Regulation of expression and secretion of galectin-3 in human monocyte-derived dendritic cells

Emerging role of galectin 3 in neuroinflammation and neurodegeneration

Neuroinflammation and neurodegeneration are key processes that mediate the development and progression of neurological diseases. However, the mechanisms modulating these processes in different diseases remain incompletely understood. Advances in single cell based multi-omic analyses have helped to identify distinct molecular signatures such as Lgals3 that is associated with neuroinflammation and neurodegeneration in the central nervous system (CNS). Lgals3 encodes galectin-3 (Gal3), a β-galactoside and glycan binding glycoprotein that is frequently upregulated by reactive microglia/macrophages in the CNS during various neurological diseases. While Gal3 has previously been associated with non-CNS inflammatory and fibrotic diseases, recent studies highlight Gal3 as a prominent regulator of inflammation and neuroaxonal damage in the CNS during diseases such as multiple sclerosis, Alzheimer's disease, and Parkinson's disease. In this review, we summarize the pleiotropic functions of Gal3 and discuss evidence that demonstrates its detrimental role in neuroinflammation and neurodegeneration during different neurological diseases. We also consider the challenges of translating preclinical observations into targeting Gal3 in the human CNS.

Differential O- and Glycosphingolipid Glycosylation in Human Pancreatic Adenocarcinoma Cells With Opposite Morphology and Metastatic Behavior

Changes in the glycosylation profile of cancer cells have been strongly associated with cancer progression. To increase our insights into the role of glycosylation in human pancreatic ductal adenocarcinoma (PDAC), we performed a study on O-glycans and glycosphingolipid (GSL) glycans of the PDAC cell lines Pa-Tu-8988T (PaTu-T) and Pa-Tu-8988S (PaTu-S). These cell lines are derived from the same patient, but show an almost opposite phenotype, morphology and capacity to metastasize, and may thus provide an attractive model to study the role of glycosylation in progression of PDAC. Gene-array analysis revealed that 24% of the glycosylation-related genes showed a ≥ 1.5-fold difference in expression level between the two cell lines. Subsequent validation of the data by porous graphitized carbon nano-liquid chromatography coupled to a tandem ion trap mass spectrometry and flow cytometry established major differences in O-glycans and GSL-glycans between the cell lines, including lower levels of T and sialylated Tn (sTn) antigens, neoexpression of globosides (Gb3 and Gb4), and higher levels of gangliosides in the mesenchymal-like PaTu-T cells compared to the epithelial-like PaTu-S. In addition, PaTu-S cells demonstrated a significantly higher binding of the immune-lectins macrophage galactose-type lectin and galectin-4 compared to PaTu-T. In summary, our data provide a comprehensive and differential glycan profile of two PDAC cell lines with disparate phenotypes and metastatic behavior. This will allow approaches to modulate and monitor the glycosylation of these PDAC cell lines, which opens up avenues to study the biology and metastatic behavior of PDAC.

Galectins in the Pathogenesis of Cerebrovascular Accidents: An Overview

Due to limitations of neuroimaging, such as the isodense appearance of blood to neuronal tissue in subacute hemorrhagic stroke, a body of studies have been performed to evaluate candidate biomarkers which may aid in accurate determination of cerebrovascular accident type. Beyond aiding in the delineation of stroke cause, biomarkers could also confer useful prognostic information to help clinicians plan use of resources. One of the candidate biomarkers studied for detection of cerebrovascular accident (CVA) includes a class of proteins called galectins. Galectins bind β-galactoside through a highly conserved carbohydrate recognition domain, endowing an ability to interact with carbohydrate moieties on glycoproteins, some of which are relevant to CVA response. Furthermore, galectins-1, -2, -3, -9, and -12 are expressed in tissues relevant to CVA, and some exhibit characteristics (eg, extracellular secretion) that could render feasible their detection in serum. Galectins-1 and -3 appear to have the largest amounts of preclinical evidence, consistently demonstrating increased activity and expression levels during CVA. However, a lack of standardization of biochemical assays across cohort studies limits further translation of these basic science studies. This review aims to increase awareness of the biochemical roles of galectins in CVA, while also highlighting challenges and remaining questions preventing the translation of basic science observations into a clinically useful test.

Distinct cargo-specific response landscapes underpin the complex and nuanced role of galectin-glycan interactions in clathrin-independent endocytosis

Clathrin-independent endocytosis (CIE) is a form of endocytosis that lacks a defined cytoplasmic machinery. Here, we asked whether glycan interactions, acting from the outside, could be a part of that endocytic machinery. We show that the perturbation of global cellular patterns of protein glycosylation by modulation of metabolic flux affects CIE. Interestingly, these changes in glycosylation had cargo-specific effects. For example, in HeLa cells, GlcNAc treatment, which increases glycan branching, increased major histocompatibility complex class I (MHCI) internalization but inhibited CIE of the glycoprotein CD59 molecule (CD59). The effects of knocking down the expression of galectin 3, a carbohydrate-binding protein and an important player in galectin-glycan interactions, were also cargo-specific and stimulated CD59 uptake. By contrast, inhibition of all galectin-glycan interactions by lactose inhibited CIE of both MHCI and CD59. None of these treatments affected clathrin-mediated endocytosis, implying that glycosylation changes specifically affect CIE. We also found that the galectin lattice tailors membrane fluidity and cell spreading. Furthermore, changes in membrane dynamics mediated by the galectin lattice affected macropinocytosis, an altered form of CIE, in HT1080 cells. Our results suggest that glycans play an important and nuanced role in CIE, with each cargo being affected uniquely by alterations in galectin and glycan profiles and their interactions. We conclude that galectin-driven effects exist on a continuum from stimulatory to inhibitory, with distinct CIE cargo proteins having unique response landscapes and with different cell types starting at different positions on these conceptual landscapes.

Identification of targets of IL-13 and STAT6 signaling in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a life-threatening, highly prevalent monogenic disease caused by mutations in polycystin-1 (PC1) in 85% of patients. We have previously identified a COOH-terminal cleavage fragment of PC1, PC1-p30, which interacts with the transcription factor STAT6 to promote transcription. STAT6 is aberrantly active in PKD mouse models and human ADPKD, and genetic removal or pharmacological inhibition of STAT6 attenuates disease progression. High levels of IL-13, a STAT6-activating cytokine, are found in the cyst fluid of PKD mouse models and increased IL-13 receptors in ADPKD patient tissue, suggesting that a positive feedback loop exists between IL-13 and STAT6 is activated in cystic epithelial cells and contributes to disease progression. In this study, we aimed to identify genes aberrantly regulated by STAT6 to better understand how increased IL-13/STAT6 signaling may contribute to PKD progression. We demonstrate that the expression of periostin, galectin-3, and IL-24 is upregulated in various forms of PKD and that their aberrant regulation is mediated by IL-13 and STAT6 activity. Periostin and galectin-3 have previously been implicated in PKD progression. We support these findings by showing that periostin expression is increased after IL-13 treatment in kidney epithelial cells, that galectin-3 expression is increased after injecting IL-13 in vivo and that IL-24 expression is upregulated by both IL-13 treatment and PC1-p30 overexpression in mouse and human kidney cells. Overall, these findings provide insight into the possible mechanisms by which increased IL-13/STAT6 signaling contributes to PKD progression and suggest potential therapeutic targets.

"In vitro" studies on galectin-3 in human natural killer cells

Galectin-3 (Gal-3) is a β-galactoside binding protein able to modulate both innate and adaptive immune responses. First identified in macrophages, Gal-3 has been studied widely in many mammalian immune cells, but scarcely in natural killer (NK) cells. The aim of this study was to analyze Gal-3 in human NK cells, isolated from peripheral blood mononuclear cells. Both PCR and RT-PCR analysis showed that resting human NK cells express Gal-3 mRNA, which can be modulated upon cytokine stimulation (100 U/ml IL-2 + 20 ng/ml IL-15) for different period of time (1-24 h). Western blot, cytofluorimetry, and confocal microscopy analysis clearly demonstrated that the Gal-3 gene can translate into the corresponding protein. From our results, resting NK cells, isolated from different healthy donors, can express high or low basal levels of Gal-3. In NK cells, Gal-3 was always intracellularly detected at both cytoplasm and nucleus levels, while never at the membrane surface, and its localization resulted independent from the cellular activation status. In addition, the intracellular Gal-3 can co-localize with perforin in exocytic vesicles. Cell treatment with a thiodigalactoside-based Gal-3 inhibitor (1-30 μM) slightly increased the number of degranulating NK cells, while it significantly increased the percentage of cells releasing high amounts of cytotoxic granules (+ 36 ± 3% vs. inhibitor-untreated cells at 30 μM Gal-3). In conclusion, our results demonstrate that human resting NK cells express Gal-3 at both gene and protein levels and that the Gal-3 expression can be modulated upon cytokine stimulation. In the same cells, Gal-3 always localizes intracellularly and functionally correlates with the degree of NK cell degranulation.

Unconventional Pathways of Secretion Contribute to Inflammation

In the conventional pathway of protein secretion, leader sequence-containing proteins leave the cell following processing through the endoplasmic reticulum (ER) and Golgi body. However, leaderless proteins also enter the extracellular space through mechanisms collectively known as unconventional secretion. Unconventionally secreted proteins often have vital roles in cell and organism function such as inflammation. Amongst the best-studied inflammatory unconventionally secreted proteins are interleukin (IL)-1β, IL-1α, IL-33 and high-mobility group box 1 (HMGB1). In this review we discuss the current understanding of the unconventional secretion of these proteins and highlight future areas of research such as the role of nuclear localisation.

Lack of galectin-3 increases Jagged1/Notch activation in bone marrow-derived dendritic cells and promotes dysregulation of T helper cell polarization

Galectin-3, an endogenous glycan-binding protein, is abundantly expressed at sites of inflammation and immune cell activation. Although this lectin has been implicated in the control of T helper (Th) polarization, the mechanisms underlying this effect are not well understood. Here, we investigated the role of endogenous galectin-3 during the course of experimental Leishmania major infection using galectin-3-deficient (Lgals3(-/-)) mice in a BALB/c background and the involvement of Notch signaling pathway in this process. Lgals3(-/-) mice displayed an augmented, although mixed Th1/Th2 responses compared with wild-type (WT) mice. Concomitantly, lymph node and footpad lesion cells from infected Lgals3(-/-) mice showed enhanced levels of Notch signaling components (Notch-1, Jagged1, Jagged2 and Notch target gene Hes-1). Bone marrow-derived dendritic cells (BMDCs) from uninfected Lgals3(-/-) mice also displayed increased expression of the Notch ligands Delta-like-4 and Jagged1 and pro-inflammatory cytokines. In addition, activation of Notch signaling in BMDCs upon stimulation with Jagged1 was more pronounced in Lgals3(-/-) BMDCs compared to WT BMDCs; this condition resulted in increased production of IL-6 by Lgals3(-/-) BMDCs. Finally, addition of exogenous galectin-3 to Lgals3(-/-) BMDCs partially reverted the increased sensitivity to Jagged1 stimulation. Our results suggest that endogenous galectin-3 regulates Notch signaling activation in BMDCs and influences polarization of T helper responses, thus increasing susceptibility to L. major infection.

Treatment with Trichuris suis soluble products during monocyte-to-macrophage differentiation reduces inflammatory responses through epigenetic remodeling

Helminths have strong immunoregulatory properties that may be exploited in treatment of chronic immune disorders, such as multiple sclerosis and inflammatory bowel disease. Essential players in the pathogenesis of these diseases are proinflammatory macrophages. We present evidence that helminths modulate the function and phenotype of these innate immune cells. We found that soluble products derived from the Trichuris suis (TsSP) significantly affect the differentiation of monocytes into macrophages and their subsequent polarization. TsSPs reduce the expression and production of inflammatory cytokines, including IL-6 and TNF, in human proinflammatory M1 macrophages. TsSPs induce a concomitant anti-inflammatory M2 signature, with increased IL-10 production. Furthermore, they suppress CHIT activity and enhance secretion of matrix metalloproteinase 9. Short-term triggering of monocytes with TsSPs early during monocyte-to-macrophage differentiation imprinted these phenotypic alterations, suggesting long-lasting epigenetic changes. The TsSP-induced effects in M1 macrophages were completely reversed by inhibiting histone deacetylases, which corresponded with decreased histone acetylation at the TNF and IL6 promoters. These results demonstrate that TsSPs have a potent and sustained immunomodulatory effect on human macrophage differentiation and polarization through epigenetic remodeling and provide new insights into the mechanisms by which helminths modulate human immune responses.-Hoeksema, M. A., Laan, L. C., Postma, J. J., Cummings, R. D., de Winther, M. P. J., Dijkstra, C. D., van Die, I., Kooij, G. Treatment with Trichuris suis soluble products during monocyte-to-macrophage differentiation reduces inflammatory responses through epigenetic remodeling.

Molecular regulation of galectin-3 expression and therapeutic implication in cancer progression

Galectin-3, a multifunctional protein, distributes inside and outside cells and plays an important role in tumor cell adhesion, proliferation, differentiation, angiogenesis, and metastasis in multiple tumors. Changes in galectin-3 expression are commonly seen in cancer and pre-cancerous conditions. Therefore, to understand the molecular regulation of galectin-3 expression could aid the development of new approach for cancer treatment. This review summarizes different expression of galectin-3 in cancer cells and patients' serum, the regulation mechanism and the potential therapeutic targets of galectin-3 in cancer progression.

Trichuris suis soluble products induce Rab7b expression and limit TLR4 responses in human dendritic cells

Inflammatory immune disorders such as inflammatory bowel disease and multiple sclerosis are major health problems. Currently, the intestinal whipworm Trichuris suis is being explored in clinical trials to reduce inflammation in these diseases; however, the mechanisms by which the parasite affects the host immune system are not known. Here we determined the effects of T. suis soluble products (SPs) on Toll-like receptor-4 (TLR4)-stimulated human dendritic cells (DCs) using Illumina bead chip gene arrays. Pathway analysis of lipopolysaccharide-stimulated DCs with or without T. suis treatment showed that co-stimulation with T. suis SPs resulted in a downregulation of both the myeloid differentiation primary response gene 88-dependent and the TIR-domain-containing adaptor-inducing interferon-β-dependent signalling pathways triggered by TLR4. These data were verified using quantitative real-time PCR of several key genes within these pathways and/or defining their protein levels. In addition, T. suis SPs induce Rab7b, a negative regulator of TLR4 signalling that interferes with its trafficking, which coincided with a reduced surface expression of TLR4. These data indicate that the mechanism by which T. suis SPs reduce inflammatory responses is through suppression of both TLR4 signalling and surface expression on DCs.

Schistosoma mansoni Soluble Egg Antigens Induce Expression of the Negative Regulators SOCS1 and SHP1 in Human Dendritic Cells via Interaction with the Mannose Receptor

Schistosomiasis is a common debilitating human parasitic disease in (sub)tropical areas, however, schistosome infections can also protect against a variety of inflammatory diseases. This has raised broad interest in the mechanisms by which Schistosoma modulate the immune system into an anti-inflammatory and regulatory state. Human dendritic cells (DCs) show many phenotypic changes upon contact with Schistosoma mansoni soluble egg antigens (SEA). We here show that oxidation of SEA glycans, but not heat-denaturation, abrogates the capacity of SEA to suppress both LPS-induced cytokine secretion and DC proliferation, indicating an important role of SEA glycans in these processes. Remarkably, interaction of SEA glycans with DCs results in a strongly increased expression of Suppressor Of Cytokine Signalling1 (SOCS1) and SH2-containing protein tyrosine Phosphatase-1 (SHP1), important negative regulators of TLR4 signalling. In addition, SEA induces the secretion of transforming growth factor β (TGF-β), and the surface expression of the costimulatory molecules Programmed Death Ligand-1 (PD-L1) and OX40 ligand (OX40L), which are known phenotypic markers for the capacity of DCs to polarize naïve T cells into Th2/Treg cell subsets. Inhibition of mannose receptor (MR)-mediated internalization of SEA into DCs by blocking with allyl α-D-mannoside or anti-MR antibodies, significantly reduced SOCS1 and SHP1 expression. In conclusion, we demonstrate that SEA glycans are essential for induction of enhanced SOCS1 and SHP1 levels in DCs via the MR. Our data provide novel mechanistic evidence for the potential of S. mansoni SEA glycans to modulate human DCs, which may contribute to the capacity of SEA to down-regulate inflammatory responses.

Downregulating galectin-3 inhibits proinflammatory cytokine production by human monocyte-derived dendritic cells via RNA interference

Galectin-3 (Gal-3), a β-galactoside-binding lectin, serves as a pattern-recognition receptor (PRR) of dendritic cells (DCs) in regulating proinflammatory cytokine production. Galectin-3 (Gal-3) siRNA downregulates expression of IL-6, IL-1β and IL-23 p19, while upregulates IL-10 and IL-12 p35 in TLR/NLR stimulated human MoDCs. Furthermore, Gal-3 siRNA-treated MoDCs enhanced IFN-γ production in SEB-stimulated CD45RO CD4 T-cells, but attenuated IL-17A and IL-5 production by CD4 T-cells. Addition of neutralizing antibodies against Gal-3, or recombinant Gal-3 did not differentially modulate IL-23 p19 versus IL-12 p35. The data indicate that intracellular Gal-3 acts as cytokine hub of human DCs in responding to innate immunity signals. Gal-3 downregulation reprograms proinflammatory cytokine production by MoDCs that inhibit Th2/Th17 development.

CD98 positive eosinophils contribute to T helper 1 pattern inflammation

BACKGROUND AND AIMS

The pathogenesis of inflammatory bowel disease (IBD) has not been fully understood yet. Eosinophils (Eo) are one type of the major proinflammatory cells of the chronic inflammation in the intestine. CD98 is involved in the pathogenesis of a number of inflammations. This study aims to elucidate the role of CD98(+) Eos in the initiation of intestinal inflammation.

METHODS

The colon biopsies were collected from 60 patients with IBD. The expression of CD98 in the biopsies was examined by immunohistochemistry. The serum levels of the flagellin (FGN) antibody and Eo-derived mediators in the culture supernatants were assessed by enzyme-linked immunosorbent assay. The role of FGN on Eo activation was examined in a cell culture model. The role of FGN in the induction of colitis was observed in a mouse model.

RESULTS

Compared to normal controls, the frequency of CD98(+) Eos was markedly increased in the IBD colon mucosa. FGN were detected in the colon biopsies and in the sera of IBD patients. Exposure to FGN induced the expression of galectin 3 (the ligand of CD98) in dendritic cells. The exposure to galectin 3 activated the CD98(+) Eos. After treatment with FGN intrarectally, mice with eosinophilia showed severe inflammation in the colon.

CONCLUSIONS

The interaction of galectin 3 and CD98 can induce Eos to release chemical mediators that contributes to the initiation of the intestinal inflammation.

Trichuris suis-induced modulation of human dendritic cell function is glycan-mediated

Human monocyte-derived dendritic cells (DCs) show remarkable phenotypic changes upon direct contact with soluble products (SPs) of Trichuris suis, a pig whipworm that is experimentally used in therapies to ameliorate inflammation in patients with Crohn's disease and multiple sclerosis. These changes may contribute to the observed induction of a T helper 2 (Th2) response and the suppression of Toll-like receptor (TLR)-induced Th1 and Th17 responses by human DCs primed with T. suis SPs. Here it is demonstrated that glycans of T. suis SPs contribute significantly to the suppression of the lipopolysaccharide (LPS)-induced expression in DCs of a broad variety of cytokines and chemokines, including important pro-inflammatory mediators such as TNF-α, IL-6, IL-12, lymphotoxin α (LTA), C-C Motif Ligand (CCL)2, C-X-C Motif Ligands (CXCL)9 and CXCL10. In addition, the data show that human DCs strongly bind T. suis SP-glycans via the C-type lectin receptors (CLRs) mannose receptor (MR) and DC-specific ICAM-3-grabbing non-integrin (DC-SIGN). The interaction of DCs with T. suis glycans likely involves mannose-type glycans, rather than fucosylated glycans, which differs from DC binding to soluble egg antigens of the human worm parasite, Schistosoma mansoni. In addition, macrophage galactose-type lectin (MGL) recognises T. suis SPs, which may contribute to the interaction with immature DCs or other MGL-expressing immune cells such as macrophages. The interaction of T. suis glycans with CLRs of human DCs may be essential for the ability of T. suis to suppress a pro-inflammatory phenotype of human DCs. The finding that the T. suis-induced modulation of human DC function is glycan-mediated is novel and indicates that helminth glycans contribute to the dampening of inflammation in a wide range of human inflammatory diseases.

Galectin-1 and galectin-3 expression profiles in classically and alternatively activated human macrophages

BACKGROUND

Galectins have been identified as modulators of many monocyte/macrophage functions. In the response to a wide range of environmental cues macrophages may exhibit different biochemical and biological characteristics, but two main subtypes, classically (M1) and alternatively (M2) activated macrophages have been recognized. To contribute to elucidation of role and regulation of galectin-1 and galectin-3 in differently activated macrophages we explored their expression profiles in these cells.

METHODS

Human monocytes obtained from blood donors were differentiated into classically (M1) and alternatively (M2a/M2c) activated macrophages. Gene and protein expression levels of intra- and extracellular galectins were investigated by qRT-PCR, Western-blot, flow cytometry, and ELISA while cytokine and surface receptor expression profiling was performed by flow cytometry.

RESULTS

Differentiation/polarization of human monocytes into classically (M1) and alternatively (M2a/M2c) activated macrophages was followed by profound changes of galectin-3 expression and its proteolytic cleavage. Expression and secretion of Gal-3 was tightly regulated and significantly differed among classically (M1) and alternatively (M2a/M2c) activated macrophages, while the differences of galectin-1 expression profiles were not as pronounced. Human monocytes exhibited high amount of free galectin-3 receptors, while on both types of activated macrophages were fully saturated.

CONCLUSIONS

Galectin-3 is more distinctive descriptor of macrophages differentiation/activation than galectin-1. Its specific expression and secretion pattern in M1 vs. M2a/M2c macrophages contributes to better understanding of its role and regulation in these cells.

GENERAL SIGNIFICANCE

Recognition of distinct galectin-1 and galectin-3 expression profiles in differently activated macrophages provides a new insight on biological characteristics of these cells and sheds a new light of galectin-3 as a modulator of individual macrophage subset. This article is part of a Special Issue entitled Glycoproteomics.

Differential glycosylation of MUC1 and CEACAM5 between normal mucosa and tumour tissue of colon cancer patients

Altered glycosylation in epithelial cancers may play an important role in tumour progression, as it may affect tumour cell migration and antigen presentation by antigen presenting cells. We specifically characterise the glycosylation patterns of two tumour antigens that are highly expressed in cancer tissue and often detected in their secreted form in serum: the epithelial mucin MUC1 and carcinoembryonic antigen (CEA, also called CEACAM5). We analysed 48 colorectal cancer patients, comparing normal colon and tumour epithelium within each patient. Lectin binding was studied by a standardised CEA/MUC1 capture ELISA, using several plant lectins, and the human C-type lectins MGL and DC-SIGN, and Galectin-3. Peanut agglutinin (PNA) bound to MUC1 from tumour tissue in particular, suggests increased expression of the Thomsen-Friedenreich antigen (TF-antigen) (Core 1, Galβ1-3GalNAc-Ser/Thr). Only small amounts of Tn-antigen (GalNAcα-Ser/Thr) expression was observed, but the human C-type lectin MGL showed increased binding to tumour-associated MUC1. Furthermore, sialylation was greatly enhanced. In sharp contrast, tumour-associated CEA (CEACAM5) contained high levels of the blood-group related carbohydrates, Lewis X and Lewis Y. This correlated strongly with the interaction of the human C-type lectin DC-SIGN to tumour-associated CEA, suggesting that CEA can be recognized and taken up by antigen presenting cells. In addition, increased mannose expression was observed and branched N-glycans were prominent, and this correlated well with human Galectin-3 binding. These data demonstrate that individual tumour antigens contain distinct glycan structures associated with cancer and, since glycans affect cellular interactions with its microenvironment, this may have consequences for progression of the disease.

Serum galectin-2, -4, and -8 are greatly increased in colon and breast cancer patients and promote cancer cell adhesion to blood vascular endothelium

PURPOSE

Adhesion of disseminating tumor cells to the blood vascular endothelium is a pivotal step in metastasis. Previous investigations have shown that galectin-3 concentrations are increased in the bloodstream of patients with cancer and that galectin-3 promotes adhesion of disseminating tumor cells to vascular endothelium in vitro and experimental metastasis in vivo. This study determined the levels of galectin-1, -2, -3, -4, -8, and -9 in the sera of healthy people and patients with colon and breast cancer and assessed the influence of these galectins on cancer-endothelium adhesion.

EXPERIMENTAL DESIGN

Serum galectins and auto-anti-MUC1 antibodies were assessed using ELISA and mucin protein (MUC1) glycan microarrays, and cancer-endothelium adhesion was determined using monolayers of human microvascular lung endothelial cells.

RESULTS

The levels of serum galectin-2, -3, -4, and -8 were significantly increased up to 31-fold in patients with cancer and, in particular, those with metastases. As previously shown for galectin-3, the presence of these galectins enhances cancer-endothelium adhesion by interaction with the Thomsen-Friedenreich (TF; Galβ1,3GalNAcα-) disaccharide on cancer-associated MUC1. This causes MUC1 cell surface polarization, thus exposing underlying adhesion molecules that promote cancer-endothelium adhesion. Elevated circulating galectin-2 levels were associated with increased mortality in patients with colorectal cancer, but this association was suppressed when anti-MUC1 antibodies with specificity for the TF epitope of MUC1 were also present in the circulation.

CONCLUSIONS

Increased circulation of several members of the galectin family is common in patients with cancer and these may, like circulating galectin-3, also be involved in metastasis promotion.

Advanced glycation end products inhibit both infection and transmission in trans of HIV-1 from monocyte-derived dendritic cells to autologous T cells

Highly active antiretroviral therapy is associated with carbohydrate metabolic alterations that may lead to diabetes. One consequence of hyperglycemia is the formation of advanced glycation end products (AGEs) that are involved in diabetes complications. We investigated the impact of AGEs on the infection of monocyte-derived dendritic cells (MDDCs) by HIV-1 and the ability of MDDCs to transmit the virus to T cells. We showed that AGEs could inhibit infection of MDDCs with primary R5-tropic HIV-1(Ba-L) by up to 85 ± 9.2% and with primary X4-tropic HIV-1(VN44) by up to 60 ± 8.5%. This inhibitory effect of AGEs was not prevented by a neutralizing anti-receptor for advanced glycation end products (anti-RAGE) Ab, demonstrating a RAGE-independent mechanism. Moreover, AGEs inhibited by 70-80% the transmission in trans of the virus to CD4 T cells. Despite the inhibitory effect of AGEs on both MDDC infection and virus transmission in trans, no inhibition of virus attachment to cell membrane was observed, confirming that attachment and transmission of the virus involve independent mechanisms. The inhibitory effect of AGEs on infection was associated with a RAGE-independent downregulation of CD4 at the cell membrane and by a RAGE-dependent repression of the CXCR4 and CCR5 HIV-1 receptors. AGEs induce the secretion of proinflammatory cytokines IL-6, TNF-α, and IL-12, but not RANTES or MIP-1α, and did not lead to MDDC maturation as demonstrated by the lack of expression of the CD83 molecule. Taken together, our results suggest that AGEs can play an inhibiting role in HIV-1 infection in patients who accumulate circulating AGEs, including patients treated with protease inhibitors that developed diabetes.

Pivotal advance: The promotion of soluble DC-SIGN release by inflammatory signals and its enhancement of cytomegalovirus-mediated cis-infection of myeloid dendritic cells

DC-SIGN is a member of the C-type lectin family. Mainly expressed by myeloid DCs, it is involved in the capture and internalization of pathogens, including human CMV. Several transcripts have been identified, some of which code for putative soluble proteins. However, little is known about the regulation and the functional properties of such putative sDC-SIGN variants. To better understand how sDC-SIGN could be involved in CMV infection, we set out to characterize biochemical and functional properties of rDC-SIGN as well as naturally occurring sDC-SIGN. We first developed a specific, quantitative ELISA and then used it to detect the presence sDC-SIGN in in vitro-generated DC culture supernatants as cell-free secreted tetramers. Next, in correlation with their inflammatory status, we demonstrated the presence of sDC-SIGN in several human body fluids, including serum, joint fluids, and BALs. CMV infection of human tissues was also shown to promote sDC-SIGN release. Based on the analysis of the cytokine/chemokine content of sDC-SIGN culture supernatants, we identified IFN-γ and CXCL8/IL-8 as inducers of sDC-SIGN production by MoDC. Finally, we demonstrated that sDC-SIGN was able to interact with CMV gB under native conditions, leading to a significant increase in MoDC CMV infection. Overall, our results confirm that sDC-SIGN, like its well-known, counterpart mDC-SIGN, may play a pivotal role in CMV-mediated pathogenesis.