María F. Troncoso

GALECTINS: MATRICELLULAR GLYCAN-BINDING PROTEINS LINKING CELL ADHESION, MIGRATION, AND SURVIVAL

Abstract.Galectins are a taxonomically widespread family of glycan-binding proteins, defined by at least one conserved carbohydrate-recognition domain with a canonical amino acid sequence and affinity for β-galactosides. Because of their anti-adhesive as well as pro-adhesive extracellular functions, galectins appear to be a novel class of adhesion-modulating proteins collectively known as matricellular proteins (which include thrombospondin, SPARC, tenascin, hevin, and disintegrins). Accordingly, galectins can display de-adhesive effects when presented as soluble proteins to cells in a strong adhesive state. In this context, the de-adhesive properties of galectins should be considered as physiologically relevant as the proadhesive effects of these glycan-binding proteins. This article focuses on the roles of mammalian galectins in cell adhesion, spreading, and migration, and the crossregulation of these functions. Although careful attention should be paid when examining individual galectin functions due to overlapping distributions, these intriguing glycan-binding proteins offer promising possibilities for the treatment and intervention of a wide variety of pathological processes, including cancer, inflammation, and autoimmunity.

Modulation of endothelial cell migration and angiogenesis: a novel function for the “tandem-repeat” lectin galectin-8

Angiogenesis, the growth of new capillaries from preexisting blood vessels, is a complex process involving endothelial cell (EC) activation, disruption of vascular basement membranes, and migration and proliferation of ECs. Glycan‐mediated recognition has been proposed to play an instrumental role in mediating cell‐cell and cell‐matrix interactions. Ga‐lectins (Gal), a family of glycan‐binding proteins with affinity for β‐galactosides and a conserved sequence motif, can decipher glycan‐containing information and mediate cell‐cell communication. Galectin‐8 (Gal‐8), a member of this family, is a bivalent “tandem‐repeat”‐type galectin, which possesses 2 CRDs connected by a linker peptide. Here, we show that Gal‐8 is endowed with proangiogeneic properties. Functional assays revealed a critical role for this lectin in the regulation of capillary‐tube formation and EC migration. Moreover, Matrigel, either supplemented with Gal‐8 or vascular endothelial growth factor (VEGF), injected in mice resulted in induction of in vivo angiogenesis. Remarkably, Gal‐8 was expressed both in the cytoplasm and nucleus in ECs of normal and tumor vessels. Furthermore, CD166 [activated leukocyte cell adhesion molecule (ALCAM)] was identified as a specific Gal‐8‐binding partner in normal vascular ECs. Collectively, these data provide the first evidence demonstrating an essential role for Gal‐8 in the regulation of angiogenesis with critical implications in tumor biology.—CCárdenasrdenas Delgado, V. M., Nugnes, L. G., Colombo, L. L., Troncoso, M. F., Fernández, M. M., Malchiodi, E. L., Frahm, I., Croci, D. O., Compagno, D., Rabinovich, G. A., Wolfenstein‐Todel, C., Elola, M. T. Modulation of endothelial cell migration and angiogenesis: a novel function for the “tandem‐repeat” lectin galectin‐8. FASEB J. 25, 242–254 (2011). www.fasebj.org

Novel roles of galectin-1 in hepatocellular carcinoma cell adhesion, polarization, and in vivo tumor growth.

Galectin‐1 (Gal‐1), a widely expressed β‐galactoside–binding protein, exerts pleiotropic biological functions. Gal‐1 is up‐regulated in hepatocarcinoma cells, although its role in liver pathophysiology remains uncertain. We investigated the effects of Gal‐1 on HepG2 hepatocellular carcinoma (HCC) cell adhesion and polarization. Soluble and immobilized recombinant Gal‐1 (rGal‐1) promoted HepG2 cell adhesion to uncoated plates and also increased adhesion to laminin. Antibody‐mediated blockade experiments revealed the involvement of different integrins as critical mediators of these biological effects. In addition, exposure to rGal‐1 markedly accelerated the development of apical bile canaliculi as shown by TRITC‐phalloidin labeling and immunostaining for multidrug resistance associated‐protein 2 (MRP2). Notably, rGal‐1 did not interfere with multidrug resistance protein 1/P‐glycoprotein or MRP2 apical localization, neither with transfer nor secretion of 5‐chloromethylfluorescein diacetate through MRP2. Stimulation of cell adhesion and polarization by rGal‐1 was abrogated in the presence of thiodigalactoside, a galectin‐specific sugar, suggesting the involvement of protein–carbohydrate interactions in these effects. Additionally, Gal‐1 effects were abrogated in the presence of wortmmanin, PD98059 or H89, suggesting involvement of phosphoinositide 3‐kinase (PI3K), mitogen‐activated protein kinase and cyclic adenosine monophosphate–dependent protein kinase signaling pathways in these functions. Finally, expression levels of this endogenous lectin correlated with HCC cell adhesion and polarization and up‐regulation of Gal‐1–favored growth of hepatocarcinoma in vivo. Conclusion: Our results provide the first evidence of a role of Gal‐1 in modulating HCC cell adhesion, polarization, and in vivo tumor growth, with critical implications in liver pathophysiology. (HEPATOLOGY 2011;)

Galectin-1 circumvents lysolecithin-induced demyelination through the modulation of microglial polarization/phagocytosis and oligodendroglial differentiation.

Galectin-1 (Gal-1), a member of a highly conserved family of animal lectins, binds to the common disaccharide [Galβ(1-4)-GlcNAc] on both N- and O-glycans decorating cell surface glycoconjugates. Current evidence supports a role for Gal-1 in the pathophysiology of multiple sclerosis (MS), one of the most prevalent chronic inflammatory diseases. Previous studies showed that Gal-1 exerts neuroprotective effects by promoting microglial deactivation in a model of autoimmune neuroinflammation and induces axonal regeneration in spinal cord injury. Seeking a model that could link demyelination, oligodendrocyte (OLG) responses and microglial activation, here we used a lysolecithin (LPC)-induced demyelination model to evaluate the ability of Gal-1 to preserve myelin without taking part in T-cell modulation. Gal-1 treatment after LPC-induced demyelination promoted a significant decrease in the demyelinated area and fostered more efficient remyelination, concomitantly with an attenuated oligodendroglial progenitor response reflecting less severe myelination damage. These results were accompanied by a decrease in the area of microglial activation with a shift toward an M2-polarized microglial phenotype and diminished astroglial activation. In vitro studies further showed that, mechanistically, Gal-1 targets activated microglia, promoting an increase in their myelin phagocytic capacity and their shift toward an M2 phenotype, and leads to oligodendroglial differentiation. Therefore, this study supports the use of Gal-1 as a potential treatment for demyelinating diseases such as MS.

Galectin-1 Controls the Proliferation and Migration of Liver Sinusoidal Endothelial Cells and Their Interaction With Hepatocarcinoma Cells.

Galectin‐1 (Gal1), a β‐galactoside‐binding protein elevated in hepatocellular carcinoma (HCC), promotes epithelial‐mesenchymal transition (EMT) and its expression correlates with HCC growth, invasiveness, and metastasis. During the early stages of HCC, transforming growth factor β1 (TGF‐β1) acts as a tumor suppressor; however in advanced stages, HCC cells lose their cytostatic response to TGF‐β1 and undergo EMT. Here, we investigated the role of Gal1 on liver endothelial cell biology, and the interplay between Gal1 and TGF‐β1 in HCC progression. By Western blot and immunofluorescence, we analyzed Gal1 expression, secretion and localization in HepG2 and HuH‐7 human HCC cells, and in SK‐HEP‐1 human liver sinusoidal endothelial cells (SECs). We used loss‐of‐function and gain‐of‐function experiments to down‐ or up‐regulate Gal1 expression, respectively, in HepG2 cells. We cultured SK‐HEP‐1 cells with conditioned media from HCC cells secreting different levels of Gal1, and demonstrated that Gal1 derived from tumor hepatocytes induced its own expression in SECs. Colorimetric and scratch‐wound assays revealed that secretion of Gal1 by HCC cells induced SEC proliferation and migration. Moreover, by fluorescence microscopy we demonstrated that Gal1 promoted glycan‐dependent heterotypic adhesion of HepG2 cells to SK‐HEP‐1 SECs. Furthermore, TGF‐β1 induced Gal1 expression and secretion by HCC cells, and promoted HepG2 cell adhesion to SK‐HEP‐1 SECs through a Gal1‐dependent mechanism. Finally, Gal1 modulated HepG2 cell proliferation and sensitivity to TGF‐β1‐induced growth inhibition. Our results suggest that Gal1 and TGF‐β1 might function coordinately within the HCC microenvironment to regulate tumor growth, invasion, metastasis, and angiogenesis. J. Cell. Physiol. 231: 1522–1533, 2016.

Contribution of galectin-1, a glycan-binding protein, to gastrointestinal tumor progression

Gastrointestinal cancer is a group of tumors that affect multiple sites of the digestive system, including the stomach, liver, colon and pancreas. These cancers are very aggressive and rapidly metastasize, thus identifying effective targets is crucial for treatment. Galectin-1 (Gal-1) belongs to a family of glycan-binding proteins, or lectins, with the ability to cross-link specific glycoconjugates. A variety of biological activities have been attributed to Gal-1 at different steps of tumor progression. Herein, we summarize the current literature regarding the roles of Gal-1 in gastrointestinal malignancies. Accumulating evidence shows that Gal-1 is drastically up-regulated in human gastric cancer, hepatocellular carcinoma, colorectal cancer and pancreatic ductal adenocarcinoma tissues, both in tumor epithelial and tumor-associated stromal cells. Moreover, Gal-1 makes a crucial contribution to the pathogenesis of gastrointestinal malignancies, favoring tumor development, aggressiveness, metastasis, immunosuppression and angiogenesis. We also highlight that alterations in Gal-1-specific glycoepitopes may be relevant for gastrointestinal cancer progression. Despite the findings obtained so far, further functional studies are still required. Elucidating the precise molecular mechanisms modulated by Gal-1 underlying gastrointestinal tumor progression, might lead to the development of novel Gal-1-based diagnostic methods and/or therapies.