Endogenous galactoside-binding lectins: a new class of functional tumor cell surface molecules related to metastasis

Structural and biochemical insight into a modular β-1,4-galactan synthase in plants

Rhamnogalacturonan I (RGI) is a structurally complex pectic polysaccharide with a backbone of alternating rhamnose and galacturonic acid residues substituted with arabinan and galactan side chains. Galactan synthase 1 (GalS1) transfers galactose and arabinose to either extend or cap the β-1,4-galactan side chains of RGI, respectively. Here we report the structure of GalS1 from Populus trichocarpa, showing a modular protein consisting of an N-terminal domain that represents the founding member of a new family of carbohydrate-binding module, CBM95, and a C-terminal glycosyltransferase family 92 (GT92) catalytic domain that adopts a GT-A fold. GalS1 exists as a dimer in vitro, with stem domains interacting across the chains in a 'handshake' orientation that is essential for maintaining stability and activity. In addition to understanding the enzymatic mechanism of GalS1, we gained insight into the donor and acceptor substrate binding sites using deep evolutionary analysis, molecular simulations and biochemical studies. Combining all the results, a mechanism for GalS1 catalysis and a new model for pectic galactan side-chain addition are proposed.

Endometrial galectin-3 causes endometriosis by supporting eutopic endometrial cell survival and engraftment in the peritoneal cavity

PROBLEM

The pathogenesis of endometriosis remains unclear. Endometrial cells in retrograde menstruation are considered the source of endometriosis; therefore, we hypothesized that the eutopic endometrium may provide clues regarding the pathogenesis. We aimed to clarify the role of eutopic endometrial cells in endometriosis development.

METHOD OF STUDY

Eutopic endometrial tissues were obtained from patients with or without endometriosis, and expression of cell surface molecules in eutopic endometrial stromal cells (ESCs) was evaluated via iTRAQ-based proteomic analysis. Based on the results, we focused on galectin-3. Galectin-3 expression in clinical samples was confirmed by immunohistochemistry and Western blot analysis. The concentration of secreted galectin-3 was measured using enzyme-linked immunosorbent assays. Adhesion and migration of ESCs were evaluated by in vitro adhesion and wound healing assays. The cytotoxicity of natural killer cells was measured via calcein release assays. Cell proliferation was measured using the CyQUANT Cell Proliferation Assay Kit.

RESULTS

iTRAQ analysis revealed that galectin-3 expression was specifically elevated in the ESCs from endometriosis patients. Immunohistochemistry confirmed galectin-3 overexpression in the eutopic endometrium of endometriosis, irrespective of the menstrual phase. Galectin-3 was overexpressed and secreted by the eutopic ESCs from patients with endometriosis compared to that from patients without endometriosis. Galectin-3 expression in ESCs increased adhesion and migration, whereas galectin-3 inhibitors impaired these processes. Galectin-3 reduced the cytotoxicity of natural killer cells toward ESCs, while not affecting cell proliferation.

CONCLUSION

Galectin-3 promotes peritoneal engraftment of ESCs due to impaired immune surveillance in the peritoneal cavity and increases ESCs adhesion and migration to the peritoneum.

Regulation of wound healing and fibrosis by galectins

Galectins are a family of proteins with at least one carbohydrate-recognition domain. Galectins are present in various tissues and organs and participate in different physiological and pathological molecular reactions in vivo. Wound healing is the basic process of traumatic disease recovery. Wound healing involves three overlapping stages: inflammation, proliferation, and remodelling. Furthermore, a comparison of wound healing with the tumour microenvironment revealed that galectin plays a key role in the wound healing process. The current review describes the role of galectin in inflammation, angiogenesis, re-epithelialisation, and fibrous scar formation and evaluates its potential as a therapeutic drug for wounds.

Carbohydrate-protein template synthesized high mannose loading gold nanoclusters: A powerful fluorescence probe for sensitive Concanavalin A detection and specific breast cancer cell imaging

Protein-encapsulated gold nanoclusters (Au NCs) have recently gained much attention in biosensing and bioimaging applications owing to their remarkable fluorescence properties, nontoxicity and good biocompatibility. In this work, the mannose was grafted onto the bovine serum albumin (BSA) encapsulated Au NCs (BSA-Au NCs) to produce a mannose functionalized BSA-Au NCs (Man-BSA-Au NCs) as a new fluorescence probe for Concanavalin A (Con A) detection and human breast cancer cell imaging. A new strategy with mannose-BSA conjugates as template was firstly applied for the synthesis of Man-BSA-Au NCs, leading to a high loading of mannose (767.6 ± 7.2 mg/L) onto BSA-Au NCs. The as-prepared Man-BSA-Au NCs showed advantages of facile preparation, good monodispersity and strong red-emission. Notably, aggregation-induced fluorescence quenching of Man-BSA-Au NCs was triggered by Con A due to the multivalent cooperative interactions between mannose and Con A, which was subsequently confirmed by MALDI-TOF MS. Hence highly selective and sensitive fluorescence detection of Con A was achieved by using Man-BSA-Au NCs as a fluorescence sensor. A good linear relationship was obtained over the range of 0.01-1 μM (R² = 0.994) with a detection limit of 0.62 nM (S/N = 3). The developed sensor was then applied to determine Con A in human serum with acceptable recoveries of 93.70-104.8%. Moreover, based on the specific recognition between mannose and overexpressed mannose receptors on human breast cancer cells, the Man-BSA-Au NCs were successfully utilized for cancer cell imaging with good specificity.

Galectins in prostate and bladder cancer: tumorigenic roles and clinical opportunities

Advanced prostate and bladder cancer are two outstanding unmet medical needs for urological oncologists. The high prevalence of these tumours, lack of effective biomarkers and limited effective treatment options highlight the importance of basic research in these diseases. Galectins are a family of β-galactoside-binding proteins that are frequently altered (upregulated or downregulated) in a wide range of tumours and have roles in different stages of tumour development and progression, including immune evasion. In particular, altered expression levels of different members of the galectin family have been reported in prostate and bladder cancers, which, together with the aberrant glycosylation patterns found in tumour cells and the constituent cell types of the tumour microenvironment, can result in malignant transformation and tumour progression. Understanding the roles of galectin family proteins in the development and progression of prostate and bladder cancer could yield key insights to inform the clinical management of these diseases.

Impact of Galectin-1 on Trophoblast Stem Cell Differentiation and Invasion in In Vitro Implantation Model

Trophoblast stem cells (TSCs) differentiate in an orderly manner, which plays an important role in the process of embryo implantation, placentation, and early pregnancy maintenance. At the maternal-fetal interface, the dialogue is crucial between trophoblast cells and endometrial epithelial cells. Previous studies suggested that galectin-1 (Gal-1) may play an important role in placental development. In this study, we used Ishikawa (IK) cells-TSC coculture model to simulate the maternal-fetal interface and induce the differentiation of TSCs by differentiation media. The messenger RNA level of each cell type markers, fusion markers, and Gal-1 was detected by quantitative reverse transcription polymerase chain reaction during the differentiation of TSCs. Wound healing and transwell invasion assays were used to detect the migration and invasion ability in each group. We found that coculture with IK cells or conditioned media from IK cells could promote the differentiation and invasion of TSCs and increase Gal-1 expression in TSCs. Furthermore, recombinant Gal-1 could also promote the differentiation and invasion of TSCs, suggesting that some of IK cells secretion increase the expression of Gal-1 in TSCs during implantation, which then induced trophoblast differentiation and invasion in vitro. These findings provide significant insights into the biology of embryo-maternal interactions with the importance of Gal-1 in TSCs for the successful establishment and maintenance of pregnancy.

Antimetastatic pectic polysaccharide from Decalepis hamiltonii; galectin-3 inhibition and immune-modulation

Melanoma is a malignant neoplasm of major concern because of its high mortality rate and failure of chemotherapy. Previously we have shown that galectin-3, a galactose specific lectin, plays a pivotal role in the initiation of metastasis. It was hypothesized that blocking galectin-3 with galactose rich dietary pectic polymer would inhibit metastasis. The current study analyzes the preventive effect and mode of action of a pectic polymer from Swallow Root (Decalepis hamiltonii) in a preventative study of B16F10 cells lung colonization. Matrix metalloproteinase (MMPs) activity was assayed by zymography. Apoptotic/proliferative markers and cytokines were analyzed by immunoassay. Results indicated ~88% inhibition of lung colonization by SRPP as compared to 60% by CPP and only 7% by GRPP. Further molecular analysis revealed that galectin-3 blockade was associated with down regulation of MMPs and NFκB. Activation of caspases supported the apoptotic effect of SRPP. Infiltration of inflammatory cells into the lung was evidenced by presence of CD11b+ cells and release of the pro-inflammatory cytokine-IL-17, indicating inflammation during the cancer cell colonization process. SRPP enhanced the release of IL-12 that enables the reduction of inflammation. Our data for the first time indicate the effective anti-metastatic effect of SRPP due to both galectin-3 blockade and immunomodulation.

A Jacalin-Related Lectin Regulated the Formation of Aerial Mycelium and Fruiting Body in Flammulina velutipes

Flammulina velutipes, one of the most popular mushroom species in the world, has been recognized as a useful model system to study the biochemical and physiological aspects of the formation and elongation of fruit body. However, few reports have been published on the regulation of fruiting body formation in F. velutipes at the molecular level. In this study, a jacalin-related lectin gene from F. velutipes was characterized. The phylogenetic tree revealed that Fv-JRL1 clustered with other basidiomycete jacalin-like lectins. Moreover, the transcriptional pattern of the Fv-JRL1 gene in different developmental stages of F. velutipes implied that Fv-JRL1 could be important for formation of fruit body. Additionally, RNA interference (RNAi) and overexpression analyses provided powerful evidence that the lectin gene Fv-JRL1 from F. velutipes plays important roles in fruiting body formation.

Binding of galectin-1 to breast cancer cells MCF7 induces apoptosis and inhibition of proliferation in vitro in a 2D- and 3D- cell culture model

Background

Galectin-1 (gal-1) belongs to the family of β-galactoside-binding proteins which primarily recognizes the Galβ1-4GlcNAc sequences of oligosaccharides associated with several cell surface glycoconjugates. The lectin recognizes correspondent glycoepitopes on human breast cancer cells. Galectin-1 is expressed both in normal and malignant tissues. Lymphatic organs naturally possessing high rates of apoptotic cells, express high levels of Galectin-1. Furthermore galectin-1 can initiate T cell apoptosis. Binding of galectin-1 to trophoblast tumor cells presenting the oncofetal Thomsen-Friedenreich (TF) carbohydrate antigen inhibits tumor cell proliferation. In this study we examined the impact galectin-1 has in vitro on cell proliferation, apoptotic potential and metabolic activity of MCF-7 and T-47D breast cancer cells in dependence to their expression of the Thomsen-Friedenreich (TF) tumor antigen.

Methods

For proliferation and apoptosis assays cells were grown in presence of 10, 30 and 60 μg gal-1/ml medium. Cell proliferation was determined by a BrdU uptake ELISA.

Detection of apoptotic cells was done by M30 cyto death staining, in situ nick translation and by a nucleosome ELISA method. Furthermore we studied the impact galectin-1 has on the metabolic activity of MCF-7 and T-47D cells in a homotypic three-dimensional spheroid cell culture model mimicking a micro tumour environment.

Results

Gal-1 inhibited proliferation of MCF-7 cells (strong expression of the TF epitope) but did not significantly change proliferation of T-47D cells (weak expression of the TF epitope). The incubation of MCF-7 cells with gal-1 raised number of apoptotic cells significantly. Treating the spheroids with 30 μg/ml galectin-1 in addition to standard chemotherapeutic regimes (FEC, TAC) resulted in further suppression of the metabolic activity in MCF-7 cells whereas T-47D cells were not affected.

Conclusions

Our results demonstrate that galectin-1 can inhibit proliferation und metabolic cell activity and induce apoptosis in breast tumor cell lines with high expression levels of the Thomsen-Friedenreich (TF) antigen in monolayer and spheroid cell culture models.

Biotinidase Resistant 68Gallium-Radioligand Based on Biotin/Avidin Interaction for Pretargeting: Synthesis and Preclinical Evaluation

A new macrocyclic system 2,2'-(12-amino-11,13-dioxo-1,4,7,10-tetraazacyclotridecane-4,7-diyl)diacetic acid (ATRIDAT) was designed for coordinating metals in +2 and +3 oxidation states particularly ⁶⁸Ga(III), for PET imaging. ATRIDAT was conjugated to d-biotin for pretargeting via biotin-avidin interaction. This model provides high tumor targeting efficiency and stability to biotinidase activity leading to modest signal amplification at the tumor site. Cyclization of triethylenetetramine with protected diethylamino malonate resulted in the formation of 13 membered diamide ring. d-Biotin was then anchored on the pendant amine rendering α-methyne carbon to the biotinamide bond which blocks the biotinidase enzyme activity. Biotinidase stability assay showed remarkable stability toward the action of biotinidase with ∼95% remaining intact after treatment following 4 h. Binding affinity experiments such as HABA assay, competitive displacement studies with d-biotin and CD showed high binding affinity of the molecule with avidin in nanomolar range. Biotin conjugate was successfully radiolabeled with ⁶⁸Ga(III) with radiolabeling efficiency of ∼70% and then purified to get 99.9% radiochemical yield. IC₅₀ of the compound was found to be 2.36 mM in HEK cell line and 0.82 mM in A549 as assessed in MTT assay. In biodistribution studies, the major route of excretion was found to be renal. Significant uptake of 4.15 ± 0.35% was observed in tumor in the avidin pretreated mouse at 1 h. μPET images also showed a high tumor to muscle ratio of 26.8 and tumor to kidney ratio of 1.74 at 1 h post-injection after avidin treatment.

Tumor-associated antigens: Tn antigen, sTn antigen, and T antigen

Glycosylation is one of the major posttranslational modifications of proteins. N-glycosylation (Asn-linked) and O-glycosylation (Ser/Thr-linked) are the two main forms. Abnormal O-glycosylation is frequently observed on the surface of tumor cells, and is associated with an adverse outcome and poor prognosis in patients with cancer. O-glycans (Tn, sTn, and T antigen) can be synthesized in the Golgi apparatus with the aid of several glycosyltransferases (such as T-synthase and ST6GalNAc-I) in a suitable environment. The unique molecular chaperone of T-synthase is Cosmc, which helps T-synthase to fold correctly in the endoplasmic reticulum. Dysregulation of these glycosyltransferases, molecular chaperones, or the environment is involved in the dysregulation of O-glycans. Tn, sTn, and T antigen neo- or over-expression occurs in many types of cancer including gastric, colon, breast, lung, esophageal, prostate, and endometrial cancer. This review discusses the major synthetic pathway of O-glycans and the mechanism by which Tn, sTn, and T antigens promote tumor metastasis.

Endothelial integrin α3β1 stabilizes carbohydrate-mediated tumor/endothelial cell adhesion and induces macromolecular signaling complex formation at the endothelial cell membrane

Blood borne metastatic tumor cell adhesion to endothelial cells constitutes a critical rate-limiting step in hematogenous cancer metastasis. Interactions between cancer associated carbohydrate Thomsen-Friedenreich antigen (TF-Ag) and endothelium-expressed galectin-3 (Gal-3) have been identified as the leading molecular mechanism initiating tumor/endothelial cell adhesion in several types of cancer. However, it is unknown how these rather weak and transient carbohydrate/lectin mediated interactions are stabilized. Here, using Western blot and LC tandem mass spectrometry analyses of pull-downs utilizing TF-Ag loaded gold nanoparticles, we identified Gal-3, endothelial integrin α3β1, Src kinase, as well as 5 additional molecules mapping onto focal adhesion pathway as parts of the macromolecular complexes formed at the endothelial cell membranes downstream of TF-Ag/Gal-3 interactions. In a modified parallel flow chamber assay, inhibiting α3β1 integrin greatly reduced the strength of tumor/endothelial cell interactions without affecting the initial cancer cell adhesion. Further, the macromolecular complex induced by TF-Ag/Gal-3/α3β1 interactions activates Src kinase, p38, and ERK1/2, pathways in endothelial cells in a time- and α3β1-dependent manner. We conclude that, following the initial metastatic cell attachment to endothelial cells mediated by TF-Ag/Gal-3 interactions, endothelial integrin α3β1 stabilizes tumor/endothelial cell adhesion and induces the formation of macromolecular signaling complex activating several major signaling pathways in endothelial cells.

Overexpression of galectin-3 enhances migration of colon cancer cells related to activation of the K-Ras-Raf-Erk1/2 pathway

BACKGROUND

Galectin-3 has been independently correlated with malignant behavior in human colon cancer. The involvement of galectin-3 in the invasiveness of colon cancer cells remains to be determined. We investigated whether galectin-3 was involved in the colon cancer cell migration mediated by certain kinase pathways.

METHODS

We studied 2 colon cancer cell lines (DLD-1 and Caco2) and clinical samples. Immunostaining and Western blotting were used to analyze the expression of galectin-3 in vitro and in the clinical samples. Short hairpin RNA and overexpression of galectin-3 were used to study loss- and gain-of-function in a wound-healing assay and a Transwell migration assay, and Western blotting was used to study the Ras-Raf signaling pathway.

RESULTS

Galectin-3 was expressed at lower levels in DLD-1 than in Caco2 cells. The lower galectin-3 level in DLD-1 cells was associated with decreased cell migration, in comparison with that of Caco2 cells. Overexpression of galectin-3 increased the migration rate of DLD-1, while knockdown of galectin-3 decreased the migration. Overexpression of galectin-3 was correlated with increased lamellipodia formation and distal lung localization in a mouse model. The galectin-3 enhancement of DLD-1 cell migration was mediated by K-Ras, Raf and Erk1/2 pathway activation, but not the H-Ras, p38, or JNK activation.

CONCLUSIONS

Galectin-3 plays an important role in regulating colon cancer cell migration and potential distal localization. The galectin-3 enhancement of cell migration is mediated through the K-Ras-Raf-Erk1/2 pathway. Specific targeting of the K-Ras-Raf-Erk1/2 pathway may be useful for treating colon cancers associated with increased galectin-3 expression.

Proteomic comparison of mcf-7 tumoursphere and monolayer cultures

Breast cancer is a heterogenous disease, composed of tumour cells with differing gene expressions and phenotypes. Very few antigens have been identified and a better understanding of tumour initiating-cells as targets for therapy is critically needed. Recently, a rare subpopulation of cells within tumours has been described with the ability to: (i) initiate and sustain tumour growth; (ii) resist traditional therapies and allow for secondary tumour dissemination; and (iii) display some of the characteristics of stem cells such as self-renewal. These cells are termed tumour-initiating cells or cancer stem cells, or alternatively, in the case of breast cancer, breast cancer stem cells. Previous studies have demonstrated that breast cancer stem cells can be enriched for in “tumoursphere” culture. Proteomics represents a novel way to investigate protein expression between cells. We hypothesise that characterisation of the proteome of the breast cancer line MCF-7 tumourspheres compared to adherent/differentiated cells identifies proteins of novel interest for further isolating or targeting breast cancer stem cells. We present evidence that: (i) the proteome of adherent cells is different to the proteome of cells grown in sphere medium from either early passage (passage 2) or late passage (passage 5) spheres; (ii) that spheres are enriched in expression of a variety of tumour-relevant proteins (including MUC1 and Galectin-3); and (iii) that targeting of one of these identified proteins (galectin-3) using an inhibitor (N-acetyllactosamine) decreases sphere formation/self-renewal of MCF-7 cancer stem cells in vitro and tumourigenicity in vivo. Hence, proteomic analysis of tumourspheres may find use in identifying novel targets for future therapy. The therapeutic targeting of breast cancer stem cells, a highly clinically relevant sub-population of tumour cells, has the potential to eliminate residual disease and may become an important component of a multi-modality treatment of cancer.

Absence of galectin-3 immunostaining in fine-needle aspiration cytology specimens from papillary thyroid carcinoma is associated with favorable pathological indices

BACKGROUND

Galectin-3 (G3) immunostaining of fine-needle aspiration (FNA) samples from thyroid nodules is very useful for the diagnosis of malignancy. The objective of the present study was to determine whether the absence of G3 immunostaining in preoperative FNA samples is associated with favorable clinicopathological parameters, including lymph node (LN) metastasis, in papillary thyroid carcinoma (PTC).

METHODS

The records of 868 patients with PTC who had prethyroidectomy ultrasonography-guided FNA with G3 immunostaining between January 2006 and December 2009 were retrospectively reviewed. G3 immunostaining was considered positive if the percentage of tumor cells showing definite cytoplasmic immunostaining exceeded 5%. Patients who had negative G3 immunostaining of FNA samples were assigned to the G3-negative (G3N) group; whereas those who had positive G3 immunostaining were assigned to the G3-positive (G3P) group.

RESULTS

There were 92 patients who were assigned to the G3N group (10.6%) because of the negative staining for G3 in the preoperative FNA samples from their thyroid nodules. The proportion of PTC subtypes in the G3N and G3P groups was similar (p=0.376). There was less frequent thyroid capsular invasion (46.7% vs. 66.5%, p<0.001), extrathyroidal extension (28.3% vs. 48.5%, p<0.001), and LN metastasis (22.2% vs. 48.7%, p<0.001) in the G3N group than the G3P group. In multivariate regression analysis, G3N expression predicted a lower risk of LN metastasis (odds ratio=0.37, 95% confidence interval 0.18-0.78) after adjustment for other clinicopathological parameters. Over a median follow-up of 33 months, no association was observed between G3N and disease-free survival.

CONCLUSION

The absence of G3 expression in FNA samples from PTC is associated with pathological parameters considered less aggressive than is the case for PTCs with G3 expression, including being a negative predictor of negative LN involvement. Long-term follow-up studies, however, are needed to verify whether G3N patients have lower recurrence and mortality rates.

Galectin-3 binding and metastasis

Galectin-3 is a member of a family of carbohydrate-binding proteins. It is present in the nucleus, the -cytoplasm, and also the extracellular matrix (ECM) of many normal and neoplastic cell types. Reports show an upregulation of this protein in transformed and metastatic cell lines (Raz and Lotan Cancer Metastasis Rev 6: 433-452, 1987; Raz et al. Int J Cancer 46: 871-877, 1990). Moreover, in many human carcinomas, an increased expression of galectin-3 correlates with progressive tumor stages (Lotan et al. Int J Cancer 56: 474-480, 1994; Bresalier et al. Gastroenterology 115: 287-296, 1998; Nangia-Makker et al. Int J Oncol 7: 1079-1087, 1995; Xu et al. Am J Pathol 147: 815-822, 1995).Several lines of analysis have demonstrated that the galectins participate in cell-cell and cell-matrix interactions by recognizing and binding complementary glycoconjugates and thereby play a crucial role in normal and pathological processes. Elevated expression of the protein is associated with an increased capacity for anchorage-independent growth, homotypic aggregation, and tumor cell lung colonization (Lotan et al. Cancer Res 45: 4349-4353, 1985; Lotan and Raz J Cell Biochem 37: 107-117, 1988; Meromsky et al. Cancer Res 46: 5270-5275, 1986). In this chapter we describe the methods of purification of galectin-3 from transformed Escherichia coli and some of the commonly used functional assays for analyzing galectin-3 binding.

Is galectin-1 a trigger for trophoblast cell fusion?: the MAP-kinase pathway and syncytium formation in trophoblast tumour cells BeWo

Galectin-1 (gal-1), a member of the mammalian β-galactoside-binding proteins, exerts biological effects by recognition of glycan ligands, including those involved in cell adhesion and growth regulation. In a previous study, we demonstrated that gal-1 induces cell differentiation processes on the membrane of choriocarcinoma cells BeWo, including the receptor tyrosine kinases, REarranged during transfection, janus kinase 2 and vascular endothelial growth factor receptor 3. Within this study, we examined which mitogen-activated protein kinases (MAPK) and serine/threonine kinases were phoshorylated by gal-1. Out of a number of 21 different MAPKs and other serine/threonine kinases, the stimulation of BeWo cells with gal-1 showed a significant alteration of signal intensity in extracellular-regulated kinases 1/2 (ERK1/2), Akt-3, Akt-pan and glycogen synthase kinase-α/β (GSK-3α/β). We demonstrated that gal-1 significantly inhibited ERK1/2, Akt-3/pan and GSK-3α/β phosphorylation in BeWo cells and in addition induced Elk1 transcription factor activation. In contrast to gal-1 effects, MAPK inhibitor U0126 reduced syncytium formation of BeWo cells. The results of our data showed that phosphorylation of MAP kinases are involved in gal-1-induced signal transduction processes in BeWo cells. Additional results obtained with MAPK inhibitor U0126 close the gap between syncytium formation induced by gal-1 and MAPK activation in trophoblast cells. Furthermore, we demonstrated that gal-1 induces the activation of Elk1, a transcription factor that is activated by MAPK pathways.

The role of galectin-1 in trophoblast differentiation and signal transduction

Galectins are proteins with the ability to bind β-galactosides through a conserved carbohydrate recognition domain. Galectin-1 exerts its biological effects by binding glycan ligands on proteins involved in cell adhesion and growth regulation. Galectin-1 inhibits trophoblast cell proliferation and induces syncytium formation. Its down-regulation in the syncytiotrophoblast has been associated with early pregnancy loss. In the choriocarcinoma-derived BeWo cells the galectin-1 induced growth inhibition is apoptosis-independent, but rather appears to be mediated by binding to cell surface receptors, such as the receptor tyrosine kinases REarranged during Transfection (RET) and Janus Kinase (JAK) 2 as well as vascular endothelial growth factor receptor 3. On the syncytiotrophoblast and extravillous trophoblast galectin-1 binds the Thomsen-Friedenreich disaccharide on mucin-1. The cell differentiation processes induced by binding to these receptors ultimately lead to the inhibition of proliferation and syncytium formation.

Pancreatic adenocarcinoma upregulated factor promotes metastasis by regulating TLR/CXCR4 activation

Pancreatic adenocarcinoma upregulated factor (PAUF) is overproduced in certain types of cancer. However, little is known of the tumorigenic function of PAUF. In this study, we report the X-ray crystal structure of PAUF and reveal that PAUF is a mammalian lectin normally found in plant lectins. We also identify PAUF as an endogenous ligand of Toll-like receptor 2 (TLR2) and TLR4 by screening extracellular domain receptor pools. We further confirmed the specificity of the PAUF-TLR2 interaction. PAUF induces extracellular signal-regulated kinase (ERK) phosphorylation and activates the IKK-β-mediated TPL2/MEK/ERK signaling pathway through TLR2. In agreement with the result of TLR2-mediated ERK activation by PAUF, PAUF induces increased expression of the protumorigenic cytokines RANTES and MIF in THP-1 cells. However, PAUF does not fully activate Iκ-B-α signaling pathways in THP-1 cells, and fails to translocate the p65 subunit of the nuclear factor-κB (NF-κB) complex into the nucleus, resulting in no NF-κB activation. Surprisingly, we found that PAUF also associated with the CXC chemokine receptor (CXCR4)-TLR2 complex and inhibited CXCR4-dependent, TLR2-mediated NF-κB activation. Together, these findings suggest that the new cancer-associated ligand, PAUF, may activate TLR-mediated ERK signaling to produce the protumorigenic cytokines, but inhibits TLR-mediated NF-κB signaling, thereby facilitating tumor growth and escape from innate immune surveillance.

Sialylated Lewis x antigen bearing glycoproteins in human plasma

Recent studies have shown that antibodies targeting Lewis x (Le(x)) antigen are a valuable tool in the isolation and identification of glycoproteins in plasma. A focus of this study was to determine whether sialylated Lewis x (sLe(x)) antigen carrying glycoproteins occur in human plasma and whether an antibody targeting this antigen could be used to isolate and identify glycoproteins bearing this antigen. An additional objective was to determine the degree to which proteins conjugated to Le(x) and sLe(x) antigens are similar in structure. A specific anti-sLe(x) antibody (anti-sLe(x)Ab), CHO-131, immobilized in an immunoaffinity column was used to select a set of specific sLe(x) bearing proteins from human plasma, after which they were identified by either of two analytical strategies. One approach was to further resolve the affinity selected proteins by reversed phase chromatography (RPC), tryptic digest the RPC fractions, and identify peptide fragments by MALDI-MS/MS. The second was to tryptic digest the affinity selected protein fraction, further resolve the tryptic fragments by RPC, and identify peptides from RPC fractions by MALDI-MS/MS. Histidine-rich glycoprotein, plasminogen, apolipoprotein A-I, vitronectin, proteoglycan-4, clusterin, Ig gamma-2 chain C region, Ig mu chain C region, and interalpha-trypsin inhibitor heavy chain H4 were found to change three folds or more in association with breast cancer. Fifty percent of the glycoproteins carrying either sLe(x) antigen from CHO-131 selection, Le(x) antigen from selection with TG-1 antibody, or both were found to be changed three folds or more in concentration in breast cancer plasma relative to controls.

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

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

Serum level of galectin-3 in human bladder cancer

We examine serum level of galectin-3 in patients with bladder cancer. We used serum samples of 67 patients with urological diseases and classified these patients into bladder cancer group (n=43) and control group (n=24). Galectin-3 concentration was measured by ELISA (Human Galectin-3 Assay Kit, IBL). And we selected the patient with high serum galectin-3 concentration (Urothelial Carcinoma, G3, pT3a pN0M0), we performed immunohistochemical staining with the VECTASTAIN ABC (Avidin Biotinylated enzyme Complex) system. Median value of serum galectin-3 concentration was 1068 pg/ml (range 551-2028) in the cancer group vs 584 pg/ml (range 259-1262) in controls. Serum galectin-3 concentration of the bladder cancer patients was statistically higher than that of controls (p<0.0005). There was no apparent correlation in serum galectin-3 concentration with the clinico-pathological features such as stage and grade. Higher expression of galectin-3 was observed in bladder cancer tissue than in normal bladder tissue. We suggest the measurement of serum galectin-3 is useful for diagnosis of bladder cancer.

111In-labeled galectin-3-targeting peptide as a SPECT agent for imaging breast tumors

Galectin-3 is a member of the galectin family of beta-galactoside-binding animal lectins. Galectin-3 is overexpressed in a wide range of neoplasms and is associated with tumor growth and metastases. Given this fact, radiolabeled galectin-3-targeting molecules may be useful for the noninvasive imaging of tumors expressing galectin-3, as well as for targeted radionuclide therapy. In this study, the tumor cell-targeting and SPECT properties of a galectin-3-avid peptide identified from bacteriophage display were evaluated in human breast carcinoma cells and in human breast tumor-bearing mice.

METHODS

The galectin-3-avid peptide G3-C12 (ANTPCGPYTHDCPVKR) was synthesized with a Gly-Ser-Gly (GSG) linker at the amino terminus. After conjugation with 1,4,7,10-tetra-azacyclododecane-N,N',N''N'''-tetraacetic acid (DOTA), the peptide was labeled with (111)In. The radiochemical purity and stability of the compound was assessed by high-performance liquid chromatography. MDA-MB-435 human breast carcinoma cells expressing galectin-3 were used to characterize the in vitro binding properties of the radiolabeled compound. SCID mice bearing MDA-MB-435 xenografts were used as an in vivo model for biodistribution and imaging studies with the (111)In-labeled peptide.

RESULTS

(111)In-DOTA(GSG)-G3-C12 bound specifically to galectin-3-expressing MDA-MB-435 cells. The radiolabeled peptide was stable in serum and was found intact in excreted urine for at least 1 h. Competitive binding experiments indicated that the radiolabeled peptide exhibited an inhibitory concentration of 50% of 200.00+/-6.70 nM for cultured breast carcinoma cells. In vivo biodistribution studies revealed that tumor uptake was 1.2+/-0.24, 0.75+/-0.05, and 0.6+/-0.04 (mean +/- SD) percentage injected dose per gram at 30 min, 1.0 h, and 2.0 h after injection of the radiotracer, respectively. SPECT/CT studies with (111)In-DOTA(GSG)-G3-C12 showed excellent tumor uptake and contrast in the tumor-bearing mice. Specificity of peptide binding was demonstrated by successful blocking (52%) of in vivo tumor uptake of (111)In-DOTA(GSG)-G3-C12 in the presence of its nonradiolabeled counterpart at 2 h after injection.

CONCLUSION

This study demonstrated the successful use of a new radiolabeled peptide for the noninvasive imaging of galectin-3-positive breast tumors. This peptide may be a promising candidate for future clinical applications.

Adhesive properties of metastasizing tumour cells

Cancer metastasis depends on a functional property which enables tumour cells to depart from the primary site of growth, to disseminate to distant organs and to establish secondary growth. The acquisition of a metastatic phenotype by neoplastic cells most probably involves alterations in their adhesive properties as the migrating cells continuously break and establish cellular contacts throughout the process. In vitro, normal cells of either mesenchymal or epithelial origin usually depend on adhesion to and spreading on a solid substratum (anchoring) for cell division. Neoplastic cells, however, are free of dependence on the support of solid substrata for cell proliferation (anchorage independent). The search for the characteristic alterations in cell adhesion, spreading and morphology which may accompany neoplastic transformation in general and cancer metastasis in particular has engendered a wide range of research activities. These studies have led to the identification of various membrane receptors that mediate cell-cell and cell-extracellular matrix recognition and adhesion on normal and tumour cells. Central to this is the effect of cell adhesion on cell shape and cytoskeleton organization in relation to metastasis. The use of specific antibodies, ligands, drugs and culture conditions permits exploration and identification of some of the macromolecules involved in tumour cell adhesion in vitro and metastasis in vivo. Nevertheless the specificity of the interactions which might determine organ-specific metastasis remains to be elucidated. This paper discusses the interrelation between cell adhesion, cell shape, cytoskeleton and metastasis.

Inhibition of galectin-3 mediated cellular interactions by pectic polysaccharides from dietary sources

Pectic polysaccharides from dietary sources such as Decalepis hamiltonii--swallow root (SRPP), Hemidesmus indicus (HPP), Nigella sativa--black cumin (BCPP), Andrographis serpyllifolia-(APP), Zingiber officinale--ginger (GRPP) and, citrus pectin (CPP) were examined for galectin inhibitory activity. Inhibition of (a) galectin-3 of MDA-MB-231 cells induced hemagglutination of red blood cells; (b) galectin-3 mediated interaction between normal/metastatic human buccal cells (NBC)/(MBC) and; (c) invasion of MDA-MB-231 and MBC in the invasive chamber was assessed. Results indicated that SRPP inhibited hemagglutination at Minimum Inhibitory Concentration (MIC) of 1.86 microg ml(-1) equivalent of carbohydrate as apposed to those of BCPP (130 microg ml(-1)), APP (40 microg ml(-1)), HPP (40 microg ml(-1)) and CPP (25 microg ml(-1)). GRPP even at concentration >1-6 mg ml(-1) did not inhibit agglutination. Also SRPP showed approximately 15 and 2 fold potent anti hemagglutination activity relative to that of galectin-3 specific sugars-galactose (MIC-27.1 microg ml(-1)) and lactose (MIC-4.16 microg ml(-1)) respectively. Further, SRPP at 10 microg ml(-1) inhibited agglutination of NBC by galectin-3 of MDA-MB-231 cells. Modified swallow root pectic polysaccharide (MSRPP) of 50 kDa retained anti hemagglutination activity (MIC of 1.03 microg ml(-1)) and inhibited MDA-MB-231 and MBC invasion by 73 and 50% with an IC(50) of 136 and 200 microg ml(-1) respectively. Both SRPP and MSRPP induced apoptosis up to 80% at 100 microg ml(-1) concentration by activating approximately 2 and 8 folds of Caspase-3 activity. Sugar composition analysis and its correlation with the galectin inhibitory property indicated that pectic polysaccharides with higher arabinose and galactose content-arabinogalactan inhibited hemagglutination significantly.

Galectins - potential targets for cancer therapy

Galectins are a family of galactose binding lectins that have become the focus of attention of cancer biologists due to their numerous regulatory roles in normal cellular metabolism and also because of their altered levels in various cancers. They are reportedly similar to several prominent and established modulators of apoptosis. In this review, we present a brief outline of the advancements in the methodology used to detect and identify them and their therapeutic applications in cancer. Their possible interactions with other glycoconjugates are also discussed and a vision for their future use in diagnosis and therapeutics is provided.

Binding of galectin-1 (gal-1) to the Thomsen–Friedenreich (TF) antigen on trophoblast cells and inhibition of proliferation of trophoblast tumor cells in vitro by gal-1 or an anti-TF antibody

Galectin-1 (gal-1), a member of the mammalian beta-galactoside-binding proteins, recognizes preferentially Galbeta1-4GlcNAc sequences of several cell surface oligosaccharides. We demonstrate histochemically that the lectin recognizes appropriate glycotopes on the syncytiotrophoblast and extravillous trophoblast layer from second trimester human placenta and on BeWo chorion carcinoma cells. Gal-1 binding to BeWo cells was diminished by the Thomsen-Friedreich (TF)-disaccharide (Galbeta1-3GalNAc-) conjugated to polyacrylamide (TF-PAA). Gal-1 also inhibited BeWo cell proliferation in a concentration-dependent manner. Similar antiproliferative effects were also observed with an anti-TF monoclonal antibody (mAb, A78-G/A7). Therefore, we conclude that ligation of Galbeta1-4GlcNAc and Galbeta1-3GalNAc epitopes on BeWo cells may have regulatory effects on cell proliferation.

Expressions of galectin-3, glutathione S-transferase A2 and peroxiredoxin-1 by nonylphenol-incubated Caco-2 cells and reduction in transepithelial electrical resistance by nonylphenol

Nonylphenol, an estrogenic xenobiotic widely used in the manufacture of plastics and detergents, has been found in drinking water and may therefore enter the body through the oral route. Thus, intestinal cells lining the alimentary tract serve as the body's first line of defense against this compound. In this study, the effects of nonylphenol on the human intestinal cell line Caco-2 were determined using transepithelial electrical resistance (TEER) measurement and proteomics. Results show that 10 microM nonylphenol can disrupt the tight-junction permeability of Caco-2 cells in approximately 15 min. Incubating the cells with 1 or 10 microM nonylphenol for 6 days resulted in the enhanced expressions of galectin-3 (approximately 4-fold vs. control with 1 microM; 2-fold with 10 microM), glutathione S-transferase A2 (approximately 8-fold with 1 microM; 5-fold with 10 microM) and peroxiredoxin-1 (approximately 6-fold with 1 microM; 4-fold with 10 microM). These expressions may represent a possible consortium of mechanisms by which the cells protect themselves against nonylphenol-induced stresses. To the best of our knowledge, this is the first study on the effects of nonylphenol on Caco-2 cells.

An antifungal protein from flageolet beans

A protein with antifungal and hemagglutinating activities was isolated from dried flageolet beans (Phaseolus vulgaris cv. 'Flageolet Bean'). The protein was unadsorbed on DEAE-cellulose but adsorbed on Affi-gel blue gel and CM-cellulose. The protein demonstrated antifungal activity against Mycophaerella arachidicola with an IC50 of 9.8 microM, but was inactive toward Fusarium oxysporum and Botrytis cinerea. Its hemagglutinating activity could not be inhibited by a variety of the sugars tested. The activity was stable up to 60 degrees C. At 70 degrees C, 75% of the hemagglutinating activity remained while no activity was discernible at and above 100 degrees C. The hemagglutinating activity was stable in the presence of a variety of monovalent, divalent and trivalent chlorides, and also when the ambient pH changed from 3 to 12. It did not exert any mitogenic activity on mouse splenocytes in vitro. Neither did it inhibit HIV-1 reverse transcriptase. It inhibited [3H-methyl]-thymidine incorporation into leukemia L1210 cells with an IC50 of about 4 microM.

Galectin-3 inhibits tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by activating Akt in human bladder carcinoma cells

The antiapoptotic molecule galectin-3 was previously shown to regulate CD95, a member of the tumor necrosis factor (TNF) family of proteins in the apoptotic signaling pathway. Here, we question the generality of the phenomenon by studying a different member of this family of proteins [e.g., TNF-related apoptosis-inducing ligand (TRAIL), which induces apoptosis in a wide variety of cancer cells]. Overexpression of galectin-3 in J82 human bladder carcinoma cells rendered them resistant to TRAIL-induced apoptosis, whereas phosphatidylinositol 3-kinase (PI3K) inhibitors (wortmannin and LY-294002) blocked the galectin-3 protecting effect. Because Akt is a major downstream PI3K target reported to play a role in TRAIL-induced apoptosis, we questioned the possible relationship between galectin-3 and Akt. Parental J82 and the control vector-transfected J82 cells (barely detectable galectin-3) exhibit low level of constitutively active Akt, resulting in sensitivity to TRAIL. On the other hand, J82 cells overexpressing galectin-3 cells expressed a high level of constitutively active Akt and were resistant to TRAIL. Moreover, the blockage of TRAIL-induced apoptosis in J82 cells seemed to be mediated by Akt through the inhibition of BID cleavage. These results suggest that galectin-3 involves Akt as a modulator molecule in protecting bladder carcinoma cells from TRAIL-induced apoptosis.

Differential Cellular Expression of Galectin Family mRNAs in the Epithelial Cells of the Mouse Digestive Tract

Galectin is an animal lectin that recognizes β-galactosides of glycoconjugates and is abundant in the gut. This study revealed the cellular expression of galectin subtypes throughout the mouse digestive tract by in situ hybridization. Signals for five subtypes (galectin-2, -3, -4/6, and -7) were detected exclusively in the epithelia. In the glandular stomach, galectin-2 and -4/6 were predominantly expressed from gastric pits to neck of gastric glands, where mucous cells were the main cellular sources. The small intestine exhibited intense, maturation-associated expressions of galectin-2, -3, and -4/6 mRNAs. Galectin-2 was intensely expressed from crypts to the base of villi, whereas transcripts of galectin-3 gathered at villous tips. Signals for galectin-4/6 were most intense at the lower half of villi. Galectin-2 was also expressed in goblet cells of the small intestine but not in those of the large intestine. In the large intestine, galectin-4/6 predominated, and the upper half of crypts simultaneously contained transcripts of galectin-3. Stratified epithelium from the lip to forestomach and anus intensely expressed galectin-7 with weak expressions of galectin-3. Because galectins in the digestive tract may be multi-functional, information on their cell/stage-specific expression contributes to a better understanding of the functions and pathological involvements of galectins.

Expression of core 2 beta1,6-N-acetylglucosaminyltransferase facilitates prostate cancer progression

Cell surface carbohydrates expressed on epithelial cells are thought to play an important role in tumor progression. Previously, we have shown that expression of core 2-branched O-glycans is closely correlated with vessel invasion and depth of invasion in colon and lung carcinomas. In this study, we found that expression of core 2 beta1,6-N-acetylglucosaminyltransferase-1, Core2GnT, is positively correlated with the progression of prostate cancer in human patients. Statistical analysis demonstrated that Core2GnT is an independent predictor for progressed pathological stage (pT3) and for prostate-specific antigen (PSA) relapse. To determine directly the roles of Core2GnT in prostate cancer progression, we set up an experimental tumor model using the LNCaP prostate cancer cell line. Because this line does not express Core2GnT, we established an LNCaP line stably expressing Core2GnT, LNCap-Core2GnT, by transfecting cDNA encoding Core2GnT. When mock-transfected LNCaP cells and LNCaP-Core2GnT were inoculated in the prostate of nude mice, LNCaP-Core2GnT cells produced three times heavier prostate tumors than mock-transfected LNCaP cells. Furthermore, we found that LNCaP-Core2GnT cells adhered more strongly to prostate stromal cells, type IV collagen and laminin than did LNCaP-mock cells, but LNCaP and LNCaP-Core2GnT cells grew almost at the same rate on plates coated with type IV collagen or laminin. These results indicate that Core2GnT is an extremely useful prognostic marker for prostate cancer progression. The results also suggest that acquiring Core2GnT in prostate carcinoma cells facilitates adhesion to type IV collagen and laminin, and this increased adhesion may be a cause for aggressive tumor formation by prostate cancer cells expressing Core2GnT.

Extracellular nucleotides activate Runx2 in the osteoblast-like HOBIT cell line: a possible molecular link between mechanical stress and osteoblasts' response

Dynamic mechanical loading increases bone density and strength and promotes osteoblast proliferation, differentiation and matrix production, by acting at the gene expression level. Molecular mechanisms through which mechanical forces are conversed into biochemical signalling in bone are still poorly understood. A growing body of evidence point to extracellular nucleotides (i.e., ATP and UTP) as soluble factors released in response to mechanical stimulation in different cell systems. Runx2, a fundamental transcription factor involved in controlling osteoblasts differentiation, has been recently identified as a target of mechanical signals in osteoblastic cells. We tested the hypothesis that these extracellular nucleotides could be able to activate Runx2 in the human osteoblastic HOBIT cell line. We found that ATP and UTP treatments, as well as hypotonic stress, promote a significant stimulation of Runx2 DNA-binding activity via a mechanism involving PKC and distinct mitogen-activated protein kinase cascades. In fact, by using the specific inhibitors SB203580 (specific for p38 MAPK) and PD98059 (specific for ERK-1/2 MAPK), we found that ERK-1/2, but not p38, play a major role in Runx2 activation. On the contrary, another important transcription factor, i.e., Egr-1, that we previously demonstrated being activated by extracellular released nucleotides in this osteoblastic cell line, demonstrated to be susceptible to both ERK-1/2 and p38 kinases. These data suggest a possible differential involvement of these two transcription factors in response to extracellularly released nucleotides. The biological relevance of our data is strengthened by the finding that a target gene of Runx2, i.e., Galectin-3, is up-regulated by ATP stimulation of HOBIT cells with a comparable kinetic of that found for Runx2. Since it is known that osteocytes are the primary mechanosensory cells of the bone, we hypothesize that they may signal mechanical loading to osteoblasts through release of extracellular nucleotides. Altogether, these data suggest a molecular mechanism explaining the purinoreceptors-mediated activation of specific gene expression in osteoblasts and could be of help in setting up new pharmacological strategies for the intervention in bone loss pathologies.

Introduction to galectins

Good evidence suggest roles of galectins in cancer, immunity and inflammation, and development, but a unifying picture of their biological function is lacking. Instead galectins appear to have a particularly diverse, bewildering but intriguing array of activities both inside and outside cells--"clear truths and mysteries are inextricably twined". Fortunately this has not discouraged but rather enthused a large number of good galectin researchers, some of which have contributed to this special issue of Glycoconjugate Journal to provide a personal, critical status of the field. Here we will give a brief introduction to the galectins as a protein family with some comments on nomenclature.

90K (Mac-2 BP) and galectins in tumor progression and metastasis

Galectins and their ligands have been implicated in cell transformation and cancer metastasis, and found to have prognostic value. Mac-2 BP, also known as 90K, is a highly glycosylated, secreted protein extensively studied in human cancer, which binds galectin-1, galectin-3 and galectin-7. High expression levels of 90K are associated with a shorter survival, the occurrence of metastasis or a reduced response to chemotherapy in patients with different types of malignancy. The mechanisms underlying the prognostic significance of 90K and galectins in cancer are far from being understood, although they may be related to the ability of these proteins to interact and, to some extent, modulate cell-cell and cell-matrix adhesion and apoptosis. The resulting scenario is even more complex, as data have been presented that all these proteins might be associated with either a positive or a negative outcome of the patients. It is hypothesised that different galectins and galectin ligands with overlapping or opposite functions, expressed in different tumors during the different steps of the metastatic cascade might play a crucial role in tumor progression.