Galectin-8 binding to integrins inhibits cell adhesion and induces apoptosis

Engineered intrinsically fluorescent galectin-8 variants with altered valency, ligand recognition and biological activity

Galectin-8 is a small soluble lectin with two carbohydrate recognition domains (CRDs). N- and C-terminal CRDs of Gal-8 differ in their specificity for glycan ligands. Here, we wanted to find out whether oligomerization of individual CRDs of galectin-8 affects its biological activity. Using green fluorescent protein polygons (GFPp) as an oligomerization scaffold, we generated intrinsically fluorescent CRDs with altered valency. We show that oligomers of C-CRD are characterized by significant cell surface affinity. Furthermore, the multivalency of the resulting variants has an impact on cellular activities such as cell signaling, heparin binding and proliferation. Our data indicates that tunable valence is a useful tool for modifying the biological activity of CRDs of galectins.

Unveiling the molecular characteristics and antibacterial activity of tandem-repeat-type Galectin-8 in large yellow croaker (Larimichthys crocea)

Galectin-8 (Gal-8) is a versatile carbohydrate-binding protein with pivotal roles in immune regulation and cellular processes. This study introduces a novel galectin-8 protein, LcGal-8, from the large yellow croaker (Larimichthys crocea), showcasing typical characteristics of tandem-repeat-type galectins, including the absence of a signal peptide or transmembrane region and the presence of conserved sugar-binding motifs. Phylogenetic analysis reveals its conservation among fish species. Expression profiling indicates widespread distribution in immune tissues, particularly the spleen, implicating involvement in immune processes. The subcellular localization analysis reveals that LcGal-8 is present in both the cytoplasm and nucleus. Upon bacterial challenge, LcGal-8 is up-regulated in immune tissues, suggesting a role in host defense. Functional assays demonstrate that LcGal-8 can agglutinate gram-negative bacteria. The recombinant LcGal-8 protein agglutinates red blood cells from the large yellow croaker independently of Ca2⁺, however, this activity is inhibited by lipopolysaccharide (LPS) at 2.5 μg/mL. Fluorescence detection kits and scanning electron microscopy (SEM) confirm the agglutination and bactericidal effects of LcGal-8 against various gram-negative bacteria, including Vibrio harveyi, Aeromondaceae hydrophila, Aeromondaceae veronii, Pseudomonas plecoglossicida, Edwardsiella tarda. These findings contribute valuable insights into the genetic basis of disease resistance in the large yellow croaker and could support molecular breeding strategies to enhance disease resistance.

B4GALT1-dependent galectin-8 binding with TGF-β receptor suppresses colorectal cancer progression and metastasis

Transforming growth factor (TGF)-β signaling is critical for epithelial-mesenchymal transition (EMT) and colorectal cancer (CRC) metastasis. Disruption of Smad-depednent TGF-β signaling has been shown in CRC cells. However, TGF-β receptor remains expressed on CRC cells. Here, we investigated whether the cooperation between tumor-associated N-glycosylation and a glycan-binding protein modulated the TGF-β-driven signaling and metastasis of CRC. We showed that galectin-8, a galactose-binding lectin, hampered TGF-β-induced EMT by interacting with the type II TGF-β receptor and competing with TGF-β binding. Depletion of galectin-8 promoted the migration of CRC cells by increasing TGF-β-receptor-mediated RAS and Src signaling, which was attenuated after recombinant galectin-8 treatment. Treatment with recombinant galectin-8 also induces JNK-dependent apoptosis in CRC cells. The anti-migratory effect of galectin-8 depended on β4-galactosyltransferase-I (B4GALT1), an enzyme involved in N-glycan synthesis. Increased B4GALT1 expression was observed in clinical CRC samples. Depletion of B4GALT1 reduced the metastatic potential of CRC cells. Furthermore, inducible expression of galectin-8 attenuated tumor development and metastasis of CRC cells in an intra-splenic injection model. Our results thus demonstrate that galectin-8 alters non-canonical TGF-β response in CRC cells and suppresses CRC progression.

Galectin-8 inhibition and functions in immune response and tumor biology

Galectins are among organisms' most abundantly expressed lectins (carbohydrate-binding proteins) that specifically bind β-galactosides. They act not only outside the cell, where they bind to extracellular matrix glycans, but also inside the cell, where they have a significant impact on signaling pathways. Galectin-8 is a galectin family protein encoded by the LGALS8 gene. Its role is evident in both T- and B-cell immunity and in the innate immune response, where it acts directly on dendritic cells and induces some pro-inflammatory cytokines. Galectin-8 also plays an important role in the defense against bacterial and viral infections. It is known to promote antibacterial autophagy by recognizing and binding glycans present on the vacuolar membrane, thus acting as a danger receptor. The most important role of galectin-8 is the regulation of cancer growth, metastasis, tumor progression, and tumor cell survival. Importantly, the expression of galectins is typically higher in tumor tissues than in noncancerous tissues. In this review article, we focus on galectin-8 and its function in immune response, microbial infections, and cancer. Given all of these functions of galectin-8, we emphasize the importance of developing new and selective galectin-8 inhibitors and report the current status of their development.

Vascular galectins in tumor angiogenesis and cancer immunity

Sustained tumor angiogenesis, i.e., the induction and maintenance of blood vessel growth by tumor cells, is one of the hallmarks of cancer. The vascularization of malignant tissues not only facilitates tumor growth and metastasis, but also contributes to immune evasion. Important players in all these processes are the endothelial cells which line the luminal side of blood vessel. In the tumor vasculature, these cells are actively involved in angiogenesis as well in the hampered recruitment of immune cells. This is the result of the abnormal tumor microenvironment which triggers both angiostimulatory and immune inhibitory gene expression profiles in endothelial cells. In recent years, it has become evident that galectins constitute a protein family that is expressed in the tumor endothelium. Moreover, several members of this glycan-binding protein family have been found to facilitate tumor angiogenesis and stimulate immune suppression. All this has identified galectins as potential therapeutic targets to simultaneously hamper tumor angiogenesis and alleviate immune suppression. The current review provides a brief introduction in the human galectin protein family. The current knowledge regarding the expression and regulation of galectins in endothelial cells is summarized. Furthermore, an overview of the role that endothelial galectins play in tumor angiogenesis and tumor immunomodulation is provided. Finally, some outstanding questions are discussed that should be addressed by future research efforts. This will help to fully understand the contribution of endothelial galectins to tumor progression and to exploit endothelial galectins for cancer therapy.

Expression of Intracellular Galectin-8 and -9 in Endometrial Cancer

Endometrial cancer (EC) is a common gynecological cancer worldwide. Treatment has been improved in recent years; however, in advanced stages, therapeutic options are still limited. The expression of galectins is increased in several tumor types and that they are involved in important cell processes. Large studies on endometrial cancer are still pending; Specimens of 225 patients with EC were immunohistochemically stained with antibodies for Gal-8 and Gal-9. Expression was correlated with histopathological variables. The cytosolic expression of both galectins is associated with grading and survival. Cytosolic Galectin-8 expression is a positive prognostic factor for overall survival (OS) and progression-free survival (PFS), while nuclear Gal-8 expression correlates only to OS. The cytosolic presence of Galectin-9 is correlated with a better prognosis regarding OS. Our results suggest that expression of both galectins is associated with OS and PFS in EC. Further studies are needed to understand the underlying molecular mechanisms.

Galectin-8 modulates human osteoclast activity partly through isoform-specific interactions

In overactive human osteoclasts, we previously identified an alternative splicing event in LGALS8, encoding galectin-8, resulting in decreased expression of the long isoform. Galectin-8, which modulates cell-matrix interactions and functions intracellularly as a danger recognition receptor, has never been associated with osteoclast biology. In human osteoclasts, inhibition of galectin-8 expression revealed its roles in bone resorption, osteoclast nuclearity, and mTORC1 signaling regulation. Galectin-8 isoform-specific inhibition asserted a predominant role for the short isoform in bone resorption. Moreover, a liquid chromatography with tandem mass spectrometry (LC-MS/MS) proteomic analysis of galectin-8 isoforms performed in HEK293T cells identified 22 proteins shared by both isoforms. Meanwhile, nine interacting partners were specific for the short isoform, and none were unique to the long isoform. Interactors specific for the galectin-8 short isoform included cell adhesion proteins and lysosomal proteins. We confirmed the interactions of galectin-8 with CLCN3, CLCN7, LAMP1, and LAMP2, all known to localize to secretory vesicles, in human osteoclasts. Altogether, our study reveals direct roles of galectin-8 in osteoclast activity, mostly attributable to the short isoform.

Ginseng-derived type I rhamnogalacturonan polysaccharide binds to galectin-8 and antagonizes its function

Background

Panax ginseng Meyer polysaccharides exhibit various biological functions, like antagonizing galectin-3-mediated cell adhesion and migration. Galectin-8 (Gal-8), with its linker-joined N- and C-terminal carbohydrate recognition domains (CRDs), is also crucial to these biological processes, and thus plays a role in various pathological disorders. Yet the effect of ginseng-derived polysaccharides in modulating Gal-8 function has remained unclear.

Methods

P. ginseng-derived pectin was chromatographically isolated and enzymatically digested to obtain a series of polysaccharides. Biolayer Interferometry (BLI) quantified their binding affinity to Gal-8, and their inhibitory effects on Gal-8 was assessed by hemagglutination, cell migration and T-cell apoptosis.

Results

Our ginseng-derived pectin polysaccharides consist mostly of rhamnogalacturonan-I (RG-I) and homogalacturonan (HG). BLI shows that Gal-8 binding rests primarily in RG-I and its β-1,4-galactan side chains, with sub-micromolar KD values. Both N- and C-terminal Gal-8 CRDs bind RG-I, with binding correlated with Gal-8-mediated function.

Conclusion

P. ginseng RG-I pectin β-1,4-galactan side chains are crucial to binding Gal-8 and antagonizing its function. This study enhances our understanding of galectin-sugar interactions, information that may be used in the development of pharmaceutical agents targeting Gal-8.

The universe of galectin-binding partners and their functions in health and disease

Galectins, a family of evolutionarily conserved glycan-binding proteins, play key roles in diverse biological processes including tissue repair, adipogenesis, immune cell homeostasis, angiogenesis, and pathogen recognition. Dysregulation of galectins and their ligands has been observed in a wide range of pathologic conditions including cancer, autoimmune inflammation, infection, fibrosis, and metabolic disorders. Through protein-glycan or protein-protein interactions, these endogenous lectins can shape the initiation, perpetuation, and resolution of these processes, suggesting their potential roles in disease monitoring and treatment. However, despite considerable progress, a full understanding of the biology and therapeutic potential of galectins has not been reached due to their diversity, multiplicity of cell targets, and receptor promiscuity. In this article, we discuss the multiple galectin-binding partners present in different cell types, focusing on their contributions to selected physiologic and pathologic settings. Understanding the molecular bases of galectin-ligand interactions, particularly their glycan-dependency, the biochemical nature of selected receptors, and underlying signaling events, might contribute to designing rational therapeutic strategies to control a broad range of pathologic conditions.

Hypoxia Controls the Glycome Signature and Galectin-8-Ligand Axis to Promote Protumorigenic Properties of Metastatic Melanoma

The prognosis for patients with metastatic melanoma (MM) involving distant organs is grim, and treatment resistance is potentiated by tumor-initiating cells (TICs) that thrive under hypoxia. MM cells, including TICs, express a unique glycome featuring i-linear poly-N-acetyllactosamines through the loss of I-branching enzyme, β1,6 N-acetylglucosaminyltransferase 2. Whether hypoxia instructs MM TIC development by modulating the glycome signature remains unknown. In this study, we explored hypoxia-dependent alterations in MM glycome‒associated genes and found that β1,6 N-acetylglucosaminyltransferase 2 was downregulated and a galectin (Gal)-8-ligand axis, involving both extracellular and cell-intrinsic Gal-8, was induced. Low β1,6 N-acetylglucosaminyltransferase 2 levels correlated with poor patient outcomes, and patient serum samples were elevated for Gal-8. Depressed β1,6 N-acetylglucosaminyltransferase 2 in MM cells upregulated TIC marker, NGFR/CD271, whereas loss of MM cell‒intrinsic Gal-8 markedly lowered NGFR and reduced TIC activity in vivo. Extracellular Gal-8 bound preferentially to i-linear poly-N-acetyllactosamines on N-glycans of the TIC marker and prometastatic molecule CD44, among other receptors, and activated prosurvival factor protein kinase B. This study reveals the importance of hypoxia governing the MM glycome by enforcing i-linear poly-N-acetyllactosamine and Gal-8 expression. This mechanistic investigation also uncovers glycome-dependent regulation of pro-MM factor, NGFR, implicating i-linear poly-N-acetyllactosamine and Gal-8 as biomarkers and therapeutic targets of MM.

Investigation of anti-galectin-8 levels in patients with multiple sclerosis: A consort-clinical study

BACKGROUND

Galectins are a family of endogenous mammalian lectins involved in pathogen recognition, killing, and facilitating the entry of microbial pathogens and parasites into the host. They are the intermediators that decipher glycan-containing information about the host immune cells and microbial structures to modulate signaling events that cause cellular proliferation, chemotaxis, cytokine secretion, and cell-to-cell communication. They have subgroups that take place in different roles in the immune system. The effect of galectin-8 on multiple sclerosis disease (MS) has been studied in the literature, but the results seemed unclear. In this study, we aimed to determine anti-galectin-8 (anti-Gal-8) levels in MS and their potential use as biomarkers.

METHODS

In this experimental study, 45 MS patients diagnosed according to McDonald criteria were included in the patient group. The healthy control group contained 45 people without MS diagnosis and any risk factors. Demographic data, height, weight, body mass index, blood glucose, thyroid-stimulating hormone, alanine transaminase, aspartate transaminase, creatinine, low-density lipoprotein, anti-Gal-8 levels, the prevalence of hypertension, diabetes mellitus and coronary artery disease were recorded. In addition, the expanded disability status scale and disease duration were evaluated in the patient group. Data were presented as mean ± standard deviations.

RESULTS

The mean blood anti-galectin-8 value of the patient group was 4.84 ± 4.53 ng/mL, while it was 4.67 ± 3.40 ng/mL in the control group, and the difference in these values was found statistically insignificant (P > .05). Moreover, body mass index, glucose, alanine transaminase, aspartate transaminase, thyroid-stimulating hormone, and low-density lipoprotein levels were also statistically insignificant (P > .05).

CONCLUSION

This study examined anti-Gal-8 levels in MS patients. The relationship between MS and galectin-8 and anti-Gal-8 levels in patients needs further clarification. As a result, the study's results could help elucidate the pathogenesis of MS and give more evidence for diagnosis.

KIT Mutations Correlate with Higher Galectin Levels and Brain Metastasis in Breast and Non-Small Cell Lung Cancer

To investigate a potential role for galectins as biomarkers that enable diagnosis or prognostication of breast or non-small cell lung cancer, the serum levels of galectins -1, -3, -7, -8, and -9 of cancer patients determined by ELISA assays were compared to the mutation status of 50 known cancer-critical genes, which were determined using multiplex PCR in tumors of the same patients. Mutations in the KIT proto-oncogene, which codes for the c-Kit protein, a receptor tyrosine kinase, correlated with higher levels of galectins -1, -3, -8, and -9 in breast cancer patients and galectin-1 in non-small cell lung cancer patients. Mutations in the KIT gene were more likely found in brain metastases from both of these primary cancers. The most common KIT mutation in our panel was p.M541L, a missense mutation in the transmembrane domain of the c-Kit protein. These results demonstrate an association between KIT oncogenic signaling and elevated serum galectins in patients with metastatic disease. Changes in protein trafficking and the glycocalyx composition of cancer cells may explain the observed alterations in galectin expression. This study can be useful for the targeted selection of receptor tyrosine kinase and galectin inhibitor anti-cancer treatments.

Galectin-8 and -9 as prognostic factors for cervical cancer

Purpose

Galectins are carbohydrate-binding proteins with multiple effects on cell biology. Research shows that they play an important role in tumor development and progression. Therefore, in this study, the presence of Galectin-8 and -9 (Gal), both already known as prognostic factors in other tumor entities, were investigated in cervical cancer. Our aim was to examine the association of Gal-8 and -9 expression with histopathological markers and survival of the patients.

Methods

Gal-8 and -9 expression was investigated in 250 cervical cancer samples by immunohistochemistry. The staining was evaluated using the immunoreactive score (IRS). The results were correlated to clinical and pathological data. The correlation of Gal-8 and -9 expression with overall and relapse-free survival was analyzed.

Results

Expression of Gal-8 was associated with negative N-status and lower FIGO status. Detection of Gal-9 was connected to negative N-status and lower grading regarding all specimens. A correlation of Gal-9 with lower FIGO status was detected for squamous cell carcinoma (SCC) only. Expression of Gal-8 was associated with relapse-free survival of SCC patients in a positive manner. Gal-9 expression was associated with better overall survival.

Conclusion

Our results suggest that expression of both galectins is inversely associated with tumor stage and progression. Gal-8 expression is associated with relapse-free survival of patients with SCC, while presence of Gal-9 in cervical cancer is associated with a better prognosis in regard of overall survival.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00404-022-06449-9.

Galectin-8, cytokines, and the storm

Galectin-8 (Gal-8) belongs to a family of animal lectins that modulate cell adhesion, cell proliferation, apoptosis, and immune responses. Recent studies have shown that mammalian Gal-8 induces in an autocrine and paracrine manner, the expression and secretion of cytokines and chemokines such as RANKL, IL-6, IL-1β, SDF-1, and MCP-1. This involves Gal-8 binding to receptor complexes that include MRC2/uPAR/LRP1, integrins, and CD44. Receptors ligation triggers FAK, ERK, Akt, and the JNK signaling pathways, leading to induction of NF-κB that promotes cytokine expression. Indeed, immune-competent Gal-8 knockout (KO) mice express systemic lower levels of cytokines and chemokines while the opposite is true for Gal-8 transgenic animals. Cytokine and chemokine secretion, induced by Gal-8, promotes the migration of cancer cells toward cells expressing this lectin. Accordingly, Gal-8 KO mice experience reduced tumor size and smaller and fewer metastatic lesions when injected with cancer cells. These observations suggest the existence of a ‘vicious cycle’ whereby Gal-8 expression and secretion promotes the secretion of cytokines and chemokines that further promote Gal-8 expression. This ‘vicious cycle’ could enhance the development of a ‘cytokine storm’ which is a key contributor to the poor prognosis of COVID-19 patients.

TMEM182 interacts with integrin beta 1 and regulates myoblast differentiation and muscle regeneration

BACKGROUND

Transmembrane proteins are vital for intercellular signalling and play important roles in the control of cell fate. However, their physiological functions and mechanisms of action in myogenesis and muscle disorders remain largely unexplored. It has been found that transmembrane protein 182 (TMEM182) is dramatically up-regulated during myogenesis, but its detailed functions remain unclear. This study aimed to analyse the function of TMEM182 during myogenesis and muscle regeneration.

METHODS

RNA sequencing, quantitative real-time polymerase chain reaction, and immunofluorescence approaches were used to analyse TMEM182 expression during myoblast differentiation. A dual-luciferase reporter assay was used to identify the promoter region of the TMEM182 gene, and a chromatin immunoprecipitation assay was used to investigate the regulation TMEM182 transcription by MyoD. We used chickens and TMEM182-knockout mice as in vivo models to examine the function of TMEM182 in muscle growth and muscle regeneration. Chickens and mouse primary myoblasts were used to extend the findings to in vitro effects on myoblast differentiation and fusion. Co-immunoprecipitation and mass spectrometry were used to identify the interaction between TMEM182 and integrin beta 1 (ITGB1). The molecular mechanism by which TMEM182 regulates myogenesis and muscle regeneration was examined by Transwell migration, cell wound healing, adhesion, glutathione-S-transferse pull down, protein purification, and RNA immunoprecipitation assays.

RESULTS

TMEM182 was specifically expressed in skeletal muscle and adipose tissue and was regulated at the transcriptional level by the myogenic regulatory factor MyoD1. Functionally, TMEM182 inhibited myoblast differentiation and fusion. The in vivo studies indicated that TMEM182 induced muscle fibre atrophy and delayed muscle regeneration. TMEM182 knockout in mice led to significant increases in body weight, muscle mass, muscle fibre number, and muscle fibre diameter. Skeletal muscle regeneration was accelerated in TMEM182-knockout mice. Furthermore, we revealed that the inhibitory roles of TMEM182 in skeletal muscle depend on ITGB1, an essential membrane receptor involved in cell adhesion and muscle formation. TMEM182 directly interacted with ITGB1, and this interaction required an extracellular hybrid domain of ITGB1 (aa 387-470) and a conserved region (aa 52-62) within the large extracellular loop of TMEM182. Mechanistically, TMEM182 modulated ITGB1 activation by coordinating the association between ITGB1 and laminin and regulating the intracellular signalling of ITGB1. Myogenic deletion of TMEM182 increased the binding activity of ITGB1 to laminin and induced the activation of the FAK-ERK and FAK-Akt signalling axes during myogenesis.

CONCLUSIONS

Our data reveal that TMEM182 is a novel negative regulator of myogenic differentiation and muscle regeneration.

Computational repurposing of therapeutic small molecules from cancer to pulmonary hypertension

Cancer therapies are being considered for treating rare noncancerous diseases like pulmonary hypertension (PH), but effective computational screening is lacking. Via transcriptomic differential dependency analyses leveraging parallels between cancer and PH, we mapped a landscape of cancer drug functions dependent upon rewiring of PH gene clusters. Bromodomain and extra-terminal motif (BET) protein inhibitors were predicted to rely upon several gene clusters inclusive of galectin-8 (LGALS8). Correspondingly, LGALS8 was found to mediate the BET inhibitor–dependent control of endothelial apoptosis, an essential role for PH in vivo. Separately, a piperlongumine analog’s actions were predicted to depend upon the iron-sulfur biogenesis gene ISCU. Correspondingly, the analog was found to inhibit ISCU glutathionylation, rescuing oxidative metabolism, decreasing endothelial apoptosis, and improving PH. Thus, we identified crucial drug-gene axes central to endothelial dysfunction and therapeutic priorities for PH. These results establish a wide-ranging, network dependency platform to redefine cancer drugs for use in noncancerous conditions.

Galectins in Endothelial Cell Biology and Angiogenesis: The Basics

Angiogenesis, the growth of new blood vessels out of existing vessels, is a complex and tightly regulated process. It is executed by the cells that cover the inner surface of the vasculature, i.e., the endothelial cells. During angiogenesis, these cells adopt different phenotypes, which allows them to proliferate and migrate, and to form tube-like structures that eventually result in the generation of a functional neovasculature. Multiple internal and external cues control these processes and the galectin protein family was found to be indispensable for proper execution of angiogenesis. Over the last three decades, several members of this glycan-binding protein family have been linked to endothelial cell functioning and to different steps of the angiogenesis cascade. This review provides a basic overview of our current knowledge regarding galectins in angiogenesis. It covers the main findings with regard to the endothelial expression of galectins and highlights their role in endothelial cell function and biology.

Unraveling How Tumor-Derived Galectins Contribute to Anti-Cancer Immunity Failure

Simple Summary

This review compiles our current knowledge of one of the main pathways activated by tumors to escape immune attack. Indeed, it integrates the current understanding of how tumor-derived circulating galectins affect the elicitation of effective anti-tumor immunity. It focuses on several relevant topics: which are the main galectins produced by tumors, how soluble galectins circulate throughout biological liquids (taking a body-settled gradient concentration into account), the conditions required for the galectins’ functions to be accomplished at the tumor and tumor-distant sites, and how the physicochemical properties of the microenvironment in each tissue determine their functions. These are no mere semantic definitions as they define which functions can be performed in said tissues instead. Finally, we discuss the promising future of galectins as targets in cancer immunotherapy and some outstanding questions in the field.

Abstract

Current data indicates that anti-tumor T cell-mediated immunity correlates with a better prognosis in cancer patients. However, it has widely been demonstrated that tumor cells negatively manage immune attack by activating several immune-suppressive mechanisms. It is, therefore, essential to fully understand how lymphocytes are activated in a tumor microenvironment and, above all, how to prevent these cells from becoming dysfunctional. Tumors produce galectins-1, -3, -7, -8, and -9 as one of the major molecular mechanisms to evade immune control of tumor development. These galectins impact different steps in the establishment of the anti-tumor immune responses. Here, we carry out a critical dissection on the mechanisms through which tumor-derived galectins can influence the production and the functionality of anti-tumor T lymphocytes. This knowledge may help us design more effective immunotherapies to treat human cancers.

Differential cellular responses to adhesive interactions with galectin-8- and fibronectin-coated substrates

The mechanisms underlying the cellular response to extracellular matrices (ECMs) that consist of multiple adhesive ligands are still poorly understood. Here, we address this topic by monitoring specific cellular responses to two different extracellular adhesion molecules - the main integrin ligand fibronectin and galectin-8, a lectin that binds β-galactoside residues  - as well as to mixtures of the two proteins. Compared with cell spreading on fibronectin, cell spreading on galectin-8-coated substrates resulted in increased projected cell area, more-pronounced extension of filopodia and, yet, the inability to form focal adhesions and stress fibers. These differences can be partially reversed by experimental manipulations of small G-proteins of the Rho family and their downstream targets, such as formins, the Arp2/3 complex and Rho kinase. We also show that the physical adhesion of cells to galectin-8 was stronger than adhesion to fibronectin. Notably, galectin-8 and fibronectin differently regulate cell spreading and focal adhesion formation, yet act synergistically to upregulate the number and length of filopodia. The physiological significance of the coherent cellular response to a molecularly complex matrix is discussed. This article has an associated First Person interview with the first author of the paper.

Molecular characterization, expression analysis and immune effect of Galectin-8 from Japanese flounder (Paralichthys olivaceus)

Galectin-8 gene belongs to the agglutinin family, which can specifically recognize β-galactoside bonds and play essential roles in many biological processes. In this study, we researched the sequence characteristics and immune-related function of Galectin-8 gene in Japanese flounder Paralichthys olivaceus, named PoGalectin-8. The results showed that the open reading frame of PoGalectin-8 was 891 bp, which encoding a protein with 296 amino acid residues and containing typical HXNPR and WGXEE motifs in the N-terminal and C-terminal CRD domains. Sequence alignment showed that PoGalectin-8 was conserved in different aquatic animals and exhibited the highest similarity (95.27%) with Seriola dumerili. PoGalectin-8 expressed in all detected tissues and exhibited the highest expression level in spleen, followed by skin and kidney. After infected by Edwardsiella tarda, the expression of PoGalectin-8 was down-regulated in the spleen and skin tissues of P. olivaceus. Further to study its immune-related functions, the recombinant PoGalectin-8 (rPoGalectin-8) was expressed and purified. The rPoGalectin-8 can specifically bind to lipopolysaccharide and peptidoglycan, the main components of cell walls from Gram-negative and Gram-positive bacteria. Bacteria binding and the microbial agglutinating experiments showed that the rPoGalectin-8 could bind and agglutinate all examined Gram-positive and Gram-negative bacteria. This study implied that PoGalectin-8, as a pattern recognition receptor, may play important roles during immune responses against bacterial infection, which laid a foundation for further functional identification of Galectin-8 in aquatic animal immunity.

Galectin-8 Is Upregulated in Keratinocytes by IL-17A and Promotes Proliferation by Regulating Mitosis in Psoriasis

Psoriasis is a chronic inflammatory skin disease that develops under the influence of the IL-23/T helper 17 cell axis and is characterized by intense inflammation and prominent epidermal hyperplasia. In this study, we demonstrate that galectin-8, a β-galactoside‒binding lectin, is upregulated in the epidermis of human psoriatic skin lesions as well as in a mouse model of psoriasis induced by intradermal IL-23 injections and in IL-17A‒treated keratinocytes. We show that keratinocyte proliferation is less prominent in galectin-8‒knockout mice after intradermal IL-23 treatment than in wild-type mice. In addition, we show that galectin-8 levels in keratinocytes are positively correlated with the ability of the cells to proliferate and that transitioning from mitosis into G1 phase is delayed in galectin-8‒knockout HaCaT cells after cell-cycle synchronization and release. We demonstrate by immunofluorescence staining and immunoblotting the presence of galectin-8 within the mitotic apparatus. We reveal by coimmunoprecipitation and mass spectrometry analysis that α-tubulin interacts with galectin-8 during mitosis. Finally, we show that in the absence of galectin-8, pericentrin compactness is lessened and mitotic microtubule length is shortened, as demonstrated by immunofluorescence staining. We conclude that galectin-8 is upregulated in psoriasis and contributes to the hyperproliferation of keratinocytes by maintaining centrosome integrity during mitosis through interacting with α-tubulin.

Full-length galectin-8 and separate carbohydrate recognition domains: the whole is greater than the sum of its parts?

Galectin-8 (Gal-8) is a tandem-repeat type galectin with affinity for β-galactosides, bearing two carbohydrate recognition domains (CRD) connected by a linker peptide. The N- and C-terminal domains (Gal-8N and Gal-8C) share 35% homology, and their glycan ligand specificity is notably dissimilar: while Gal-8N shows strong affinity for α(2-3)-sialylated oligosaccharides, Gal-8C has higher affinity for non-sialylated oligosaccharides, including poly-N-acetyllactosamine and/ or A and B blood group structures. Particularly relevant for understanding the biological role of this lectin, full-length Gal-8 can bind cell surface glycoconjugates with broader affinity than the isolated Gal-8N and Gal-8C domains, a trait also described for other tandem-repeat galectins. Herein, we aim to discuss the potential use of separate CRDs in modelling tandem-repeat galectin-8 and its biological functions. For this purpose, we will cover several aspects of the structure-function relationship of this protein including crystallographic structures, glycan specificity, cell function and biological roles, with the ultimate goal of understanding the potential role of each CRD in predicting full-length Gal-8 involvement in relevant biological processes.

The Animal Lectin Galectin-8 Promotes Cytokine Expression and Metastatic Tumor Growth in Mice

Secreted animal lectins of the galectin family are key players in cancer growth and metastasis. Here we show that galectin-8 (gal-8) induces the expression and secretion of cytokines and chemokines such as SDF-1 and MCP-1 in a number of cell types. This involves gal-8 binding to a uPAR/LRP1/integrin complex that activates JNK and the NFkB pathway. Cytokine and chemokine secretion, induced by gal-8, promotes migration of cancer cells toward cells treated with this lectin. Indeed, immune-competent gal-8 knockout (KO) mice express systemic lower levels of cytokines and chemokines while the opposite is true for gal-8 transgenic animals. Accordingly, gal-8 KO mice experience reduced tumor size and smaller and fewer metastatic lesions when injected with cancer cells. These results suggest the existence of a 'vicious cycle' whereby gal-8 secreted by the tumor microenvironment, promotes secretion of chemoattractants at the metastatic niche that promote further recruitment of tumor cells to that site. This study further implicate gal-8 in control of cancer progression and metastasis through its effects on the production of immunoregulatory cytokines.

A tandem-repeat galectin-1 from Apostichopus japonicus with broad PAMP recognition pattern and antibacterial activity

Galectins belong to the family of carbohydrate-binding proteins and play major roles in the immune and inflammatory responses of both vertebrates and invertebrates. In the present study, one novel galectin-1 protein named AjGal-1 was identified from Apostichopus japonicas with an open reading frame of 1179 bp encoding a polypeptide of 392 amino acids. The deduced amino acids sequence of AjGal-1 contained three carbohydrate recognition domains (CRDs) which shared 34-37% identity with that of other galectin proteins from echinodermata, fishes, and birds. In the phylogenetic tree, AjGal-1 was closely clustered with galectins from Mesocentrotus nudus and Paracentrotus lividus. The mRNA transcripts of AjGal-1 were ubiquitously expressed in all the detected tissues, including gut, longitudinal muscle, gonad, coelomocytes, respiratory tree, tentacle and body wall, with the highest expression level in coelomocytes. After Vibrio splendidus stimulation, the mRNA expression levels of AjGal-1 in coelomocytes were significantly increased at 6 and 12 h (P < 0.01) compared with that in control group, and went back to normal level at 72 h. The recombinant protein of AjGal-1 (rAjGal-1) could bind various PAMPs including d-galactose, lipopolysaccharide (LPS), peptidoglycan (PGN) and mannose (Man), and exhibited the highest affinity to d-galactose. Meanwhile, rAjGal-1 could also bind and agglutinate different kinds of microorganisms, including gram-negative bacteria (V. splendidus and Escherichia coli), gram-positive bacteria (Micrococus leteus), and fungi (Pichia pastoris). rAjGal-1 also exhibited anti-microbial activity against V. splendidus and E. coli. All these results suggested that AjGal-1 could function as an important PRR with broad spectrum of microbial recognition and anti-microbial activity against the invading pathogen in A. japonicas.

Identification and characterization of a novel galectin from the mud crab Scylla paramamosain

Galectins are a family of β-galactoside-binding lectins that play key roles in the invertebrate innate immunity system, but no galectin genes have been identified in the mud crab (Scylla paramamosain) so far. The present study is the first to clone a galectin gene (SpGal) from S. paramamosain, by the rapid amplification of cDNA ends technique based on expressed sequence tags. The full-length cDNA of SpGal was 3142 bp. Its open reading frame encoded a polypeptide of 280 amino acids containing a GLECT/Gal-bind lectin domain and a potential N-glycosylation site. The deduced amino acid sequence and multi-domain organization of SpGal were highly similar to those of invertebrate galectins, and phylogenetic analysis showed that SpGal was closely related to galectin isolated from Portunus trituberculatus. The mRNA transcripts of SpGal were found to be constitutively expressed in a wide range of tissues, with its expression level being higher in the hepatopancreas, gill, and hemocytes. The mRNA expression level of SpGal increased rapidly after the crabs were stimulated by Vibrio alginolyticus, and the maximum expression appeared at 6 h after the challenge. The lipopolysaccharide-binding ability of SpGal was dependent on its concentration, and it also exhibited agglutination activity with three Gram-negative (Aeromonas hydrophila, Chryseobacterium indologenes and Vibrio alginolyticus) and three Gram-positive (Bacillus aquimaris, Staphylococcus aureus and Micrococcus lysodeik) bacterial strains. In addition, hemagglutination activity with rabbit erythrocytes was observed in the absence of d-galactose. These results indicate that SpGal in S. paramamosain acts as a pattern recognition receptor to recognize a broad spectrum of microbes. The findings together indicate that SpGal plays an important role in the innate immune mechanisms of S. paramamosain against pathogenic infection.

Galectin-8 induces endothelial hyperpermeability through the eNOS pathway involving S-nitrosylation-mediated adherens junction disassembly

The permeability of endothelial cells is regulated by the stability of the adherens junctions, which is highly sensitive to kinase-mediated phosphorylation and endothelial nitric oxide synthase (eNOS)-mediated S-nitrosylation of its protein components. Solid tumors can produce a variety of factors that stimulate these signaling pathways leading to endothelial cell hyperpermeability. This generates stromal conditions that facilitate tumoral growth and dissemination. Galectin-8 (Gal-8) is overexpressed in several carcinomas and has a variety of cellular effects that can contribute to tumor pathogenicity, including angiogenesis. Here we explored whether Gal-8 has also a role in endothelial permeability. We show that recombinant Gal-8 activates eNOS, induces S-nitrosylation of p120-catenin (p120) and dissociation of adherens junction, leading to hyperpermeability of the human endothelial cell line EAhy926. This pathway involves focal-adhesion kinase (FAK) activation downstream of eNOS as a requirement for eNOS-mediated p120 S-nitrosylation. This suggests a reciprocal, yet little understood, regulation of phosphorylation and S-nitrosylation events acting upon adherens junction permeability. In addition, glutathione S-transferase (GST)-Gal-8 pull-down experiments and function-blocking β1-integrin antibodies point to β1-integrins as cell surface components involved in Gal-8-induced hyperpermeability. Endogenous Gal-8 secreted from the breast cancer cell line MCF-7 has similar hyperpermeability and signaling effects. Furthermore, the mouse cremaster model system showed that Gal-8 also activates eNOS, induces S-nitrosylation of adherens junction components and is an effective hyperpermeability agent in vivo. These results add endothelial permeability regulation by S-nitrosylation as a new function of Gal-8 that can potentially contribute to the pathogenicity of tumors overexpressing this lectin.

Galectin-8 in the onset of the immune response and inflammation

Galectins (Gals), a family of mammalian lectins, have emerged as key regulators of the immune response, being implicated in several physiologic and pathologic conditions. Lately, there is increasing data regarding the participation of Galectin-8 (Gal-8) in both the adaptive and innate immune responses, as well as its high expression in inflammatory disorders. Here, we focus on the pro- and anti-inflammatory properties of Gal-8 and discuss the potential use of this lectin in order to shape the immune response, according to the context.

Comprehensive transcriptomic view of the role of the LGALS12 gene in porcine subcutaneous and intramuscular adipocytes

Background

Livestock production aims to provide meats of high and consistent eating quality. Insufficient intramuscular (IM) fat and excessive subcutaneous (SC) fat are paramount pork quality challenges. IM fat and SC fat, which are modulated by the adipogenesis of IM and SC adipocytes, play key roles in pork quality. Galectin-12 (LGALS12) was proven to be an important regulator of fat deposition in porcine. However, the current knowledge of the transcriptome-wide role of LGALS12 in adipocytes is still limited. This study was aimed to discover the different regulatory mechanisms of LGALS12 in porcine IM and SC adipocyte.

Results

The siRNA-mediated knockdown of the expression of LGALS12 identified 1075 and 3016 differentially expressed genes (DEGs) in IM and SC adipocytes, respectively. Among these, 585 were up- and 490 were downregulated in the IM adipocytes, while 2186 were up- and 830 were downregulated in the SC adipocytes. Moreover, 418 DGEs were observed only in the IM adipocytes, 2359 DGEs only in the SC adipocytes, and 657 DGEs in both types of adipocytes. According to Gene Ontology (GO) analysis, DEGs in both IM and SC adipocytes were mainly enriched in categories related to lipids or fat cell differentiation. Pathway analysis of the DEGs revealed 88 changed signaling pathways in the IM adipocytes and 86 in the SC adipocytes. The signaling pathways present in only one type of adipocyte were identified from among the top 50 signaling pathways in each type of adipocyte. Four signaling pathways, encompassing PI3K-AKT, cardiac muscle contraction, fatty acid metabolism and Ras, were significantly enriched in the IM adipocytes. On the other hand, four different signaling pathways, encompassing TNF, WNT, cGMP-PKG and NF-kappa B, were greatly enriched in the SC ones. The pathway changes were confirmed by chemical inhibition assays.

Conclusions

Our data reveals that LGALS12 knockdown alters the expression of numerous genes involved in key biological processes in the development of adipocytes. These observations provide a global view of the role of LGALS12 in porcine IM and SC adipocytes; thus, improving our understanding of the regulatory mechanisms by which this gene acts in fat development.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5891-y) contains supplementary material, which is available to authorized users.

GALECTIN-8 Is a Neuroprotective Factor in the Brain that Can Be Neutralized by Human Autoantibodies

Galectin-8 (Gal-8) is a glycan-binding protein that modulates a variety of cellular processes interacting with cell surface glycoproteins. Neutralizing anti-Gal-8 antibodies that block Gal-8 functions have been described in autoimmune and inflammatory disorders, likely playing pathogenic roles. In the brain, Gal-8 is highly expressed in the choroid plexus and accordingly has been detected in human cerebrospinal fluid. It protects against central nervous system autoimmune damage through its immune-suppressive potential. Whether Gal-8 plays a direct role upon neurons remains unknown. Here, we show that Gal-8 protects hippocampal neurons in primary culture against damaging conditions such as nutrient deprivation, glutamate-induced excitotoxicity, hydrogen peroxide (H₂O₂)-induced oxidative stress, and β-amyloid oligomers (Aβo). This protective action is manifested even after 2 h of exposure to the harmful condition. Pull-down assays demonstrate binding of Gal-8 to selected β1-integrins, including α3 and α5β1. Furthermore, Gal-8 activates β1-integrins, ERK1/2, and PI3K/AKT signaling pathways that mediate neuroprotection. Hippocampal neurons in primary culture produce and secrete Gal-8, and their survival decreases upon incubation with human function-blocking Gal-8 autoantibodies obtained from lupus patients. Despite the low levels of Gal-8 expression detected by real-time PCR in hippocampus, compared with other brain regions, the complete lack of Gal-8 in Gal-8 KO mice determines higher levels of apoptosis upon H₂O₂ stereotaxic injection in this region. Therefore, endogenous Gal-8 likely contributes to generate a neuroprotective environment in the brain, which might be eventually counteracted by human function-blocking autoantibodies.

Deciphering the galectin-12 protein interactome reveals a major impact of galectin-12 on glutamine anaplerosis in colon cancer cells

Galectins are β-galactoside binding proteins which possess a variety of functions including modulation of apoptosis, growth and differentiation. Hence, alterations in the expression profile have been associated with loss of cellular homeostasis contributing to tumor growth and progression. Though galectin-12 is significantly downregulated in several tumor entities, including colon cancer, its impact on cellular homeostasis as well as galectin-12 specific binding partners have not been identified so far. We therefore established an experimental strategy which is based on reversible cross-link immunoprecipitation to capture the galectin-12 protein interactome in colon cancer cells. By applying this approach, we identified 10 novel candidates of galectin-12 interacting proteins including the neutral amino acid exchanger SLC1A5. Remarkably, we uncovered that binding of galectin-12 to SLC1A5 significantly reduced glutamine uptake in our model cell line. Consequently, utilization of glutamine carbon for biomass synthesis was profoundly affected, suggesting galectin-12 as a novel inhibitor of glutamine anaplerosis in colon cancer cells. More detailed analysis revealed that colon cancer cells can counteract galectin-12 mediated glutamine deprivation by induction of compensatory mechanisms which facilitate adaption to low-glutamine conditions and thus survival.

Dual knockdown of Galectin-8 and its glycosylated ligand, the activated leukocyte cell adhesion molecule (ALCAM/CD166), synergistically delays in vivo breast cancer growth

Galectin-8 (Gal-8), a 'tandem-repeat'-type galectin, has been described as a modulator of cellular functions including adhesion, spreading, growth arrest, apoptosis, pathogen recognition, autophagy, and immunomodulation. We have previously shown that activated leukocyte cell adhesion molecule (ALCAM), also known as CD166, serves as a receptor for endogenous Gal-8. ALCAM is a member of the immunoglobulin superfamily involved in cell-cell adhesion through homophilic (ALCAM-ALCAM) and heterophilic (i.e. ALCAM-CD6) interactions in different tissues. Here we investigated the physiologic relevance of ALCAM-Gal-8 association and glycosylation-dependent mechanisms governing these interactions. We found that silencing of ALCAM in MDA-MB-231 triple negative breast cancer cells decreases cell adhesion and migration onto Gal-8-coated surfaces in a glycan-dependent fashion. Remarkably, either Gal-8 or ALCAM silencing also disrupted cell-cell adhesion, and led to reduced tumor growth in a murine model of triple negative breast cancer. Moreover, structural characterization of endogenous ALCAM N-glycosylation showed abundant permissive structures for Gal-8 binding. Importantly, we also found that cell sialylation controls Gal-8-mediated cell adhesion. Altogether, these findings demonstrate a central role of either ALCAM or Gal-8 (or both) in controlling triple negative breast cancer.

Serum biomarker panels for the diagnosis of gastric cancer

Gastric cancer is a leading cause of mortality due to neoplastic disease. Although early detection of gastric cancers can decrease the mortality rate, it remains a diagnostic challenge because of the lack of effective biomarkers. In this study, fifteen gastric cancer patients and ten healthy subjects were recruited to assess novel serum biomarkers for gastric cancer using antibody microarray technology. ELISA was utilized to validate the antibody array results. As a result, compared to the controls, eleven cytokines were found to be significantly increased in gastric cancer, including interferon gamma receptor 1 (IFNGR1), neurogenic locus notch homolog protein 3 (Notch‐3), tumor necrosis factor receptor superfamily member 19L (TNFRSF19L), growth hormone receptor (GHR), signaling lymphocytic activation molecule family 8 (SLAMF8), folate receptor beta (FR‐beta), integrin alpha 5, galectin‐8, erythropoietin‐producing hepatocellular A1 (EphA1), epiregulin, and fibroblast growth factor 12 (FGF‐12) with P < 0.05. ELISA validation supported the results of the antibody array. More importantly, most of these eleven cytokines, including IFNGR1, TNFRSF19L, GHR, SLAMF8, FR‐beta, and integrin alpha 5 were discovered to be elevated in gastric cancer serum samples for the first time in this study, suggesting that these proteins may serve as novel biomarkers for the early diagnosis and prognosis determination of gastric cancer.

Galectin-8 induces functional disease markers in human osteoarthritis and cooperates with galectins-1 and -3

The reading of glycan-encoded signals by tissue lectins is considered a major route of the flow of biological information in many (patho)physiological processes. The arising challenge for current research is to proceed from work on a distinct protein to family-wide testing of lectin function. Having previously identified homodimeric galectin-1 and chimera-type galectin-3 as molecular switches in osteoarthritis progression, we here provide proof-of-principle evidence for an intra-network cooperation of galectins with three types of modular architecture. We show that the presence of tandem-repeat-type galectin-8 significantly correlated with cartilage degeneration and that it is secreted by osteoarthritic chondrocytes. Glycan-inhibitable surface binding of galectin-8 to these cells increased gene transcription and the secretion of functional disease markers. The natural variant galectin-8 (F19Y) was less active than the prevalent form. Genome-wide array analysis revealed induction of a pro-degradative/inflammatory gene signature, largely under control of NF-κB signaling. This signature overlapped with respective gene-expression patterns elicited by galectins-1 and -3, but also presented supplementary features. Functional assays with mixtures of galectins that mimic the pathophysiological status unveiled cooperation between the three galectins. Our findings shape the novel concept to consider individual galectins as part of a so far not realized teamwork in osteoarthritis pathogenesis, with relevance beyond this disease.

Galactoside-binding lectin in Solen grandis as a pattern recognition receptor mediating opsonization

Galactoside-binding lectin (galectin) is a type of pathogen recognition molecule that occupies an important position in the invertebrate innate immunity system. Our previous study has identified a galectin gene in mollusk Solen grandis (SgGal-1) and illustrated its potential roles in innate immunity. By the functional study using recombinant protein and specific antibody, here, we confirmed the pivotal roles of SgGal-1 in immune defense of S. grandis. SgGal-1 protein was expressed in many tested tissues including gill, mantle, hepatopancreas and gonad, except hemocytes and muscle. The recombinant SgGal-1 (rSgGal-1) bound PGN and β-glucan instead of LPS in vitro, and it further caused significant agglutination of five different microbes, suggesting SgGal-1 served as a pattern recognition receptor (PRR) involved in immune defense of mollusk. Furthermore, SgGal-1 recruited hemocytes to encapsulate, which was blocked by anti-rSgGal-1 serum. In the meantime, rSgGal-1 as well as promoted the phagocytosis of hemocytes against Escherichia coli in vitro. All these results suggested that SgGal-1 in S. grandis not only acted as a PRR recognizing microbes but also directly participated in the process of immune opsonization to protect the host from pathogenic infection.

Clinical characteristics and prognostic significance of galectins for patients with gastric cancer: A meta-analysis

OBJECTIVE

To explore the relationships between the expression level of different galectins and its prognostic value for patients with gastric cancer.

METHODS

The PubMed, EMbase, the Cochrane Library and Web of Science databases were systematically searched. All the eligible studies were included according to the inclusion and exclusion criteria. All the relevant data was extracted by two independent researchers. The quality assessment was conducted according to the evaluation of the quality of prognosis study which published by Harden in 2006. The STATA 12.0 software was used to perform a meta-analysis.

RESULTS

All of 8 retrospective case-controlled studies involving 2093 patients with gastric cancer were included in this study. The results of meta-analysis presented that the elevated galectin-1 which is related to the poor overall survival (HR = 1.85, 95% CI: 1.33-2.58; P < 0.001) may predicted a larger tumor size (OR = 2.20, 95% CI: 1.35-3.35; P = 0.001) and was positively associated with the higher expression of VEGF (OR = 1.44, 95% CI: 1.14-1.82; P = 0.002). Moreover, the decreased galectin-3 (HR = 0.49, 95% CI: 0.36-0.67; P < 0.001), galectin-8 (HR = 0.49, 95% CI: 0.36-0.67; P < 0.001) and galectin-9 (HR = 0.78, 95% CI: 0.66-0.92; P = 0.003) were also significantly associated with poorer prognosis. Our meta-analysis also showed that lower expression of galectin-3 was also related to lymphatic vessel invasion (OR = 0.48, 95% CI: 0.26-0.89; P = 0.018), worse TNM stages (OR = 0.47, 95% CI: 0.32-0.40; P < 0.001), deeper invasive depth (OR = 0.33, 95% CI: 0.21-0.51; P < 0.001) and poorer differentiation grade (OR = 0.10, 95% CI: 0.04-0.25; P < 0.001).

CONCLUSIONS

High expression of galectin-1 or low expression of galectin-3, -8 and -9 were significantly related to a poorer prognosis for patients with gastric cancer. The expression level of galectins was associated with clinical characteristics and were potential independent prognostic predictor for GC patients.

Regulation of TNF-Related Apoptosis-Inducing Ligand Signaling by Glycosylation

Tumor necrosis-factor related apoptosis-inducing ligand, also known as TRAIL or APO2L (Apo-2 ligand), is a cytokine of the TNF superfamily acknowledged for its ability to trigger selective apoptosis in tumor cells while being relatively safe towards normal cells. Its binding to its cognate agonist receptors, namely death receptor 4 (DR4) and/or DR5, can induce the formation of a membrane-bound macromolecular complex, coined DISC (death-signaling inducing complex), necessary and sufficient to engage the apoptotic machinery. At the very proximal level, TRAIL DISC formation and activation of apoptosis is regulated both by antagonist receptors and by glycosylation. Remarkably, though, despite the fact that all membrane-bound TRAIL receptors harbor putative glycosylation sites, only pro-apoptotic signaling through DR4 and DR5 has, so far, been found to be regulated by N- and O-glycosylation, respectively. Because putative N-glycosylation sequons and O-glycosylation sites are also found and conserved in all these receptors throughout all animal species (in which these receptors have been identified), glycosylation is likely to play a more prominent role than anticipated in regulating receptor/receptor interactions or trafficking, ultimately defining cell fate through TRAIL stimulation. This review aims to present and discuss these emerging concepts, the comprehension of which is likely to lead to innovative anticancer therapies.

Integrins Were Involved in Soybean Agglutinin Induced Cell Apoptosis in IPEC-J2

Soybean agglutinin (SBA), is a non-fiber carbohydrate related protein and a major anti-nutritional factor. Integrins, transmembrane glycoproteins, are involved in many biological processes. Although recent work suggested that integrins are involved in SBA-induced cell-cycle alterations, no comprehensive study has reported whether integrins are involved in SBA-induced cell apoptosis (SCA) in IPEC-J2. The relationship between SBA and integrins are still unclear. We aimed to elucidate the effects of SBA on IPEC-J2 cell proliferation and cell apoptosis; to study the roles of integrins in IPEC-J2 normal cell apoptosis (NCA) and SCA; and to illustrate the relationship and connection type between SBA and integrins. Thus, IPEC-J2 cells were treated with SBA at the levels of 0, 0.125, 0.25, 0.5, 1.0 or 2.0 mg/mL to determine cell proliferation and cell apoptosis. The cells were divided into control, SBA treated groups, integrin inhibitor groups, and SBA + integrin inhibitor groups to determine the integrin function in SCA. The results showed that SBA significantly (p < 0.05) lowered cell proliferation and induced cell apoptosis in IPEC-J2 (p < 0.05). Inhibition of any integrin type induced the cell apoptosis (p < 0.05) and these integrins were involved in SCA (p < 0.05). Even SBA had no physical connection with integrins, an association was detected between SBA and α-actinin-2 ACTN2 (integrin-binding protein). Additionally, SBA reduced the mRNA expression of integrins by down regulating the gene expression level of ACTN2. We concluded an evidence for the anti-nutritional mechanism of SBA by ACTN2 with integrins. Further trials are needed to prove whether ACTN2 is the only protein for connecting SBA with integrin.

Identification of novel prognostic indicators for triple-negative breast cancer patients through integrative analysis of cancer genomics data and protein interactome data

Triple negative breast cancers (TNBCs) are highly heterogeneous and aggressive without targeted treatment. Here, we aim to systematically dissect TNBCs from a prognosis point of view by building a subnetwork atlas for TNBC prognosis through integrating multi-dimensional cancer genomics data from The Cancer Genome Atlas (TCGA) project and the interactome data from three different interaction networks. The subnetworks are represented as the protein-protein interaction modules perturbed by multiple genetic and epigenetic interacting mechanisms contributing to patient survival. Predictive power of these subnetwork-derived prognostic models is evaluated using Monte Carlo cross-validation and the concordance index (C-index). We uncover subnetwork biomarkers of low oncogenic GTPase activity, low ubiquitin/proteasome degradation, effective protection from oxidative damage, and tightly immune response are linked to better prognosis. Such a systematic approach to integrate massive amount of cancer genomics data into clinical practice for TNBC prognosis can effectively dissect the molecular mechanisms underlying TNBC patient outcomes and provide potential opportunities to optimize treatment and develop therapeutics.

Proteomic Dissection of Nanotopography-Sensitive Mechanotransductive Signaling Hubs that Foster Neuronal Differentiation in PC12 Cells

Neuronal cells are competent in precisely sensing nanotopographical features of their microenvironment. The perceived microenvironmental information will be “interpreted” by mechanotransductive processes and impacts on neuronal functioning and differentiation. Attempts to influence neuronal differentiation by engineering substrates that mimic appropriate extracellular matrix (ECM) topographies are hampered by the fact that profound details of mechanosensing/-transduction complexity remain elusive. Introducing omics methods into these biomaterial approaches has the potential to provide a deeper insight into the molecular processes and signaling cascades underlying mechanosensing/-transduction but their exigence in cellular material is often opposed by technical limitations of major substrate top-down fabrication methods. Supersonic cluster beam deposition (SCBD) allows instead the bottom-up fabrication of nanostructured substrates over large areas characterized by a quantitatively controllable ECM-like nanoroughness that has been recently shown to foster neuron differentiation and maturation. Exploiting this capacity of SCBD, we challenged mechanosensing/-transduction and differentiative behavior of neuron-like PC12 cells with diverse nanotopographies and/or changes of their biomechanical status, and analyzed their phosphoproteomic profiles in these settings. Versatile proteins that can be associated to significant processes along the mechanotransductive signal sequence, i.e., cell/cell interaction, glycocalyx and ECM, membrane/f-actin linkage and integrin activation, cell/substrate interaction, integrin adhesion complex, actomyosin organization/cellular mechanics, nuclear organization, and transcriptional regulation, were affected. The phosphoproteomic data suggested furthermore an involvement of ILK, mTOR, Wnt, and calcium signaling in these nanotopography- and/or cell mechanics-related processes. Altogether, potential nanotopography-sensitive mechanotransductive signaling hubs participating in neuronal differentiation were dissected.

Galectin-8 induces partial epithelial-mesenchymal transition with invasive tumorigenic capabilities involving a FAK/EGFR/proteasome pathway in Madin-Darby canine kidney cells

Epithelial cells can acquire invasive and tumorigenic capabilities through epithelial–mesenchymal-transition (EMT). The glycan-binding protein galectin-8 (Gal-8) activates selective β1-integrins involved in EMT and is overexpressed by certain carcinomas. Here we show that Gal-8 overexpression or exogenous addition promotes proliferation, migration, and invasion in nontumoral Madin–Darby canine kidney (MDCK) cells, involving focal-adhesion kinase (FAK)-mediated transactivation of the epidermal growth factor receptor (EGFR), likely triggered by α5β1integrin binding. Under subconfluent conditions, Gal-8–overexpressing MDCK cells (MDCK-Gal-8^H) display hallmarks of EMT, including decreased E-cadherin and up-regulated expression of vimentin, fibronectin, and Snail, as well as increased β-catenin activity. Changes related to migration/invasion included higher expression of α5β1 integrin, extracellular matrix-degrading MMP13 and urokinase plasminogen activator/urokinase plasminogen activator receptor (uPA/uPAR) protease systems. Gal-8–stimulated FAK/EGFR pathway leads to proteasome overactivity characteristic of cancer cells. Yet MDCK-Gal-8^H cells still develop apical/basolateral polarity reverting EMT markers and proteasome activity under confluence. This is due to the opposite segregation of Gal-8 secretion (apical) and β1-integrins distribution (basolateral). Strikingly, MDCK-Gal-8^H cells acquired tumorigenic potential, as reflected in anchorage-independent growth in soft agar and tumor generation in immunodeficient NSG mice. Therefore, Gal-8 can promote oncogenic-like transformation of epithelial cells through partial and reversible EMT, accompanied by higher proliferation, migration/invasion, and tumorigenic properties.

The roles of galectins in parasitic infections

Galectins is a family of multifunctional lectins. Fifteen galectins have been identified from a variety of cells and tissues of vertebrates and invertebrates. Galectins have been shown to play pivotal roles in host-pathogen interaction such as adhesion of pathogens to host cells and activation of host innate and adaptive immunity. In recent years, the roles of galectins during parasite infections have gained increasing attention. Galectins produced by different hosts can act as pattern recognition receptors detecting conserved pathogen-associated molecular patterns of parasites, while galectins produced by parasites can modulate host responses. This review summarizes some recent studies on the roles of galectins produced by parasitic protozoa, nematodes, and trematodes and their hosts. Understanding the roles of galectins in host-parasite interactions may provide targets for immune intervention and therapies of parasitic infections.

Harnessing benefit from targeting tumor associated carbohydrate antigens

Integrating additive or synergistic antitumor effects that focus on distinct elements of tumor biology are the most rational strategies for cancer treatment. Treatments for breast cancer have increased overall survival, but remain limited by lack of efficacy in a subset of breast cancer patients. The real challenge is to define what elements of tumor biology make the most sense to be integrated. An emerging strategy is to consider a systems biology approach to impact multiple interactions in networks as compare with hitting a specific protein-protein interaction target. In this review, we consider how targeting tumor associated carbohydrate antigens (TACA) that are fundamental to signal pathways might be tailored to harness benefit from combination therapy of sustained immunity with chemotherapy. An approach we are developing makes use of a carbohydrate mimetic peptide (CMP) to induce polyspecific antibodies, which by their nature have numerous on and off target effects. Linking multi-target TACA recognition with mechanisms affecting tumor growth in the context of network heterogeneity and concepts of immune surveillance to tumor cells and the type of breast cancer patients that would benefit from such an approach provides a novel integrative treatment.

Structure-based rationale for differential recognition of lacto- and neolacto- series glycosphingolipids by the N-terminal domain of human galectin-8

Glycosphingolipids are ubiquitous cell surface molecules undertaking fundamental cellular processes. Lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT) are the representative core structures for lacto- and neolacto-series glycosphingolipids. These glycolipids are the carriers to the blood group antigen and human natural killer antigens mainly found on blood cells, and are also principal components in human milk, contributing to infant health. The β-galactoside recognising galectins mediate various cellular functions of these glycosphingolipids. We report crystallographic structures of the galectin-8 N-terminal domain (galectin-8N) in complex with LNT and LNnT. We reveal the first example in which the non-reducing end of LNT binds to the primary binding site of a galectin, and provide a structure-based rationale for the significant ten-fold difference in binding affinities of galectin-8N toward LNT compared to LNnT, such a magnitude of difference not being observed for any other galectin. In addition, the LNnT complex showed that the unique Arg59 has ability to adopt a new orientation, and comparison of glycerol- and lactose-bound galectin-8N structures reveals a minimum atomic framework for ligand recognition. Overall, these results enhance our understanding of glycosphingolipids interactions with galectin-8N, and highlight a structure-based rationale for its significantly different affinity for components of biologically relevant glycosphingolipids.

Crystallization of Galectin-8 Linker Reveals Intricate Relationship between the N-terminal Tail and the Linker

Galectin-8 (Gal-8) plays a significant role in normal immunological function as well as in cancer. This lectin contains two carbohydrate recognition domains (CRD) connected by a peptide linker. The N-terminal CRD determines ligand binding specificity, whereas the linker has been proposed to regulate overall Gal-8 function, including multimerization and biological activity. Here, we crystallized the Gal-8 N-terminal CRD with the peptide linker using a crystallization condition that contains Ni²⁺. The Ni²⁺ ion was found to be complexed between two CRDs via crystal packing contacts. The coordination between Ni²⁺ and Asp25 plays an indirect role in determining the structure of β-strand F0 and in influencing the linker conformation which could not be defined due to its dynamic nature. The linker was also shortened in situ and crystallized under a different condition, leading to a higher resolution structure refined to 1.08 Å. This crystal structure allowed definition of a short portion of the linker interacting with the Gal-8 N-terminal tail via ionic interactions and hydrogen bonds. Observation of two Gal-8 N-terminal CRD structures implies that the N-terminal tail and the linker may influence each other’s conformation. In addition, under specific crystallization conditions, glycerol could replace lactose and was observed at the carbohydrate binding site. However, glycerol did not show inhibition activity in hemagglutination assay.

Deep phylogenomics of a tandem-repeat galectin regulating appendicular skeletal pattern formation

BACKGROUND

A multiscale network of two galectins Galectin-1 (Gal-1) and Galectin-8 (Gal-8) patterns the avian limb skeleton. Among vertebrates with paired appendages, chondrichthyan fins typically have one or more cartilage plates and many repeating parallel endoskeletal elements, actinopterygian fins have more varied patterns of nodules, bars and plates, while tetrapod limbs exhibit tandem arrays of few, proximodistally increasing numbers of elements. We applied a comparative genomic and protein evolution approach to understand the origin of the galectin patterning network. Having previously observed a phylogenetic constraint on Gal-1 structure across vertebrates, we asked whether evolutionary changes of Gal-8 could have critically contributed to the origin of the tetrapod pattern.

RESULTS

Translocations, duplications, and losses of Gal-8 genes in Actinopterygii established them in different genomic locations from those that the Sarcopterygii (including the tetrapods) share with chondrichthyans. The sarcopterygian Gal-8 genes acquired a potentially regulatory non-coding motif and underwent purifying selection. The actinopterygian Gal-8 genes, in contrast, did not acquire the non-coding motif and underwent positive selection.

CONCLUSION

These observations interpreted through the lens of a reaction-diffusion-adhesion model based on avian experimental findings can account for the distinct endoskeletal patterns of cartilaginous, ray-finned, and lobe-finned fishes, and the stereotypical limb skeletons of tetrapods.

Galectin-8 promotes migration and proliferation and prevents apoptosis in U87 glioblastoma cells

Background

Glioblastoma is one of the most aggressive cancers of the brain. Malignant traits of glioblastoma cells include elevated migration, proliferation and survival capabilities. Galectins are unconventionally secreted glycan-binding proteins that modulate processes of cell adhesion, migration, proliferation and apoptosis by interacting with beta-galactosides of cell surface glycoproteins and the extracellular matrix. Galectin-8 is one of the galectins highly expressed in glioblastoma cells. It has a unique selectivity for terminally sialylated glycans recently found enhanced in these highly malignant cells. A previous study in glioblastoma cell lines reported that Gal-8 coating a plastic surface stimulates two-dimensional motility. Because in other cells Gal-8 arrests proliferation and induces apoptosis, here we extend its study by analyzing all of these processes in a U87 glioblastoma cell model.

Methods

We used immunoblot and RT-PCR for Gal-8 expression analysis, recombinant Gal-8 produced in a bacteria system for Gal-8 treatment of the cells, and shRNA in lentivirus transduction for Gal-8 silencing. Cell migration as assessed in transwell filters. Cell proliferation, cell cycle and apoptosis were analyzed by FACS.

Results

Gal-8 as a soluble stimulus triggered chemotactic migration of U87 cells across the polycarbonate filter of transwell chambers, almost as intensively as fetal bovine serum. Unexpectedly, Gal-8 also enhanced U87 cell growth. Co-incubation of Gal-8 with lactose, which blocks galectin–glycan interactions, abrogated both effects. Immunoblot showed Gal-8 in conditioned media reflecting its secretion. U87 cells transduced with silencing shRNA in a lentiviral vector expressed and secreted 30–40 % of their normal Gal-8 levels. These cells maintained their migratory capabilities, but decreased their proliferation rate and underwent higher levels of apoptosis, as revealed by flow cytometry analysis of cell cycle, CFSE and activated caspase-3 staining. Proliferation seemed to be more sensitive than migration to Gal-8 expression levels.

Conclusions

Gal-8, either secreted or exogenously enriched in the media, and acting through extracellular glycan interactions, constitutes a strong stimulus of directional migration in glioblastoma U87 cells and for the first time emerges as a factor that promotes proliferation and prevents apoptosis in cancerous cells. These properties could potentially contribute to the exaggerated malignancy of glioblastoma cells.

Galectin-8 is associated with recurrence and survival of patients with non-metastatic gastric cancer after surgery

The expression of galectin family has been unraveled in many malignant tumors and related with clinical outcomes. Our current study aims to investigate the prognostic value of galectin-8 expression and refine the current risk stratification system in non-metastatic gastric cancer patients. We retrospectively enrolled 421 patients with gastric cancer from Zhongshan Hospital, Fudan University in 2008. The expression of galectin-8 was detected by immunohistochemistry, and its association with clinicopathological features and prognostic outcomes were assessed. We found that galectin-8 expression was significantly associated with tumor size (P = 0.007), T stage (P = 0.001), N stage (P < 0.001), and tumor node metastasis (TNM) stage (P < 0.001). In addition, low galectin-8 expression indicated poor overall survival (OS) (P < 0.001) and disease-free survival (DFS) (P < 0.001). Furthermore, galectin-8 expression level was identified as an independent favorable prognostic factor for OS (P < 0.001). A predictive nomogram was generated with identified independent prognosticators to evaluate patient OS at 3 and 5 years. Our study suggested that galectin-8 is a potential independent favorable prognostic biomarker for survival and recurrence of patients with gastric cancer after surgical resection and the integration of intratumoral galectin-8 expression level into current TNM staging system would help to refine individual risk stratification.

Glycosylation-dependent binding of galectin-8 to activated leukocyte cell adhesion molecule (ALCAM/CD166) promotes its surface segregation on breast cancer cells

BACKGROUND

We previously demonstrated that the activated leukocyte cell adhesion molecule (ALCAM/CD166) can interact with galectin-8 (Gal-8) in endothelial cells. ALCAM is a member of the immunoglobulin superfamily that promotes homophilic and heterophilic cell-cell interactions. Gal-8 is a "tandem-repeat"-type galectin, known as a matricellular protein involved in cell adhesion. Here, we analyzed the physical interaction between both molecules in breast cancer cells and the functional relevance of this phenomenon.

METHODS

We performed binding assays by surface plasmon resonance to study the interaction between Gal-8 and the recombinant glycosylated ALCAM ectodomain or endogenous ALCAM from MDA-MB-231 breast cancer cells. We also analyzed the binding of ALCAM-silenced or control breast cancer cells to immobilized Gal-8 by SPR. In internalization assays, we evaluated the influence of Gal-8 on ALCAM surface localization.

RESULTS

We showed that recombinant glycosylated ALCAM and endogenous ALCAM from breast carcinoma cells physically interacted with Gal-8 in a glycosylation-dependent fashion displaying a differential behavior compared to non-glycosylated ALCAM. Moreover, ALCAM-silenced breast cancer cells exhibited reduced binding to Gal-8 relative to control cells. Importantly, exogenously added Gal-8 provoked ALCAM segregation, probably trapping this adhesion molecule at the surface of breast cancer cells.

CONCLUSIONS

Our data indicate that Gal-8 interacts with ALCAM at the surface of breast cancer cells through glycosylation-dependent mechanisms.

GENERAL SIGNIFICANCE

A novel heterophilic interaction between ALCAM and Gal-8 is demonstrated here, suggesting its physiologic relevance in the biology of breast cancer cells.

Characterization of a double-CRD-mutated Gal-8 recombinant protein that retains co-stimulatory activity on antigen-specific T-cell response

Galectins (Gals) constitute a family of mammalian lectins with affinity for β-galactosides, characterized by the presence of conserved CRDs (carbohydrate-recognition domains). We have found previously that Gal-8, from the tandem-repeat group with two linked CRDs, exerts two separate actions on CD4(+)T-cells: antigen-independent proliferation and, at lower concentration, antigen-specific co-stimulation. Whereas proliferation can be ascribed to the pro-inflammatory role of Gal-8, the co-stimulatory activity of borderline T-cell-specific responses allows the proposal of Gal-8 as an adjuvant in vaccination. To study the relevance of glycan-lectin interaction to these T-cell activities, we generated a double-mutated protein (Gal-8mut) by replacing canonical arginine residues on each CRD, so as to abolish sugar-binding capacity. As expected, Gal-8mut was unable to bind to lactosyl-Sepharose, confirming that lactose recognition was precluded; however, preservation of lectin activity was still evident since Gal-8mut displayed haemoagglutinatory effects and binding capacity to the T-cell surface. To search for glycan affinity, a glycan microarray analysis was conducted which revealed that Gal-8mut lost most low- and intermediate-, but retained high-, affinity interactions, mainly to polylactosamines and blood group antigens. These findings were supported further by molecular modelling. Regarding biological activity, Gal-8mut was unable to induce T-cell proliferation, but efficiently co-stimulated antigen-specific responses, bothin vitroandin vivo.Therefore Gal-8mut represents a useful tool to dissect the specificities of lectin-glycan interactions underlying distinctive Gal-8 activities on T-cell biology. Moreover, given its distinguishing properties, Gal-8mut could be used to enhance borderline immune responses without the non-specific pro-inflammatory activity or other potential adverse effects.

Epididymal protein ASF is a D-galactose-specific lectin with apoptotic effect on human breast cancer cell line MCF7

Isolated caprine epididymal plasma glycoprotein "anti sticking factor" (ASF) interacts with caudal sperm surface in a D-galactose dependent manner. ASF acts as a Ca(2+) dependent soluble lectin principally activated in acidic pH. As a D-galactose specific lectin, it has a specific affinity for fibronectin as well as fibronectin receptor, i.e. integrins α5β3 and α5β1. By virtue of this particular property, it hampers the in vitro adhesion of the adherent breast cancer cell MCF7 with fibronectin. The effective anti-adhesive concentration of ASF promotes p53 dependent apoptosis in MCF7, which was established by Hoechst 33342 staining, DNA fragmentation assay, FITC tagged Annexin-V flowcytometry and western blot analysis. We suggest that ASF inhibits fibronectin-integrin interactions by binding with them and induces adhesion dependent apoptosis on adherent MCF7.