Dichotomy in the laminin-binding properties of soluble and membrane-bound human galactoside-binding protein

Regulation of tumor progression by extracellular galectin-3

The relationship between a tumor cell and its microenvironment is bi-directional. The proteins expressed by the tumor cells alter the signatures on the seemingly normal stromal cells within the microenvironment, while the tumor cell signatures reflect the changes that occur as these cells interact with the host microenvironment. Galectin-3 is a carbohydrate-binding protein that is over-expressed in a variety of tumors and immune cells in response to various stimuli. Ever since its discovery, it has been associated with cell and extracellular matrix interactions. However, in the last decade, an extensive accumulation of data has changed the perspective of this multifunctional protein. The unique structure of this protein, consisting of a carbohydrate-binding domain and a matrix metalloproteinase cleavable domain, enables it to interact with a plethora of ligands in a carbohydrate-dependent or independent manner. It is now becoming evident that galectin-3 is involved with a variety of extracellular functions like cell adhesion, migration, invasion, angiogenesis, immune functions, apoptosis and endocytosis. Galectin-3 is a substrate for matrix metalloproteinases and its cleavage plays an important role in tumor progression and can be used as a surrogate diagnostic marker for in vivo MMP activity.

Galectin-3 may contribute to Cisplatin resistance in clear cell carcinoma of the ovary

Our previous findings suggested that lower cell proliferation of clear cell carcinoma (CCC) of the ovary may contribute to its resistance to chemotherapy. We conducted the present study to find the gene that regulates cell proliferation of CCC and to elucidate whether it contributes to cisplatin (CDDP) resistance. Complementary DNA microarray analysis revealed that the gene expression level of galectin-3 of CCC cell lines (KK, RMG-I, HAC-2) was over threefold higher than that of ovarian serous adenocarcinoma (SAC) cell lines (HRA, KF). S-phase fraction increased after knocking down galectin-3 using small interfering RNA in RMG-I, KK, and HAC-2 cells. The protein expression of p27 decreased after knocking down galectin-3. CDDP-induced apoptosis was increased after knocking down galectin-3, and this cytotoxic effect was canceled by roscovitine. Immunohistochemical staining showed that galectin-3 expression in tumors of 20 CCC was significantly more frequent than that of 20 SAC (70.0% vs 15.0%, P = 0.0004). The present study showed that the expression of galectin-3 in CCC might contribute to its lower cell proliferation and lead to CDDP resistance.

Alterations in galectin-3 expression and distribution correlate with breast cancer progression: functional analysis of galectin-3 in breast epithelial-endothelial interactions

To define the role of galectin-3 in breast cancer progression, we have used a novel three-dimensional co-culture system that recapitulates in vivo reciprocal functional breast epithelial-endothelial cell-cell and cell-matrix interactions, and examined the expression of galectin-3 mRNA and protein in human breast tumors and xenografts. Galectin-3 is required for the stabilization of epithelial-endothelial interaction networks because immunoneutralization with galectin-3 antibodies abolishes the interactions in a dose-dependent manner. Co-culture of epithelial cells with endothelial cells results in increase in levels of secreted galectin-3 and presence of proteolytically processed form of galectin-3 in the conditioned media. In contrast, intracellular galectin-3 predominantly exists in the intact form. This difference in sensitivity to proteolytic processing of secreted versus intracellular galectin-3 probably arises from differences in accessibility of protease-sensitive sites, levels, and/or type of activated protease(s), and may be indicative of different functional roles for intact and processed galectin-3. To determine whether the proteolytically cleaved galectin-3 retains its ability to bind to endothelial cells, binding assays were performed with the full-length and matrix metallopeoteinase-2-cleaved recombinant galectin-3. Although a dose-dependent increase in binding to human umbilical vein endothelial cells was observed with both full-length and cleaved galectin-3, proteolytically cleaved galectin-3 displayed approximately 20-fold higher affinity for human umbilical vein endothelial cells as compared to the full-length protein. Examination of galectin-3 expression in breast tumors and xenografts revealed elevated levels of galectin-3 mRNA and protein in the luminal epithelial cells of normal and benign ducts, down-regulation in early grades of ductal carcinoma in situ (DCIS), and re-expression in peripheral tumor cells as DCIS lesions progressed to comedo-DCIS and invasive carcinomas. These data suggest that galectin-3 expression is associated with specific morphological precursor subtypes of breast cancer and undergoes a transitional shift in expression from luminal to peripheral cells as tumors progressed to comedo-DCIS or invasive carcinomas. Such a localized expression of galectin-3 in cancer cells proximal to the stroma could lead to increased invasive potential by inducing novel or better interactions with the stromal counterparts.

Alteration of the cytoplasmic/nuclear expression pattern of galectin-3 correlates with prostate carcinoma progression

Galectin-3, a member of the beta-galactoside-binding lectin family, is involved in a variety of biological events including interactions with galactose-containing glycoconjugates, cell proliferation, differentiation and apoptosis. Galectin-3 appears to intervene during tumor progression and altered expression patterns have been reported in a variety of malignancies. In our study, we have examined the expression of galectin-3 in a population of 145 prostate carcinoma samples using immunohistochemistry. We found that most of the non-tumoral prostatic glands exhibited moderate immunostaining for galectin-3 localized in both nucleus and cytoplasm. In prostatic cancer cells, galectin-3 was usually not expressed or decreased compared with the normal glands. Interestingly, when galectin-3 was detected in the cancer cells, it was consistently excluded from the nucleus and only present in the cytoplasmic compartment. The latter observation was also made for prostatic intraepithelial neoplasia (PIN) cells. Furthermore, we found that the levels of galectin-3 expression in the cancer cells were significantly associated with prostate-specific antigen (PSA) relapse in univariate analysis (p = 0.044). Cytoplasmic expression of galectin-3 in the carcinoma cells was an independent predictor of disease progression in multivariate analysis, after the pathological stage and the Gleason score. Our data demonstrate that galectin-3 is generally down-regulated in human prostate carcinoma cells, and consistently excluded from the nucleus. Interestingly, specific cytoplasmic expression of galectin-3 in a subset of lesions is associated with disease progression. These results suggest that galectin-3 might play anti-tumor activities when present in the nucleus, whereas it could favor tumor progression when expressed in the cytoplasm. Further studies should determine the exact role and mechanisms by which galectin-3 differentially affects cell behavior in the different locations where it is expressed.

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

The control of cellular adhesion to extracellular matrix proteins is poorly understood. In the present analyses, we set out to test the hypothesis that high galectin-3 concentration on the cell surface downregulates cellular adhesion to the extracellular matrix proteins. Various tumor cell lines were briefly incubated without or with galectin-3 and then allowed to adhere to wells coated with laminin-1, collagen IV and fibronectin. Our data demonstrated that the cells which were incubated with galectin-3 prior to plating had significantly reduced adhesion to extracellular matrix proteins. This inhibition involved the carbohydrate recognition domain of the lectin because adhesion was achieved in the presence of galectin-3 and lactose but not galectin-3 and sucrose. Furthermore we demonstrated that galectin-3 associates with alpha 1 beta 1 integrin in a lactose dependent manner.

Expression of the 67-kD laminin receptor, galectin-1, and galectin-3 in advanced human uterine adenocarcinoma

Alterations of tumor cell interactions with laminin, a basement membrane glycoprotein, are consistent features of the invasive and metastatic phenotype. Qualitative and quantitative changes in the expression of cell surface laminin-binding proteins have been correlated with the ability of cancer cells to cross basement membranes during the metastatic cascade. Such phenotypic modifications are usually associated with poor prognosis. In this study, the authors examined the possibility that expression of three laminin-binding proteins, the 67-kD laminin receptor (67LR), galectin-1, and galectin-3, is altered in human endometrial cancer in a fashion similar to that reported in other carcinomas, such as breast, colon, and ovarian cancer. Twenty advanced uterine adenocarcinomas were analyzed for expression of these three molecules using immunoperoxidase staining and specific antibodies. The authors found a significant increase in the expression of the 67LR and galectin-1 in cancer cells compared with normal adjacent endometrium (P = .0004 and .0022, respectively). As observed in other carcinomas, a significant down-regulation of galectin-3 expression was found in endometrial cancer cells compared with normal mucosa (P = .02). In the galectin-3 positive tumors, galectin-3 was detected in the cytoplasm and/or nucleus of cancer cells. Interestingly, tumors in which galectin-3 was detected only in the cytoplasm were characterized by deeper invasion of the myometrium than lesions where galectin-3 was found both in nucleus and cytoplasm (P = .02). This study shows an alteration of nonintegrin laminin-binding protein expression in advanced human endometrial cancer. Further studies on larger populations should determine the prognostic value of the detection of these laminin-binding proteins in endometrial carcinoma. Inverse modulation of the 67LR and galectin-3 appears to be a phenotypical feature of invasive carcinoma.

Effects of natural complex carbohydrate (citrus pectin) on murine melanoma cell properties related to galectin-3 functions

Citrus pectin (CP) and pH-modified citrus pectin (MCP) are highly branched and non-branched complex polysaccharides, respectively, rich in galactoside residues, capable of combining with the carbohydrate-binding domain of galectin-3. We reported previously that intravenous injection of B16-F1 murine melanoma cells with CP or MCP into syngeneic mice resulted in a significant increase or decrease of lung colonization, respectively (Platt D, Raz A (1992) J Natl Cancer Inst 84:438-42). Here we studied the effects of these polysaccharides on cell-cell and cell-matrix interactions mediated by carbohydrate-recognition. MCP, but not CP, inhibited B16-F1 melanoma cells adhesion to laminin and asialofetuin-induced homotypic aggregation. Both polysaccharides inhibited anchorage-independent growth of B16-F1 cells in semisolid medium, i.e. agarose. These results indicate that carbohydrate-recognition by cell surface galectin-3 may be involved in cell-extracellular matrix interaction and play a role in anchorage-independent growth as well as the in vivo embolization of tumour cells.

Expression of galactoside-specific endogenous lectins and their ligands in human oral squamous cell carcinoma

Human endogenous lectins have a wide spectrum of biological functions. The present study analyses the expression of beta-galactoside specific and N-acetyl-D-galactosamine specific endogenous lectins in oral squamous cell carcinomas using biotinylated neoglycoproteins. The expression pattern of beta-galactosyl-containing glycoconjugates or ligands of beta-galactoside specific lectins in these tissues was also studied using an endogenous biotinylated lectin, the human 14-kDa lectin. For comparison a galactoside specific plant lectin from mistletoe, Viscum album was also employed. The results demonstrate that oral squamous cell carcinomas mainly express accessible binding sites for lactosylated neoglycoprotein (90%) while few carcinomas expressed mild amount of N-acetyl-D-galactosamine specific binding sites (40%). There was no difference in the binding patterns of these probes between well and less differentiated carcinomas. Expression of these neoglycoprotein binding sites were mostly concentrated in immature basaloid cells, indicating a possible association with cell proliferation. The binding pattern of D-galactosyl specific lectins (human 14-kDa and mistletoe lectins) showed conspicuous differences. This feature emphasizes the caution that needs to be exercised in interpreting the biological significance of results attained using plant lectins on human tissue.

Expression of a 31-kDa lactoside-binding lectin in normal human gastric mucosa and in primary and metastatic gastric carcinomas

The expression of lactoside-binding lectin L-31 was analyzed in normal mucosa and in primary and metastatic gastric carcinomas. Immunoblotting revealed L-31 lectin in extracts of normal and malignant gastric tissues from 26 patients. The L-31 level was higher in tumor than in normal tissue in 9/26 cases, similar in 14/26 cases, and lower in 3/26 cases. Anti-L-31 monoclonal antibodies (MAbs) were used in immunohistochemical analyses to compare lectin expression in specimens of primary gastric carcinomas and adjacent normal mucosa from 39 patients and in specimens of metastases and the corresponding primary gastric carcinomas from 74 patients. The lectin was detected in normal gastric epithelial cells and in all gastric carcinoma specimens, albeit in varying amounts. The L-31 level was significantly higher in the primary tumor than in adjacent normal tissue in 55% of the well-differentiated tubular carcinoma cases and in 50% of stage-III and -IV tumors. L-31 expression in liver metastases from well-differentiated tubular primary gastric carcinomas was higher in 31% of the cases relative to the corresponding primary cancers. Likewise, L-31 expression in metastases from poorly differentiated gastric carcinomas in lymph nodes was higher in 38% of the cases compared to the primary cancers. The higher expression of L-31 in primary cancers and metastases of certain types implicates this lectin in the metastatic phenotype, but the presence of L-31 in a primary cancer is not sufficient to allow the metastatic propensity of the tumor to be predicted.

Increased LAMP-2 polylactosamine glycosylation is associated with its slower Golgi transit during establishment of a polarized MDCK epithelial monolayer

An endogenous Madin-Darby canine kidney (MDCK) lysosomal membrane glycoprotein that exhibits a basolateral targeting pathway to the lysosome is shown here to exhibit significant N-terminal amino acid sequence identity to lysosomal associated membrane proteins (LAMP-2) of other species. During establishment of the MDCK monolayer after only 1 d of culture, this canine LAMP-2 has a larger molecular size (110 kDa) than following formation of a confluent monolayer after 3 d of culture (100 kDa) due to the increased presence of N-linked polylactosamine oligosaccharide chains. Neither polylactosamine glycosylation of LAMP-2 in MDCK cells nor truncation of N-linked oligosaccharide chains of LAMP-2 in a ricin-resistant MDCK-RCAR cell line influenced the basolateral polarity of its targeting. However, the rate of basolateral delivery of LAMP-2 in MDCK cells plated for 3 d was significantly faster (t1/2 = 28 min) than in 1-d cells (t1/2 = 40 min); in MDCK-RCAR cells the rate of basolateral delivery at both 1 and 3 d of plating was similar (t1/2 = 40 min). The rate differential in MDCK cells occurred after arrival of LAMP-2 to the Golgi apparatus because the rate of acquisition of endoglycosidase H resistance was the same (t1/2 = 25 min) at both days of plating. The rate of transit of LAMP-2 through the Golgi apparatus to the basolateral domain was therefore far more rapid (approximately 4-fold) in 3 d compared with 1-d MDCK cultures. The increased polylactosamine glycosylation of MDCK LAMP-2 at early times of plating during the establishment of a confluent epithelial monolayer may thus be related to its longer residence time in the Golgi apparatus.