Regulation of cellular adhesion to extracellular matrix proteins by galectin-3

Galectin-3 expression is induced in renal β-intercalated cells during metabolic acidosis

The adaptation of the cortical collecting duct (CCD) to metabolic acidosis requires the polymerization and deposition in the extracellular matrix of the novel protein hensin. HCO3−-secreting β-intercalated cells remove apical Cl−:HCO3−exchangers and may reverse functional polarity to secrete protons. Using intercalated cells in culture, we found that galectin-3 facilitated hensin polymerization, thereby causing their differentiation into the H+-secreting cell phenotype. We examined the expression of galectin-3 in the rabbit kidney and its relationship to hensin during metabolic acidosis. In control kidneys, galectin-3 was expressed in the cortical and medullary collecting ducts. In the outer cortex 26 ± 3% of CCD cells expressed galectin-3 compared with 64 ± 3% of the cells of the inner cortex. In the CCD, galectin-3 was rarely expressed in β-intercalated cells, being primarily present in α-intercalated and principal cells. During metabolic acidosis, the intensity of cellular staining for galectin-3 increased and more cells began to express it; the percentage of CCD cells expressing galectin-3 increased from 26 ± 3 to 66 ± 3% in the outer cortex and from 64 ± 3 to 78 ± 4% in the inner cortex. This was particularly evident in β-intercalated cells where expression was found in only 8 ± 2% in control animals but in 75 ± 2% during metabolic acidosis in the outer cortex and similarly for the inner cortex (26 ± 6 to 90 ± 7%). Importantly, both galectin-3 and hensin were found in the extracellular matrix of microdissected CCDs; and during metabolic acidosis, many more cells exhibited this extracellular colocalization. Thus galectin-3 may play several important roles in the CCD, including mediating the adaptation of β-intercalated cells during metabolic acidosis.

Galectin-9: a new endometrial epithelial marker for the mid- and late-secretory and decidual phases in humans

CONTEXT

The galectin family has been reported to play a role in the regulation of cell growth, cell adhesion, apoptosis, inflammation, and immunomodulation, all of which are important for endometrial function, as well as implantation.

OBJECTIVE

The objective of the study was to investigate the expression and regulation of galectin-9, a beta-galactoside-binding lectin in the human endometrium.

DESIGN

Galectin-9 mRNA and protein were analyzed in dated endometrial biopsies throughout the menstrual cycle and in human early-pregnancy decidua, as well as in the different endometrial cell compartments. Regulation of galectin-9 by estradiol, progesterone, epidermal growth factor, and interferon-gamma in endometrial epithelial cells in vitro was studied.

RESULTS

Galectin-9 mRNA analyzed by RNase protection assay is expressed in the human endometrium, specifically in the human endometrial epithelial cells but not in stromal or immune cells. It is expressed at very low concentrations during the proliferative phase and the early-secretory phase and shows a sharp and significant increase in the mid- and late-secretory phases, the window of implantation, as well as in the decidua. Accordingly, galectin-9 protein is also exclusively increased in human endometrial epithelial cells during the mid- and late-secretory phases and in the decidua, however, not in endometrial stromal cells or decidualized cells in vivo or in vitro. A regulation in vitro by estradiol, progesterone, epidermal growth factor, and interferon-gamma could not be detected.

CONCLUSIONS

Based on these findings and on the functional studies of other galectins, we suggest galectin-9 as a novel endometrial marker for the mid- and late-secretory and decidual phases.

Cancer cell-secreted proteomes as a basis for searching potential tumor markers: nasopharyngeal carcinoma as a model

Nasopharyngeal carcinoma (NPC) is commonly diagnosed late due to its deep location and vague symptoms. To identify biomarkers for early NPC diagnosis, secreted proteomes of two NPC cell lines were analyzed. Proteins in the NPC cell-line cultured media were systematically identified by SDS-PAGE combined with MALDI-TOF MS. Twenty-three proteins were found in cultured media from both NPC cell lines. Among them, fibronectin, Mac-2 binding protein (Mac-2 BP), and plasminogen activator inhibitor 1 (PAI-1) were further confirmed by Western blot analysis. These three proteins were highly expressed in NPC biopsies, but weakly or not expressed in normal nasopharyngeal tissues. The serum levels of the three proteins were significantly higher in NPC patients (n = 46) than in normal controls (n = 47) (p < 0.01). NPC nude mice model (n = 9) also showed elevated levels of serum Mac-2 BP and PAI-1 compared with tumor-free mice (n = 9) (p < 0.01). Systematic analysis of cancer cell-secreted proteomes combined with animal tumor models can be a feasible, convenient strategy for searching multiple potential tumor markers. Furthermore, our work shows that fibronectin, Mac-2 BP, and PAI-1 may be potential markers for diagnosis of NPC.

Role of hensin in mediating the adaptation of the cortical collecting duct to metabolic acidosis

PURPOSE OF REVIEW

The cortical collecting duct is able to secrete HCO3-, a state that can be converted to acid secretion during metabolic acidosis. Bicarbonate secretion in this segment is mediated by beta-intercalated cells whereas alpha-intercalated cells perform acid secretion. During metabolic acidosis, the number of beta-intercalated cells is reduced while that of alpha-intercalated cells increases without a change in the total number of intercalated cells, suggesting conversion of one cell type to another. Using an immortalized intercalated cell line we found that this adaptation is mediated by an extracellular protein named hensin. Hensin is secreted as a monomer which is then polymerized in the extracellular environment by a complex process requiring at least three other proteins.

RECENT FINDINGS

We describe that a cyclophilin, via its cis/trans prolyl isomerase activity, is required for this polymerization. This may explain the distal renal tubular acidosis observed with cyclosporin A therapy. In addition, galectin-3 is needed to aggregate the protein. Finally, we recently found that activation of integrins is also necessary for the development of the hensin fiber. Hensin is expressed in all epithelia and deletion of its gene is embryonic lethal at an early stage when the first columnar epithelia develop.

SUMMARY

These studies suggest that the response of intercalated cells to metabolic acidosis uses a pathway that is involved in terminal differentiation of columnar epithelia.

Development of age-dependent glomerular lesions in galectin-3/AGE-receptor-3 knockout mice

Aging is characterized by renal functional and structural abnormalities resembling those observed in diabetes. These changes have been related to the progressive accumulation of advanced glycation end-products (AGEs) and cumulative oxidative stress occurring in both conditions. We previously reported that galectin-3 ablation is associated with increased susceptibility to diabetes- and AGE-induced glomerulopathy, thus indicating a protective role of galectin-3 as an AGE receptor. To investigate the role of the AGE/AGE receptor pathway in the pathogenesis of age-related renal disease, we evaluated the development of glomerular lesions in aging galectin-3 knockout (KO) vs. wild-type (WT) mice and their relation to the increased AGE levels and oxidative stress characterizing the aging process. KO mice showed significantly more pronounced age-dependent increases in proteinuria, albuminuria, glomerular sclerosis, and glomerular and mesangial areas, starting at 18 mo, as well as renal extracellular matrix mRNA and protein expression, starting at 12 mo vs. age-matched WT mice. Circulating and renal AGEs, plasma isoprostane 8-epi-PGF2alpha levels, glomerular content of the glycoxidation and lipoxidation products N(epsilon)-carboxymethyllysine and 4-hydroxy-2-nonenal, and renal nuclear factor-kappaB activity also increased more markedly with age in KO than WT mice. AGE levels correlated significantly with renal functional and structural parameters. These data indicate that aging galectin-3 KO mice develop more pronounced changes in renal function and structure than coeval WT mice, in parallel with a more marked degree of AGE accumulation, oxidative stress, and associated low-grade inflammation, thus supporting the concept that the AGE/AGE receptor pathway is implicated in age-related renal disease.

Regulatory Roles of Galectins in the Immune Response

Galectins are a family of animal lectins with affinity for beta-galactosides. They are differentially expressed by various immune cells and their expression levels appear to be dependent on cell differentiation and activation. They can interact with cell-surface and extracellular matrix glycoconjugates (glycoproteins and glycolipids), through lectin-carbohydrate interactions. Through this action, they can promote cell growth, affect cell survival, modulate cell adhesions, and induce cell migration. They appear to do so by binding to different glycoconjugates decorated by suitable saccharides, rather than through specific receptors. Galectins do not have a classical signal peptide and are often localized in intracellular compartments, including the nucleus. Intracellularly, they can regulate cell growth and survival by interacting with cytoplasmic and nuclear proteins, through protein-protein interactions, thereby affecting intracellular signaling pathways. Current research indicates that galectins play important roles in the immune response through regulating the homeostasis and functions of the immune cells.

Galectin-3 as an immunohistochemical tool to distinguish pilocytic astrocytomas from diffuse astrocytomas, and glioblastomas from anaplastic oligodendrogliomas

The distinction of astrocytomas and oligodendrogliomas, mainly pilocytic astrocytomas (PILOs) from infiltrating astrocytomas and oligodendrogliomas (ODs), and high-grade oligodendrogliomas from glioblastomas (GBMs), poses a serious clinical problem. There is no useful immunohistochemical (IHC) marker to differentiate these gliomas, and sometimes the differential diagnosis between them is arbitrary. We identified galectin-3 (Gal-3) as a possible tool to differentiate them based on gene expression profiles of GBMs. We confirmed the differential expression in 45 surgical samples (thirteen GBMs; seven PILOs; 5 grade II ODs; 5 anaplastic oligodendrogliomas [AODs], including 2 Oligo-astrocytomas; 8 diffuse astrocytomas [ASTs], and 7 non-neoplastic samples) by quantification of Gal-3 gene expression by real-time quantitative PCR (rt-PCR). Higher expression of Gal-3 was observed in GBMs and PILOs than in OD, AODs and ASTs. The IHC expression of Gal-3 was evaluated in 90 specimens (fifteen PlLOs, fourteen ASTs, 10 anaplastic astrocytomas, fifteen GBMs, eleven ODs, fifteen AODs, and 10 dysembryoplastic neuroepithelial tumors). The mean labeling score for Gal-3 determined according to the percentage of labeled cells in the tumor bulk was significantly different in GBMs versus AODs and in PILOs versus ASTs. Hence, Gal-3 is differentially expressed in central nervous system tumors, making IHC detection of Gal-3 a useful tool in distinguishing between these gliomas.

Multifaceted role of galectin-3 on human glioblastoma cell motility

Astrocytic tumors' aggressiveness results from an imbalance between cell proliferation and cell death favoring growth, but also from the propensity of tumor cells to detach from the primary tumor site, migrate, and invade the surrounding parenchyma. Astrocytic tumor progression is known to be associated with an increased expression of galectin-3. We investigated in cell culture how galectin-3 expression affects astrocytoma cell motility. Galectin-3 deficient cells were obtained by stable transfection of the U373 glioblastoma cell line with a specific expression antisense plasmid. Cultured galectin-3 deficient glioblastoma cells showed increased motility potential on laminin and modifications in the cytoskeleton reorganization. In addition, c-DNA microarrays and quantitative immunofluorescence analysis showed that galectin-3 deficient U373 cells have an increased expression of integrins-alpha6 and -beta1, proteins known to be implicated in the regulation of cell adhesion.

Expression of galectin-3 in primary and metastatic melanoma: immunohistochemical studies on human lesions and nude mice xenograft tumors

Galectins are a large family of proteins which bind galactoside-containing glycans. Their role in cancer seems to be important since members of the family may mediate cell adhesion and modulate cell growth. Galectin-3 (Gal-3) is expressed in the nucleus, in the cytoplasm and on the cell surface, and can also be secreted into the extracellular matrix. A series of experimental and clinical data have been reported which indicate that Gal-3 may play a putative role in carcinogenesis, cancer progression and the process of metastasis. To study the possible correlation between Gal-3 expression and malignant potential in primary melanoma lesions, we conducted an immunohistochemical study with monoclonal anti-Gal-3 antibody in a series of primary and metastatic melanoma lesions as well as benign skin pigmented lesions. We also developed a xenograft melanoma model in nude mice with two melanoma cell lines (ATCC G-361 and ATCC HT-144) and assessed staining with the Gal-3 antibody in the xenografts and the metastases. The expression of anti-Gal-3 staining was determined semiquantitatively. The expression of Gal-3 was higher in thin primary melanoma lesions than in benign pigmented skin lesions or metastases and seemed to correlate inversely with the aggressiveness as estimated by the Breslow index which is recognized as the main prognostic factor in melanoma. We propose Gal-3 expression in melanoma as a diagnostic and/or a prognostic parameter and suggest that further studies of such a role for Gal-3 are warranted.

Galectins as modulators of tumour progression

Galectins are a family of animal lectins with diverse biological activities. They function both extracellularly, by interacting with cell-surface and extracellular matrix glycoproteins and glycolipids, and intracellularly, by interacting with cytoplasmic and nuclear proteins to modulate signalling pathways. Current research indicates that galectins have important roles in cancer; they contribute to neoplastic transformation, tumour cell survival, angiogenesis and tumour metastasis. They can modulate the immune and inflammatory responses and might have a key role helping tumours to escape immune surveillance. How do the different members of the Galectin family contribute to these diverse aspects of tumour biology?

Galectin-3 and soluble fibrinogen act in concert to modulate neutrophil activation and survival: involvement of alternative MAPK pathways

Galectin-3 (Gal-3), a member of a family of highly conserved carbohydrate-binding proteins, has recently emerged as a novel cellular modulator at inflammatory foci. Here we investigated the effects of Gal-3 on central effector functions of human neutrophils, including phagocytosis, exocytosis of secretory granules, and survival. We examined the effects of Gal-3 alone or in combination with soluble fibrinogen (sFbg), an extracellular mediator that plays a key role during the early phase of the inflammatory response through binding to integrin receptors. In addition we evaluated the intracellular signals triggered by these mediators in human neutrophils. Human neutrophils incubated with recombinant Gal-3 alone increased their phagocytic activity and CD66 surface expression. In contrast to the known antiapoptotic effect of Gal-3 on many cellular types, Gal-3 enhanced PMN apoptotic rate. Preincubation with Gal-3 primed neutrophils to the effects of sFbg, resulting in a synergistic action on degranulation. On the other hand, Gal-3 and sFbg had opposite effects on PMN survival, and the simultaneous action of both agonists partially counteracted the proapoptotic effects of Gal-3. In addition, although sFbg induced its effects through the activation of the ERKs, Gal-3 led to p38 phosphorylation. Disruption of this signaling pathway abrogated Gal-3-mediated modulation of neutrophil degranulation, phagocytosis, and apoptosis. Together, our results support the notion that Gal-3 and sFbg are two physiological mediators present at inflammatory sites that activate different components of the MAPK pathway and could be acting in concert to modulate the functionality and life span of neutrophils.

Regulation of cellular homeostasis by galectins

Members of the galectin family are presently known to participate in cellular homeostasis by modulating cell growth, controlling cell cycle progression, and inducing or inhibiting apoptosis. Both intracellular and extracellular activities of galectins have been described, with the former typically independent of lectin activity, and the latter mediated by lectin activity. Galectin-1 and -3 are recognized as activators and inducers of cell stasis in extracellular capacities. Galectin-1, -7, -8, -9 and -12 are characterized as promoters or inducers of apoptosis, while galectin-3 is demonstrated as an inhibitor of apoptosis intracellularly. Localization studies of galectins have established that these proteins can segregate into multiple intracellular compartments, and the preference for segregation is dependent on the status of the cell. Localization would, therefore, likely correspond to compartmental function. While galectin-1 and -3 have been the most abundantly expressed and extensively studied, and therefore, the members best understood, expanding interest in galectins has resulted in description of new members that display more restricted expression patterns, suggesting more specific activity. Nevertheless, as demonstrated for many members, it appears that a major feature of the galectin family is the homeostatic regulation of cells.

The role of very late antigen-1 in immune-mediated inflammation

The alpha1beta1 integrin, also known as "very late antigen" (VLA)-1, is normally expressed on mesenchymal cells, some epithelial cells, activated T cells, and macrophages, and interacts, via the I-domain of the extracellular domain of the alpha1 subunit, with collagen molecules in the extracellular matrix (ECM). By "outside-in" transmembranal signaling to the interior of the cell, it mediates adhesion, migration, proliferation, remodeling of the ECM, and cytokine secretion by endothelial cells, mesangial cells, fibroblasts, and immunocytes. Importantly, its expressions and functions are enhanced by inflammatory cytokines including interferon (IFN)gamma and tumor necrosis factor (TNF)alpha, thus augmenting angiogenesis and fibrosis linked, in particular, to inflammation. Moreover, within the immune system, VLA-1 marks effector memory CD4+ and CD8+ T cells that are retained in extralymphatic tissues by interactions of the integrin with collagen and produce high levels of IFNgamma. Thus, immune-mediated inflammation in vivo is inhibited by blockade of the VLA-1-collagen interaction in experimental animal models of arthritis, colitis, nephritis, and graft versus host disease (GVHD), suggesting that inhibiting the interaction of the alpha1 I-domain with its ligands or modulating "outside-in" signaling by VLA-1 would be a useful approach in the human diseases simulated by these experimental models.

Galectin-3/AGE-receptor 3 knockout mice show accelerated AGE-induced glomerular injury: evidence for a protective role of galectin-3 as an AGE receptor

We previously showed that mice lacking galectin-3/AGE-receptor 3 develop accelerated diabetic glomerulopathy. To further investigate the role of galectin-3/AGE-receptor function in the pathogenesis of diabetic renal disease, galectin-3 knockout (KO) and coeval wild-type (WT) mice were injected for 3 months with 30 microg/day of N(epsilon)-carboxymethyllysine (CML)-modified or unmodified mouse serum albumin (MSA). Despite receiving equal doses of CML, KO had higher circulating and renal AGE levels and showed more marked renal functional and structural changes than WT mice, with significantly higher proteinuria, albuminuria, glomerular, and mesangial area and glomerular sclerosis index. Renal 4-hydroxy-2-nonenal content and NFkappaB activation were also more pronounced in KO-CML vs. WT-CML. Kidney mRNA levels of fibronectin, laminin, collagen IV, and TGF-beta were up-regulated, whereas those of matrix metalloproteinase-2 and -14 were down-regulated, again more markedly in KO-CML than WT-CML mice. Basal and CML-induced RAGE and 80K-H mRNA levels were higher in KO vs. WT mice. MSA injection did not produce any significant effect in both genotypes. The association of galectin-3 ablation with enhanced susceptibility to AGE-induced renal disease, increased AGE levels and signaling, and altered AGE-receptor pattern indicates that galectin-3 is operating in vivo as an AGE receptor to afford protection toward AGE-dependent tissue injury.

Galectin-3-positive cell infiltration in human diabetic nephropathy

BACKGROUND

Galectin-3 has several functions, such as cell proliferation, regulation of apoptosis and interaction of cell adhesion, and has a high binding affinity for advanced glycation end products. In animal models with diabetic nephropathy (DMN) or acute renal failure, galectin-3 is known to be upregulated. However, galectin-3 expression has not been investigated in human kidney diseases.

METHODS

Using immunohistochemistry we examined galectin-3 expression in renal biopsy specimens obtained from 37 patients with nephropathy: DMN (n = 9), IgA nephropathy (n = 9), crescentic glomerulonephritis (n = 8), membranous nephropathy (n = 6) and minimal change nephrotic syndrome (n = 5).

RESULTS

In normal human kidney, galectin-3 was found in distal tubuli, but not in glomeruli. However, galectin-3-positive cell infiltration was observed in glomeruli of 12 patients. Galectin-3-positive cells, also stained with CD68, were significantly more numerous in glomeruli of DMN than in glomeruli of other nephropathies. The ratio of galectin-3-positive cells to the total number of macrophages in tubules was also significantly increased in DMN. There was a significant correlation between the number of galectin-3-positive cells in glomeruli and urinary protein excretion in all patients (r = 0.616, P<0.001). In diabetic patients, the number of galectin-3-positive cells in glomeruli closely correlated with the regression rate of renal function (r = -0.930, P<0.005).

CONCLUSION

These findings suggest that galectin-3-positive cell infiltration may play an important role in the progression of DMN, and the degree of its expression may be predictive of poor prognosis of DMN.

Galectin-3 surface expression on human adult chondrocytes: a potential substrate for collagenase-3

BACKGROUND

Galectin-3 is a lectin detected in mature and early hypertrophic chondrocytes; osteoarthritic (OA) chondrocytes can re-express hypertrophic markers.

OBJECTIVE

To investigate the synthesis and subcellular localisation of galectin-3 in adult chondrocytes as well as the possibility of cleavage of galectin-3 by collagenase-1 and -3.

METHODS

Galectin-3 was assessed by immunohistochemistry and real time polymerase chain reaction (PCR) in normal and OA cartilage. Its localisation was investigated by subcellular fractionation, immunocytology, and flow cytometry. Proteolysis of galectin-3 by collagenase-1 and -3 was determined by in vitro assay.

RESULTS

Galectin-3 expression was increased 2.4-fold as measured by reverse transcriptase (RT)-PCR (p<0.05, n = 5) and threefold by immunohistochemistry (p<0.003 n = 6) in OA cartilage compared with normal cartilage. In adult chondrocytes, galectin-3 was found in the cytosol and membrane enriched fractions. Both immunocytology and flow cytometry confirmed the presence of galectin-3 at the surface of chondrocytes. A strong correlation was found between integrin-beta1 and galectin-3 expression at the surface of chondrocytes. Moreover, collagenase-3 cleaved galectin-3 with a higher activity than collagenase-1. The proteolysed sites generated were identical to those produced by gelatinases A and B.

CONCLUSION

Galectin-3 may play a part in OA, having two roles, one intracellular and not yet identified, and another at the cell surface, possibly related to the interaction of chondrocytes and the cartilage matrix.

NG2 proteoglycan promotes endothelial cell motility and angiogenesis via engagement of galectin-3 and alpha3beta1 integrin

The NG2 proteoglycan is expressed by microvascular pericytes in newly formed blood vessels. We have used in vitro and in vivo models to investigate the role of NG2 in cross-talk between pericytes and endothelial cells (EC). Binding of soluble NG2 to the EC surface induces cell motility and multicellular network formation in vitro and stimulates corneal angiogenesis in vivo. Biochemical data demonstrate the involvement of both galectin-3 and alpha3beta1 integrin in the EC response to NG2 and show that NG2, galectin-3, and alpha3beta1 form a complex on the cell surface. Transmembrane signaling via alpha3beta1 is responsible for EC motility and morphogenesis in this system. Galectin-3-dependent oligomerization may potentiate NG2-mediated activation of alpha3beta1. In conjunction with recent studies demonstrating the early involvement of pericytes in angiogenesis, these data suggest that pericyte-derived NG2 is an important factor in promoting EC migration and morphogenesis during the early stages of neovascularization.

Role of galectin-3 in diabetic nephropathy

The advanced glycosylation end products (AGE) participate in the pathogenesis of nephropathy and other diabetic complications through several mechanisms, including their binding to cell surface receptors. The AGE receptors include RAGE, the macrophage scavenger receptors, OST-48 (AGE-R1), 80K-H (AGE-R2), and galectin-3 (AGE-R3). Galectin-3 interacts with the beta-galactoside residues of cell surface and matrix glycoproteins via the carbohydrate recognition domain and with intracellular proteins via peptide-peptide associations mediated by its N-terminus domain. These structural properties enable galectin-3 to exert multiple functions, including the mRNA splicing activity, the control of cell cycle, the regulation of cell adhesion, the modulation of allergic reactions, and the binding of AGE. The lack of transmembrane anchor sequence or signal peptide suggests that it is associated with other AGE receptors, possibly AGE-R1 and AGE-R2, to form an AGE-receptor complex, rather than playing an independent role. In target tissues of diabetic vascular complications, such as the endothelium and mesangium, galectin-3 is weakly expressed under basal conditions and is markedly upregulated by the diabetic milieu (and to a lesser extent by aging). Galectin-3-deficient mice were found to develop accelerated diabetic glomerulopathy versus the wild-type animals, as evidenced by the more pronounced increase in proteinuria, mesangial expansion, and matrix gene expression. This was associated with a more marked renal/glomerular AGE accumulation, suggesting that it was attributable to the lack of galectin-3 AGE-receptor function. These data indicate that galectin-3 is upregulated under diabetic conditions and is operating in vivo to provide protection toward AGE-induced tissue injury, as opposed to RAGE.

Carbohydrate binding proteins galectin-1 and galectin-3 in human trabecular meshwork

PURPOSE

Galectins are a family of carbohydrate binding proteins involved in a variety of biological processes including cell-cell and cell-matrix interactions. We examined galectin-1 and galectin-3 to determine if galectins are expressed in the human trabecular meshwork and Schlemm's canal.

METHODS

Human trabecular meshworks were dissected from donor eyes within 12 hr of death. Galectin-1 and galectin-3 expression was examined by RT-PCR and Western blot analysis. Immunohistochemistry of galectin-1 and galectin-3 was analyzed in normal and glaucomatous tissue.

RESULTS

Expression of mRNA and protein of Galectin-1 (14 kDa) and galectin-3 (31 kDa) was found in the outflow pathway. Immunostaining revealed galectin-1 and galectin-3 throughout the meshwork, cells lining Schlemm's canal, and extracellular spaces in the inner and outer walls of the canal. Comparison of normal, POAG and PEX samples revealed no difference in location or intensity for either galectin-1 and galectin-3.

CONCLUSION

Galectin-1 and galectin-3 are present in human trabecular meshwork of normal and glaucomatous eyes.

Expression of liver-intestine cadherin and its possible interaction with galectin-3 in ductal adenocarcinoma of the pancreas

Liver-intestine (LI) cadherin represents a novel type of cadherin within the cadherin superfamily, and is distinguished from other cadherins by specific structural and functional features. Among normal tissues, LI-cadherin is known to be expressed in the intestinal mucosa, while its expression in cancerous tissue has not been investigated to date, except in gastric carcinoma. In the present study we investigated LI-cadherin expression immunohistochemically using our newly established monoclonal antibody in a large set (n = 102) of tumor specimens from patients with ductal adenocarcinoma of the pancreas, and correlated the findings with the patients' survival. LI-cadherin expression was seen focally in normal pancreatic ducts. In carcinoma, well-differentiated carcinoma cases strongly expressed LI-cadherin, whereas less differentiated areas and poorly differentiated carcinoma cases expressed less or were negative. Kaplan-Meier analysis for all patients demonstrated that high LI-cadherin expression (>25% of cells stained positive) correlated with good survival (P < 0.001). Cox regression analyses demonstrated that LI-cadherin expression was one of the strongest predictors of outcome, independent of all other variables, and low LI-cadherin expression correlated with tumor de-differentiation and advanced stage. Furthermore, galectin-3 was identified as being coimmunoprecipitated with LI-cadherin and this interaction was inhibited by lactose in a dose-dependent manner, but not by sucrose. Because galectin-3 has been observed to show a similar expression pattern to LI-cadherin in ductal adenocarcinoma of the pancreas, expression of LI-cadherin and this interaction could have some role in ductal adenocarcinoma of the pancreas.

Expression of human intestinal mucin is modulated by the beta-galactoside binding protein galectin-3 in colon cancer

BACKGROUND & AIMS

Alterations in the production of the beta-galactoside binding protein galectin-3 and of MUC2 intestinal mucin have been independently correlated with the malignant behavior of human colon cancer cells. MUC2 mucin is a major ligand for galectin-3, and colon cancer cells that differ quantitatively in MUC2 expression may also vary in expression of galectin-3. The current study was designed to investigate the relationship between galectin-3 production and MUC2 mucin synthesis by human colon cancer cells.

METHODS

The effect of galectin-3 on MUC2 mucin production was assessed by stable transfection of sense and antisense galectin-3 expression constructs under the control of constitutive or tetracycline-inducible promoters into human colon cancer cells. Galectin-3 and MUC2 expression were determined by fluorescence-activated cell sorter (cell surface galectin-3), Western and Northern analysis (galectin-3, MUC2), and gel filtration of secreted high-weight glycoprotein (MUC2). In vitro results were confirmed in vivo by analysis of cecal xenografts in athymic mice.

RESULTS

Colon cancer cells with high levels of galectin-3 also had high levels of MUC2 mucin, whereas those with low galectin-3 levels had low MUC2 levels. Alterations in galectin-3 levels by expression of sense or antisense galectin-3 constructs resulted in parallel alterations of MUC2 protein and RNA. Induction of antisense to galectin-3 in vivo was associated with decreases in both galectin-3 and MUC2 protein in cecal xenografts.

CONCLUSIONS

The beta-galactoside binding protein galectin-3 modulates the expression of its major ligand MUC2 mucin in human colon cancer cells. This may have important implications for understanding the role of galectin-3 in colon cancer metastasis.

Biological activities of ecalectin: a novel eosinophil-activating factor

Ecalectin, produced by Ag-stimulated T lymphocytes, is a potent eosinophil-specific chemoattractant in vitro as well as in vivo and thus is implicated in allergic responses. Ecalectin differs structurally from other known eosinophil chemoattractants (ECAs); ecalectin belongs to the galectin family defined by their affinity for beta-galactosides and by their conserved carbohydrate recognition domains. These characteristic features suggest that ecalectin has unique activities associated with allergic inflammation besides ECA activity. Conversely, ecalectin may mediate ECA activity by binding to a receptor of a known ECA via affinity for the beta-galactosides present on this receptor. In this study, we have tested whether ecalectin mediates ECA activity by binding to a receptor of a known ECA, and we have assessed its effects on eosinophils. Ecalectin did not mediate ECA activity by binding to the IL-5R or to CCR3. Also, the ECA activity of ecalectin was mainly chemokinetic. In addition, ecalectin induced concentration-dependent eosinophil aggregation, a marker for eosinophil activation. Ecalectin induced concentration-dependent superoxide production from eosinophils but did not induce degranulation; usually these two events are coupled in eosinophil activation. Moreover, ecalectin directly prolonged eosinophil survival in vitro and did not trigger eosinophils to secrete cytokines that prolong eosinophil survival. These results demonstrate that ecalectin has several unique effects on eosinophils. Therefore, we conclude that ecalectin is a novel eosinophil-activating factor. Presumably, these effects allow ecalectin to play a distinctive role in allergic inflammation.

Galectin-3 is strongly up-regulated in nonapoptosing mammary epithelial cells during rat mammary gland involution

Galectin-3 is an endogenous mammalian lectin that binds to ABH carbohydrate antigens. Here we show that galectin-3 is strongly up-regulated during mammary gland involution and that it is expressed virtually exclusively on nonapoptotic cells. We demonstrate that dexamethasone, an inhibitor of the second phase of mammary gland involution, potently suppresses up-regulation of galectin-3 as judged immunohistochemically and on western blots, suggesting that systemic hormone levels regulate galectin-3 expression during involution. However, at the RNA level galectin-3 expression is rapidly up-regulated on the onset of involution but remains consistantly high during the first and second phase of involution regardless of dexamethasone treatment. These data suggest that the up-regulation of galectin-3 in the involuting mammary gland is not only controlled transcriptionally but also regulated posttranscriptionally under the control of systemic glucocorticoid hormones involved in coordinating the involution process.

The constitutive expression of galectin-3 is downregulated in the intestinal epithelia of Crohn's disease patients, and tumour necrosis factor alpha decreases the level of galectin-3-specific mRNA in HCT-8 cells

OBJECTIVE

Galectin-3, a lectin with specificity for beta galactoside, is expressed by a variety of cells, including intestinal epithelial cells. Among other functions, galectin-3 mediates cell adhesion and is involved in inflammatory processes. In this study, we assessed the expression of galectin-3 in intestinal epithelial cells from Crohn's disease patients (n = 10), ileum adjacent to resected colon carcinoma (n = 9), unspecific bowel inflammation (n = 1), diverticulosis (n = 1), ulcerative colitis (n = 3) and healthy jejunum used for interposition in larynx carcinoma (n = 1). The role of cytokines on galectin-3 expression was a further aim of our study.

METHODS

The galectin-3 distribution in intestinal epithelia was analysed by immunohistochemistry, immunoblotting, immunofluorescence and reverse transcriptase polymerase chain reaction (RT-PCR). Human intestinal epithelial cell line (HCT-8) and primary cultured intestinal epithelial cells were treated with cytokines, and the effects on galectin-3 expression were determined by RT-PCR.

RESULTS

Galectin-3 showed a homogeneous distribution in epithelia from control patients. In contrast, in epithelial cells from Crohn's disease lesions, galectin-3 staining was strongly spotted and heterogeneous. In inflamed and reorganized tissue, galectin-3 expression was markedly reduced, and was associated with disintegration of epithelia. Primary cultured epithelial cells as well as HCT-8 cells expressed galectin-3 protein and mRNA. Incubation of HCT-8 cells with tumour necrosis factor alpha (TNF-alpha), but not with other cytokines, substantially reduced galectin-3 expression as shown by semiquantitative RT-PCR.

CONCLUSIONS

Downregulation of galectin-3 in the intestinal epithelium of Crohn's disease patients may be a consequence of enhanced TNF-alpha production by inflammatory cells, thereby contributing to the pathophysiology of the disease.

Galectin-3 mediates the endocytosis of beta-1 integrins by breast carcinoma cells

Galectin-3, a beta-galactoside binding lectin, has been demonstrated to play a key role(s) in cell to extracellular matrix interaction. The precise mechanism by which it modulates cellular adhesion is presently unclear and warrants further studies. We hereby report that galectin-3 mediates the endocytosis of beta-1 integrins in a lactose-dependent manner. Interestingly we observed that galectin-3 was also rapidly internalized by the cells via the same pathway and the internalization was completely blocked by lactose. The endocytosis process was temperature dependent and was inhibited by filipin but not chlorpromazine. The endocytosis of galectin-3 and beta-1 integrins by the cells was accompanied by rapid cell spreading due to cytoskeletal reorganization. The data suggest a novel mechanism by which galectin-3 and beta-1 integrins are internalized into breast carcinoma cells via a cavaleolae-like pathway of endocytosis.

Accelerated diabetic glomerulopathy in galectin-3/AGE receptor 3 knockout mice

Several molecules were shown to bind advanced glycation end products (AGEs) in vitro, but it is not known whether they all serve as AGE receptors and which functional role they play in vivo. We investigated the role of galectin-3, a multifunctional lectin with (anti)adhesive and growth-regulating properties, as an AGE receptor and its contribution to the development of diabetic glomerular disease, using a knockout mouse model. Galectin-3 knockout mice obtained by gene ablation and the corresponding wild-type mice were rendered diabetic with streptozotocin and killed 4 months later, together with age-matched nondiabetic controls. Despite a comparable degree of metabolic derangement, galectin-3-deficient mice developed accelerated glomerulopathy vs. the wild-type animals, as evidenced by the more pronounced increase in proteinuria, extracellular matrix gene expression, and mesangial expansion. This was associated with a more marked renal/glomerular AGE accumulation, indicating it was attributable to the lack of galectin-3 AGE receptor function. The galectin-3-deficient genotype was associated with reduced expression of receptors implicated in AGE removal (macrophage scavenger receptor A and AGE-R1) and increased expression of those mediating cell activation (RAGE and AGE-R2). These results show that the galectin-3-regulated AGE receptor pathway is operating in vivo and protects toward AGE-induced tissue injury in contrast to that through RAGE.

Galectins as modulators of cell adhesion

The galectins are a family of carbohydrate-binding proteins that are distributed widely in metazoan organisms. Each galectin exhibits a specific pattern of expression in various cells and tissues, and expression is often closely regulated during development. Although these proteins are found mainly in the cell cytoplasm, some are secreted from cells and interact with appropriately glycosylated proteins at the cell surface or within the extracellular matrix. These receptors include cell-adhesion molecules such as integrins, and matrix glycoproteins such as laminin and fibronectin isoforms. Recent studies have increased understanding of the roles of the galectins in regulating cell-cell and cell-matrix adhesion. These interactions are critically involved in modulation of normal cellular motility and polarity and during tissue formation, and loss of adhesive function is implicated in several disease states including tumour progression, inflammation and cystic development in branching epithelia such as kidney tubules. This review discusses recent progress in defining the specificities and mechanisms of action of secreted galectins as multifunctional cell regulators.

Proteomic analysis of dendritic cell-derived exosomes: a secreted subcellular compartment distinct from apoptotic vesicles

Dendritic cells constitutively secrete a population of small (50-90 nm diameter) Ag-presenting vesicles called exosomes. When sensitized with tumor antigenic peptides, dendritic cells produce exosomes, which stimulate anti-tumor immune responses and the rejection of established tumors in mice. Using a systematic proteomic approach, we establish the first extensive protein map of a particular exosome population; 21 new exosomal proteins were thus identified. Most proteins present in exosomes are related to endocytic compartments. New exosomal residents include cytosolic proteins most likely involved in exosome biogenesis and function, mainly cytoskeleton-related (cofilin, profilin I, and elongation factor 1alpha) and intracellular membrane transport and signaling factors (such as several annexins, rab 7 and 11, rap1B, and syntenin). Importantly, we also identified a novel category of exosomal proteins related to apoptosis: thioredoxin peroxidase II, Alix, 14-3-3, and galectin-3. These findings led us to analyze possible structural relationships between exosomes and microvesicles released by apoptotic cells. We show that although they both represent secreted populations of membrane vesicles relevant to immune responses, exosomes and apoptotic vesicles are biochemically and morphologically distinct. Therefore, in addition to cytokines, dendritic cells produce a specific population of membrane vesicles, exosomes, with unique molecular composition and strong immunostimulating properties.

Cloning and characterisation of tandem-repeat type galectin in rainbow trout (Oncorhynchus mykiss)

Fish beta-galactoside binding lectin (galectin) cDNA was cloned from the cDNA library of rainbow trout (Oncorhynchus mykiss) head kidney. The clone contained a single open reading frame encoding 341 amino acids (aa) (38 kDa protein), including the initiator methionine. Significant sequence homology to mammalian galectin-9 (40-55% identity) was observed. Its amino acid sequence showed two distinct N- and C-terminal domains (148 and 130 aa, respectively) connected by a peptide linker (63 aa). The galectin contains two consensus WG-E-R/K motifs thought to play an essential role in sugar-binding, indicating that this lectin is a member of the tandem-repeat type galectins which have not been identified in fish. The 1.6 kDa mRNA of the lectin was found by Northern blot analyses to be widely expressed in the spleen, head kidney, thymus, peritoneal exudate cells, ovary, gills and heart. Southern blot analyses with the probe for C-terminal of the lectin showed the existence of two hybridising genes. These results suggest that rainbow trout has at least one tandem-repeat type galectin as well as proto-type galectin.

Galectin-3 modulates ureteric bud branching in organ culture of the developing mouse kidney

Galectin-3 is a mammalian beta-galactoside-specific lectin with functions in cell growth, adhesion, and neoplastic transformation. On the basis of expression patterns in humans, it is proposed that galectin-3 modulates fetal collecting duct growth. This article provides evidence that galectin-3 can modulate branching morphogenesis of the mouse ureteric bud/collecting duct lineage. With the use of immunohistochemistry, galectin-3 was not detected in early metanephrogenesis but was upregulated later in fetal kidney maturation when the protein was prominent in basal domains of medullary collecting ducts. Addition of galectin-3 to embryonic days 11 and 12 whole metanephric cultures inhibited ureteric bud branching, whereas galectin-1 did not perturb morphogenesis, nor did a galectin-3 mutant lacking wild-type high-affinity binding to extended oligosaccharides. Exogenous galectin-3 retarded conversion of renal mesenchyme to nephrons in whole metanephric explants but did not affect nephron induction by spinal cord in isolated renal mesenchymes. Finally, addition of a blocking antiserum to galectin-3 caused dilation and distortion of developing epithelia in embryonic day 12 metanephroi cultured for 1 wk. The upregulation of galectin-3 protein during kidney maturation, predominantly at sites where it could mediate cell/matrix interactions, seems to modulate growth of the ureteric tree.

Efficacy of galectins in the amelioration of nephrotoxic serum nephritis in Wistar Kyoto rats

BACKGROUND

Galectins are characterized by specific affinity for beta-galactoside sugars, and they play a role in diverse biological processes, including cell adhesion, cell proliferation, and apoptosis. Galectin-1, -3, and -9 have been implicated in modulating the immune response.

METHODS

Nephrotoxic serum nephritis, which is characterized by crescent formation and glomerular influx of CD8+ cells into glomerular capillaries, was induced in Wistar Kyoto (WKY) rats by injecting rabbit antiglomerular basement membrane serum. Following induction, the rats were treated either with phosphate-buffered saline or dexamethasone, galectin-1, galectin-3, or galectin-9 on alternate days and were sacrificed at day 14. At day 8, splenic lymphocytes were isolated and employed for terminal deoxytransferase-mediated uridine triphosphate nick end-labeling (TUNEL) assay to assess the degree of apoptosis, and the kidneys were utilized to determine the extent of influx of CD4(+) and CD8(+) cells and glomerular damage.

RESULTS

Dexamethasone induced a marked apoptosis of splenic CD4(+) and CD8(+) cells, and it inhibited the production of anti-rabbit IgG and the influx of CD8+ cells and macrophages into the renal glomeruli. Crescent formation and excretion of urinary proteins were also reduced. Galectin-9 failed to induce apoptosis in the CD4(+) cells; however, it induced apoptosis in the CD8(+) cells and inhibited the infiltration of CD8(+) cells. Although galectin-1 and -3 did not induce the apoptosis in the T cells, they inhibited the accumulation of macrophages in the renal glomeruli. Like dexamethasone, the galectins also reduced the crescentic formation, proliferation of glomerular cells, and excretion of urinary proteins.

CONCLUSIONS

Galectin-9 selectively induces apoptosis of the activated CD8(+) cells, while the macrophage influx into the kidney is modulated by all three galectins. This finding raises an interesting possibility for the utility of galectins in the modulation of macrophages that are involved in immune-mediated glomerular diseases.

Role of galectin-3 as a receptor for advanced glycosylation end products

The advanced glycosylation end product (AGE)-binding proteins identified so far include the components of the AGE-receptor complex p60, p90 and galectin-3, receptor for advanced glycosylation end products (RAGE), and the macrophage scavenger receptor types I and II. Galectin-3 interacts with beta-galactoside residues of several cell surface and matrix glycoproteins through the carbohydrate recognition domain and is also capable of peptide-peptide associations mediated by its N-terminus domain. These structural properties enable galectin-3 to exert multiple functions, including the modulation of cell adhesion, the control of cell cycle, and the mRNA splicing activity. Moreover, in macrophages, astrocytes, and endothelial cells, galectin-3 has been shown to exhibit a high-affinity binding for AGEs; the lack of a transmembrane anchor sequence or signal peptide suggests that it associates with other AGE-receptor components rather than playing an independent role as AGE-receptor. In tissues that are targets of diabetic vascular complications, such as the mesangium and the endothelium, galectin-3 is not expressed or only weakly expressed under basal conditions, at variance with p90 and p60 but becomes detectable with aging and is induced or up-regulated by the diabetic milieu, which only slightly affects the expression of p90 or p60. This (over)expression of galectin-3 may in turn modulate AGE-receptor-mediated events by modifying the function of the AGE-receptor complex, which could play a role in the pathogenesis of target tissue injury. Up-regulated galectin-3 expression may also exert direct effects on tissue remodeling, independently of AGE ligands, by virtue of its adhesive and growth regulating properties.

Up-regulation of galectin-3 in acute renal failure of the rat

Galectin-3, a multifunctional beta-galactoside-binding lectin, is known to participate in development, oncogenesis, cell-to-cell attachment, and inflammation. We studied to determine whether galectin-3 is associated with cell injury and regeneration in two types of acute renal failure (ARF), namely ischemic and toxic ARF. In ischemia/reperfusion renal injury in rats (bilateral renal pedicles clamped for 40 minutes), galectin-3 mRNA began to increase at 2 hours and extended by 6.2-fold at 48 hours (P: < 0.01 versus normal control rats), and then decreased by 28 days after injury. In addition, a significant negative correlation between galectin-3 mRNA expression and serum reciprocal creatinine was shown at 48 hours after injury (n = 13, r = -0.94, P: < 0.0001). In folic acid-induced ARF, galectin-3 mRNA was found to be up-regulated at 2 hours after injury and increased levels continued until at least 7 days post-injury. In immunohistochemistry, at 2 hours following reperfusion, galectin-3 began to develop in proximal convoluted tubules. From 6 hours up to 48 hours, galectin-3 was also found in proximal straight tubules, distal tubules, thick ascending limbs, and collecting ducts. In later stages of regeneration, galectin-3 expressions were found in macrophages. In conclusion, we demonstrated that galectin-3 expressions were markedly up-regulated in both ischemic and toxic types of ARF. Galectin-3 may play an important role in acute tubular injury and the following regeneration stage.

Fruiting body development in Coprinus cinereus: regulated expression of two galectins secreted by a non-classical pathway

Fruiting body formation in the basidiomycete Coprinus cinereus is a developmental process that occurs as a response of the mycelium to external stimuli. First, localized, highly branched hyphal structures (knots) are formed as a reaction to nutritional depletion. Hyphal-knot formation is repressed by light; however, light signals are essential for the development of the hyphal knot into an embryonic fruiting body (primordium) as well as karyogamy, meiosis and fruiting body maturation. The role of the different environmental signals in the initial phases of fruiting body development was analysed. It was observed that two fungal galectins, Cgl1 and Cgl2, are differentially regulated during fruiting body formation. cgl2 expression initiated in early stages of fruiting body development (hyphal knot formation) and was maintained until maturation of the fruiting body, whereas cgl1 was specifically expressed in primordia and mature fruiting bodies. Immunofluorescence and immuno-electron microscopy studies detected galectins within specific fruiting body tissues. They localized in the extracellular matrix and the cell wall but also in membrane-bound bodies in the cytoplasm. Heterologous expression of Cgl2 in Saccharomyces cerevisiae indicated that secretion of this protein occurred independently of the classical secretory pathway.

Galectin-3 decreases in mice exposed to immobilization stress

Using M3/38 monoclonal antibody we have analyzed effects of immobilization stress on the expression of galectin-3 in liver, spleen and peritoneal macrophages from adult RFM and C3H mice, as well as from aged C3H mice (total of 22 animals). In all analyzed tissues, immobilization stress caused a significant decrease in the expression of galectin-3, ranging from 14% to 47%. The decrease of galectin-3 was observed in both strains of mice, as well as in old animals. Moreover, the same range of decrease (approximately 50%) was observed when cells grown in vitro were exposed to subculturing, or heat-shock. Although the biological significance of this effect is not known, it is very interesting that a single episode of immobilization stress was sufficient to cause a significant decrease in galectin-3, implicating that this beta-galactoside-binding lectin might be involved in the physiological response to psychological stress.

Novel mechanism that Trypanosoma cruzi uses to adhere to the extracellular matrix mediated by human galectin-3

Binding of Trypanosoma cruzi trypomastigotes to laminin is enhanced by galectin-3, a beta-galactoside binding lectin. The galectin-3 enhanced binding of trypanosomes to laminin is inhibited by lactose. Co-immunoprecipitations indicate that galectin-3 binds to the 45, 32 and 30 kDa trypanosome surface proteins. Binding of galectin-3 to the 45, 32 and 30 kDa surface proteins is inhibited by lactose. Polyclonal and a monoclonal antibodies to galectin-3 immunoprecipitated a major 64 kDa trypanosome surface protein. T. cruzi monoclonal antibody to mucin recognized the 45 kDa surface protein. The 45, 32 and 30 kDa surface proteins interact with galectin-3 in order to enhance trypanosome adhesion to laminin.

Secretion of the galectin family of mammalian carbohydrate-binding proteins

Galectins are cytosolic proteins that lack any signal sequence for transport into the endoplasmic reticulum and are not glycosylated, although several galectins contain consensus sites for N-glycosylation, indicating that these proteins do not traverse the ER-Golgi network. However, there is abundant evidence for the extracellular localisation of some galectins at cell surfaces, in the extracellular matrix and in cell secretions consistent with other evidence for extracellular roles of galectins as modulators of cell adhesion and signalling. How then are galectins secreted if not through the classical secretory pathway? Do all galectins share the same secretory pathway? Can a particular galectin utilise more than one secretory pathway? If galectins play important extracellular roles how is their secretion regulated in relation to function? These are still largely unanswered questions but recent studies are beginning to give glimpses into some novel aspects of the secretion of these intriguing proteins.

High-resolution structure of the conger eel galectin, congerin I, in lactose-liganded and ligand-free forms: emergence of a new structure class by accelerated evolution

BACKGROUND

Congerin I is a member of the galectin (animal beta-galactoside-binding lectin) family and is found in the skin mucus of conger eel. The galectin family proteins perform a variety of biological activities. Because of its histological localization and activity against marine bacteria and starfish embryos, congerin I is thought to take part in the eels' biological defense system against parasites.

RESULTS

The crystal structure of congerin I has been determined in both lactose-liganded and ligand-free forms to 1. 5 A and 1.6 A resolution, respectively. The protein is a homodimer of 15 kDa subunits. Congerin I has a beta-sheet topology that is markedly different from those of known relatives. One of the beta-strands is exchanged between two identical subunits. This strand swap might increase the dimer stability. Of the known galectin complexes, congerin I forms the most extensive interaction with lactose molecules. Most of these interactions are substituted by similar interactions with water molecules, including a pi-electron hydrogen bond, in the ligand-free form. This observation indicates an increased affinity of congerin I for the ligand.

CONCLUSIONS

The genes for congerin I and an isoform, congerin II, are known to have evolved under positive selection pressure. The strand swap and the modification in the carbohydrate-binding site might enhance the cross-linking activity, and should be the most apparent consequence of positive selection. The protein has been adapted to functioning in skin mucus that is in direct contact with surrounding environments by an enhancement in cross-linking activity. The structure of congerin I demonstrates the emergence of a new structure class by accelerated evolution under selection pressure.

Domain organization of Mac-2 binding protein and its oligomerization to linear and ring-like structures

The multidomain Mac-2 binding protein (M2BP) is present in serum and in the extracellular matrix in the form of linear and ring-shaped oligomers, which interact with galectin-3, fibronectin, collagens, integrins and other large glycoproteins. Domain 1 of M2BP (M2BP-1) shows homology with the cysteine-rich SRCR domain of scavanger receptor. Domains 2 and 3 are related to the dimerization domains BTB/POZ and IVR of the Drosophila kelch protein. Recombinant M2BP, its N-terminal domain M2BP-1 and a fragment consisting of putative domains 2, 3 and 4 (M2BP-2,3,4) were investigated by scanning transmission electron microscopy, transmission electron microscopy, analytical ultracentrifugation and binding assays. The ring oligomers formed by the intact protein are comprised of approximately 14 nm long segments composed of two 92 kDa M2BP monomers. Although the rings vary in size, decamers predominate. The various linear oligomers also observed are probably ring precursors, dimers predominate. M2BP-1 exhibits a native fold, does not oligomerize and is inactive in cell attachment. M2BP-2,3,4 aggregates to heterogeneous, protein filled ring-like structures as shown by metal shadowed preparations. These aggregates retain the cell-adhesive potential indicating native folding. It is hypothesized that the rings provide an interaction pattern for multivalent interactions of M2BP with target molecules or complexes of ligands.

Endogenous galectins and effect of galectin hapten inhibitors on the differentiation of the chick mesonephros

Galectins are galactoside-binding lectins. In the mesonephros of the chick embryo, the 16-kDa galectin is abundant in the glomerular and tubular basement membranes where it colocalizes with fibronectin and laminin. To test whether galectin-glycoprotein interactions could play a role in mesonephric development, the effects of the galectin hapten inhibitors thiodigalactoside (TDG) and lactose on the differentiation of the cultured mesonephros were investigated. When compared to control saccharide-free or maltose-treated cultures, mesonephroi cultured in the presence of TDG and lactose exhibited defects in tissue organization. These included a distorted tubule shape, pseudo-stratification of the tubular epithelium, and detachment of glomerular podocytes from the basement membrane. The presence of molecular differentiation markers in the developing mesonephros was investigated. In vivo, expression of the epithelial-specific cell adhesion molecule E-cadherin is restricted to differentiated tubular epithelial cells, whereas the intermediate filament protein vimentin is present in mesonephrogenic mesenchyme and is undetectable in tubular epithelial cells. In mesonephroi cultured in the absence of sugars or in the presence of maltose, the expression pattern of these two marker molecules resembles that found in the mesonephros in vivo. In contrast, in the mesonephroi cultured in the presence of TDG and lactose, the epithelial tubular cells expressing E-cadherin also express vimentin. Re-expression of vimentin in the tubular epithelial cells could indicate a partial reversal to a mesenchymal phenotype. Results suggest that galectin-glycoprotein interactions in the basement membrane are important in the maintenance of the renal epithelial phenotype. Dev Dyn 1999;215:248-263.

Specific inhibition of T-cell adhesion to extracellular matrix and proinflammatory cytokine secretion by human recombinant galectin-1

The migration of immune cells through the extracellular matrix (ECM) towards inflammatory sites is co-ordinated by receptors recognizing ECM glycoproteins, chemokines and proinflammatory cytokines. In this context, galectins are secreted to the extracellular milieu, where they recognize poly-N-acetyllactosamine chains on major ECM glycoproteins, such as fibronectin and laminin. We investigated the possibility that galectin-1 could modulate the adhesion of human T cells to ECM and ECM components. T cells were purified from human blood, activated with interleukin-2 (IL-2), labelled, and incubated further with intact immobilized ECM and ECM glycoproteins in the presence of increasing concentrations of human recombinant galectin-1, or its more stable, related, C2-S molecule obtained by site-directed mutagenesis. The presence of galectin-1 was shown to inhibit T-cell adhesion to intact ECM, laminin and fibronectin, and to a lesser extent to collagen type IV, in a dose-dependent manner. This effect was specifically blocked by anti-galectin-1 antibody and was dependent on the lectin's carbohydrate-binding properties. The inhibition of T-cell adhesion by galectin-1 correlates with the ability of this molecule to block the re-organization of the activated cell's actin cytoskeleton. Furthermore, tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) production was markedly reduced when IL-2-activated T cells were incubated with galectin-1 or its mutant. This effect was prevented by beta-galactoside-related sugars. The present study reveals an alternative inhibitory mechanism for explaining the suppressive properties of the galectin-1 subfamily on inflammatory and autoimmune processes.

Galectins: a key intersection between glycobiology and immunology

Galectins are a family of evolutionarily conserved animal lectins, widely distributed from lower invertebrates to mammals. They share sequence and structure similarities in the carbohydrate recognition domain and specificity for polylactosamine-enriched glycoconjugates. In the last few years significant experimental data have been accumulated concerning their participation in different biological processes requiring carbohydrate recognition such as cell adhesion, cell growth regulation, inflammation, immunomodulation, apoptosis and metastasis. In the present review we will discuss some exciting questions and advances in galectin research, highlighting the significance of these proteins in immunological processes and their implications in biomedical research, disease diagnosis and clinical intervention. Designing novel therapeutic strategies based on carbohydrate recognition will provide answers for the treatment of autoimmune disorders, inflammatory processes, allergic reactions and tumor spreading.