Juan P. Cerliani

Glycosylation-Dependent Lectin-Receptor Interactions Preserve Angiogenesis in Anti-VEGF Refractory Tumors

The clinical benefit conferred by vascular endothelial growth factors (VEGF)-targeted therapies is variable, and tumors from treated patients eventually reinitiate growth. Here, we identify a glycosylation-dependent pathway that compensates for the absence of cognate ligand and preserves angiogenesis in response to VEGF blockade. Remodeling of the endothelial cell (EC) surface glycome selectively regulated binding of galectin-1 (Gal1), which upon recognition of complex N-glycans on VEGFR2, activated VEGF-like signaling. Vessels within anti-VEGF-sensitive tumors exhibited high levels of α2-6-linked sialic acid, which prevented Gal1 binding. In contrast, anti-VEGF refractory tumors secreted increased Gal1 and their associated vasculature displayed glycosylation patterns that facilitated Gal1-EC interactions. Interruption of β1-6GlcNAc branching in ECs or silencing of tumor-derived Gal1 converted refractory into anti-VEGF-sensitive tumors, whereas elimination of α2-6-linked sialic acid conferred resistance to anti-VEGF. Disruption of the Gal1-N-glycan axis promoted vascular remodeling, immune cell influx and tumor growth inhibition. Thus, targeting glycosylation-dependent lectin-receptor interactions may increase the efficacy of anti-VEGF treatment.

Galectin-1 Deactivates Classically Activated Microglia and Protects from Inflammation-Induced Neurodegeneration

Inflammation-mediated neurodegeneration occurs inxa0the acute and the chronic phases of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Classically activated (M1) microglia are key players mediating this process. Here, we identified Galectin-1 (Gal1), an endogenous glycan-binding protein, as a pivotal regulator of M1 microglial activation that targets the activation of p38MAPK-, CREB-, and NF-κB-dependent signaling pathways and hierarchically suppresses downstream proinflammatory mediators, such as iNOS, TNF, and CCL2. Gal1 bound to core 2 O-glycans on CD45, favoring retention of this glycoprotein on the microglial cell surface and augmenting its phosphatase activity and inhibitory function. Gal1 was highly expressed in the acute phase ofxa0EAE, and its targeted deletion resulted in pronounced inflammation-induced neurodegeneration. Adoptive transfer of Gal1-secreting astrocytes or administration of recombinant Gal1 suppressed EAE through mechanisms involving microglial deactivation. Thus, Gal1-glycan interactions are essential in tempering microglial activation, brain inflammation, and neurodegeneration, with critical therapeutic implications for MS.

Targeting Galectin-1 Overcomes Breast Cancer-Associated Immunosuppression and Prevents Metastatic Disease

Galectin-1 (Gal1), an evolutionarily conserved glycan-binding protein, contributes to the creation of an immunosuppressed microenvironment at sites of tumor growth. In spite of considerable progress in elucidating its role in tumor-immune escape, the mechanisms underlying the inhibitory functions of Gal1 remain obscure. Here, we investigated the contribution of tumor Gal1 to tumor growth, metastasis, and immunosuppression in breast cancer. We found that the frequency of Gal1(+) cells in human breast cancer biopsies correlated positively with tumor grade, while specimens from patients with benign hyperplasia showed negative or limited Gal1 staining. To examine the pathophysiologic relevance of Gal1 in breast cancer, we used the metastatic mouse mammary tumor 4T1, which expresses and secretes substantial amounts of Gal1. Silencing Gal1 expression in this model induced a marked reduction in both tumor growth and the number of lung metastases. This effect was abrogated when mice were inoculated with wild-type 4T1 tumor cells in their contralateral flank, suggesting involvement of a systemic modulation of the immune response. Gal1 attenuation in 4T1 cells also reduced the frequency of CD4(+)CD25(+) Foxp3(+) regulatory T (T(reg)) cells within the tumor, draining lymph nodes, spleen, and lung metastases. Further, it abrogated the immunosuppressive function of T(reg) cells and selectively lowered the expression of the T-cell regulatory molecule LAT (linker for activation of T cells) on these cells, disarming their suppressive activity. Taken together, our results offer a preclinical proof of concept that therapeutic targeting of Gal1 can overcome breast cancer-associated immunosuppression and can prevent metastatic disease.

Disrupting galectin-1 interactions with N-glycans suppresses hypoxia-driven angiogenesis and tumorigenesis in Kaposi’s sarcoma

Disrupting Gal-1 interactions with N-glycans prevents hypoxia-driven angiogenesis to suppress tumorigenesis of Kaposi’s sarcoma

Cancer Stem Cell‐Like Phenotype and Survival Are Coordinately Regulated by Akt/FoxO/Bim Pathway

Many solid tumors contain a subpopulation of cells with stem characteristics and these are known as cancer stem cells (CSCs) or tumor‐initiating cells (TICs). These cells drive tumor growth and appear to be regulated by molecular pathway different from other cells in the tumor bulk. Here, we set out to determine whether elements of the PI3K‐AKT pathway are necessary to maintain the CSC‐like phenotype in breast tumor cells and for these cells to survive, bearing in mind that the identification of such elements is likely to be relevant to define future therapeutic targets. Our results demonstrate a close relationship between the maintenance of the CSC‐like phenotype and the survival of these TICs. Inhibiting PI3K activity, or eliminating AKT activity, mostly that of the AKT1 isoform, produces a clear drop in TICs survival, and a reduction in the generation and growth of CD44High/CD24Low mammospheres. Surprisingly, the apoptosis of these TICs that is triggered by AKT1 deficiency is also associated with a loss of the stem cell/mesenchymal phenotype and a recovery of epithelial‐like markers. Finally, we define downstream effectors that are responsible for controlling the CSC‐phenotype, such as FoxO‐Bim, and the death of these cells in the absence of AKT1. In summary, these data closely link the maintenance of the stem cell‐like phenotype and the survival of these cells to the AKT‐FoxO‐Bim pathway. Stem Cells 2015;33:646–660

Nuclear factor (NF)-κB controls expression of the immunoregulatory glycan-binding protein galectin-1

The inflammatory response is a self-limiting process which involves the sequential activation of signaling pathways leading to the production of both pro- and anti-inflammatory mediators. Galectin-1 (Gal-1), an endogenous lectin found in peripheral lymphoid organs and inflammatory sites, elicits a broad spectrum of biological functions predominantly by acting as a potent anti-inflammatory factor and as a suppressive agent for T-cell responses. However, the molecular pathways underlying Gal-1 expression and function remain poorly understood. Here we identified a regulatory loop linking Gal-1 expression and function to NF-κB activation. NF-κB-activating stimuli increased Gal-1 expression on T cells, an effect which could be selectively prevented by inhibitors of NF-κB signaling. Accordingly, transient transfection of the p65 subunit of NF-κB was sufficient to induce high Gal-1 expression. Using in silico studies and chromatin immunoprecipitation analysis we have identified a functional NF-κB binding site within the first intron of the LGALS1 gene. In addition, our results show that exogenous Gal-1 can attenuate NF-κB activation, as shown by inhibition of IκB-α degradation induced by pro-inflammatory stimuli, higher cytoplasmic retention of p65, lower NF-κB DNA binding activity and impaired transcriptional activation of target genes. The present study suggest a novel regulatory loop by which NF-κB induces expression of Gal-1, which in turn may lead to negative control of NF-κB signaling.

Regulatory role of glycans in the control of hypoxia-driven angiogenesis and sensitivity to anti-angiogenic treatment

Abnormal glycosylation is a typical hallmark of the transition from healthy to neoplastic tissues. Although the importance of glycans and glycan-binding proteins in cancer-related processes such as tumor cell adhesion, migration, metastasis and immune escape has been largely appreciated, our awareness of the impact of lectin-glycan recognition in tumor vascularization is relatively new. Regulated glycosylation can influence vascular biology by controlling trafficking, endocytosis and signaling of endothelial cell (EC) receptors including vascular endothelial growth factor receptors, platelet EC adhesion molecule, Notch and integrins. In addition, glycans may control angiogenesis by regulating migration of endothelial tip cells and influencing EC survival and vascular permeability. Recent evidence indicated that changes in the EC surface glycome may also serve on-and-off switches that control galectin binding to signaling receptors by displaying or masking-specific glycan epitopes. These glycosylation-dependent lectin-receptor interactions can link tumor hypoxia to EC signaling and control tumor sensitivity to anti-angiogenic treatment.

Translating the ‘Sugar Code’ into Immune and Vascular Signaling Programs

The vast range and complexity of glycan structures and their dynamic variations in health and disease have presented formidable challenges toward understanding the biological significance of these molecules. Despite these limitations, compelling evidence highlights a major role for galectins, a family of soluble glycan-binding proteins, as endogenous decoders that translate glycan-containing information into a broad spectrum of cellular responses by modulating receptor clustering, reorganization, endocytosis, and signaling. Here, we underscore pioneer findings and recent advances in understanding the biology of galectin-glycan interactions in myeloid, lymphoid, and endothelial compartments, highlighting important pathways by which these multivalent complexes control immune and vascular programs. Implementation of novel glycoanalytical approaches, as well as the use of genetically engineered cell and organism models, have allowed glycans and galectins to be explored across a range of cellular processes.

Endogenous lectins shape the function of dendritic cells and tailor adaptive immunity: mechanisms and biomedical applications.

In spite of their central role in orchestrating immunity, dendritic cells (DCs) can also limit harmful reactions and promote immune tolerance by inducing T cell anergy or favoring the differentiation of T regulatory (T(reg)) cells. Several factors may influence the decision of DCs to become immunogenic or tolerogenic including the nature of antigenic challenge, the engagement of selective pathogen recognition receptors (PRRs) and the balance of cytokines and growth factors. In addition, mounting evidence indicates a key role of endogenous lectins including C-type lectins, siglecs and galectins in shaping DC immunogenicity and tailoring adaptive immune responses, through recognition of specific glycan signatures on invading pathogens or host cells. While galectins are in general secreted proteins that act in a paracrine or autocrine manner, all known siglecs and most C-type lectins are membrane-bound receptors that convey glycan-containing information into DC differentiation or maturation programs. Yet, some of the signaling pathways triggered by endogenous lectins converge in similar functional outcomes regardless of divergences in their structure, homology or glycan-binding specificity. To gain a more complete understanding on the role of protein-glycan interactions in DC biology, here we will integrate scattered information on these structurally-divergent but functionally-related lectins and their potential biomedical applications.

Galectin-1 Prevents Infection and Damage Induced by Trypanosoma cruzi on Cardiac Cells

Background Chronic Chagas cardiomyopathy caused by Trypanosoma cruzi is the result of a pathologic process starting during the acute phase of parasite infection. Among different factors, the specific recognition of glycan structures by glycan-binding proteins from the parasite or from the mammalian host cells may play a critical role in the evolution of the infection. Methodology and Principal Findings Here we investigated the contribution of galectin–1 (Gal–1), an endogenous glycan-binding protein abundantly expressed in human and mouse heart, to the pathophysiology of T. cruzi infection, particularly in the context of cardiac pathology. We found that exposure of HL–1 cardiac cells to Gal–1 reduced the percentage of infection by two different T. cruzi strains, Tulahuén (TcVI) and Brazil (TcI). In addition, Gal–1 prevented exposure of phosphatidylserine and early events in the apoptotic program by parasite infection on HL–1 cells. These effects were not mediated by direct interaction with the parasite surface, suggesting that Gal–1 may act through binding to host cells. Moreover, we also observed that T. cruzi infection altered the glycophenotype of cardiac cells, reducing binding of exogenous Gal–1 to the cell surface. Consistent with these data, Gal–1 deficient (Lgals1 -/-) mice showed increased parasitemia, reduced signs of inflammation in heart and skeletal muscle tissues, and lower survival rates as compared to wild-type (WT) mice in response to intraperitoneal infection with T. cruzi Tulahuén strain. Conclusion/Significance Our results indicate that Gal–1 modulates T. cruzi infection of cardiac cells, highlighting the relevance of galectins and their ligands as regulators of host-parasite interactions.