Galectins, a family of glycan-binding proteins, influence tumor progression by modulating interactions between tumor, endothelial, stromal, and immune cells. Despite considerable progress in identifying the roles of individual galectins in tumor biology, an integrated portrait of the galectin network in different tumor microenvironments is still missing. We undertook this study to analyze the "galectin signature" of the human prostate cancer microenvironment with the overarching goal of selecting novel-molecular targets for prognostic and therapeutic purposes. In examining androgen-responsive and castration-resistant prostate cancer cells and primary tumors representing different stages of the disease, we found that galectin-1 (Gal-1) was the most abundantly expressed galectin in prostate cancer tissue and was markedly upregulated during disease progression. In contrast, all other galectins were expressed at lower levels: Gal-3, -4, -9, and -12 were downregulated during disease evolution, whereas expression of Gal-8 was unchanged. Given the prominent regulation of Gal-1 during prostate cancer progression and its predominant localization at the tumor-vascular interface, we analyzed the potential role of this endogenous lectin in prostate cancer angiogenesis. In human prostate cancer tissue arrays, Gal-1 expression correlated with the presence of blood vessels, particularly in advanced stages of the disease. Silencing Gal-1 in prostate cancer cells reduced tumor vascularization without altering expression of other angiogenesis-related genes. Collectively, our findings identify a dynamically regulated "galectin-specific signature" that accompanies disease evolution in prostate cancer, and they highlight a major role for Gal-1 as a tractable target for antiangiogenic therapy in advanced stages of the disease. Cancer Res; 73(1); 86-96. Ó2012 AACR.

Regulators of G-protein signaling (RGS) constitute a family of proteins involved in the negative regulation of signaling through heterotrimeric G protein-coupled receptors (GPCRs). Several RGS proteins have been implicated in the down-regulation of chemokine signaling in hematopoietic cells. The chemokine stromal-cell-derived factor 1 (SDF-1) activates migration of hematopoietic progenitors cells but fails to activate mature megakaryocytes despite high levels of CXC chemokine receptor 4 (CXCR4) receptor expression in these cells. This prompted us to analyze RGS expression and function during megakaryocyte differentiation. We found that RGS16 and RGS18 mRNA expression was up-regulated during this process. Overexpressing RGS16 mRNA in the megakaryocytic MO7e cell line inhibited SDF-1-induced migration, mitogenactivated protein kinase (MAPK) and protein kinase B (AKT) activation, whereas RGS18 overexpression had no effect on CXCR4 signaling. Knocking down RGS16 mRNA via lentiviral-mediated RNA interference increased CXCR4 signaling in MO7e cells and in primary megakaryocytes. Thus, our data reveal that RGS16 is a negative regulator of CXCR4 signaling in megakaryocytes. We postulate that RGS16 regulation is a mechanism that controls megakaryocyte maturation by regulating signals from the microenvironment. ( IntroductionChemokines and their receptor(s) are broadly expressed in different tissues and regulate cell migration as well as several other important biologic processes. 1 The chemokine stromal-cell-derived factor 1 (SDF-1) is a stromal-cell-derived factor that interacts with a specific receptor CXC chemokine receptor 4 (CXCR4) and plays a role in B lymphopoiesis and bone marrow myelopoiesis. Studies using mutant mice with targeted gene disruption have revealed that SDF-1 and CXCR4 are essential for B-cell differentiation, for colonization of bone marrow by hematopoietic stem cells (HSCs) and myeloid lineage during ontogeny as well as for blood-vessel formation in gastrointestinal tract, cardiac ventricular septum formation, and cerebellar differentiation. 2,3 SDF-1CXCR4 signaling appears to be essential for the homing of hematopoietic stem/progenitor cells because treatment of immature human hematopoietic progenitor cells with anti-CXCR4 antibodies prevents their short-term engraftment into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. [4][5][6] In addition, transplantation of CXCR4 Ϫ/Ϫ fetal liver cells results in low numbers of B-lymphoid and myeloid lineage precursors in bone marrow but increased numbers in the peripheral blood compared with control animals. 7 Proteolytic cleavage of the N-terminus of CXCR4 and of SDF-1 is one mechanism that has been identified for the regulation of CXCR4/SDF1 signaling in circulating and mobilized blood cells. 8 The process of megakaryopoiesis occurs within a complex bone marrow microenvironment where chemokines, cytokines, and adhesive interactions play a major role. At the end of their maturation, polyploid megakaryocytes (MKs) migrate through bone m...

Galectin-1 (Gal1), a β-galactoside-binding protein abundantly expressed in tumor microenvironments, is associated with the development of metastasis in hepatocellular carcinomas (HCC). However, the precise roles of Gal1 in HCC cell invasiveness and dissemination are uncertain. Here, we investigated whether Gal1 mediate epithelial-mesenchymal transition (EMT) in HCC cells, a key process during cancer progression. We used the well-differentiated and low invasive HepG2 cells and performed 'gain-of-function' and 'loss-function' experiments by transfecting cells with Gal1 cDNA constructs or by siRNA strategies, respectively. Epithelial and mesenchymal markers expression, changes in apico-basal polarity, independent-anchorage growth, and activation of specific signaling pathways were studied using Western blot, fluorescence microscopy, soft-agar assays, and FOP/TOP flash reporter system. Gal1 up-regulation in HepG2 cells induced down-regulation of the adherens junction protein E-cadherin and increased expression of the transcription factor Snail, one of the main inducers of EMT in HCC. Enhanced Gal1 expression facilitated the transition from epithelial cell morphology towards a fibroblastoid phenotype and favored up-regulation of the mesenchymal marker vimentin in HCC cells. Cells overexpressing Gal1 showed enhanced anchorage-independent growth and loss of apico-basal polarity. Remarkably, Gal1 promoted Akt activation, β-catenin nuclear translocation, TCF4/LEF1 transcriptional activity and increased cyclin D1 and c-Myc expression, suggesting activation of the Wnt pathway. Furthermore, Gal1 overexpression induced E-cadherin downregulation through a PI3K/Akt-dependent mechanism. Our results provide the first evidence of a role of Gal1 as an inducer of EMT in HCC cells, with critical implications in HCC metastasis.

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. Galectins (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.

BackgroundProstate carcinomas are initially dependent on androgens, and castration or androgen antagonists inhibit their growth. After some time though, tumors become resistant and recur with a poor prognosis. The majority of resistant tumors still expresses a functional androgen receptor (AR), frequently amplified or mutated.Methodology/Principal FindingsTo test the hypothesis that AR is not only expressed, but is still a key therapeutic target in advanced carcinomas, we injected siRNA targeting AR into mice bearing exponentially growing castration-resistant tumors. Quantification of siRNA into tumors and mouse tissues demonstrated their efficient uptake. This uptake silenced AR in the prostate, testes and tumors. AR silencing in tumors strongly inhibited their growth, and importantly, also markedly repressed the VEGF production and angiogenesis.Conclusions/SignificanceOur results demonstrate that carcinomas resistant to hormonal manipulations still depend on the expression of the androgen receptor for their development in vivo. The siRNA-directed silencing of AR, which allows targeting overexpressed as well as mutated isoforms, triggers a strong antitumoral and antiangiogenic effect. siRNA-directed silencing of this key gene in advanced and resistant prostate tumors opens promising new therapeutic perspectives and tools.

Galectin-8 (gal-8) is a "tandem-repeat"-type galectin, containing two carbohydrate recognition domains connected by a linker peptide. gal-8 is expressed both in the cytoplasm and nucleus in vascular endothelial cells (ECs) from normal and tumor-associated blood vessels, and in lymphatic endothelial cells. Herein, we describe a novel role for gal-8 in the regulation of vascular and lymphatic angiogenesis and provide evidence of its critical implications in tumor biology. Functional assays revealed central roles for gal-8 in the control of capillary-tube formation, EC migration and in vivo angiogenesis. So far, two endothelial ligands have been described for gal-8, namely podoplanin in lymphatic vessels and CD166 (ALCAM, activated leukocyte cell adhesion molecule) in vascular ECs. Other related gal-8 functions are also summarized here, including cell adhesion and migration, which collectively demonstrate the multi-functionality of this complex lectin. Thus, gal-8 is an important component of the angiogenesis network, and an essential molecule in the extracellular matrix by providing molecular anchoring to this surrounding matrix. The implications of gal-8 in tumor angiogenesis remain to be further explored, but it is exciting to speculate that modulating gal-8-glycan interactions could be used to block lymphatic-vascular connections vital for metastasis.

Specific NF-κB/Rel proteins regulate murine dendritic cell (DC) survival, differentiation, and activation, but little is known of their role in human cells because of limited loss-of-function analyses. RNA interference (RNAi) is a mechanism to effectively silence gene expression via sequence-specific double-stranded small interfering RNAs (siRNAs). RNAi was used to assess the role of the p50 (NF-κB1) protein in the maturation and activation of cultured human monocyte-derived DC (MoDC). Transfection of cultured MoDC with siRNAs reduced p50 mRNA and protein levels in a specific, dose-dependent, and time-dependent manner. Basal or maturation-induced expression of HLA-DR and costimulatory molecules were not affected, whereas transcription of the IL-12 p40 gene and the secretion of IL-12αβ were reduced. Such MoDC induced less IFN-γ production by T cells in MLR. This is the first report of RNAi-induced phenotype in human primary DC with a method that caused no measurable toxicity or type-I IFN response. siRNAs appear useful for the study of signaling pathways in immune cells, revealing a pivotal requirement for p50 in MoDC for IL-12 production and induction of optimal type-1 immune responses.

Galectins are small proteins with pleiotropic functions, which depend on both their lectin (glycan recognition) and non-lectin (recognition of other biomolecules besides glycans) interactions. Currently, 15 members of this family have been described in mammals, each with its structural and ligand recognition particularities. The galectin/ligand interaction translates into a plethora of biological functions that are particular for each cell/tissue type. In this sense, the cells of the immune system are highly sensitive to the action of these small and essential proteins. While galectins play central roles in tumor progression, they are also excellent negative regulators (checkpoints) of the immune cell functions, participating in the creation of a microenvironment that promotes tumor escape. This review aims to give an updated view on how galectins control the tumor’s immune attack depending on the tumor microenvironment, because determining which galectins are essential and the role they play will help to develop future clinical trials and benefit patients with incurable cancer.