Multidrug resistance (MDR), an unfavorable factor compromising the treatment efficacy of anticancer drugs, involves the upregulation of ATP binding cassette (ABC) transporters and induction of galectin-3 signaling. Galectin-3 plays an anti-apoptotic role in many cancer cells and regulates various pathways to activate MDR. Thus, the inhibition of galectin-3 has the potential to enhance the efficacy of the anticancer drug epirubicin. In this study, we examined the effects and mechanisms of silencing galectin-3 via RNA interference (RNAi) on the β-catenin/GSK-3β pathway in human colon adenocarcinoma Caco-2 cells. Galectin-3 knockdown increased the intracellular accumulation of epirubicin in Caco-2 cells; suppressed the mRNA expression of galectin-3, β-catenin, cyclin D1, c-myc, P-glycoprotein (P-gp), MDR-associated protein (MRP) 1, and MRP2; and downregulated the protein expression of P-gp, cyclin D1, galectin-3, β-catenin, c-Myc, and Bcl-2. Moreover, galectin-3 RNAi treatment significantly increased the mRNA level of GSK-3β, Bax, caspase-3, and caspase-9; remarkably increased the Bax-to-Bcl-2 ratio; and upregulated the GSK-3β and Bax protein expressions. Apoptosis was induced by galectin-3 RNAi and/or epirubicin as demonstrated by chromatin condensation, a higher sub-G1 phase proportion, and increased caspase-3 and caspase-9 activity, indicating an intrinsic/mitochondrial apoptosis pathway. Epirubicin-mediated resistance was effectively inhibited via galectin-3 RNAi treatment. However, these phenomena could be rescued after galectin-3 overexpression. We show for the first time that the silencing of galectin-3 sensitizes MDR cells to epirubicin by inhibiting ABC transporters and activating the mitochondrial pathway of apoptosis through modulation of the β-catenin/GSK-3β pathway in human colon cancer cells.
Aberrant neuroinflammation is suspected to contribute to the pathogenesis of myriad neurological diseases. As such, determining the pathways that promote or inhibit glial activation is of interest. Activation of the surface glycoprotein T-cell immunoglobulin and mucin-domain containing protein 3 (Tim-3) by the lectin galectin-9 has been implicated in promoting innate immune cell activation by potentiating or synergizing toll-like receptor (TLR) signaling. In the present study we examined the role of the Tim-3/galectin-9 pathway in glial activation in vitro.
Primary monocultures of microglia or astrocytes, co-cultures containing microglia and astrocytes, and mixed glial cultures consisting of microglia, astrocytes and oligodendrocytes were stimulated with poly(I:C) or LPS, and galectin-9 up-regulation was determined. The effect of endogenous galectin-9 production on microglial activation was examined using cultures from wild-type and Lgals9 null mice. The ability for recombinant galectin-9 to promote microglia activation was also assessed. Tim-3 expression on microglia and BV2 cells was examined by qPCR and flow cytometry and its necessity in transducing the galectin-9 signal was determined using a Tim-3 specific neutralizing antibody or recombinant soluble Tim-3.
Astrocytes potentiated TNF production from microglia following TLR stimulation. Poly(I:C) stimulation increased galectin-9 expression in microglia and microglial-derived factors promoted galectin-9 up-regulation in astrocytes. Astrocyte-derived galectin-9 in turn enhanced microglial TNF production. Similarly, recombinant galectin-9 enhanced poly(I:C)-induced microglial TNF and IL-6 production. Inhibition of Tim-3 did not alter TNF production in mixed glial cultures stimulated with poly(I:C).
Galectin-9 functions as an astrocyte-microglia communication signal and promotes cytokine production from microglia in a Tim-3 independent manner. Activation of CNS galectin-9 likely modulates neuroinflammatory processes in which TNF and IL-6 contribute to either pathology or reparation.
Electronic supplementary material
The online version of this article (doi:10.1186/s12974-014-0144-0) contains supplementary material, which is available to authorized users.
Galectin-9; TNFα; Astrocytes; Microglia activation; Poly(I:C); Neuroinflammation
Galectin-3, a member of the beta-galactoside-binding lectin family, is a multifunctional protein with various biological functions, including the proliferation and differentiation of tumor cells, angiogenesis, cancer progression, and metastasis. We aimed to clarify if expression of galectin-3 is related to the clinicopathological characteristics and prognosis of hepatocellular carcinoma (HCC) patients, and to explore the possible mechanisms of galectin-3 in hepatocellular carcinoma.
First, we investigated galectin-3 mRNA and protein expression by using RT-PCR and Western blotting. Second, tissues from 165 HCC patients were used to evaluate clinicopathological characteristics and prognosis through immunohistochemical analyses. Furthermore, the functions of galectin-3 were analyzed with respect to the proliferation, cell cycle,apoptosis, migration, and invasion of HCC cell lines. Finally, we analyzed galectin-3 expression and micro-vessel density (MVD) by immunohistochemistry (IHC) to find its correlation with angiogenesis in Hepatocellular Carcinoma. Flow cytometer was used to explore apoptosis and Western-blot was used to detect the pathway proteins of apoptosis.
Galectin-3 showed high expression at the mRNA and protein levels in HCC cancer tissues and cell lines. Clinicopathological analyses revealed that increased expression of galectin-3 in tumors was closely associated with a poor prognosis. Galectin-3 knockdown by siRNA significantly inhibited cell growth, migration, and invasion, and induced apoptosis in HCC cells in vitro, whereas galectin-3 overexpression promoted cell growth, migration, and invasion. Correlation analysis of galectin-3 expression and micro-vessel density (MVD) showed that galectin-3 expression in tumor cells stimulates angiogenesis. The observed regulation of cell apoptosis was accompanied by the galectin-3-mediated modulation of caspase3 signaling pathways in HCC cells.
These data suggest that galectin-3 plays an important part in HCC progression and may serve as a prognostic factor for HCC.
Galectin-3; Hepatocellular carcinoma; Angiogenesis; Apoptosis; Prognostic factor
Rationale: Idiopathic pulmonary fibrosis (IPF) is a chronic dysregulated response to alveolar epithelial injury with differentiation of epithelial cells and fibroblasts into matrix-secreting myofibroblasts resulting in lung scaring. The prognosis is poor and there are no effective therapies or reliable biomarkers. Galectin-3 is a β-galactoside binding lectin that is highly expressed in fibrotic tissue of diverse etiologies.
Objectives: To examine the role of galectin-3 in pulmonary fibrosis.
Methods: We used genetic deletion and pharmacologic inhibition in well-characterized murine models of lung fibrosis. Further mechanistic studies were performed in vitro and on samples from patients with IPF.
Measurements and Main Results: Transforming growth factor (TGF)-β and bleomycin-induced lung fibrosis was dramatically reduced in mice deficient in galectin-3, manifest by reduced TGF-β1–induced EMT and myofibroblast activation and collagen production. Galectin-3 reduced phosphorylation and nuclear translocation of β-catenin but had no effect on Smad2/3 phosphorylation. A novel inhibitor of galectin-3, TD139, blocked TGF-β–induced β-catenin activation in vitro and in vivo and attenuated the late-stage progression of lung fibrosis after bleomycin. There was increased expression of galectin-3 in the bronchoalveolar lavage fluid and serum from patients with stable IPF compared with nonspecific interstitial pneumonitis and controls, which rose sharply during an acute exacerbation suggesting that galectin-3 may be a marker of active fibrosis in IPF and that strategies that block galectin-3 may be effective in treating acute fibrotic exacerbations of IPF.
Conclusions: This study identifies galectin-3 as an important regulator of lung fibrosis and provides a proof of principle for galectin-3 inhibition as a potential novel therapeutic strategy for IPF.
fibrosis; epithelial cells; fibroblasts
Galectin-1 is a lectin recognized by galactoside-containing glycoproteins, and is involved in cancer progression and metastasis. The role of galectin-1 in radiosensitivity has not previously been investigated. Therefore, this study tests whether galectin-1 is involved in the radiosensitivity mediated by the H-Ras signaling pathway using cervical carcinoma cell lines. A knockdown of galectin-1 expression in HeLa cells decreased clonogenic survival following irradiation. The clonogenic survival increased in both HeLa and C33A cells with galectin-1 overexpression. The overexpression or knockdown of galectin-1 did not alter radiosensitivity, whereas H-Ras was silenced in both cell lines. Whereas K-Ras was knocked down, galectin-1 restored the radiosensitivity in HeLa cells and C33A cells. The knockdown of galectin-1 increased the high-dose radiation-induced cell death of HeLa cells transfected by constitutively active H-Ras. The knockdown of galectin-1 inhibited the radiation-induced phosphorylation of Raf-1 and ERK in HeLa cells. Overexpression of galectin-1 enhanced the phosphorylation of Raf-1 and ERK in C33A cells following irradiation. Galectin-1 decreased the DNA damage detected using comet assay and γ-H2AX in both cells following irradiation. These findings suggest that galectin-1 mediates radioresistance through the H-Ras-dependent pathway involved in DNA damage repair.
galectin-1; cervical cancer; radiosensitivity; radioresistance; H-Ras
Galectin-4 is a carbohydrate-binding protein belonging to the galectin family. Here we provide novel evidence that galectin-4 is selectively expressed and secreted by intestinal epithelial cells and binds potently to activated peripheral and mucosal lamina propria T-cells at the CD3 epitope. The carbohydrate-dependent binding of galectin-4 at the CD3 epitope is fully functional and inhibited T cell activation, cycling and expansion. Galectin-4 induced apoptosis of activated peripheral and mucosal lamina propria T cells via calpain-, but not caspase-dependent, pathways. Providing further evidence for its important role in regulating T cell function, galectin-4 blockade by antisense oligonucleotides reduced TNF-alpha inhibitor induced T cell death. Furthermore, in T cells, galectin-4 reduced pro-inflammatory cytokine secretion including IL-17. In a model of experimental colitis, galectin-4 ameliorated mucosal inflammation, induced apoptosis of mucosal T-cells and decreased the secretion of pro-inflammatory cytokines. Our results show that galectin-4 plays a unique role in the intestine and assign a novel role of this protein in controlling intestinal inflammation by a selective induction of T cell apoptosis and cell cycle restriction. Conclusively, after defining its biological role, we propose Galectin-4 is a novel anti-inflammatory agent that could be therapeutically effective in diseases with a disturbed T cell expansion and apoptosis such as inflammatory bowel disease.
Galectin-1 is known to be one of the extracellular matrix proteins. To elucidate the biological roles of galectin-1 in cell adhesion and invasion of human anaplastic large cell lymphoma, we performed cell adhesion and invasion assays using the anaplastic large cell lymphoma cell line H-ALCL, which was previously established in our laboratory. From the cell surface lectin array, treatment with neuraminidase from Arthrobacter ureafaciens which cleaves all linkage types of cell surface sialic acid enhanced Arachis hypogaea (PNA), Helix pomatia (HPA) and Phaseolus vulgaris-L (L-PHA) lectin binding reactivity to cell surface of lymphoma cells suggesting that neuraminidase removes cell surface sialic acid. In cell adhesion and invasion assays treatment with neuraminidase markedly enhanced cell adhesion to galectin-1 and decreased cell invasive capacity through galectin-1. α2,6-linked sialic acid may be involved in masking the effect of the interaction between galectin-1 and cell surface glycans. H-ALCL cells expressed the β-galactoside-α2,6-sialyltransferase ST6Gal1. On resialylation assay by recombinant ST6Gal1 with CMP-Neu5Ac, α2,6-resialylation of L-PHA reactive oligosaccharide by ST6Gal1 resulted in inhibition of H-ALCL cell adhesion to galectin-1 compared to the desialylated H-ALCL cells. On knockdown experiments, knockdown of ST6Gal1 dramatically enhanced cell adhesion to galectin-1. N-glycosylation inhibitor swainsonine treatment resulted in enhancement of cell adhesion to galectin-1. In glycomic analysis using the lectin blocking assay treatment with PNA, Artocarpus integrifolia (Jacalin), Glycine max (SBA), Helix pomatia (HPA), Vicia villosa (VVA), Ulex europaeus (UEA-1), Triticum vulgaris (WGA), Canavalia ensiformis (ConA), Phaseolus vulgaris-L (L-PHA), Phaseolus vulgaris-E4 (E-PHA), Datura stramonium (DSA) lectins resulted in modulation of lymphoma cell to galectin-1 suggesting that several types of glycans may regulate cell adhesion to galectin-1 by steric hindrance. The adhesive capacity of H-ALCL cells is regulated by phosphatidylinositol 3 phosphate kinase (PI3K) and actin cytoskeleton, and the invasive capacity of H-ALCL cells is regulated by PI3K, mitogen-activated protein kinase (MAPK), Rho and actin cytoskeleton. Furthermore, galectin-1-induced cell death in H-ALCL cells was accompanied by inhibition of CD45 protein tyrosine phosphatase (PTP) activity. In conclusion, cell adhesion and invasion to galectin-1 appeared to be regulated by cell surface sialylation and N-glycosylation, and galectin-1 regulates cell death through inhibition of CD45 PTP activity of H-ALCL.
galectin-1; glycosylation; sialic acid; sialyltransferase; cell adhesion; cell death; lectin array
Resistance to apoptosis induced by anti-cancer drugs is a major obstacle for the treatment of aggressive forms of breast cancer. Galectin-7 (gal-7) was recently shown to be specifically expressed in basal-like but not in luminal subtypes of human breast cancer.
We generated a mutant form of gal-7 (R74S). Arginine 74 is the structural equivalent of arginine 186 found in human galectin-3. Mutation R186S was previously shown to abolish the biological function of galectin-3.
Mutation of arginine 74 induced only limited and local changes to the gal-7 fold. Recombinant forms of R74S and wtgal-7 were also equally effective at forming dimers in solution. Analysis of the thermodynamic parameters by isothermal titration calorimetry (ITC) indicated, however, that binding of lactose to gal-7 was inhibited by the R74S mutation. Using confocal microscopy and electron microscopy, we confirmed the expression of gal-7 in the cytosolic and nuclear compartments of breast cancer cells and the ability of gal-7 to translocate to mitochondria. The mutation at position 74, however, greatly reduced the expression of gal-7 in the nuclear and mitochondrial compartments. Interestingly, cells expressing mutated gal-7 were equally if not even more resistant to drug-induced apoptosis when compared to cells expressing wtgal-7. We also found that both wtgal-7 and R74S inhibited dox-induced PARP-1 cleavage and p53 protein expression. The inhibition of p53 correlated with a decrease in p21 protein expression and CDKN1A mRNA. Furthermore, analysis of nuclear and cytoplasmic fractions showed that both wild type and R74S mutant gal-7 inhibited p53 nuclear translocation, possibly by increasing degradation of cytosolic p53.
These findings pose a challenge to the paradigm that has guided the design of galectin-specific inhibitors for the treatment of cancer. This study suggests that targeting CRD-independent cytosolic gal-7 in breast cancer cells may be a valuable strategy for the treatment of this disease. Our study will thus complement efforts towards improving selectivity of targeted anticancer agents.
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Galectin-7; Localization; Apoptosis; p53; Breast cancer
Galectin-7 is considered a gene under the control of p53. However, elevated expression of galectin-7 has been reported in several forms of cancer harboring an inactive p53 pathway. This is especially true for breast cancer where galectin-7 expression is readily expressed in a high proportion in basal-like breast cancer tissues, conferring cancer cells with increased resistance to cell death and metastatic properties. These observations suggest that other transcription factors are capable of inducing galectin-7 expression. In the present work, we have examined the role of CCAAT/enhancer-binding protein beta (C/EBPβ) in inducing expression of galectin-7. C/EBP proteins have been shown to contribute to breast cancer by upregulating pro-metastatic genes. We paid particular attention to C/EBPβ-2 (also known as LAP2), the most transcriptionally active of the C/EBPβ isoforms. Our results showed that ectopic expression of C/EBPβ-2 in human breast cancer cells was sufficient to induce expression of galectin-7 at both the mRNA and protein levels. In silico analysis further revealed the presence of an established CEBP element in the galectin-7 promoter. Mutation of this binding site abolished the transcriptional activity of the galectin-7 promoter. Chromatin immunoprecipitation analysis confirmed that C/EBPβ-2 binds to the endogenous galectin-7 promoter. Analysis of galectin-7 protein expression in normal epithelia and in breast carcinoma by immunohistochemistry further showed the expression pattern of C/EBPβ closely micmicked that of galectin-7, most notably in mammary myoepithelial cells and basal-like breast cancer where galectin-7 is preferentially expressed. Taken together, our findings suggest that C/EBPβ is an important mediator of galectin-7 gene activation in breast cancer cells and highlight the different transcriptional mechanisms controlling galectin-7 in cancer cells.
Galectin-3 is a human lectin involved in many cellular processes including differentiation, apoptosis, angiogenesis, neoplastic transformation, and metastasis. We evaluated galectin-3C, an N-terminally truncated form of galectin-3 that is thought to act as a dominant negative inhibitor, as a potential treatment for multiple myeloma (MM). Galectin-3 was expressed at varying levels by all 9 human MM cell lines tested. In vitro galectin-3C exhibited modest anti-proliferative effects on MM cells and inhibited chemotaxis and invasion of U266 MM cells induced by stromal cell-derived factor (SDF)-1α. Galectin-3C facilitated the anticancer activity of bortezomib, a proteasome inhibitor approved by the FDA for MM treatment. Galectin-3C and bortezomib also synergistically inhibited MM-induced angiogenesis activity in vitro. Delivery of galectin-3C intravenously via an osmotic pump in a subcutaneous U266 cell NOD/SCID mouse model of MM significantly inhibited tumor growth. The average tumor volume of bortezomib-treated animals was 19.6% and of galectin-3C treated animals was 13.5% of the average volume of the untreated controls at day 35. The maximal effect was obtained with the combination of galectin-3C with bortezomib that afforded a reduction of 94% in the mean tumor volume compared to the untreated controls at day 35. In conclusion, this is the first study to show that inhibition of galectin-3 is efficacious in a murine model of human MM. Our results demonstrated that galectin-3C alone was efficacious in a xenograft mouse model of human MM, and that it enhanced the anti-tumor activity of bortezomib in vitro and in vivo. These data provide the rationale for continued testing of galectin-3C towards initiation of clinical trials for treatment of MM.
Galectin-3, the only chimera galectin found in vertebrates, is one of the best-studied galectins. It is expressed in several cell types and is involved in a broad range of physiological and pathological processes, such as cell adhesion, cell activation and chemoattraction, cell cycle, apoptosis, and cell growth and differentiation. However, this molecule raises special interest due to its role in regulating cancer cell activities. Galectin-3 has high affinity for β-1,6-N-acetylglucosamine branched glycans, which are formed by the action of the β1,6-N-acetylglucosaminyltransferase V (Mgat5). Mgat5-related changes in protein/lipid glycosylation on cell surface lead to alterations in the clustering of membrane proteins through lattice formation, resulting in functional advantages for tumor cells. Galectin-3 presence enhances migration and/or invasion of many tumors. Galectin-3-dependent clustering of integrins promotes ligand-induced integrin activation, leading to cell motility. Galectin-3 binding to mucin-1 increases transendothelial invasion, decreasing metastasis-free survival in an experimental metastasis model. Galectin-3 also affects endothelial cell behavior by regulating capillary tube formation. This lectin is found in the tumor stroma, suggesting a role for microenvironmental galectin-3 in tumor progression. Galectin-3 also seems to be involved in the recruitment of tumor-associated macrophages, possibly contributing to angiogenesis and tumor growth. This lectin can be a relevant factor in turning bone marrow in a sanctuary for leukemia cells, favoring resistance to therapy. Finally, galectin-3 seems to play a relevant role in orchestrating distinct cell events in tumor microenvironment and for this reason, it can be considered a target in tumor therapies. In conclusion, this review aims to describe the processes of tumor progression and metastasis involving extracellular galectin-3 and its expression and regulation.
galectin-3; cancer; metastasis; glycosylation; Mgat5; lattices; tumor microenvironment
Nucleoporin Nup98 is a component of the nuclear pore complex, and is important in transport across the nuclear pore. Many studies implicate nucleoporin in cancer progression, but no direct mechanistic studies of its effect in cancer have been reported. We show here that Nup98 specifically regulates nucleus–cytoplasm transport of galectin-3, which is a β-galactoside-binding protein that affects adhesion, migration, and cancer progression, and controls cell growth through the β-catenin signaling pathway in cancer cells. Nup98 interacted with galectin-3 on the nuclear membrane, and promoted galectin-3 cytoplasmic translocation whereas other nucleoporins did not show these functions. Inversely, silencing of Nup98 expression by siRNA technique localized galectin-3 to the nucleus and retarded cell growth, which was rescued by Nup98 transfection. In addition, Nup98 RNA interference significantly suppressed downstream mRNA expression in the β-catenin pathway, such as cyclin D1 and FRA-1, while nuclear galectin-3 binds to β-catenin to inhibit transcriptional activity. Reduced expression of β-catenin target genes is consistent with the Nup98 reduction and the galectin-3–nucleus translocation rate. Overall, the results show Nup98’s involvement in nuclear–cytoplasm translocation of galectin-3 and β-catenin signaling pathway in regulating cell proliferation, and the results depicted here suggest a novel therapeutic target/modality for cancers.
Nucleoporin; Nuclear pore complex; Galectin-3; Nuclear transport; Cancer progression
Premature senescence induced by oncogenic stimuli or tumor suppressor activation plays opposing roles in tumorigenesis. Here, we propose that galectin-3, a β-galactoside-binding lectin, regulates premature senescence without oncogenic stress. We detected premature senescence, decreased Skp2, and increased p27KIP1 expression in galectin-3 knockout MEFs and galectin-3-depleted gastric cancer cells. Interestingly, galectin-3 depletion did not affect other senescence inducers such as p14ARF, p16INK4A, and p21WAF1/CIP1, suggesting that galectin-3-regulated senescence is p27KIP1 dependent. We demonstrate that galectin-3 depletion decreases retinoblastoma protein (Rb) phosphorylation (Ser780, Ser807/811), cyclin D1 and CDK4 expression, and E2F1 transcriptional activation. Galectin-3 directly interacts with the cyclin D1/CDK4 complex and promotes hyperphosphorylation of Rb. It also blocks the inhibition of E2F1 transcription, thereby increasing the expression of Skp2 and reducing the stability of p27KIP1 to promote the proliferation of gastric cancer cells. Xenograft mice with galectin-3-depleted gastric cancer cells display tumor growth retardation that is reversed by Skp2 overexpression. Increased expression of galectin-3 is also associated with the advanced TNM (tumor, lymph node, metastasis) system, clinicopathological stage, and lymph node metastases. The probability of survival was significantly decreased in gastric cancer patients with galectin-3high p27KIP1-lowcells. Taken together, our results show that galectin-3 may accelerate gastric tumorigenesis by inhibiting premature senescence.
Wnt/β-catenin signaling plays an essential role in colon carcinogenesis. Galectin-3, a β-galactoside-binding protein, has been implicated in Wnt signaling, but the precise mechanisms by which galectin-3 modulates the Wnt pathway are unknown. In the present study, we determined the effects of galectin-3 on the Wnt/β-catenin pathway in colon cancer cells, and the mechanisms involved. Galectin-3 levels were manipulated in human colon cancer cells by stable transfection of galectin-3 antisense, shRNA or full length galectin-3 cDNA, and effects on β-catenin levels, subcellular distribution, and Wnt signaling determined. Galectin-3 levels correlated with β-catenin levels in a variety of colon cancer cell lines. Down-regulation of galectin-3 resulted in decreased β-catenin protein levels but no change in β-catenin mRNA levels, suggesting that galectin-3 modulates β-catenin by another mechanism. Reduction of galectin-3 led to reduced nuclear β-catenin with a concomitant decrease in TCF4 transcriptional activity and expression of its target genes. Conversely, transfection of galectin-3 cDNA into colon cancer cells increased β-catenin expression and TCF4 transcriptional activity. Down-regulation of galectin-3 resulted in AKT and glycogen synthase kinase (GSK)-3β dephosphorylation and increased GSK activity, increasing β-catenin phosphorylation and degradation. Ly294002, an inhibitor of phosphatidylinositol 3-kinase, and dominant-negative AKT suppressed TCF4 transcriptional activity induced by galectin-3, while LiCl, a GSK-3β inhibitor, increased TCF4 activity, mimicking the effects of galectin-3. These results suggest that galectin-3 mediates Wnt signaling, at least in part, by regulating GSK-3β phosphorylation and activity via the PI3K/AKT pathway, and thus the degradation of β-catenin in colon cancer cells.
Galectin-3; β-catenin; TCF4; GSK-3β activity; PI3K/AKT pathway
Clear cell renal cell carcinoma, a solid growing tumor, is the most common tumor in human kidney. Evaluating the usefulness of β-galactoside binding galectin-3 as a diagnostic marker for this type of cancer could open avenues for preventive and therapeutic strategies by employing specific inhibitors of the lectin. To study a putative correlation between the extent of galectin-3 and the development of clear cell renal cell carcinoma, we monitored the quantity and distribution of this lectin in tissue samples from 39 patients.
Galectin-3 concentrations in normal, intermediate and tumor tissues were examined by immunofluorescence microscopy and on immunoblots with antibodies directed against galectin-3 and renal control proteins. The cell nuclei were isolated to determine quantities of galectin-3 that were transferred into this compartment in normal or tumor samples.
Immunofluorescence data revealed a mosaic pattern of galectin-3 expression in collecting ducts and distal tubules of normal kidney. Galectin-3 expression was significantly increased in 79% of tumor samples as compared to normal tissues. Furthermore, we observed an increase in nuclear translocation of the lectin in tumor tissues.
Our data indicate that changes in the cellular level of galectin-3 correlate with the development of clear cell renal cell carcinoma, which is in line with previously published data on this specific type of tumor. In most of these studies the lectin tends to be highly expressed in tumor tissues. Furthermore, this study suggests that the increase in the proportion of galectin-3 affects the balance from a cytosolic distribution towards translocation into the nucleus.
clear cell renal cell carcinoma; galectin-3; tumorigenesis; nuclear translocation
Galectin-7 was initially described as a marker of epithelial differentiation expressed in the stratified epithelium of various tissues. Like other members of the galectin family, its expression level is often significantly altered in cancer cells. In breast cancer, its expression is significantly augmented in aggressive molecular subtypes, most notably in estrogen receptor-negative tumors and in cell lines with a basal-like phenotype. Studies using experimental mouse models have further shown high expression of galectin-7 was sufficient to increase the metastatic behavior of poorly metastatic breast cancer cells, rendering them more resistant to apoptosis. This expression pattern in breast cancer cells is unexpected because galectin-7 was originally identified as a p53-induced gene. To address this paradox, we have examined the molecular mechanisms regulating galectin-7 in breast cancer cells. Our results showed that transfection of breast cancer cells with expression vectors encoding mutant p53 was sufficient to induce galectin-7 at both mRNA and protein levels. Doxorubicin treatment of breast cancer cells harboring a mutant p53 also induced galectin-7. This induction was specific since knockdown of endogenous mutant p53 inhibited doxorubicin-induced galectin-7 expression. The p53-induced galectin-7 expression in breast cancer cells correlated with increased NF-κB activity and was inhibited by NF-κB inhibitors, indicating that the ability of mutant p53 to induce galectin-7 was dependent on NF-κB activity. The implication of NF-κB was further supported by data showing that NF-κB bound to the endogenous galectin-7 promoter and that TNFα-induced galectin-7 expression was abolished by NF-κB inhibitors. Taken together, our data provide an explanation to the observed high galectin-7 expression levels in cancer cells and suggest that galectin-7 could be part of a common pathway used by mutant p53 to promote cancer progression.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis and preferentially kills tumor cells by engaging specific glycosylated death receptors, resulting in the internalization of ligand/receptor complexes and recruitment of the initiator caspase-8 to an activation platform known as the death-inducing signaling complex (DISC). However, emergence of TRAIL-resistant sub-populations may contribute to therapeutic failure. To investigate resistance mechanisms, we isolated a stable TRAIL-resistant sub-population of the metastatic colon cancer cell line LS-LIM6, designated LIM6-TR. LIM6-TR cells are impaired in endocytosis of TRAIL/death receptors complexes and failed to recruit/activate caspase-8 to the DISC upon TRAIL stimulation. Differential activation of Wnt and JNK pathways is not responsible for acquisition of TRAIL resistance. LIM6-TR cells display a marked increase in cell-surface expression of galectin-3, an endogenous lectin, which co-localizes with and binds death receptors. Silencing of galectin-3 restores TRAIL sensitivity and promotes TRAIL-mediated endocytosis of TRAIL/death receptors complexes. Inhibitors of galectin-3 and glycosylation also re-sensitize LIM6-TR to TRAIL and restore internalization of ligand/receptors complexes. These studies identify a novel TRAIL-resistance mechanism in which galectin-3 impedes trafficking of death receptor by anchoring them in glycan nano-clusters, blocking the execution of the apoptosis signal.
galectin-3; TRAIL; apoptosis; colon cancer
TRAIL induces apoptosis and preferentially kills tumor cells by engaging specific glycosylated death receptors resulting in the internalization of ligand-receptor complexes and recruitment of the initiator caspase-8 to an activation platform known as the death-inducing signaling complex (DISC). However, emergence of TRAIL-resistant sub-populations may contribute to therapeutic failure. To investigate resistance mechanisms we isolated a stable TRAIL-resistant sub-population of the metastatic colon cancer cell line LS-LIM6, designated LIM6-TR. LIM6-TR cells are impaired in endocytosis of TRAIL-death receptors complexes and failed to recruit/activate caspase-8 to the DISC upon TRAIL stimulation. Differential activation of Wnt and JNK pathways is not responsible for acquisition of TRAIL-resistance. LIM6-TR cells display a marked increase in cell-surface expression of galectin-3, an endogenous lectin, which co-localizes with and binds death receptors. Silencing of galectin-3 restores TRAIL-sensitivity and promotes TRAIL-mediated endocytosis of TRAIL-death receptors complexes. Inhibitors of galectin-3 and glycosylation also re-sensitize LIM6-TR to TRAIL and restore internalization of ligand-receptors complexes. These studies identify a novel TRAIL-resistance mechanism in which galectin-3 impedes trafficking of death receptor by anchoring them in glycan nano-clusters, blocking the execution of the apoptosis signal.
Galectin-3; TRAIL; apoptosis; colon cancer
The interaction between cell surface glycans and extracellular matrix (ECM) including galectins is known to be closely associated with tumor cell adhesion, invasion and metastasis. We analyzed the roles of cell surface sialylation or glycosylation in galectin or ECM-mediated cell adhesion and invasion of human malignant lymphoma cells. Neuraminidase from Arthrobacter ureafaciens (AU) treatment resulted in reduction of cell adhesion to galectin-8 in human anaplastic large cell lymphoma (H-ALCL) which was established in our laboratory. The knockdown of β-galactoside α-2,6-sialyltransferase (ST6Gal1) by siRNA showed inhibition of ST6Gal1 expression in the cytoplasm of H-ALCL cells on immunohistochemical findings, and showed dramatic enhancement of cell adhesion to galectin-8. On the other hand, α-2,3-specific neuraminidase treatment resulted in moderate enhancement of cell adhesion to galectin-8. We performed chemically artificial modification of cell surface O-glycans by treatment of benzyl 2-acetamido-2-deoxy-α-D-galactopyranoside (Bz-α-GalNAc) in H-ALCL. Cell adhesion to galectin-8 was enhanced by treatment of Bz-α-GalNAc suggesting that inhibition of elongation of O-glycans may enhance cell adhesion to galectin-8 in H-ALCL cells. On the other hand inhibition of elongation of N-glycosylation by tunicamycin (TM) resulted in inhibition of Phaseolus vulgaris-L (L-PHA) lectin-binding activity and inhibited cell adhesion to galectin-8,laminin and fibronectin. Neuraminidase treatment enhanced cell adhesion to laminin, and knockdown of ST6Gal1 resulted in enhancement of cell adhesion to laminin, but not to fibronectin, collagen type 1 and 4. Galectin-8 pre-treatment dramatically enhanced cell adhesion to laminin and neuraminidase treatment also enhanced cell adhesion to laminin in combination with galectin-8. Rho inhibitor, C3-transferase pre-treatment resulted in inhibition of cell invasion to galectin-8. Phosphatidylinositol 3-phosphate kinase (PI3K) inhibitor, wortmannin inhibits the cell invasive capacity to galectin-8. Neuraminidase treatment induces growth inhibition of lymphoma cells by galectin-8.
sialic acid; glycans; β-galactoside α-2; 6-sialyltransferase; cell adhesion; invasion; galectin-8; Rho; PI3K; MAPK
Galectins are a family of beta-galactoside-binding proteins that contain characteristic amino acid sequences in the carbohydrate recognition domain (CRD) of the polypeptide. The polypeptide of galectin-1 contains a single domain, the CRD. The polypeptide of galectin-3 has two domains, a carboxyl-terminal CRD fused onto a proline- and glycine-rich amino-terminal domain. In previous studies, we showed that galectin-3 is a required factor in the splicing of nuclear pre-mRNA, assayed in a cell-free system. We now document that (i) nuclear extracts derived from HeLa cells contain both galectins-1 and -3; (ii) depletion of both galectins from the nuclear extract either by lactose affinity adsorption or by double-antibody adsorption results in a concomitant loss of splicing activity; (iii) depletion of either galectin-1 or galectin-3 by specific antibody adsorption fails to remove all of the splicing activity, and the residual splicing activity is still saccharide inhibitable; (iv) either galectin-1 or galectin-3 alone is sufficient to reconstitute, at least partially, the splicing activity of nuclear extracts depleted of both galectins; and (v) although the carbohydrate recognition domain of galectin-3 (or galectin-1) is sufficient to restore splicing activity to a galectin-depleted nuclear extract, the concentration required for reconstitution is greater than that of the full-length galectin-3 polypeptide. Consistent with these functional results, double-immunofluorescence analyses show that within the nucleus, galectin-3 colocalizes with the speckled structures observed with splicing factor SC35. Similar results are also obtained with galectin-1, although in this case, there are areas of galectin-1 devoid of SC35 and vice versa. Thus, nuclear galectins exhibit functional redundancy in their splicing activity and partition, at least partially, in the nucleoplasm with another known splicing factor.
Mitochondrial dysfunction and release of pro-apoptotic factors such as cytochrome c or apoptosis-inducing factor (AIF) from mitochondria are key features of neuronal cell death. The precise mechanisms of how these proteins are released from mitochondria and their particular role in neuronal cell death signaling are however largely unknown. Here, we demonstrate by fluorescence video microscopy that 8–10 h after induction of glutamate toxicity, AIF rapidly translocates from mitochondria to the nucleus and induces nuclear fragmentation and cell death within only a few minutes. This markedly fast translocation of AIF to the nucleus is preceded by increasing translocation of the pro-apoptotic bcl-2 family member Bid (BH3-interacting domain death agonist) to mitochondria, perinuclear accumulation of Bid-loaded mitochondria, and loss of mitochondrial membrane integrity. A small molecule Bid inhibitor preserved mitochondrial membrane potential, prevented nuclear translocation of AIF, and abrogated glutamate-induced neuronal cell death, as shown by experiments using Bid small interfering RNA (siRNA). Cell death induced by truncated Bid was inhibited by AIF siRNA, indicating that caspase-independent AIF signaling is the main pathway through which Bid mediates cell death. This was further supported by experiments showing that although caspase-3 was activated, specific caspase-3 inhibition did not protect neuronal cells against glutamate toxicity. In conclusion, Bid-mediated mitochondrial release of AIF followed by rapid nuclear translocation is a major mechanism of glutamate-induced neuronal death.
HT-22 cells; glutamate; apoptosis; mitochondrial membrane potential; caspase-independent cell death
Galectin-3, a β-galactoside-binding lectin, is a cell adhesion molecule involved in the regulation of tumor progression. However, the importance of galectin-3 in Eca-109 human esophageal cancer cells has not yet been elucidated. In the present study, a lentiviral vector was designed for overexpression of galectin-3 in Eca-109 cells following plasmid-mediated transfection (Eca-109/Gal-3 cells). A negative lentiviral vector was introduced into Eca-109 cells as a control (Eca-109/Neo cells). Western blot and reverse transcription-polymerase chain reaction analyses were used to measure the expression levels of galectin-3 protein and mRNA. The proliferation of Eca-109 cells was measured by a cell counting kit-8 assay. Eca-109 cell apoptosis was determined by Annexin V/7-amino-actinomycin double-staining. The migration and invasion capacity of Eca-109 cells was determined by a Transwell assay. A total of >98% Eca-109 cells were transfected with the lentiviral vector harboring galectin-3, and galectin-3 expression was detected in Eca-109 cells, Eca-109/Gal-3 cells and Eca-109/Neo cells. Compared with non-transfected and negative control Eca-109 cells, proliferation was increased significantly in the Eca-109/Gal-3 cells (P<0.05). Galectin-3 also significantly reduced Eca-109 cell apoptosis, compared with the two control groups (P=0.007 and P=0.04, respectively). Transwell migration and invasion assays revealed that significantly greater numbers of Eca-109/Gal-3 cells crossed the artificial basement membrane (55.4±3.9) compared with either the non-transfected or negative control Eca-109 cells (30.6±1.5 and 29±2.6 respectively, P<0.05). In conclusion, galectin-3 expression was significantly increased in transfected Eca-109 esophageal cancer cells, resulting in enhanced proliferation, migration and invasion, as well as reduced apoptosis. These data indicate that galectin-3 may be a potential molecular target in the treatment of esophageal cancer.
esophageal carcinoma; galectin-3; Eca-109 cells
We investigated the role of galectin-3 on polarization of epithelial renal cells, using three-dimensional cultures of MDCK cells and also galectin-3 null mutant mouse kidneys. Collectively, data show that the absence of galectin-3 influences the stabilization of centrosomes and primary cilia, with effects on epithelial cell organization.
Galectin-3 is a β-galactoside–binding protein widely expressed in all epithelia where it is involved in tissue homeostasis and cancer progression. We recently reported unique abnormalities in the identity of membrane domains in galectin-3 null mutant mice, suggesting that galectin-3 may participate in epithelial polarity program. We investigated the potential role of galectin-3 on early events in polarization of epithelial renal cells, using three-dimensional cultures of MDCK cells and also galectin-3 null mutant mouse kidneys. We show that depletion in galectin-3 systematically leads to severe perturbations of microtubular network associated with defects in membrane compartimentation, both in vitro and in vivo. Moreover, the absence of galectin-3 impinges on the morphology of the primary cilium, which is three times longer and unusually shaped. By immunological and biochemical approaches, we could demonstrate that endogenous galectin-3 is normally associated with basal bodies and centrosomes, where it closely interacts with core proteins, such as centrin-2. However, this association transiently occurs during the process of epithelial polarization. Interestingly, galectin-3–depleted cells contain numerous centrosome-like structures, demonstrating an unexpected function of this protein in the formation and/or stability of the centrosomes. Collectively, these data establish galectin-3 as a key determinant in epithelial morphogenesis via its effect on centrosome biology.
Morphine is a widely abused, addictive drug that modulates immune function. Macrophages are a primary reservoir of HIV-1; therefore, they not only play a role in the development of this disease but also impact the overall course of disease progression. Galectin-1 is a member of a family of β-galactoside-binding lectins that are soluble adhesion molecules and that mediate direct cell-pathogen interactions during HIV-1 viral adhesion. Since the drug abuse epidemic and the HIV-1 epidemic are closely interrelated we propose that increased expression of galectin-1 induced by morphine may modulate HIV-1 infection of human monocytes-derived macrophages (MDM). Here, we show that galectin-1 gene and protein expression are potentiated by incubation with morphine. Confirming previous studies, morphine alone or galectin-1 alone enhance HIV-1 infection of MDM. Concomitant incubation with exogenous galectin-1 and morphine potentiated HIV-1 infection of MDM. We utilized a nanotechnology approach that uses gold nanorod-galectin-1 siRNA complexes (nanoplexes) to inhibit gene expression for galectin-1. We found that nanoplexes silenced gene expression for galectin-1 and the nanoplexes reversed the effects of morphine on galectin-1 expression. Furthermore, the effects of morphine on HIV-1 infection were reduced in the presence of the nanoplex.
Galectin-3 is an animal lectin that has been implicated in wound healing and is decreased in inflammatory bowel disease (IBD). Matrix metalloproteinase-7 (MMP7) also known as matrilysin-1, a protease shown to cleave extracellular matrix proteins, is highly expressed in IBD tissues, especially at the leading edge of gastrointestinal ulcers. The ability of MMP7 to cleave galectin-3 and influence wound healing has not been reported previously.
To determine whether MMP7 cleaves galectin-3 and modulates wound healing in intestinal epithelial cells.
The cleaved fragments of galectin-3 were identified by N-terminal sequencing and mass spectrometry. Western blotting was used to detect the cleaved galectin-3 products in a colonic epithelial cell line (T84 cells). Cell migration was studied by in vitro scratch method.
We demonstrate for the first time that MMP7 cleaves galectin-3 in vitro, resulting in three cleaved fragments (20.2 kDa, 18.9 kDa and 15.5 kDa). Exogenous treatment of T84 cells with recombinant MMP7 resulted in the appearance of secreted galectin-3 cleavage fragments in the supernatant. MMP7 inhibited cell migration and resulted in wound retraction and the addition of MMP7 to galectin-3 abrogated the wound healing and cell migration induced by galectin-3.
We have demonstrated that galectin-3 is a substrate for MMP7. Cleavage of galectin-3 may be one mechanism by which MMP7 inhibits wound healing. This study has significance in understanding delayed wound healing in chronic intestinal diseases like intestinal ulcers and IBD where MMP7 protein expression is elevated with a decreased galectin-3 protein expression.
MMP7; galectin-3; inflammatory bowel disease; wound healing; cell migration