Increased galectin-7 gene expression in lymphoma cells is under the control of DNA methylation

Placental Galectins in Cancer: Why We Should Pay More Attention

The first studies suggesting that abnormal expression of galectins is associated with cancer were published more than 30 years ago. Today, the role of galectins in cancer is relatively well established. We know that galectins play an active role in many types of cancer by regulating cell growth, conferring cell death resistance, or inducing local and systemic immunosuppression, allowing tumor cells to escape the host immune response. However, most of these studies have focused on very few galectins, most notably galectin-1 and galectin-3, and more recently, galectin-7 and galectin-9. Whether other galectins play a role in cancer remains unclear. This is particularly true for placental galectins, a subgroup that includes galectin-13, -14, and -16. The role of these galectins in placental development has been well described, and excellent reviews on their role during pregnancy have been published. At first sight, it was considered unlikely that placental galectins were involved in cancer. Yet, placentation and cancer progression share several cellular and molecular features, including cell invasion, immune tolerance and vascular remodeling. The development of new research tools and the concomitant increase in database repositories for high throughput gene expression data of normal and cancer tissues provide a new opportunity to examine the potential involvement of placental galectins in cancer. In this review, we discuss the possible roles of placental galectins in cancer progression and why they should be considered in cancer studies. We also address challenges associated with developing novel research tools to investigate their protumorigenic functions and design highly specific therapeutic drugs.

Galectin-7 reprograms skin carcinogenesis by fostering innate immune evasive programs

Non-melanoma skin cancer (NMSC) has risen dramatically as a result of chronic exposure to sunlight ultraviolet (UV) radiation, climatic changes and clinical conditions associated with immunosuppression. In spite of considerable progress, our understanding of the mechanisms that control NMSC development and their associated molecular and immunological landscapes is still limited. Here we demonstrated a critical role for galectin-7 (Gal-7), a β-galactoside-binding protein preferentially expressed in skin tissue, during NMSC development. Transgenic mice (Tg46) overexpressing Gal-7 in keratinocytes showed higher number of papillomas compared to WT mice or mice lacking Gal-7 (Lgals7^-/-) when subjected to a skin carcinogenesis protocol, in which tumor initiator 7,12-dimethylbenz[a]anthracene (DMBA) and tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were sequentially administered. RNAseq analysis of Tg46 tumor lesions revealed a unique profile compatible with cells of the myelomonocytic lineage infiltrating these tumors, an effect that was substantiated by a higher number of CD11b⁺Gr1⁺ cells in tumor-draining lymph nodes. Heightened c-Met activation and Cxcl-1 expression in Tg46 lesions suggested a contribution of this pathway to the recruitment of these cells. Remarkably, Gal-7 bound to the surface of CD11b⁺Ly6C^hiLy6G^lo monocytic myeloid cells and enhanced their immunosuppressive activity, as evidenced by increased IL-10 and TGF-β₁ secretion, and higher T-cell inhibitory activity. In vivo, carcinogen-treated Lgals7^-/- animals adoptively transferred with Gal-7-conditioned monocytic myeloid cells developed higher number of papillomas, whereas depletion of these cells in Tg46-treated mice led to reduction in the number of tumors. Finally, human NMSC biopsies showed increased LGALS7 mRNA and Gal-7 protein expression and displayed transcriptional profiles associated with myeloid programs, accompanied by elevated CXCL1 expression and c-Met activation. Thus, Gal-7 emerges as a critical mediator of skin carcinogenesis and a potential therapeutic target in human NMSC.

Galectin Family Members: Emerging Novel Targets for Lymphoma Therapy?

The galectin family of proteins has high affinity with β-galactoside-containing glycans. These proteins participate in cell growth and differentiation, cell adhesion, cell signal transduction, cell apoptosis, and other cellular activities. In recent years, a large number of studies have described the expression and correlation of galectins in different tumors. Each member of the family plays a vital role in tumor growth, progression, angiogenesis, adhesion, and tumor immune escape. Studies on the roles of galectins in lymphoma have mainly involved galectin-1, -3, -7, and -9. The results suggest that galectins may become novel targets for precise tumor treatment. This article reviews current research progress regarding galectins in lymphoma and provides new ideas for exploring them as novel targets for treating lymphoma and other important medical issues.

Functions and Inhibition of Galectin-7, an Emerging Target in Cellular Pathophysiology

Galectin-7 is a soluble unglycosylated lectin that is able to bind specifically to β-galactosides. It has been described to be involved in apoptosis, proliferation and differentiation, but also in cell adhesion and migration. Several disorders and diseases are discussed by covering the aforementioned biological processes. Structural features of galectin-7 are discussed as well as targeting the protein intracellularly or extracellularly. The exact molecular mechanisms that lie behind many biological processes involving galectin-7 are not known. It is therefore useful to come up with chemical probes or tools in order to obtain knowledge of the physiological processes. The objective of this review is to summarize the roles and functions of galectin-7 in the human body, providing reasons why it is necessary to design inhibitors for galectin-7, to give the reader structural insights and describe its current inhibitors.

Critical appraisal of epigenetic regulation of galectins in cancer

Galectins are defined as the glycan-binding protein containing either one or two carbohydrate-binding domains and participate in various biological functions such as developmental processes, vascularisation programs, cell migration, and immune-regulation and apoptosis. Galectins are also linked to many diseases, including cancer. They are widely spread in extracellular and intracellular spaces, and their altered expression in cancer leads to tumor progression, metastasis, angiogenesis and stemness through different signalling pathways. Promoter methylation, microRNA, and histone modification constitute the epigenetic changes that regulate galectin activity in cancer. Our review discusses the concept of epigenetics in cancer and how the aforementioned factors i.e., promoter methylation, histone modification, change in miRNAs expression affect the glycomic changes in malignancies.

Galectin-7 is elevated in endometrioid (type I) endometrial cancer and promotes cell migration

Endometrial cancer (EC) is the most commonly diagnosed gynecological malignancy in Australian women. Notably, its incidence and mortality rate is increasing. Despite this, there are limited treatment options for EC. Galectin-7 regulates tumorigenesis in numerous epithelial cancer types, but the role of galectin-7 has not been investigated in EC. It was hypothesized that galectin-7 expression would be altered in EC and contribute to the development of EC. Galectin-7 levels in EC and benign endometrium were quantified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and ELISA. The effect of recombinant galectin-7 (1 µg/ml) on cell adhesion, proliferation, apoptosis (xCELLigence and flow cytometry), migration (wound healing assay) and gene expression (RT-qPCR) was investigated using three human EC cell lines (Ishikawa, HEC1A and AN3CA). Galectin-7 gene and protein expression was significantly elevated in Grade 3 EC, compared with benign tissues. Galectin-7 was almost undetectable in Ishikawa and AN3CA cells, but highly expressed by HEC1A cells. Recombinant galectin-7 had no significant effect on cell proliferation or apoptosis in any cell line, but significantly reduced cell adhesion in Ishikawa (at 4 and 6 h) and AN3CA (at 2, 3, 4 and 6 h). Galectin-7 significantly promoted Ishikawa migration and significantly elevated collagen type IV α 1 chain and intercellular adhesion molecule 1 (ICAM1) gene expression during wound healing. The present study demonstrated that galectin-7 production increased in EC with increasing cancer grade; therefore, galectin-7 may promote the metastasis of EC by reducing cell-cell adhesion and enhancing cell migration.

Expression of galectin-7 in vulvar lichen sclerosus and its effect on dermal fibroblasts

Lichen sclerosus is a chronic and inflammatory disease. Extensive studies have focused on the epidermis, with the dermis or epidermis-dermis receiving less attention. To investigate the role of galectin-7, a keratinocyte protein, in vulvar lichen sclerosus (VLS) and its potential effects on dermal fibroblasts, immunohistochemical staining was performed with VLS tissue samples and normal control samples. The expression of galectin-7 was determined by evaluating the galectin-7 integrated density analysis, and further assessed by western blot analysis. Dermal fibroblasts were isolated from the normal tissue of the female anogenital region following sexual plastic surgery. A cell viability assay was performed on isolated dermal fibroblast cells in the presence or absence of galectin-7. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to determine the transcriptional level of collagen I and collagen III in the response to different doses of galectin-7. In the immunohistochemical analysis, galectin-7 demonstrated a significantly elevated level in VLS, compared to control tissues, which was confirmed by western blot analysis. In the analysis of primary dermal fibroblast cells, galectin-7 significantly inhibited the viability rate of fibroblasts in a dose-dependent manner. RT-qPCR data revealed that the transcription level of collagen I and collagen III were positively associated with the galectin-7 treatment concentration. The overexpression of galectin-7 is associated with the progression of VLS in the epidermis, a high concentration of galectin-7 inhibits the viability of the primary vulvar dermal fibroblasts, and stimulates the accumulation of collagen I and collagen III in dermal fibroblast cultures, thus galectin-7 may serve as a drug target during VLS progression.

Galectin-7 in Epithelial Homeostasis and Carcinomas

Galectins are small unglycosylated soluble lectins distributed both inside and outside the cells. They share a conserved domain for the recognition of carbohydrates (CRD). Although galectins have a common affinity for β-galatosides, they exhibit different binding preferences for complex glycans. First described twenty years ago, galectin-7 is a prototypic galectin, with a single CRD, able to form divalent homodimers. This lectin, which is mainly expressed in stratified epithelia, has been described in epithelial tissues as being involved in apoptotic responses, in proliferation and differentiation but also in cell adhesion and migration. Most members of the galectins family have been associated with cancer biology. One of the main functions of galectins in cancer is their immunomodulating potential and anti-angiogenic activity. Indeed, galectin-1 and -3, are already targeted in clinical trials. Another relevant function of galectins in tumour progression is their ability to regulate cell migration and cell adhesion. Among these galectins, galectin-7 is abnormally expressed in various cancers, most prominently in carcinomas, and is involved in cancer progression and metastasis but its precise functions in tumour biology remain poorly understood. In this issue, we will focus on the physiological functions of galectin-7 in epithelia and present the alterations of galectin-7 expression in carcinomas with the aim to describe its possible functions in tumour progression.

Intracellular galectin-7 expression in cancer cells results from an autocrine transcriptional mechanism and endocytosis of extracellular galectin-7

The β-galactoside binding protein galectin-7 (gal-7) is constitutively expressed at abnormally high levels in the outside milieu and intracellular compartments of many types of epithelial cancer cells, most notably in aggressive forms of ovarian and breast cancer. It is thus of utmost importance to understand how gal-7 traffics between both intracellular and extracellular compartments to develop novel drugs that target the protumorigenic functions of galectin-7. In the present work, we report that extracellular gal-7 plays a central role in controlling intracellular gal-7 in cells. It does so via two distinct yet complementary mechanisms: firstly by increasing the transcriptional activation of lgals7 gene transcription, and secondly via re-entry into the cells. Increased mRNA levels were dose- and time-dependent and occur in all cell lines tested, including ovarian and breast cancer cell lines. Addition of recombinant gal-7 to MDA-MB-231 transfected with a luciferase reporter vector containing response elements of the lgals7 promoter indicated that increased mRNA level of lgals7 occurs via de novo gene transcription. Re-entry of extracellular gal-7 inside cells was rapid, and reached cytosolic and mitochondrial compartments. Taken together, these findings reveal the existence of a positive self-amplification pathway that regulates intracellular gal-7 expression in breast and ovarian cancer cells.

Analyzing epigenetic control of galectin expression indicates silencing of galectin-12 by promoter methylation in colorectal cancer

Galectins, a class of lectins with specificity for ß-galactoside containing glycoconjugates, modulate several cellular processes that are involved in the control of normal cell growth, differentiation, cell-cell, and cell matrix interactions. Pathological alterations of the galectin expression pattern have been implicated in the development and progression of cancer. We therefore analyzed epigenetic mechanisms for control of galectin expression in 9 colorectal cancer (CRC) cell lines. Our data demonstrate that expression of galectins-1, -2, -7, -8, and -9 can be regulated by histone acetylation in CRC cell lines. In addition, the same set of galectins was also found to be modulated by DNA methylation. Of particular note, galectin-12 is silenced in all tested CRC cell lines but known to be re-expressed upon butyrate-induced differentiation and present in normal colonic mucosa. Loss of galectin-12 expression in undifferentiated CRC cells is associated with promoter hypermethylation and for the first time we provide detailed methylation analysis of the promoter region. In CRC tumor tissue, galectin-12 expression was downregulated in 66% of CRC tissue specimens as compared to adjacent normal tissue hinting to a possible tumor-suppressing function in CRC. © 2017 IUBMB Life, 69(12):962-970, 2017.

Epigenetic Bases of Aberrant Glycosylation in Cancer

In this review, the sugar portions of glycoproteins, glycolipids, and glycosaminoglycans constitute the glycome, and the genes involved in their biosynthesis, degradation, transport and recognition are referred to as “glycogenes“. The extreme complexity of the glycome requires the regulatory layer to be provided by the epigenetic mechanisms. Almost all types of cancers present glycosylation aberrations, giving rise to phenotypic changes and to the expression of tumor markers. In this review, we discuss how cancer-associated alterations of promoter methylation, histone methylation/acetylation, and miRNAs determine glycomic changes associated with the malignant phenotype. Usually, increased promoter methylation and miRNA expression induce glycogene silencing. However, treatment with demethylating agents sometimes results in silencing, rather than in a reactivation of glycogenes, suggesting the involvement of distant methylation-dependent regulatory elements. From a therapeutic perspective aimed at the normalization of the malignant glycome, it appears that miRNA targeting of cancer-deranged glycogenes can be a more specific and promising approach than the use of drugs, which broad target methylation/acetylation. A very specific type of glycosylation, the addition of GlcNAc to serine or threonine (O-GlcNAc), is not only regulated by epigenetic mechanisms, but is an epigenetic modifier of histones and transcription factors. Thus, glycosylation is both under the control of epigenetic mechanisms and is an integral part of the epigenetic code.

Clinical significance of galectin-7 in vulvar squamous cell carcinoma

The present study reports the role of galectin-7 (Gal-7) expression in vulvar squamous cell carcinoma (VSCC) and its correlation with clinicopathological variables. Gal-7 expression was immunohistochemically detected in the paraffin-embedded sections of 20 normal vulvar biopsy samples and 50 VSCC specimens. Expression was also detected in 10 normal vulvar biopsy samples and 10 VSCC specimens by western blotting. In addition, the methylation status of the promoter of the Gal-7 gene was determined in 30 VSCC specimens and 20 samples of normal vulvar tissue by methylation-specific polymerase chain reaction. Gal-7 expression was found to be significantly downregulated in the VSCC tissues compared with the normal vulvar tissues (P<0.05). Downregulation of Gal-7 was correlated with advanced clinical stage, poor tumor differentiation and regional lymph node metastasis (P<0.05). Furthermore, methylation of the Gal-7 gene promoter was significantly reduced in the vulvar normal tissues compared with the VSCC tissues (P=0.023), while increased Gal-7 promoter methylation was correlated with advanced clinical stage, poor tumor differentiation and regional lymph node metastasis (P<0.05). There was no association between patient age and Gal-7 promoter methylation. Together, these results suggested that Gal-7 has a negative impact in patients with VSCC, with malignant potential correlating with Gal-7 promoter methylation.

DNA methylation is associated with expression level changes of galectin gene in mantle wound healing process of pearl oyster, Pinctada fucata

Galectin is one important member of pattern recognition proteins that plays a pivotal role in regulating innate immune response of invertebrates. In this study, we cloned the promoter sequence of a tandem-repeat galectin from the pearl oyster Pinctada fucata (P. fucata). The quantitative real-time PCR analysis revealed that galectin mRNA expression in mantle tissues were firstly up-regulated from time points of 2 h-24 h, and then down-regulated from time points of 24 h-168 h after mantle injury. The genome methylation level of mantle tissue was inversely related to galectin mRNA expression (Pearson correlation: -0.554, P: 0.154). The "CpG4-6" methylation level in promoter region of galectin was significant positive correlated with the mRNA expression (Pearson correlation: 0.313, P: 0.049). The results indicated that galectin gene may be involved in immune response in mantle wound healing process of P. fucata, and DNA methylation may be a regulation factor of gene expression.

A Mutation in the Carbohydrate Recognition Domain Drives a Phenotypic Switch in the Role of Galectin-7 in Prostate Cancer

The observation that galectin-7 (gal-7) is specifically expressed in mammary myoepithelial (basal) cells prompted us to investigate whether this protein is expressed in the basal cells of other tissues. Given that breast and prostate cancer have remarkable underlying biological similarities and given the important roles of basal cells in prostate cancer, we examined the expression patterns and role of gal-7 in human prostate cancer. Using tissue microarray, we found that although gal-7 is readily expressed in basal cells in normal prostate tissue, it is downregulated in prostate cancer (PCa) cells. De novo expression of gal-7 in prostate cancer cells increases their sensitivity to apoptosis in response to etoposide and cisplatin. The assessment of a carbohydrate-recognition domain (CRD)-defective mutant form of gal-7 (R7S) showed that the ability of this protein to modulate apoptosis was independent of its CRD activity. This activity was also independent of its ability to translocate to the mitochondrial and nuclear compartments. However, CRD activity was necessary to inhibit the invasive behaviors of prostate cancer cells. In vivo, gal-7 overexpression in PCa cells led to a modest yet significant reduction in tumor size, while its CRD-defective mutant form significantly increased tumor growth compared to controls. Taken together, these results suggest that although de novo expression of gal-7 may be an interesting means of increasing the tumorigenic phenotypes of PCa cells, alterations in the CRD activity of this protein drive a phenotypic switch in its role in PCa cells. This CRD-independent activity represents a paradigm shift in our understanding of the functions of galectin. The R74S model will be useful to distinguish CRD-dependent and CRD-independent functions of gal-7 in cancer progression.

Control of Glycosylation-Related Genes by DNA Methylation: the Intriguing Case of the B3GALT5 Gene and Its Distinct Promoters

Glycosylation is a metabolic pathway consisting of the enzymatic modification of proteins and lipids through the stepwise addition of sugars that gives rise to glycoconjugates. To determine the full complement of glycoconjugates that cells produce (the glycome), a variety of genes are involved, many of which are regulated by DNA methylation. The aim of the present review is to briefly describe some relevant examples of glycosylation-related genes whose DNA methylation has been implicated in their regulation and to focus on the intriguing case of a glycosyltransferase gene (B3GALT5). Aberrant promoter methylation is frequently at the basis of their modulation in cancer, but in the case of B3GALT5, at least two promoters are involved in regulation, and a complex interplay is reported to occur between transcription factors, chromatin remodelling and DNA methylation of typical CpG islands or even of other CpG dinucleotides. Transcription of the B3GALT5 gene underwent a particular evolutionary fate, so that promoter hypermethylation, acting on one transcript, and hypomethylation of other sequences, acting on the other, cooperate on one gene to obtain full cancer-associated silencing. The findings may also help in unravelling the complex origin of serum CA19.9 antigen circulating in some patients.

Prostatic cell-specific regulation of the synthesis of MUC1-associated sialyl Lewis a

Sialyl Lewis antigens are selectin ligands involved in leukocyte trafficking and cancer metastasis. Biosynthesis of these selectin ligands occurs by the sequential actions of several glycosyltransferases in the Golgi apparatus following synthesis of the protein backbone in the endoplasmic reticulum. In this study, we examine how the synthesis of sialyl Lewis a (sLe^a) is regulated in prostatic cells and identify a mucin that carries this glycotope. We treat human prostatic cells including one normal and three cancerous cells with histone deacetylase inhibitors, valproic acid, tricostatin A (TSA), and suberoylanilide hydroxamic acid (SAHA), and then monitor the expression of sLe^a. We have found that SAHA enhances the production of sLe^a in normal prostatic RWPE-1 cells but not prostatic cancer cells. Employing siRNA technology and co-immunoprecipitation, we show that the sLe^a is associated with MUC1, which is confirmed by confocal immunofluorescence microscopy and proximity ligation assay. The SAHA-induced production of sLe^a in RWPE-1 cells is resulted from upregulation of B3GALT1 gene via enhancement of acetylated histone-3 and histone-4. Interestingly, PC3 and LNCaP C-81 cells do not produce detectable amounts of sLe^a despite expressing high levels of B3GALT1. However, the MUC1-associated sLe^a is generated in these cells after introduction of MUC1 cDNA. We conclude that the synthesis of sLe^a is controlled by not only peptide backbone of the glycoprotein but also glycoprotein-specific glycosyltransferases involved in the synthesis of sLe^a. Further, the SAHA induction of this selectin ligand in normal prostatic cells may pose a potentially serious side effect of this drug recently approved by the US Food and Drug Administration.

The aggressiveness of murine lymphomas selected in vivo by growth rate correlates with galectin-1 expression and response to cyclophosphamide

Although lymphomas account for almost half of blood-derived cancers that are diagnosed each year, the causes of new cases are poorly understood, as reflected by the relatively few risk factors established. Galectin-1, an immunoregulatory ß-galactoside-binding protein, has been widely associated with tumor-immune escape. The aim of the present work was to study the relationship between tumor growth rate, aggressiveness, and response to cyclophosphamide (Cy) therapy with regard to Gal-1 expression in murine T-cell lymphoma models. By means of a disruptive selection process for tumor growth rate, we generated two lymphoma variants from a parental T-cell lymphoma, which have unique characteristics in terms of tumor growth rate, spontaneous regression, metastatic capacity, Gal-1 expression and sensitivity to Cy therapy. Here, we show that Gal-1 expression strongly correlates with tumor growth rate, metastatic capacity and response to single-dose Cy therapy in T-cell lymphoma models; this association might have important consequences for evaluating prognosis and treatments of this type of tumors.

Epigenetic up-regulation of leukemia inhibitory factor (LIF) gene during the progression to breast cancer

The interleukin 6 family of cytokines including leukemia inhibitory factor (LIF) regulates the progression of several types of cancer. However, although LIF overexpression during breast cancer progression was observed in our previous report, the molecular mechanisms responsible for this deregulation remain largely unknown. Here we show that LIF expression is epigenetically up-regulated via DNA demethylation and changes in histone methylation status within its promoter region in the isogenic MCF10 model. Bisulfite sequencing revealed the CpG pairs within the promoter region are hypermethylated in normal breast epithelial cells, but extensively demethylated as breast cancer progresses. In agreement with the DNA methylation pattern, our chromatin immunoprecipitation showed that inactive epigenetic marks such as MeCP2 occupancy and histone H3-Lys9-dimethylation significantly decreased during the progression to breast cancer but an active histone mark was increased in an inverse manner. Also, the occupancy of the transcription factor Sp1, which has higher affinity for hypomethylated CpGs, increased. RNAi-mediated knockdown of LIF expression resulted in a significant reduction of cell growth and colony formation in breast cancer cells, suggesting the potential role of LIF-LIF receptor axis in autocrine stimulation of cancer cells. Collectively, our data suggest that the epigenetic up-regulation of the LIF gene likely play an important role in the development of breast cancer.

Overexpression of galectin-7, a myoepithelial cell marker, enhances spontaneous metastasis of breast cancer cells

Galectins are members of a family of beta-galactosides-binding proteins that have recently emerged as novel modulators in different aspects of cancer. The expression of galectins in tumors and/or the tissue surrounding them has been well documented. Since galectin-7 expression has been associated with epithelial tissues and varies significantly in various types of cancer, we have investigated for the first time its role in breast cancer. Using two preclinical mouse models, high levels of galectin-7 expression in breast cancer cells drastically increased their ability to metastasize to lungs and bones. Significant increases in the number of pulmonary metastases and osteolytic lesions were induced by overexpression of galectin-7 compared with control cells. In human tissues, galectin-7 was specifically found in myoepithelial cells of normal human breast tissue, but not in luminal cells. Its expression was severely altered in breast carcinoma, many samples showing greater than 70% of galectin-7 positive cells. High expression levels of galectin-7 were restricted to high-grade breast carcinomas, including HER2 overexpressing and basal-like groups. In HER2 overexpressing cases, galectin-7 expression was associated with lymph node axillary metastasis. Taken together, our results indicate that galectin-7 may represent a potential target for both specific detection and therapeutic inhibition of metastatic breast cancer.