronic inflammatory disorders.

Acid sphingomyelinase mediated release of ceramide is essential to trigger the mitochondrial pathway of apoptosis by galectin-1

The mechanism of apoptosis induced by human galectin-1, a mammalian beta-galactoside-binding protein with a remarkable cytotoxic effect on activated peripheral T cells and tumor T cell lines has been extensively investigated in this study. Here we first show that galectin-1 initiate the acid sphingomyelinase mediated release of ceramide and this event is critical in the further steps. Elevation of ceramide level coincides with exposure of phosphatidylserine on the outer cell membrane. The downstream events, decrease of Bcl-2 protein amount, depolarization of the mitochondria and activation of the caspase 9 and caspase 3 depend on production of ceramide. All downstream steps, including production of ceramide, require the generation of membrane rafts and the presence of two tyrosine kinases, p56(lck) and ZAP70. Based on our findings we suggest a model of the mechanism of galectin-1 triggered cell death.

The coming of age of galectins as immunomodulatory agents: impact of these carbohydrate binding proteins in T cell physiology and chronic inflammatory disorders

Immune cell homoeostasis is attributed to multiple distinct safety valves that are interconnected and intervene at defined checkpoints of the life cycle of immunocytes to guarantee clonal expansion and functional inactivation of self-reactive potentially autoaggressive lymphocytes. Galectins, animal lectins defined by shared consensus amino acid sequence and affinity for beta-galactose containing oligosaccharides, are found on various cells of the immune system, and their expression is associated with the differentiation and activation status of these cells. Over the past few years, galectins have been implicated in the regulation of many aspects of T cell physiology such as cell activation, differentiation, and apoptosis. In addition, a growing body of experimental evidence indicates that galectins may play critical roles in the modulation of chronic inflammatory disorders, autoimmunity, and cancer. Given the increased interest of immunologists in this field, the growing body of information raised during the past few years and the potential use of galectins as novel anti-inflammatory agents or targets for immunosuppressive drugs, we will summarise recent advances on the role of galectins in different aspects of T cell physiology and their impact in the development and/or resolution of chronic inflammatory disorders, autoimmunity, and cancer.