Endogenous galactoside-binding lectins: a new class of functional tumor cell surface molecules related to metastasis

90K (Mac-2 BP) and galectins in tumor progression and metastasis

Galectins and their ligands have been implicated in cell transformation and cancer metastasis, and found to have prognostic value. Mac-2 BP, also known as 90K, is a highly glycosylated, secreted protein extensively studied in human cancer, which binds galectin-1, galectin-3 and galectin-7. High expression levels of 90K are associated with a shorter survival, the occurrence of metastasis or a reduced response to chemotherapy in patients with different types of malignancy. The mechanisms underlying the prognostic significance of 90K and galectins in cancer are far from being understood, although they may be related to the ability of these proteins to interact and, to some extent, modulate cell-cell and cell-matrix adhesion and apoptosis. The resulting scenario is even more complex, as data have been presented that all these proteins might be associated with either a positive or a negative outcome of the patients. It is hypothesised that different galectins and galectin ligands with overlapping or opposite functions, expressed in different tumors during the different steps of the metastatic cascade might play a crucial role in tumor progression.

Galectin-3: presurgical marker of thyroid follicular epithelial cell-derived carcinomas

Preoperative follicular lesion characterisation represents an unsolved diagnostic problem in thyroid nodular disease. Although fine-needle aspiration biopsy is the most reliable preoperative diagnostic procedure, it shows inherent limitations in differentiating adenoma from follicular carcinoma and, sometimes, follicular variants of papillary carcinoma. Galectin-3 cytoplasmic neoexpression has been proposed as a peculiar feature of thyroid malignant cells, easily detectable in cytological and histological samples. The aim of this study was to re-evaluate the galectin-3 expression in a large sample of thyroid lesions using an immunohistocytochemical biotin-free detection system and a specific anti-human-galectin-3 monoclonal antibody in order to avoid the interference of technical factors, a cause of conflicting results recently reported by some authors. We analysed galectin-3 expression of 39 follicular carcinomas, 26 papillary carcinomas, and 105 adenomas in both cell-block samples and their histological counterparts. All cell-block and histological papillary carcinoma samples showed high levels of galectin-3 immunoreactivity. Thirty-four follicular carcinomas were positive, whereas 5 were negative in cell-blocks but positive in their histological counterparts. Twelve out of 105 adenomas expressed galectin-3 in cell-blocks and histological samples. The diagnostic accuracy of preoperative galectin-3 evaluation in adenomas vs follicular carcinomas was 90.0%. Galectin-3 expression was also investigated in 22 minimally-invasive follicular carcinomas. All of them showed galectin-3 immunoreactivity in both cytological and histological specimens with the exception of two cases, where galectin-3 positivity was observed only in the surgical material. The routine correct use of galectin-3, by increasing the diagnostic accuracy of conventional cytology, improves the management of thyroid nodules and can lead to a sensitive reduction of useless thyroid surgeries.

A mushroom (Ganoderma capense) lectin with spectacular thermostability, potent mitogenic activity on splenocytes, and antiproliferative activity toward tumor cells

An 18-kDa lectin, with an N-terminal sequence displaying slight similarity to some lectins and fungal immunomodulatory proteins, was isolated from the mushroom Ganoderma capense (Lloyd) Teng. It exhibited more potent mitogenic activity than that of concanavalin A toward mouse splenocytes, and antiproliferative activity toward leukemia (L1210 and M1) cells and hepatoma (HepG2) cells. The isolation procedure entailed ion exchange chromatography on Q-Sepharose, fast protein liquid chromatography (FPLC)-ion exchange chromatography on Mono S, and FPLC-gel filtration on Superdex 75. D(+)-galactose and D(+)-galactosamine specifically inhibited the hemagglutinating activity of the lectin. The hemagglutinating activity of the lectin was not affected over the temperature range 0-100 degrees C and after exposure to 100 degrees C for 60min. The activity was stable in the pH range of 4-11, and after incubation with solutions of various chlorides (from 3.125 to 50mM) including NaCl, KCl, CaCl(2), MgCl(2), ZnCl(2), MnCl(2), and AlCl(3). However, it was potentiated by 12.5-50mM FeCl(3). The lectin was devoid of HIV-1 reverse transcriptase inhibitory and antifungal activities.

Isolation and characterization of a novel lectin from the wild mushroom Xerocomus spadiceus

A lectin was isolated from extracts of fruiting bodies of the mushroom Xerocomus spadiceus using a procedure that involved ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on CM-cellulose, and gel filtration by fast protein liquid chromatography on Superdex 75. The lectin was unadsorbed on DEAE-cellulose and Affi-gel blue gel and adsorbed on CM-Sepharose. The lectin was capable of eliciting an approximately four-fold stimulation of mitogenic response in murine splenocytes. The hemagglutinating activity was stable up to 60 degrees C, halved at 70 degrees C, reduced to 25% at 75 degrees C and dwindled to an undetectable level at 80 degrees C. The activity remained unaltered in the presence of various divalent (Ca2+, Mg2+, Zn2+ and Mn2+) chlorides up to a salt concentration of 10 mM except in the case of ZnCl2. FeCl3 up to a concentration of 10 mM did not affect the hemagglutinating activity of the lectin. The hemagglutinating activity of the lectin was doubled in the presence of 5 mM AlCl3 or 10 mM ZnCl2 and quadrupled in the presence of 10 mM AlCl3. The activity was reduced in the presence of HCl and NaOH. Among the large number of carbohydrates tested, only inulin was able to inhibit the hemagglutinating activity of the lectin.

Design of a multivalent galactoside ligand for selective targeting of HPMA copolymer–doxorubicin conjugates to human colon cancer cells

N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymers have been shown to be efficient carriers for anticancer drugs because of their versatile chemistry and good biocompatibility. As demonstrated with hepatocytes, targeting efficacy of anticancer drugs could be further improved when the drug (doxorubicin) was conjugated to HPMA copolymers with biorecognisable groups, such as simple carbohydrates. The present study was devised to learn whether the cluster (multivalent) construction of carbohydrate residues could improve the targeting capability of HPMA copolymer-doxorubicin (DOX) conjugates towards human colon adenocarcinoma cells. DOX was linked via a lysosomally degradable tetrapeptide sequence to HPMA copolymers bearing galactosamine (GalN), lactose (Lac), or multivalent galactose residues (TriGal) to produce targetable polymeric drug carriers. The effect of the type of sugar moiety and its three-dimensional cluster arrangement on biorecognition by three human colon-adenocarcinoma cell lines was studied. The role of galectin-3 in the biorecognition of HPMA copolymer conjugates was explored. Biorecognition of the targetable (glycoside-bearing) conjugates decreased their IC(50) doses in comparison to the non-targetable (non-glycosylated) conjugates. The biorecognition of the TriGal-containing HPMA copolymer-doxorubicin conjugate by the cells was superior with concomitant decrease of its IC(50) doses. It is suggested that the increased cytotoxicity of the glycosylated HPMA-copolymer-DOX conjugates toward human colon-adenocarcinoma cells was caused by their biorecognition and effective internalisation via receptor-mediated endocytosis. All three human colon adenocarcinoma cell lines tested, Colo-205, SW-480 and SW-620, expressed the galectin-3 protein and the galectin-3-specific RNA. However, contrary to expectation, Colo-205 cells did not express a detectable amount of galectin-3 on the cell surface. This suggests that the binding of the glycoside-bearing HPMA copolymer-DOX conjugates to the cells was mediated not only by galectin-3. We conclude that targeting of the anticancer agent, doxorubicin, using HPMA copolymer conjugates bearing multivalent galactoside residues can improve their cytotoxicity.

Modified citrus pectin (MCP) increases the prostate-specific antigen doubling time in men with prostate cancer: a phase II pilot study

This trial investigated the tolerability and effect of modified citrus pectin (Pecta-Sol) in 13 men with prostate cancer and biochemical prostate-specific antigen (PSA) failure after localized treatment, that is, radical prostatectomy, radiation, or cryosurgery. A total of 13 men were evaluated for tolerability and 10 for efficacy. Changes in the prostate-specific antigen doubling time (PSADT) of the 10 men were the primary end point in the study. We found that the PSADT increased (P-value<0.05) in seven (70%) of 10 men after taking MCP for 12 months compared to before taking MCP. This study suggests that MCP may lengthen the PSADT in men with recurrent prostate cancer.

Animal lectins: from initial description to elaborated structural and functional classification

The genetic code connects the two biochemical dimensions of nucleic acids and proteins. Theoretical calculations on coding capacity reveal that oligosaccharides as hardware surpass peptides by more than seven orders of magnitude based on hexamer synthesis. Thus, the sugar code establishes the third dimension of biological information transfer. Using carbohydrate-binding proteins (lectins, enzymes and antibodies) the information content of such epitopes is decoded. Currently, five families of animal lectins are defined in structural terms. i.e. the C-type, I-type and P-type groups, the galectins and the pentraxins. They are involved in intra- and intercellular glycan routing using oligosaccharides as postal-code equivalents and acting as defense molecules homing in on foreign or aberrant glycosignatures, as crosslinking agent in biosignaling and as coordinator of transient or firm cell-cell/cell-matrix contacts. By delineating the driving forces toward complex formation, knowledge about the causes for specificity can be turned into design of custom-made high-affinity ligands for clinical application, e.g. in anti-adhesion therapy, drug targeting or diagnostic histopathology.

Homodimeric galectin-7 (p53-induced gene 1) is a negative growth regulator for human neuroblastoma cells

The extracellular functions of galectin-7 (p53-induced gene 1) are largely unknown. On the surface of neuroblastoma cells (SK-N-MC), the increased GM1 density, a result of upregulated ganglioside sialidase activity, is a key factor for the switch from proliferation to differentiation. We show by solid-phase and cell assays that the sugar chain of this ganglioside is a ligand for galectin-7. In serum-supplemented proliferation assays, galectin-7 reduced neuroblastoma cell growth without the appearance of features characteristic for classical apoptosis. The presence of galectin-3 blocked this effect, which mechanistically resembles that of galectin-1. By virtue of carbohydrate binding, galectin-7 thus exerts neuroblastoma growth control similar to galectin-1 despite their structural differences. In addition to p53-linked proapoptotic activity intracellularly, galectin-7, acting as a lectin on the cell surface, appears to be capable of reducing cancer cell proliferation in susceptible systems.

Galectin-3 and oncofetal-fibronectin expression in thyroid neoplasia as assessed by reverse transcription-polymerase chain reaction and immunochemistry in cytologic and pathologic specimens

Oncofetal fibronectin (onfFN) and galectin-3 (Gale-3) have been proposed as possible tools for the preoperative diagnosis of thyroid carcinomas, based on the finding that the expression of both onfFN and Gale-3 are significantly increased in papillary and anaplastic carcinomas, compared to normal thyroid tissues and follicular adenomas. In this study we analyzed the expression of these markers by immunochemical and molecular analysis of benign and malignant thyroid tumors. Sixty-five thyroid nodules, consisting of 20 follicular adenomas (FAs) and 45 papillary thyroid carcinomas (PTCs) at final histology were examined. At the molecular level, among the 45 PTCs, 44 (97.8%) showed a variable level of onfFN mRNA, while 8 of the 20 (40%) adenomas expressed the same marker. Similar results have been found analyzing Gale-3 expression: 97.8% of PTC and 55% of FAs were positive for this marker. Immunohistochemistry (IHC) for Gale-3 was positive in 42 of 45 (93.3%) PTC tissues. Staining was invariably confined to the cytoplasm, with a homogeneous distribution in the large majority of the neoplastic cells. The 3 negative cases (6.7%) were represented by 2 classic variants of PTC and 1 follicular variant of PTC. Eighteen of the 20 (90.0%) adenomas stained negative for Gale-3. A significant association was found between positive staining and malignant phenotype (p < 0.0001). Gale-3 protein expression was also performed on samples obtained by ex vivo fine-needle aspiration (FNA) in 35 PTCs by immunocytochemistry (ICC). Immunoreactivity was present in 32 (91.0%) and negative in 3 (8.8%) cases. With the exception of 1 case (negative by ICC and positive by IHC), ICC and IHC were fully concordant. In conclusion, our results indicate that a search for Gale-3 protein overexpression by IIC or ICC, but not by reverse transcription-polymerase chain reaction (RT-PCR), may yield an additional marker of malignant potential of thyroid nodular lesions, and may be a useful adjunct to the currently available diagnostic tools for the preoperative diagnosis of malignant thyroid tumors.

Expression of galectin-3 in skeletal tissues is controlled by Runx2

The beta-galatoside-specific lectin galectin-3 is expressed in vivo in osteoblasts as well as in epiphyseal cartilage. Here we show that in vitro, galectin-3 expression is up-regulated in the preosteoblastic cell line MC3T3-E1 during the matrix maturation stage of the osteoblast developmental sequence. Expression persists into late differentiation stages when the mature osteoblastic phenotype is established. The skeletal expression pattern of galectin-3 overlaps at many sites with that of the transcription factor Runx2. Runx2 is a key regulator of osteoblast development and necessary for chondrocyte differentiation in the growth plate. Both human and mouse galectin-3 promoters contain putative Runx-binding sites. The constitutive or inducible forced expression of Runx2 is sufficient for the onset of galectin-3 transcription in the mesenchymal precursor cell line C3H10T1/2. Moreover, Runx2 is able to bind to at least two sites in the galectin-3 promoter region. The crucial role of Runx2 was confirmed in Runx2-deficient mice, which are devoid of galectin-3 expression in skeletal cells. The overlapping expression pattern of galectin-3 with the other two members of the Runt family of transcription factors (Runx1 and Runx3) points to a potential regulation of the galectin-3 gene (LGALS3) by these factors in hematopoietic, skin, and dorsal root ganglial cells.

Galectin-3 expression in hyalinizing trabecular tumors of the thyroid gland

Galectin-3, a beta-galactoside-binding lectin, is overexpressed in many neoplasms and may be useful when differentiating between benign and malignant thyroid neoplasms. Recently, interest has focused on the classification and biologic behavior of hyalinizing trabecular tumors (HTTs). In this study we compared galectin-3 expression in a number of different thyroid neoplasms to gain insight into the biologic behavior of HTT. Formalin-fixed, paraffin-embedded tissues from 153 thyroid neoplasms were stained with a monoclonal antibody to galectin-3. These tumors included 58 HTTs, 60 papillary carcinomas, 21 follicular carcinomas, and 14 follicular adenomas. Reactivity was graded as negative, weak, or strong by three observers. The average patient age was similar in the patients with HTTs, papillary carcinomas, and follicular adenomas. The patients with follicular carcinomas were approximately a decade older than all other groups of patients. All groups of thyroid neoplasms occurred more frequently in female patients. Follow-up revealed metastatic disease in patients with papillary (36.6%) and follicular carcinomas (19%) but not in patients with follicular adenomas or HTTs. Galectin-3 immunostaining showed that 60% of the HTTs were negative or had weak (H) (1+) staining and 40% had strong (2-3+) staining. In the majority of the reactive cases, staining was diffuse and predominantly cytoplasmic. Fifty of the 60 (83%) papillary carcinomas and 11 of the 21 (52%) follicular carcinomas showed strong immunostaining. The immunostaining was also diffuse in the majority of papillary and follicular carcinomas. The strong immunoreactivity seen in most of the carcinomas was in contrast to the relatively weak or negative immunostaining in the majority of follicular adenomas (93%). The immunophenotype of HTT, as characterized by galectin-3 expression, is intermediate between that of benign and malignant thyroid tumors, suggesting that some tumors with strong staining may behave like carcinomas, although this was not noted in our cases. Our study suggests that the variable pattern of galectin-3 expression may reflect a difference in biologic behavior between HTT and papillary thyroid carcinoma.

The role of galactose, lactose, and galactose valency in the biorecognition of N-(2-hydroxypropyl)methacrylamide copolymers by human colon adenocarcinoma cells

PURPOSE

To examine the beta-galactoside and beta-lactoside binding capacity of three human colon-adenocarcinoma cell lines and their sugar specificity, using N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates of galactosamine, lactose, and triantennary galactose.

METHODS

Three types of HPMA copolymers containing the saccharide epitopes galactosamine (P-Gal), lactose (P-Lac), or triantennary galactose (P-TriGal) were synthesized. The relationship between the content of the saccharide moieties, the valency of the galactose residues, and their biorecognition by the cell lines (Colo-205, SW-480, and SW-620) was investigated using flow cytometry and confocal fluorescence microscopy analysis.

RESULTS

The binding of the glycoconjugates to the human colonadenocarcinoma cell lines was dependent on the type and the number of bound sugar residues per macromolecule. The higher the sugar contents in the HPMA copolymers, the higher the extent of binding. Although introduction of galactoside residues into the HPMA copolymer resulted in a significant increase in the binding of the copolymers to the cells, low biorecognition of the lactoside-containing HPMA copolymers by all cell lines used was observed. The trivalent galactoside-containing HPMA copolymers did not yield a notable glycoside cluster effect for the beta-galactoside-binding lectin expressed on human colon-adenocarcinoma cells. Among the various cell line little differences in the extent of binding of the glycopolymers to the cells were observed. The data on the internalization of HPMA copolymer conjugates obtained by confocal fluorescence microscopy correlated well with the flow cytometry analysis of their biorecognition by target cells.

CONCLUSIONS

The lectin-mediated endocytosis of the HPMA glycoconjugates in human colon cancer cell lines suggests their potential use as targeting tools of cytotoxic drugs to colon adenocarcinoma.

Purification and characterization of a new lectin from the hard roe of skipjack tuna, Katsuwonus pelamis

Fish eggs are known as a rich source of lectins. In this study we purified and characterized a lectin from unfertilized Katsuwonus pelamis hard roe. K. pelamis lectin (KPL) was purified by separation into two fractions above and below the molecular weight of 10kDa using ultramembrane, gel filtration on a Sephadex G-100, and affinity chromatography on an asialofetuin-Sepharose 4B. KPL is a glycoprotein of 140kDa, composed mainly of aspartic acid, glycine, phenylalanine, glutamic acid, threonine and serine residues. Analysis of the carbohydrate composition by gas-liquid chromatography indicated that carbohydrates constituted 14% of the total weight and this 14% is comprised of mannose, galactose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, fucose, arabinose and sialic acid. The lectin is comprised of four subunits. These subunits have a molecular mass corresponding to 35kDa. KPL specifically agglutinated human blood type A erythrocytes and, in a hemagglutination inhibitory test, the potent inhibitors were D-galactose, lactose, lactosamine, asialofetuin, N-acetyl-D-galactosamine, O-serinyl-2-acetamido-2-deoxy-alpha-D-galactopyranoside and O-serinyl-2-acetamido-2-deoxy-beta-D-galactopyranoside (O-serinyl-beta-D-GalNAc). The first 10 residues of the N-terminal region were determined as PVELCDAKCT. Furthermore it was determined that the hemagglutinating activity of KPL was dependent on divalent metal cations and that the optimum activity of KPL was exhibited at 40 degrees C and pH 6.0-8.5 in the presence of Ca2+.

Upregulation of galectins-1 and -3 in human colon cancer and their role in regulating cell migration

To probe the potential contribution of beta-galactoside-contributing epitopes and receptor proteins (gal-1 and gal-3) to colon malignancy, we first examined the expression of galectins and binding sites in clinical specimens by lectin and immunohistochemistry. Sixty-seven colonic surgical resections were studied, including 10 normal, 10 mild dysplasias, 10 severe dysplasias and 37 cancers. gal-1 and gal-3 were expressed in variable amounts in the epithelial cells and the connective tissue of normal colon. Their expression significantly increased with the degree of dysplasia, suggesting that gal-1 and gal-3 and their binding sites are related to malignant progression, while gal-8 has been associated with suppressor activity. To study the functional aspects, the influence of these galectins on the migration of 4 human colorectal cancer cell lines (HCT-15, LoVo, DLD-1, CoLo201) was studied. In agreement with histopathologic monitoring, these tumor cells were found to produce gal-3, while only CoLo201 was positive for gal-1. Except for DLD-1 and gal-1, the lines exhibited gal-1 binding sites on the surface, prompting study by computer-assisted videomicroscopy of the effect on cell migration of the presence of galectin on the culture substrate. The level of cell migration for HCT-15, LoVo and CoLo201 cells was significantly reduced by 0.15 microg/cm(2) gal-1, and the presence of a blocking antibody at least reduced this effect. gal-3 significantly reduced cell migration in all 4 of the in vitro cell lines.

The hypercoagulable state of malignancy: pathogenesis and current debate

A hypercoagulable or prothrombotic state of malignancy occurs due to the ability of tumor cells to activate the coagulation system. It has been estimated that hypercoagulation accounts for a significant percentage of mortality and morbidity in cancer patients. Prothrombotic factors in cancer include the ability of tumor cells to produce and secrete procoagulant/fibrinolytic substances and inflammatory cytokines, and the physical interaction between tumor cell and blood (monocytes, platelets, neutrophils) or vascular cells. Other mechanisms of thrombus promotion in malignancy include nonspecific factors such as the generation of acute phase reactants and necrosis (i.e., inflammation), abnormal protein metabolism (i.e., paraproteinemia), and hemodynamic compromise (i.e., stasis). In addition, anticancer therapy (i.e., surgery/chemotherapy/hormone therapy) may significantly increase the risk of thromboembolic events by similar mechanisms, e.g., procoagulant release, endothelial damage, or stimulation of tissue factor production by host cells. However, not all of the mechanisms for the production of a hypercoagulable state of cancer are entirely understood. In this review, we attempt to describe what is currently accepted about the pathophysiology of the hypercoagulable state of cancer. We also discuss whether or not to screen patients with idiopathic deep venous thrombosis for an underlying malignancy, and whether this would be beneficial to patients. It is hoped that a better understanding of these mechanisms will ultimately lead to the development of more targeted treatment to prevent thromboembolic complications in cancer patients. It is also hoped that antithrombotic strategies may also have a positive effect on the process of tumor growth and dissemination.

Oligosaccharide specificity of galectins: a search by frontal affinity chromatography

Galectins are widely distributed sugar-binding proteins whose basic specificity for beta-galactosides is conserved by evolutionarily preserved carbohydrate-recognition domains (CRDs). Although they have long been believed to be involved in diverse biological phenomena critical for multicellular organisms, in only few a cases has it been proved that their in vivo functions are actually based on specific recognition of the complex carbohydrates expressed on cell surfaces. To obtain clues to understand the physiological roles of diverse members of the galectin family, detailed analysis of their sugar-binding specificity is necessary from a comparative viewpoint. For this purpose, we recently reinforced a conventional system for frontal affinity chromatography (FAC) [J. Chromatogr., B, Biomed. Sci. Appl. 771 (2002) 67-87]. By using this system, we quantitatively analyzed the interactions at 20 degrees C between 13 galectins including 16 CRDs originating from mammals, chick, nematode, sponge, and mushroom, with 41 pyridylaminated (PA) oligosaccharides. As a result, it was confirmed that galectins require three OH groups of N-acetyllactosamine, as had previously been denoted, i.e., 4-OH and 6-OH of Gal, and 3-OH of GlcNAc. As a matter of fact, no galectin could bind to glycolipid-type glycans (e.g., GM2, GA2, Gb3), complex-type N-glycans, of which both 6-OH groups are sialylated, nor Le-related antigens (e.g., Le(x), Le(a)). On the other hand, considerable diversity was observed for individual galectins in binding specificity in terms of (1) branching of N-glycans, (2) repeating of N-acetyllactosamine units, or (3) substitutions at 2-OH or 3-OH groups of nonreducing terminal Gal. Although most galectins showed moderately enhanced affinity for branched N-glycans or repeated N-acetyllactosamines, some of them had extremely enhanced affinity for either of these multivalent glycans. Some galectins also showed particular preference for alpha1-2Fuc-, alpha1-3Gal-, alpha1-3GalNAc-, or alpha2-3NeuAc-modified glycans. To summarize, galectins have evolved their sugar-binding specificity by enhancing affinity to either "branched", "repeated", or "substituted" glycans, while conserving their ability to recognize basic disaccharide units, Galbeta1-3/4GlcNAc. On these bases, they are considered to exert specialized functions in diverse biological phenomena, which may include formation of local cell-surface microdomains (raft) by sorting glycoconjugate members for each cell type.

Lack of expression of galectin-3 is associated with a poor outcome in node-negative patients with laryngeal squamous-cell carcinoma

PURPOSE

Galectin-3 is a pleiotropic carbohydrate-binding protein participating in a variety of normal and pathologic processes, including cancer progression. This study was aimed at evaluating the prognostic value of galectin-3 expression in node-negative laryngeal squamous-cell carcinoma (SCC).

PATIENTS AND METHODS

Galectin-3 expression was analyzed by immunohistochemistry using M3/38 monoclonal antibody, in a single-institution series of 73 node-negative laryngeal SCC patients (median follow-up, 52 months; range, 2 to 90 months).

RESULTS

Forty-two (57.5%) of 73 patients expressed galectin-3. Galectin-3 expression was positively associated with tumor keratinization and histologic grade. A significant correlation was found between galectin-3 tumor positivity and longer relapse-free and overall survival. In univariate analysis, high-grade (grade 3 or 4) tumors, nonkeratinizing tumors, and galectin-3-negative tumors showed a significantly increased risk of relapse and death. In multivariate analysis, only galectin-3 expression retained an independent prognostic significance for both relapse-free and overall survival.

CONCLUSION

We conclude that the absence of galectin-3 expression is an independent negative prognostic marker in laryngeal SCC patients. Thus, histochemical detection of galectin-3 in these tumors could be useful for the selection of node-negative patients with potentially unfavorable outcomes, to establish adjuvant therapy protocols.

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.

Diagnostic utility of galectin-3 and CD26/DPPIV as preoperative diagnostic markers for thyroid nodules

The aim of this study was to search for diagnostic markers that could correctly identify thyroid nodular lesions requiring urgent surgical treatment. We investigated whether galectin-3 and dipeptidyl peptidase IV (CD26/DPPIV) could be potential markers for improving the diagnostic accuracy of conventional cytology. Seventy-nine patients with histologically proven thyroid diseases were analyzed. The immunocytochemical staining results showed galectin-3 expression in neoplastic cells of all 37 papillary carcinomas, five of six follicular carcinomas, all three anaplastic carcinomas, one of three medullary carcinomas, and two of 14 follicular adenomas. All 16 adenomatous goiters were negative for galectin-3 immunostaining. On the other hand, all 37 papillary carcinomas, all six follicular carcinomas, and one of three anaplastic carcinomas revealed CD26/DPPIV expression, whereas all three medullary carcinomas were negative. Among benign thyroid lesions, four of 14 follicular adenomas and two of 16 adenomatous goiters exhibited varying degrees of immunoreactivity for CD26/DPPIV. RT-PCR analysis demonstrated overexpression of galectin-3 and CD26/DPPIV mRNAs in all six papillary and all three follicular carcinomas analyzed, whereas the mRNA expressions of these molecules were barely or not detectable in benign thyroid lesions and normal thyroid tissues, except for one case of follicular adenoma. In conclusion, we demonstrate that galectin-3 and CD26/DPPIV were consistently coexpressed at protein and mRNA levels in differentiated thyroid carcinomas. We propose that combined immunostaining for galectin-3 and CD26/DPPIV in the preoperative evaluation of thyroid nodules may play a role in accurate cytodiagnosis.

Galectin-3 phosphorylation is required for its anti-apoptotic function and cell cycle arrest

Galectin-3, a beta-galactoside-binding protein, is implicated in cell growth, adhesion, differentiation, and tumor progression by interactions with its ligands. Recent studies have revealed that galectin-3 suppresses apoptosis and anoikis that contribute to cell survival during metastatic cascades. Previously, it has been shown that human galectin-3 undergoes post-translational signaling modification of Ser(6) phosphorylation that acts as an "on/off" switch for its sugar-binding capability. We questioned whether galectin-3 phosphorylation is required for its anti-apoptotic function. Serine to alanine (S6A) and serine to glutamic acid (S6E) mutations were produced at the casein kinase I phosphorylation site in galectin-3. The cDNAs were transfected into a breast carcinoma cell line BT-549 that innately expresses no galectin-3. Metabolic labeling revealed that only wild type galectin-3 undergoes phosphorylation in vivo. Expression of Ser(6) mutants of galectin-3 failed to protect cells from cisplatin-induced cell death and poly(ADP-ribose) polymerase from degradation when compared with wild type galectin-3. The non-phosphorylated galectin-3 mutants failed to protect cells from anoikis with G(1) arrest when cells were cultured in suspension. In response to a loss of cell-substrate interactions, only cells expressing wild type galectin-3 down-regulated cyclin A expression and up-regulated cyclin D(1) and cyclin-dependent kinase inhibitors, i.e. p21(WAF1/CIP1) and p27(KIP1) expression levels. These results demonstrate that galectin-3 phosphorylation regulates its anti-apoptotic signaling activity.

Galectin-3-mediated adherence ofProteus mirabilisto Madin-Darby canine kidney cells

Proteus mirabilis is an important cause of urinary tract infections (UTIs) and can result in acute pyelonephritis. Proteus mirabilis expresses several, morphologically distinct, fimbrial species, and previous studies have shown that the nonagglutinating fimbriae (NAF) mediate bacterial adherence to a number of cell lines, including Madin-Darby canine kidney (MDCK) cells. Immunoblot overlay analysis of the plasma membrane fraction from MDCK cells with purified NAF revealed a 34-kDa band, which has been analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Database search identified galectin-3 as a potential protein candidate. Immunocytochemical assay of MDCK cells with a galectin-3-specific monoclonal antibody, anti-Mac-2, confirmed its presence on the plasma membrane extracellular surface. Preincubation of P. mirabilis with anti-Mac-2 monoclonal antibodies, specific for galectin-3, resulted in the inhibition of bacterial binding to MDCK cells. These data suggest a role for galectin-3, interacting with appropriately glycosylated surface receptors and P. mirabilis fimbriae, as a mediator of bacterial adherence in vitro.Key words: bacterial adherence, fimbriae, galectin-3, mass spectrometry.

Genetic basis of human breast cancer metastasis

Once cancer cells have spread and formed secondary masses, breast cancers are largely incurable even with state-of-the-art medicine. To improve diagnosis and therapy, better markers are needed to distinguish cells which have a high probability for causing clinically relevant, macroscopic metastases. In this review, we summarize the several genes that regulate breast cancer metastasis. Two categories of genes are presented--metastasis activator (ras, MEK1, mta1, proteinases, adhesion molecules, chemoattractants/receptors, autotaxin, PKC, S100A4, RhoC, osteopontin) and metastasis suppressor (Nm23, E-cadherin, TIMPs, KiSS1, Kai1, Maspin, MKK4, BRMS1). While the mechanisms of action for most of these genes are not fully elucidated, some clues are emerging and are presented.

Galectin-8 Functions as a Matricellular Modulator of Cell Adhesion

The interaction of cells with the extracellular matrix regulates cell adhesion and motility. Here we demonstrate that different cell types adhere and spread when cultured in serum-free medium on immobilized galectin-8, a mammalian beta-galactoside-binding protein. At maximal doses, galectin-8 is equipotent to fibronectin in promoting cell adhesion and spreading. Cell adhesion to immobilized galectin-8 is mediated by sugar-protein interactions with integrins, and galectin-8 triggers integrin-mediated signaling cascades including Tyr phosphorylation of focal adhesion kinase and paxillin. Cell adhesion is potentiated in the presence of Mn(2+), whereas it is interrupted in the presence of soluble galectin-8, integrin beta(1) inhibitory antibodies, EDTA, or thiodigalactoside but not by RGD peptides. Furthermore, cells readily adhere onto immobilized monoclonal galectin-8 antibodies, which are equipotent to integrin antibodies in promoting cell adhesion. Cell adhesion to immobilized galectin-8 is partially inhibited by serum proteins, suggesting that complex formation between immobilized galectin-8 and serum components generates a matrix that is less supportive of cell adhesion. Accordingly, cell motility on immobilized galectin-8 readily takes place in the presence of serum. Truncation of the C-terminal half of galectin-8, including one of its two carbohydrate recognition domains, largely abolishes its ability to modulate cell adhesion, indicating that both carbohydrate recognition domains are required to maintain a functional form of galectin-8. Collectively, our findings implicate galectin-8 as a physiological modulator of cell adhesion. When immobilized, it functions as a matrix protein equipotent to fibronectin in promoting cell adhesion by ligation and clustering of cell surface integrin receptors. In contrast, when present in excess as a soluble ligand, galectin-8 (like fibronectin) forms a complex with integrins that negatively regulates cell adhesion. Because of its dual effects on the adhesive properties of the cells and its association with fibronectin, galectin-8 might be considered a novel type of matricellular protein.

Cell surface-expressed Thomsen-Friedenreich antigen in colon cancer is predominantly carried on high molecular weight splice variants of CD44

Increased mucosal expression of TF, the Thomsen-Friedenreich oncofetal blood group antigen (galactose beta1-3 N-acetylgalactosamine alpha-) occurs in colon cancer and colitis. This allows binding of TF-specific lectins, such as peanut agglutinin (PNA), which is mitogenic to the colorectal epithelium. To identify the cell surface TF-expressing glycoprotein(s), HT29 and Caco2 colon cancer cells were surface-labeled with Na[(125)I] and subjected to PNA-agarose affinity purification and electrophoresis. Proteins, approximately 110-180 kDa, present in HT29 but not Caco2 were identified by Western blotting as high molecular weight splice variants of CD44 (CD44v). Selective removal of TF antigen by Streptococcus pneumoniae endo-alpha-N-acetylgalactosaminidase substantially reduced PNA binding to CD44v. Immunoprecipitated CD44v from HT29 cell extracts also expressed sialyl-Tn (sialyl 2-6 N-acetylgalactosaminealpha-). Incubation of PNA 15 microg/ml with HT29 cells caused no additional proliferative effect in the presence of anti-CD44v6 mAb. In colon cancer tissue extracts (N = 3) PNA bound to CD44v but not to standard CD44. These data show that CD44v is a major PNA-binding glycoprotein in colon cancer cells. Because CD44 high molecular weight splice variants are present in colon cancer and inflammatory bowel disease tissue but are absent from normal mucosa, these results may also explain the increased PNA reactivity in colon cancer and inflammatory bowel disease. The coexpression of oncofetal carbohydrate antigens TF and sialyl-Tn on CD44 splice variants provides a link between cancer-associated changes in glycosylation and CD44 splicing, both of which correlate with increased metastatic potential.

Differentiation therapy of human cancer: basic science and clinical applications

Current cancer therapies are highly toxic and often nonspecific. A potentially less toxic approach to treating this prevalent disease employs agents that modify cancer cell differentiation, termed 'differentiation therapy.' This approach is based on the tacit assumption that many neoplastic cell types exhibit reversible defects in differentiation, which upon appropriate treatment, results in tumor reprogramming and a concomitant loss in proliferative capacity and induction of terminal differentiation or apoptosis (programmed cell death). Laboratory studies that focus on elucidating mechanisms of action are demonstrating the effectiveness of 'differentiation therapy,' which is now beginning to show translational promise in the clinical setting.

Galectins structure and function--a synopsis

The 20 or so galectins expected to be found in man, and their many possible functional effects promise a rich and fruitful research field in the future. At present, the biomedically most promising areas for use of galectins or their ligands are in inflammation, immunity, and cancer. Many good stories can be formulated, but the field lacks the cohesion of knowing basic galectin function. The only basic common denominators among galectins are beta-galactoside binding, and the unusual combination of intra- and extracellular expression with non-classical secretion in between. Maybe that is all there is, and nature has used these properties for multiple, otherwise unrelated functions. Then again, maybe there is some deeper common function that has so far been overlooked. If it exists, this probably lies somewhere in the detailed integration of galectin activity in the complexities of cell physiology.

A cell-based drug delivery system for lung targeting: II. Therapeutic activities on B16-F10 melanoma in mouse lungs

The in vitro and in vivo anticancer activities of doxorubicin-loaded B16-F10 murine melanoma cells (DLTC) were evaluated. DLTC showed similar growth-inhibitory effects against live B16-F10 cells with doxorubicin solution in cell culture system, with the IC50 of 0.11 microM and 0.17 microM, respectively. However, DLTC demonstrated higher effectiveness than the free solution in treating mouse lung cancer caused by live B16-F10 cells. Syngeneic C57BL mice were inoculated intravenously with live B16-F10 cells first, and then received daily treatment of intravenous injections of doxorubicin in either DLTC or free solution form. Compared with the control group treated with phosphate-buffered saline, DLTC eradicated almost all the lung cancer colonies (>99%), while the free solution form reduced the colonies by 61%, when the treatment was given at an early stage. If the treatment started after the establishment of micrometastatic colonies in the mouse lungs, DLTC and free solution treatment resulted in 85% and 30% cancer reduction, respectively. Additional experiments demonstrated that the reduction of lung cancer colonies by DLTC was related to the initial treatment time: the earlier the treatment, the greater the effect. In conclusion, DLTC showed better therapeutic outcomes than free solution form in treating lung cancer of our animal model.

A cell-based drug delivery system for lung targeting: I. Preparation and pharmacokinetics

A drug-loaded tumor cell (DLTC) system has been developed for lung metastasis-targeting drug delivery. Doxorubicin was loaded into B16-F10 murine melanoma cells (96 microg/10(6) cells). The loading process led to the death of all the carrier cells. The diameter of DLTC was 15.03+/-2.36 microm (mean +/- SD). The amount and rate of doxorubicin being released from the DLTC mainly depended on the drug loading and carrier cell concentration. Over a 6-month storage in phosphate buffered saline (PBS) at 4 degrees C, the decrease in intracellular drug concentration and the carrier cell number were less than 25% and 5%, respectively. After a bolus injection of 30 microg doxorubicin in either DLTC form or free solution into the mice tail veins, drug deposit in the lung from DLTC was 3.6-fold of that achieved by free drug solution. The latter resulted in higher drug content in liver and spleen. Extensive trypsinization of DLTC reduced its lung targeting effect by 30%, and the density of surface adhesion molecule GM3 on DLTC surface by 25%. In conclusion, this DLTC system demonstrated a lung-targeting activity that may be partially attributed to its specific surface characteristics.

Immunohistochemical detection of galectin-3 in canine gastric carcinomas

Galectin-3 was detected immunohistochemically in nine canine gastric carcinomas. In normal gastric tissue adjacent to the neoplasms, the gastric epithelial cells showed faint immunolabelling for galectin-3, but in all the tumours the neoplastic cells showed moderate to strong immunolabelling. Galectin-3 was localized in the cytoplasm of the normal mucosal cells, whereas it was found in both the cytoplasm and the nucleus of the neoplastic cells. Positive cells typically exhibited dark brown coloration of the nucleus or cytoplasm, without background labelling. The results suggest that galactin-3 has a pathophysiological role in canine gastric carcinoma.

Uncoupling of chondrocyte death and vascular invasion in mouse galectin 3 null mutant bones

Galectin 3 is a beta-galactoside binding protein which localizes to the cytoplasm of proliferative, mature, and hypertrophic chondrocytes in the growth plate cartilage of developing long bones. To elucidate the function of galectin 3 during bone development, we examined the epiphyseal femurs and tibias of fetal mice carrying a null mutation for the galectin 3 gene. Detailed histological and ultrastructural studies identified abnormalities in the cells of the proliferative, mature, and hypertrophic zones and in the extracellular matrix of the hypertrophic zone, as well as a reduction in the total number of hypertrophic chondrocytes. The expression patterns of several chondrocyte and bone cell markers were analyzed and revealed a subtle modification of Ihh expression in the galectin 3 mutant growth plate. A striking difference was observed at the chondrovascular junction where many empty lacunae are present. In addition, large numbers of condensed chondrocytes exhibiting characteristic signs of cell death were found in the late hypertrophic zone, indicating that the rate of chondrocyte death is increased in the mutants. These results suggest a role for galectin 3 as a regulator of chondrocyte survival. In addition, this unique phenotype shows that the elimination of chondrocytes and vascular invasion can be uncoupled and indicates that galectin 3 may play a role in the coordination between chondrocyte death and metaphyseal vascularization.

Galactosyl receptor, a cell surface C-type lectin of normal and tumoral prostate epithelial cells with binding affinity to endothelial cells

BACKGROUND

The mechanism of bone metastasis of prostate cancer involves the interaction of cell surface receptor(s) on cancer cells with ligand(s) on bone marrow endothelial cell surfaces. The rat galactosyl receptor gene generates two mRNA species by differential splicing: one species encodes a protein identical to the minor form of hepatocyte asialoglycoprotein receptor and displays a galactose/N-acetyl-galactosamine-recognition domain; the other encodes a protein with identical intracellular and transmembrane domains but with a different extracellular domain lacking the carbohydrate-recognition domain (CRD). Both proteins appear to coexist as a heterooligomer on the surface of normal mouse, rat, and human prostate epithelial cells and human prostate cancer cells, including the PC-3 cell line. The CRD of galactosyl receptor mediates adhesion of normal and tumoral prostate cells to the surfaces of a human bone marrow endothelial cell line. The use of inhibitors targeting the CRD would be very valuable in hindering the binding of prostate cancer cells to endothelial cells, thus decreasing the incidence of hematogenous metastasis to bone.

METHODS

Molecular biology, immunohistochemistry, flow cytometry, and a cell aggregation assay were used to determine the expression and role of the galactosyl receptor in cell adhesion.

RESULTS

Immunoblotting experiments demonstrated that each component of the heterooligomer has a mass of 54 kDa, ascribed in part to associated carbohydrates. An oligonucleotide probe showed the presence of both galactosyl receptor forms in rat prostate and testis, but not in liver, kidney, and spleen. Antibodies to the CRD and a segment of the nonhomologous extracellular domain of the galactosyl receptor blocked cell adhesion to endothelial cell monolayers.

CONCLUSIONS

The galactosyl receptor provides a valuable target for the development and use of synthetic ligands capable of disrupting endothelial cell-prostate cancer cell interaction, the first step in prostate cancer bone metastasis.

Differential regulation of constitutive and retinoic acid-induced galectin-1 gene transcription in murine embryonal carcinoma and myoblastic cells

Galectin-1 (gal-1), a galactoside-binding lectin, is found in many vertebrate tissues and its expression is regulated during development. We had found that gal-1 expression is increased in F9 murine embryonal carcinoma cells concurrently with induction of differentiation by all-trans retinoic acid (RA). In contrast, gal-1 expression was constitutively high in murine myoblastic C2C12 cells. Therefore, we used these two cell types as models to begin to understand the mechanisms underlying constitutive and RA-induced gal-1 expression. We transfected transiently into F9 cells a series of reporter constructs containing different deletions of the 5' upstream region of the gal-1 gene promoter placed upstream of the chloramphenicol acetyltransferase reporter cDNA and evaluated the activation of transcription by RA treatment. The results indicate that the induction of gal-1 by RA is regulated at least partially at the level of transcription. A strong RA responsiveness region was found within the sequence from -1578 to -1448 upstream of the transcription start site (+1). In contrast, the high constitutive gal-1 expression in C2C12 cells appeared to be mediated by a sequence within the promoter region from -62 to +1, which contains an Sp1 consensus sequence. A gel electrophoretic mobility shift assay indicated that the transcription factor SP1 bound to the gal-1 Sp1 site and mutagenesis of this Sp1 site abolished both the binding of nuclear proteins to the mutated Sp1 site and the high constitutive expression of the gal-1 gene. The results demonstrate that gal-1 expression is cell type-specific and suggest that different factors regulate constitutive and RA-induced gal-1 expression.

Expression of galectin-1 mRNA correlates with the malignant potential of human gliomas and expression of antisense galectin-1 inhibits the growth of 9 glioma cells

Although its precise function has not yet been established, galectin-1 seems to play a role in tumor progression. In this study, we investigated galectin-1 mRNA expression in human glioma specimens and glioma cell lines. Northern blot analysis showed higher galectin-1 mRNA levels in glioma tissues. The 0.7-kb galectin-1 mRNA transcript was detected, and the expression level correlated with the malignant state, from low-grade astrocytoma to glioblastoma. In several human glioma specimens, immunohistochemical examination with antiserum against a synthetic peptide corresponding to the predicted C-terminal sequence of the protein showed high levels of galectin-1 expression. To clarify the correlation between the expression of galectin-1 and the malignancy of gliomas, we examined whether expression of antisense galectin-1 would suppress tumor growth in rat 9L cells that express high levels of galectin-1. The cells were transfected with a plasmid DNA that produces antisense galectin-1 mRNA under the control of the metallothionein promoter, and stable clones expressing low levels of galectin-1 protein in comparison with control clones were isolated. Cells with low levels of galectin-1 displayed dramatic phenotypic changes in their morphology and growth properties compared with vector-transfected control 9L cells. Our data suggest that decreased expression of galectin-1 may arrest the growth of rat 9L cells.

Effects of lectins with different carbohydrate-binding specificities on hepatoma, choriocarcinoma, melanoma and osteosarcoma cell lines

The effects of lectins with different carbohydrate-binding specificities on human hepatoma (H3B), human choriocarcinoma (JAr), mouse melanoma (B16) and rat osteosarcoma (ROS) cell lines were investigated. Cell viability was estimated by uptake of crystal violet. Wheat germ lectin was the lectin with the most deleterious effect on the viability of H3B, JAr and ROS cell lines. The cytotoxicity of lectins with similar sugar-binding specificity to wheat germ lectin, including Maackia amurensis lectin and Solanum tuberosum lectin, was weaker than that of wheat germ lectin. N-acetylgalactosamine-and galactose-binding Tricholoma mongolicum lectin ranked third, after wheat germ lectin and Maackia amurensis lectin, with regard to its effect on H3B, and ranked, together with Maackia amurensis lectin, as the lectins with the second most pronounced effects on ROS. However, the cytotoxic effects of Tricholoma mongolicum lectin on JAr were much weaker than those of Maackia amurensis lectin, Solanum tuberosum lectin and Anguilla anguilla lectin. Artocarpus integrifolia lectin, Lens culinaris lectin and Anguilla anguilla lectin possessed milder cytotoxicity than the remaining lectins. which were approximately equipotent. The mannose-binding Narcissus pseudonarcissus and Lens culinaris lectins were only weakly cytotoxic, the exception being a stronger effect on H3B. The N-acetylgalactosamine-binding Glycine max lectin and methylgalactose-binding Artocarpus integrifolia lectin similarly exhibited low cytotoxicity. It can thus be concluded that in general the ranking was wheat germ lectin > Maackia amurensis lectin approximately Trichloma mongolicum lectins > other aforementioned lectins in cytotoxicity. A particular lectin may manifest more conspicuous toxicity on certain cell lines and less on others.

Recent advances in breast cancer biology

Breast cancer remains the leading cause of death in American women 30 to 70 years of age, and research in the field of breast cancer continues at an explosive pace. Our understanding of the molecular basis of familial breast cancer has advanced significantly through investigation of the tumor suppressor gene BRCA1, as has our knowledge of the role of the ATM gene and predisposition to breast cancer in ataxia-telangiectasia carriers. In addition, progress has been made in understanding the role of HER-2/neu as a prognostic factor in breast cancer. In this review, some of the recent advances in breast cancer biology that are relevant to these areas of study are highlighted.

The level of cell surface beta1,4-galactosyltransferase I influences the invasive potential of murine melanoma cells

Beta1,4-Galactosyltransferase I (GalT I) is localized on the leading lamellipodia of migrating cells, where it associates with the cytoskeleton and facilitates cell spreading and migration on basal lamina matrices. It has previously been reported that a variety of highly metastatic murine and human cell lines are characterized by elevated levels of cell surface GalT I, although the intracellular biosynthetic pool is similar between cells of high and low metastatic potential. In this study, we examined whether the elevated expression of surface GalT I characteristic of metastatic cells is instructive or incidental to their metastatic behavior by altering the expression of surface GalT I and by the use of GalT I-specific perturbants. Surface GalT I levels were positively and negatively altered on murine melanoma cells by either overexpressing full-length GalT I or by homologous recombination, respectively. The consequences of altered surface GalT I expression on cell invasion in vitro and lung colonization in vivo were determined. Increasing surface GalT I expression on cells of low metastatic potential to levels characteristic of highly metastatic cells recapitulated the highly invasive phenotype in vitro. Alternatively, decreasing surface GalT I expression on highly metastatic cells to levels characteristic of low metastatic cells reduced their invasive behavior in vitro and metastatic activity in vivo. Within the physiological range of surface GalT I expression, the invasive potential of each clonal cell line correlated strongly with the level of surface GalT I expressed. As an independent means to assess the involvement of surface GalT I in metastatic behavior, cells were pretreated with two different classes of surface GalT I perturbants, a competitive oligosaccharide substrate and a substrate modifier protein. Both perturbants inhibited metastatic colonization of the lung, whereas control reagents did not. Finally, as reported by others, surface GalT I on metastatic cells selectively interacted with one glycoprotein substrate, or ligand, of approximately 100 kDa, the identity of which remains obscure. These results show that the elevated expression of surface GalT I characteristic of highly metastatic cells contributes to their invasive phenotype in vitro and to their metastatic phenotype in vivo.

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.

Galectin-1, an alternative signal for T cell death, is increased in activated macrophages

Galectin-1 belongs to an evolutionarily conserved family of animal beta-galactoside-binding proteins, which exert their functions by crosslinking the oligosaccharides of specific glycoconjugate ligands. During the past decade, attempts to identify the functional role of galectin-1 suggested participation in the regulation of the immune response. Only in the last few years has the molecular mechanism involved in these properties been clearly elucidated, revealing a critical role for galectin-1 as an alternative signal in the generation of T cell death. In the present study we will discuss the latest advances in galectin research in the context of the regulation of the immune response, not only at the central level but also at the periphery. Moreover, we will review the purification, biochemical properties and functional significance of a novel galectin-1-like protein from activated rat macrophages, whose expression is differentially regulated according to the activation state of the cells. The novel role of a carbohydrate-binding protein in the regulation of apoptosis is providing a breakthrough in galectin research and extending the interface between immunology, glycobiology and clinical medicine.

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.

Transcriptional regulation by butyrate of mouse galectin-1 gene in embryonal carcinoma cells

Endogenous galactoside-binding lectins (galectins) have been implicated in cell adhesion, growth, differentiation, neoplastic transformation, and metastasis. Galectin-1 (gal-1), one member of this family, has been best characterized. We isolated a DNA clone containing the gal-1 gene from mouse genomic libraries, and the sequence of the 5' upstream region up to -2430 bp was determined. Our previous study showed that sodium butyrate (butyrate) induced expression of gal-1 at both mRNA and protein levels in the murine embryonal carcinoma (EC) cell line PCC4.aza1R and the induction of gal-1 by butyrate in PCC4.aza1R cells is at least partially regulated at transcriptional level. To locate the region which is responsible for the induction of gal-1 by butyrate, transient transfection of PCC4.aza1R cells with a series of gal-1 promoter/CAT chimeric gene, which have different deletions of the 5' region of the gal-1 promoter, showed that this 2430 bp sequence is a butyrate-inducible promoter, and butyrate-inducible ability remained when only a 62 bp sequence ahead of the transcription site (+1) existed. The sequence from -62 to -41 which contains an Sp1 site at -57 was important for the induction of gal-1 expression by butyrate. Gel shift assay indicated that transcription factor SP1 actually bound to that Sp1 site. The changes of two nucleotides within that Sp1 site, from GG to TT, abolished the nuclear proteins binding to that Sp1 site as well as the response to butyrate. These results suggest that the 5' proximal Sp1 site at -57 is crucial for the butyrate-induced expression of the gal-1, and the direct binding of SP1 to this Sp1 site may be involved in this induction.

A parallel association between differentiation and induction of galectin-1, and inhibition of galectin-3 by retinoic acid in mouse embryonal carcinoma F9 cells

Soluble endogenous lactoside-binding lectins, galectins, have been implicated in cell adhesion, growth, differentiation, neoplastic transformation, and metastasis. Two major classes of these lectins, galectin-1 and galectin-3, are developmentally regulated. To explore the mechanisms by which the expression of the galectins is regulated and to examine their association with the differentiation processes induced by all-trans retinoic acid (RA), dibutyryl cyclic AMP (Bt2cAMP) and their combination, we used the murine embryonal carcinoma (EC) cell line F9 and its RA-resistant mutant, RA-3-10. RA induced endodermal differentiation and a concurrent induction of galectin-1 and its complementary glycoconjugates (laminin and lysosomal-associated membrane protein, LAMP) in the F9 wild-type (wt) line, but failed to induce differentiation and had no effects on or even reduced the expression of galectin-1, laminin, and LAMP in the RA-3-10 line. On the other hand, RA inhibited expression of galectin-3 in the wild-type line but had no effect on the RA-3-10 line. The galectin-1 gene is at least partially regulated at the transcriptional level. These results demonstrate a parallel association between differentiation and induction of galectin-1, and inhibition of galectin-3 in F9 cells by RA. The study suggests that a regulated expression of galectins and their complementary glycoconjugates is involved in the differentiation pathway induced by RA in F9 cells.

Metastasis of human colon cancer is altered by modifying expression of the beta-galactoside-binding protein galectin 3

BACKGROUND & AIMS

Galectin 3 is a beta-galactoside-binding protein whose expression has been correlated with advanced tumor stage in the colon, but direct evidence for a role in metastasis is lacking. The current study was designed to more directly establish the role of galectin 3 in colon cancer metastasis.

METHODS

Galectin 3 levels were manipulated in human colon cancer cells using eukaryotic expression constructs designed to express the complete galectin 3 complementary DNA in either the sense or antisense orientation. Liver colonization was assessed in athymic mice after splenic-portal inoculation or after spontaneous metastasis during cecal growth.

RESULTS

Introduction of galectin 3 antisense into metastatic colon cancer cells (LSLiM6, HM7) resulted in a significant reduction in galectin 3-specific messenger RNA and total and cell surface galectin 3 protein. Conversely, stable integration of galectin 3 in the sense orientation resulted in an increase in cellular and cell surface galectin 3 in cells of low metastatic potential (LS174T). Reduction in galectin 3 levels was associated with a marked decrease in liver colonization and spontaneous metastasis by LSLiM6 and HM7 cells, whereas up-regulation of galectin 3 resulted in increased metastasis by LS174T cells.

CONCLUSIONS

This study provides direct evidence that galectin 3 plays an important role in colon cancer metastasis.

Lectin histochemistry of laryngeal squamous cell carcinomas

A panel of five biotinylated lectins was applied to study the presence and distribution of membrane carbohydrate residues in the normal laryngeal epithelium and in laryngeal squamous cell carcinomas (SCCs) of 86 patients with the avidin-biotin peroxidase complex technique. The lectin-binding pattern of well-differentiated SCCs was comparable to that of the spinous cells of the normal laryngeal epithelium. In the less differentiated SCCs, staining of the keratinocyte plasma membrane with lectins was either reduced or absent, indicating a decline in the glycosylation of cell surface glycoconjugates. The lectins applied here could be used in the rapid assessment of less-differentiated areas within a laryngeal SCC, but they cannot be regarded as reliable markers of laryngeal keratinocytes undergoing malignant transformation.

Cancer metastasis: a search for therapeutic inhibition

Failure of cancer treatment is often due to the growth of secondary, metastatic lesions in distant organs. Because initiation of metastasis is an early event in malignancy, patients often present not only with a primary tumor but also with occult metastases. Treatment of these metastases requires aggressive, systemic chemotherapy, since surgical removal of all metastatic foci is normally not feasible. However, drug toxicity caused by many of the currently used anticancer agents often limits chemotherapeutic approaches to malignant disease. In contrast, the development and use of novel cytostatic, antimetastatic agents could be less toxic and more applicable for long-term treatment in combating latent and/or residual disease. Practical intervention with such nontoxic agents has been envisioned as maintenance therapy after cytoreduction of a tumor or as a prophylactic treatment after the removal of a precancerous tumor exhibiting a genetic predisposition to a carcinomatous state. In this review, we discuss targets of the metastatic cell that may be potentially exploitable with chemotherapy, and present the current status of several novel, antimetastatic agents. Clinical evaluation of such agents will require new and appropriate clinical models for evaluating their antimetastatic efficacy. The recent successes achieved with certain proteinase inhibitors for the treatment of cancer are paving the way for the development of other therapeutic agents of this type, aimed at unique biochemical pathways associated with oncogenic behavior.