Brugia malayi galectin 2 is a tandem-repeat type galectin capable of binding mammalian polysaccharides

Galectins are among the most abundant excretory/secretory (ES) products of filarial worms, but their role in filarial biology is poorly understood. Galectin-2 (Lec-2), a major component of Brugia malayi extracellular vesicles, is released by filarial worms, and was recently identified in the serum of persons with loiasis. We therefore sought to clone and characterize Lec-2, and to develop reagents to examine its potential as a biomarker and its role in parasite biology. We cloned and expressed recombinant B. malayi Lec-2 (rBmLec-2), generated a Lec-2-specific monoclonal antibody (4B4), and used it to confirm the presence of Lec-2 in B. malayi ES products and whole worm lysate. We show that Lec-2 is absent in B. malayi oocytes, and increases in concentration as embryos mature. Recombinant BmLec-2 hemagglutinates rabbit red blood cells at concentrations less than 1 μg/mL, and this is abrogated by single amino acid substitutions in the predicted carbohydrate recognition domains. rBmLec-2 binds multiple LacNAc oligosaccharides on a mammalian carbohydrate array. Sera from 17/23 (78 %) persons with microfilaremic loiasis and 4/10 (40 %) persons with bancroftian filariasis had detectable antibody to Lec-2 by western blot. Our studies confirm the functionality of BmLec-2 and indicate anti-Lec-2 antibody responses are common in persons with filariasis. These studies set the stage for further examination of the role of Lec-2 in filarial biology and in filarial-host interactions.

Human galectin-2: expression profiling by RT-PCR/immunohistochemistry and its introduction as a histochemical tool for ligand localization

Sugar-encoded information of glyco-conjugates is translated into cellular responses by endogenous lectins. Galectins stand out against other lectin families due to their wide range of functions including cell adhesion, tissue invasion or growth regulation exerted at extracellular, membrane, cytoplasmic and nuclear sites. This remarkable versatility warrants close scrutiny of their emerging network, in this study with focus on homodimeric human galectin-2. We first detected presence of specific mRNA in various tissue types by processing post mortem and surgical specimens by RT-PCR protocols. Overlap of gene expression was noted with proto-type galectins-1 and -7 and also family members from the other two subgroups. To monitor expression on the level of protein a polyclonal anti-galectin-2 antibody was raised. Immunopositivity was semi-quantitatively assessed in sections of 209 human samples establishing an array both of normal tissues and samples with inflammation or benign/malignant growth. In general, positivity was predominantly epithelial without restriction of staining to certain tissue types, as fittingly indicated by our RT-PCR analysis. Staining was not limited to the cytoplasm but also included nuclear sites. To examine the suitability of the labeled lectin as a histochemical probe we biotinylated galectin-2 under activity-preserving conditions and introduced it to tissue profiling. Specific cytoplasmic staining proved the validity of the concept. Our results encourage systematic histopathologic studies by immuno- and lectin histochemistry, especially by adding galectin-2 as study object to galectin fingerprinting which has already yielded prognostic information on galectins-1, -3, -4 and -8 and hereby contributed to define functional overlap/divergence in this lectin family.

Prognostic significance of endogenous adhesion/growth-regulatory lectins in lung cancer

OBJECTIVE

To determine the expression of endogenous adhesion/growth-regulatory lectins and their binding sites using labeled tissue lectins as well as the binding profile of hyaluronic acid as an approach to define new prognostic markers.

METHODS

Sections of paraffin-embedded histological material of 481 lungs from lung tumor patients following radical lung excision processed by a routine immunohistochemical method (avidin-biotin labeling, DAB chromogen). Specific antibodies against galectins-1 and -3 and the heparin-binding lectin were tested. Staining by labeled galectins and hyaluronic acid was similarly visualized by a routine protocol. After semiquantitative assessment of staining, the results were compared with the pT and pN stages and the histological type. Survival was calculated by univariate and multivariate methods.

RESULTS

Binding of galectin-1 and its expression tended to increase, whereas the parameters for galectin-3 decreased in advanced pT and pN stages at a statistically significant level. The number of positive cases was considerably smaller among the cases with small cell lung cancer than in the group with non-small-cell lung cancer, among which adenocarcinomas figured prominently with the exception of galectin-1 expression. Kaplan-Meier computations revealed that the survival rate of patients with galectin-3-binding or galectin-1-expressing tumors was significantly poorer than that of the negative cases. In the multivariate calculations of survival lymph node metastases (p < 0.0001), histological type (p = 0.003), galectin-3-binding capacity (p = 0.01), galectin-3 expression (p = 0.03) and pT status (p = 0.003) proved to be independent prognostic factors, not correlated with the pN stage.

CONCLUSION

The expression and the capacity to bind the adhesion/growth regulatory galectin-3 is defined as an unfavorable prognostic factor not correlated with the pTN stage.

Human Galectin-2: Novel Inducer of T Cell Apoptosis with Distinct Profile of Caspase Activation

Galectin-2 is structurally closely related to galectin-1, but has a distinct expression profile primarily confined to the gastrointestinal tract. Prominent differences in the proximal promoter regions between galectins-2 and -1 concern Sp1-, hepatocyte NF-3, and T cell-specific factor-1 binding sites. Of note, these sequence elements are positioned equally in the respective regions for human and rat galectins-2. Labeled galectin-2 binds to T cells in a beta-galactoside-specific manner. In contrast to galectin-1, the glycoproteins CD3 and CD7 are not ligands, while the shared affinity to beta1 integrin (or a closely associated glycoprotein) accounts for a substantial extent of cell surface binding. The carbohydrate-dependent binding of galectin-2 induces apoptosis in activated T cells. Fluorogenic substrate and inhibitor assays reveal involvement of caspases-3 and -9, in accordance with cleavage of the DNA fragmentation factor. Enhanced cytochrome c release, disruption of the mitochondrial membrane potential, and an increase of the Bax/Bcl-2 ratio by opposite regulation of expression of both proteins add to the evidence that the intrinsic apoptotic pathway is triggered. Cell cycle distribution and expression of regulatory proteins remained unaffected. Notably, galectins-1 and -7 reduce cyclin B1 expression, defining functional differences between the structurally closely related galectins. Cytokine secretion of activated T cells was significantly shifted to the Th2 profile. Our study thus classifies galectin-2 as proapoptotic effector for activated T cells, raising a therapeutic perspective. Of importance for understanding the complex galectin network, it teaches the lesson that selection of cell surface ligands, route of signaling, and effects on regulators of cell cycle progression are markedly different between structurally closely related galectins.