Cell-type-specific expression of murine multifunctional galectin-3 and its association with follicular atresia/luteolysis in contrast to pro-apoptotic galectins-1 and -7

Galectin-3 is a multifunctional protein with modular design. A distinct expression profile was determined in various murine organs when set into relation to homodimeric galectins-1 and -7. Fittingly, the signature of putative transcription-factor-binding sites in the promoter region of the galectin-3 gene affords a toolbox for a complex combinatorial regulation, distinct from the respective sequence stretches in galectins-1 and -7. A striking example for cell-type specificity was the ovary, where these two lectins were confined to the surface epithelium. Immunohistochemically, galectin-3 was found in macrophages of the cortical interstitium between developing follicles and medullary interstitium, matching the distribution of the F4/80 antigen. With respect to atresia and luteolysis strong signals in granulosa cells of atretic preantral but not antral follicles and increasing positivity in corpora lutea upon regression coincided with DNA fragmentation. Labeled galectin-3 revealed lactose-inhibitable binding to granulosa cells. Also, slender processes of vital granulosa cells which extended into the zona pellucida were positive. This study demonstrates cell-type specificity and cycle-associated regulation for galectin-3 with increased presence in atretic preantral follicles and in late stages of luteolysis.

Duodenal phytohaemagglutinin (red kidney bean lectin) stimulates gallbladder contraction in humans

AIM

Lectins, carbohydrate-specific proteins without enzymatic activity on the ligand, are daily ingested plant proteins which survive the passage through the gastrointestinal tract in a biologically active form. Their binding to glycan determinants of natural glycoconjugates can trigger biological effects. The lectin phytohaemagglutinin (PHA) is abundantly present in red kidney beans and induces cholecystokinin (CCK) release in rats. The aim of the study was to investigate the effect of intraduodenal administration of PHA on plasma CCK levels and gallbladder contraction in humans and to elucidate potential mechanisms of action.

METHODS

Five healthy volunteers underwent four studies. After a basal intraduodenal saline infusion for 30 min, PHA or heat-inactivated PHA was infused in increasing doses: 150 microg, 1.5 mg and 15 mg for 30 min each. Intravenous saline, CCK(1) receptor antagonist dexloxiglumide or atropine were administered in random order. Gallbladder volumes were measured by ultrasonography and plasma CCK levels by radioimmunoassay.

RESULTS

Intraduodenal PHA induced gallbladder contraction in a dose-dependent fashion starting with the lowest dose. The highest dose reduced the gallbladder volume to 65.3 +/- 9.4% of basal volume (P < 0.001) whereas heat-inactivated PHA did not have any effect. Blocking CCK(1) or muscarinic receptors completely abolished PHA-stimulated gallbladder contraction (dexloxiglumide 208.7 +/- 23.7%; atropine 104 +/- 7.0% of basal volume) while none of the treatments affected CCK levels.

CONCLUSION

Duodenal administration of PHA potently stimulates gallbladder contraction in humans. This contraction is mediated via cholinergic pathway.

Serum galectin-1 and galectin-3 levels in benign and malignant nodular thyroid disease

BACKGROUND

Since the histological expression of galectins is increased in thyroid carcinoma, determination of their serum levels may provide useful preoperative information. The goal of this study was to determine if a difference in galectin serum levels could be detected between benign and malignant nodular thyroid diseases.

DESIGN

Using validated ELISAs, the concentrations of several galectins were prospectively measured in serum samples from 30 healthy individuals and preoperatively in 90 patients with thyroid disease. Seventy-one patients had multiple thyroid nodules (MTN), 13 patients had a single thyroid nodule (STN), and 6 patients had Graves' disease. Nine of 71 patients with MTN had fine-needle aspiration biopsy (FNAB) of their nodules and in 7 patients a "benign" diagnosis was made, in 0 patient a "malignant" diagnosis was made, and in 2 patients a "suspicious" diagnosis was made. Six of 13 patients with STN had FNAB of their nodules and in 2 patients a "benign" diagnosis was made, in 3 patients a "malignant" diagnosis was made, and in 1 patient a "suspicious" diagnosis was made.

RESULTS

Thyroid disease was associated with higher levels of galectins-1 and -3 compared to normal subjects. Using a threshold value of 3.2 ng/mL as a cut-off point, the measurement of serum galectin-3 separated micro- and macropapillary thyroid carcinoma (PAP_CA) from patients with nonmalignant thyroid disease with 74% specificity, 73% sensitivity, 57% positive predictive value, and 85% negative predictive value. Elevated serum galectin-3 concentrations (>3.2 ng/mL) detected 87% of macropapillary thyroid carcinomas and 67% of micropapillary thyroid carcinomas.

CONCLUSIONS

Serum levels of galectins-1 and -3 are relatively high in patients with thyroid malignancy but there is considerable overlap in serum galectin-3 concentrations between those with benign and malignant nodular thyroid disease and, to a lesser extent, between those with and without nodular thyroid disease.

Human galectins as sensors for apoptosis/necrosis-associated surface changes of granulocytes and lymphocytes

Changes in the glycomic profile can significantly affect the cells' communication with the environment. Plant lectins have so far been used to address the issue as to whether the courses of apoptosis or necrosis are associated with such alterations. We, here, initiate the study of members of the family of functionally pleiotropic human galectins in this respect. Established protocols for the induction of apoptosis/necrosis of blood cells and for flow cytometry using annexin V/propidium iodide were combined with cell surface staining using biotinylated galectins at a nontoxic concentration. The galectin panel covered members from all three subfamilies. Flow cytometry revealed specific binding of galectins to viable control cells and conspicuous staining differences when testing apoptotic or necrotic cells. Onset and especially progression of cell death led to pronounced reactivity with the proto-type galectins-1, -2, and -7 and tandem-repeat-type galectin-4. Extent of staining depended on the nature and stage of cell death, type of dying cell, and type of galectin. Galectins act as sensors for cell-death-associated surface changes. Staining of late-apoptotic polymorphonuclear cells was particularly strong. Examining the functional significance of this result may reveal a new aspect within the surveillance system to protect against autoinflammation.

Assessing the inhibitory potency of galectin ligands identified from combinatorial (glyco)peptide libraries using surface plasmon resonance spectroscopy

Combinatorial (glyco)peptide libraries offer the possibility to define effective inhibitors of protein (lectin)-glycan interactions. If a (glyco)peptide surpasses the inhibitory potency of the free sugar, then the new peptide-lectin contacts underlying the affinity enhancement may guide further rational drug design. Focusing on the adhesion/growth regulatory human galectins 1 and 3, a screening of three combinatorial solid-phase (glyco)peptide libraries, containing Gal(beta1-O)Thr, Gal(beta1-S)Cys/Gal(beta1-N)Asn, and Lac(beta1-O)Thr, with the fluorescently labeled lectins had led to a series of lead compounds. To define the inhibitory potency of a selection of resynthesized (glyco)peptides systematically, a surface plasmon resonance-based inhibition assay with immobilized asialofetuin was set up. (Glyco)Peptides with up to 66-fold potency relative to free lactose as inhibitor were characterized. The presence of lactose in the most effective glycopeptides indicated the presence of affinity-enhancing peptide-lectin contacts. In addition to drug design, they may be helpful for fine-structural analysis of the binding sites.

Marker profiling of normal keratinocytes identifies the stroma from squamous cell carcinoma of the oral cavity as a modulatory microenvironment in co-culture

PURPOSE

The microenvironment established by stromal cells may or may not influence phenotypic aspects of epithelial cells and may be relevant for tumor and stem cell biology. We address this issue for keratinocytes using tumor-derived stromal cells in a co-culture system.

MATERIALS AND METHODS

We isolated stromal cells from human squamous cell carcinoma tissue and studied their effect on phenotypic characteristics of normal human interfollicular keratinocytes in vitro.

RESULTS

Stromal fibroblasts significantly influence immuno- and lectin cytochemical properties of co-cultured normal keratinocytes. Expression of keratins 8 and 19, the nucleolar protein nucleostemin, parameters related to adhesion/growth-regulatory galectins and the epithelial-mesenchymal transition were altered. This biological activity of tumor-derived stromal cells, which did not require cell contact, appeared to be stable, because it was maintained during passaging of keratinocytes in the absence of cancer cells.

CONCLUSIONS

Tumor-derived stromal fibroblasts acquire distinct properties to shape a microenvironment conducive to altering the phenotypic characteristics of normal epithelial cells in vitro.

Phosphorylated human galectin-3: facile large-scale preparation of active lectin and detection of structural changes by CD spectroscopy

Galectin-3 has a unique modular design. Its short N-terminal stretch can be phosphorylated, relevant for nuclear export and anti-anoikis/apoptosis activity. Enzymatic modification by casein kinase 1 at constant ATP concentration yielded mg quantities of mono- and diphosphorylated derivatives at Ser5/Ser11 in a 2:1 ratio. Their carbohydrate-inhibitable binding to asialofetuin, cell surfaces of three tumor lines, rabbit erythrocytes leading to haemagglutination and cytoplasmic sites in fixed tissue sections was not markedly altered relative to phosphate-free galectin-3. Spectroscopically, phosphorylation induced alterations in the far UV CD, indicative of an increase in ordered structure. This is accompanied by changes in the environment of aromatic amino acids signified by shifts in the near UV CD.

Human galectin-2: nuclear presence in vitro and its modulation by quiescence/stress factors

Galectins have the particular capacity to interact with distinct proteins, in addition to the typical reactivity of lectins with glycans. Therefore, they can be functionally active when residing at places other than the membrane or extracellular matrix. In fact, nuclear presence of galectins-1 and -3 is solidly documented but it is an open question whether these two cases are exceptional within this lectin family. Thus, galectin-2, which shares 43% sequence identity on the protein level with galectin-1, warrants study in this respect. Based on initial immunohistochemical evidence we herein address the issue as to whether this galectin can join the category of nuclear lectins. To do so we studied different types of cell in vitro using an antibody preparation free of cross-reactivity against other tested galectins. The immunocytochemical experiments revealed that galectin-2 was present in nuclei of murine 3T3 fibroblasts and also genetically engineered human colon carcinoma cells with stable ectopic expression. Transport of galectin-2 to the nucleus could be enhanced by physical (UV light), chemical (mitomycin C, serum withdrawal) or cell biological (coculture with stromal cells) treatment modalities. As a means of further characterizing the staining profile cytochemically, a series of markers with well-defined site of residency within the nuclear compartment was tested in parallel. Importantly, no colocalization with galectins-1 and -3 and the splicing factor SC35 was detectable, the former cases also serving as inherent specificity control. In contrast, a similarity was uncovered in the case of the promyelocytic leukemia (PML) protein as marker of PML nuclear bodies. In aggregate, nuclear localization is documented for galectin-2. This attribute should thus not be considered as an exceptional finding confined to galectins-1 and -3. That even closely related family members, here galectins-1 and -2, exhibit distinct intranuclear localization patterns gives ensuing research a clear direction.

Gene-expression signature of adhesion/growth-regulatory tissue lectins (galectins) in transitional cell cancer and its prognostic relevance

AIMS

Lectins, and especially galectins, appear to be important in malignancy-associated processes. The aim was to analyse comprehensively the presence of galectins in urothelial tumours.

METHODS AND RESULTS

Non-cross-reactive antibodies against seven family members from the three subgroups (prototype: galectin-1, -2 and -7; chimera type: galectin-3; tandem-repeat type: galectin-4, -8 and -9) were used. Gene expression was monitored in specimens of normal urothelium, fresh tumour tissue and cell lines by real-time polymerase chain reaction (PCR). The presence and evidence of tumour-associated up-regulation were shown for galectin-1 and -3. This was less clear-cut for galectin-4 and -8. Galectin-7 was expressed in all cell lines; galectin-2 and -9 were detected at comparatively low levels. Galectin-2, -3 and -8 up-regulation was observed in superficial tumours, but not in muscle-invasive tumours (P < 0.05). Immunoreactivity correlated with tumour grading for galectin-1, -2 and -8, and disease-dependent mortality correlated with galectin-2 and -8 expression. Binding sites were visualized using labelled galectins.

CONCLUSIONS

The results demonstrate a complex expression pattern of the galectin network in urothelial carcinomas. Galectin-1, -2, -3 and -8 are both potential disease markers and also possible targets for bladder cancer therapy.

Prototype chicken galectins revisited: characterization of a third protein with distinctive hydrodynamic behaviour and expression pattern in organs of adult animals

Prototype galectins are versatile modulators of cell adhesion and growth via their reactivity to certain carbohydrate and protein ligands. These functions and the galectins' marked developmental regulation explain their attractiveness as models to dissect divergent evolution after gene duplication. Only two members have so far been assumed to constitute this group in chicken, namely the embryonic muscle/liver form {C-16 or CLL-I [16 kDa; chicken lactose lectin, later named CG-16 (chicken galectin-16)]} and the embryonic skin/intestine form (CLL-II or C-14; later named CG-14). In the present study, we report on the cloning and expression of a third prototype CG. It has deceptively similar electrophoretic mobility compared with recombinant C-14, the protein first isolated from embryonic skin, and turned out to be identical with the intestinal protein. Hydrodynamic properties unusual for a homodimeric galectin and characteristic traits in the proximal promoter region set it apart from the two already known CGs. Their structural vicinity to galectin-1 prompts their classification as CG-1A (CG-16)/CG-1B (CG-14), whereas sequence similarity to mammalian galectin-2 gives reason to refer to the intestinal protein as CG-2. The expression profiling by immunohistochemistry with specific antibodies discerned non-overlapping expression patterns for the three CGs in several organs of adult animals. Overall, the results reveal a network of three prototype galectins in chicken.

Temperature dependence of ligand-protein complex formation as reflected by saturation transfer difference NMR experiments

We show that temperature is an important parameter for the sensitivity of saturation transfer difference (STD) spectroscopy. A decreased intensity of STD signals is observed for lactose binding to growth-regulatory galectin7 (p53-induced gene 1), as well as for nucleotide binding to annexin A6, when the temperature is increased from 281 to 298-310 K. Opposite temperature effects on STD intensity are observed for S-peptide binding to S-protein to reconstitute RNase S. However, the STD signals for tryptophan binding to downstream regulatory element antagonist modulator of the human prodynorphin gene (DREAM)are relatively unaffected between 281 and 298 K. The known kinetics of the binding of ATP by the uncoupling protein from brown adipose tissue mitochondria (UCP1) predicted an observable STD at 310 K, but rapid sample degradation limits the experiments to much lower temperatures. Temperature strongly influences the kinetics and affinity constant of various types of complex formation and in so doing influences the observed STD effects. Therefore, temperature can be exploited to facilitate the optimization of STD-based applications, and at the same time minimize the number of test samples. STD-based screening protocols to detect new target-specific compounds may yield a larger number of potential ligands if screened at various temperatures.

Photoderivatized polymer thin films at quartz crystal microbalance surfaces: sensors for carbohydrate-protein interactions

Photoderivatized polymer-coated gold surfaces have been developed following a perfluorophenylazide-based double ligation strategy. Gold-plated quartz crystal microbalance (QCM) crystals were initially covalently functionalized with a monolayer of poly(ethylene glycol) (PEG), using photo- or thermolytic nitrene formation and insertion. The polymer surfaces were subsequently used as substrates for photoinsertion of carbohydrate-derivatized photoprobes, yielding different recognition motifs for selective protein binding. The resulting robust and biocompatible sensor surfaces were applied to a flow-through QCM instrument for monitoring lectin-carbohydrate interactions in real time. The results clearly show the predicted lectin selectivity, demonstrating the applicability of the approach.

Carbohydrate chain of ganglioside GM1 as a ligand: identification of the binding strategies of three 15 mer peptides and their divergence from the binding modes of growth-regulatory galectin-1 and cholera toxin

The branched pentasaccharide chain of ganglioside GM1 is a prominent cell surface ligand, for example, for cholera toxin or tumor growth-regulatory homodimeric galectins. This activity profile via protein recognition prompted us to examine the binding properties of peptides with this specificity. Our study provides insights into the mechanism of molecular interaction of this thus far unexplored size limit of the protein part. We used three pentadecapeptides in a combined approach of mass spectrometry, NMR spectroscopy and molecular modelling to analyze the ligand binding in solution. Availability of charged and hydrophobic functionalities affected the intramolecular flexibility of the peptides differently. Backfolding led to restrictions in two cases; the flexibility was not reduced significantly by association of the ligand in its energetically privileged conformations. Major contributions to the interaction energy arise from the sialic acid moiety contacting Arg/Lys residues and the N-terminal charge. Considerable involvement of stacking between the monovalent ligand and aromatic rings could not be detected. This carbohydrate binding strategy is similar to how an adenoviral fiber knob targets sialylated glycans. Rational manipulation for an affinity enhancement can now be directed to reduce the flexibility, exploit the potential for stacking and acquire the cross-linking capacity of the natural lectins by peptide attachment to a suitable scaffold.

Tumor suppressor p16INK4a--modulator of glycomic profile and galectin-1 expression to increase susceptibility to carbohydrate-dependent induction of anoikis in pancreatic carcinoma cells

Expression of the tumor suppressor p16(INK4a) after stable transfection can restore the susceptibility of epithelial tumor cells to anoikis. This property is linked to increases in the expression and cell-surface presence of the fibronectin receptor. Considering its glycan chains as pivotal signals, we assumed an effect of p16(INK4a) on glycosylation. To test this hypothesis for human Capan-1 pancreatic carcinoma cells, we combined microarray for selected glycosyltransferase genes with 2D chromatographic glycan profiling and plant lectin binding. Major differences between p16-positive and control cells were detected. They concerned expression of beta1,4-galactosyltransferases (down-regulation of beta1,4-galactosyltransferases-I/V and up-regulation of beta1,4-galactosyltransferase-IV) as well as decreased alpha2,3-sialylation of O-glycans and alpha2,6-sialylation of N-glycans. The changes are compatible with increased beta(1)-integrin maturation, subunit assembly and binding activity of the alpha(5)beta(1)-integrin. Of further functional relevance in line with our hypothesis, we revealed differential reactivity towards endogenous lectins, especially galectin-1. As a result of reduced sialylation, the cells' capacity to bind galectin-1 was enhanced. In parallel, the level of transcription of the galectin-1 gene increased conspicuously in p16(INK4a)-positive cells, and even figured prominently in a microarray on 1996 tumor-associated genes and in proteomic analysis. The cells therefore gain optimal responsiveness. The correlation between genetically modulated galectin-1 levels and anoikis rates in engineered transfectants inferred functional significance. To connect these findings to the fibronectin receptor, galectin-1 was shown to be co-immunoprecipitated. We conclude that p16(INK4a) orchestrates distinct aspects of glycosylation that are relevant for integrin maturation and reactivity to an endogenous effector as well as the effector's expression. This mechanism establishes a new aspect of p16(INK4a) functionality.

Substitutions in the N-glycan core as regulators of biorecognition: the case of core-fucose and bisecting GlcNAc moieties

Core fucosylation and the bisecting N-acetylglucosamine residue are prominent natural substitutions of the N-glycan core. To address the issue of whether these two substituents can modulate ligand properties of complex-type biantennary N-glycans, we performed chemoenzymatic synthesis of the respective galactosylated and alpha2,3/6-sialylated N-glycans. Neoglycoproteins were then produced to determine these glycans' reactivities with sugar receptors in solid-phase assays and with tumor cells in vitro as well as their in vivo biodistribution profiles in mice. Slight protein-type-dependent changes were noted in lectin binding, including adhesion/growth-regulatory galectins as study objects, when the data were related to properties of N-glycans without or with only one core substituent. Monitoring binding in vitro revealed cell-type-dependent changes. They delimited the ligand activity of this glycan type from that of chains with un- and monosubstituted cores. A markedly prolonged serum half-life was conferred to the neoglycoprotein by the galactose-terminated N-glycan, which together with increased organ retention of all three neoglycoproteins underscores the conspicuous relevance for glycoengineering of pharmaproteins. The predominant presentation of the two branches in the disubstituted N-glycan as extended (alpha1,3-antenna) and backfolded (alpha1,6-antenna) forms, revealed by molecular dynamics simulations, can underlie the measured characteristics. These results obtained by a combined strategy further support the concept of viewing N-glycan core substitutions as non-random additions which exert a modulatory role on ligand properties. Moreover, our data inspire us to devise new, non-natural modifications to realize the full potential of glycoengineering for diagnostic and therapeutic purposes.

Stromal fibroblasts from basal cell carcinoma affect phenotype of normal keratinocytes

BACKGROUND

Epithelial-mesenchymal interactions are important not only to direct the course of prenatal development of skin and its appendages but also to influence the behaviour of transformed epithelial cells.

OBJECTIVES

Evaluation of the role of stromal fibroblasts on the phenotype of epithelial cells of basal cell carcinoma (BCC).

METHODS

The phenotype of human BCC was compared with the in vitro model where the growth and phenotypic pattern of normal human keratinocytes were monitored in co-culture with fibroblasts prepared from stroma of BCC (BCCFs), with normal dermal fibroblasts or with two established fibroblast lines. We visualized the expression of a panel of keratins, three types of endogenous lectin [galectin (Gal)-1, Gal-3 and Gal-7], binding sites for Gal-1 and Gal-3, a proliferation marker Ki67, nucleolar protein nucleostemin (NuclS) and membrane protein Ber-EP4. A phenotype and karyotype of BCCFs were also monitored. BCCFs were also grafted to NOD/LtSz-Rag1(null) mice to evaluate their malignant potential.

RESULTS

Prolonged cultivation of BCCFs has led to morphological changes, loss of contact inhibition, loss of fibroblast surface antigens and progressive aneuploidity. However, a fully malignant phenotype did not develop as these cells did not form tumours in immunodeficient mice. Co-culture of BCCFs with normal keratinocytes in vitro led to their phenotypical changes resembling those in BCC, namely, expression of keratin 19. These keratinocytes also strongly express nuclear binding sites for Gal-1 and NuclS. This phenotype was not observed when normal keratinocytes were cultured with nontumour-originated fibroblasts.

CONCLUSIONS

These observations indicate that BCCFs may differ from normal fibroblasts and may play a regulatory role in BCC biology.

Respiratory consequences of obesity--an overview

At the beginning of the 21st century obesity has become the leading chronic disease in the world. It is a major cause of morbidity mainly in the metabolic and cardiovascular areas. Moreover, it has progressively emerged as an important risk factor for respiratory diseases, a field that is often neglected. In this article, we reviewed the current understanding of the influence of obesity in adulthood on respiratory function, obstructive sleep apnoea-hypopnoea, obesity hypoventilation syndrome and asthma.

High level of galectin-1 expression is a negative prognostic predictor of recurrence in laryngeal squamous cell carcinomas

Monitoring of gene-expression profiles is assumed to refine tumor characterization of laryngeal squamous cell carcinomas (LSCCs) with a therapeutic perspective. This is especially expected for adhesion/growth-regulatory effectors such as galectins, a class of endogenous lectins. Using computer-assisted microscopy, we investigated the prognostic value contributed by the quantitative determination of the immunohistochemical levels of expression of galectin-1, -3 and -7 in a series of 62 LSCCs including 42 low- and 20 high-stage LSCCs. As galectin-1 may have a key role leading to a tumor escape from immune surveillance, we also investigated whether or not the level of galectin-1 expression correlated with lymphocyte infiltration in LSCCs. The immunohistochemical determination of expression of galectin-1 is of prognostic value in human squamous laryngeal cancers. LSCCs that display high levels of galectin-1 have worse prognoses than laryngeal cancers with low levels of galectin-1 expression. Elevation of galectin-1 levels in laryngeal cancers can contribute to the process of tumor immune escape by killing the activated T-cells and other protumoral activities such as promoting motility or activity of oncogenic H-Ras proteins. The quantitative determination of galectin-1 in LSCCs is an independent prognostic marker when opposed to TNM staging. It has the potential to identify patients unlikely to benefit from T-cell-mediated immunotherapy, although the definitive effector function from its pro- and antitumoral activity profile has not been delineated.

The conformation of the C-glycosyl analogue of N-acetyl-lactosamine in the free state and bound to a toxic plant agglutinin and human adhesion/growth-regulatory galectin-1

The conformational behavior of the C-glycoside analogue of N-acetyl-lactosamine, beta-C-Gal-(1-->4)-beta-GlcNAc-OMe, 1, has been studied using a combination of molecular mechanics calculations and NMR spectroscopy (J and NOE data). It is shown that the C-disaccharide populates three distinctive conformational families in solution, the major one being the anti-psi conformation. Of note, this conformation is only marginally populated for the O-disaccharide. Due to its conspicuous role in the regulation of adhesion, growth and tissue invasion of tumors and its avid binding to N-acetyl-lactosamine human, galectin-1 was tested as a receptor. This endogenous lectin recognizes a local minimum of 1, the syn-PhiPsi conformer, and thus a conformational selection process is correlated with the molecular recognition event.