Differential expression of endogenous sugar-binding proteins (lectins) in murine tumor model systems with metastatic capacity

Use of lectins as diagnostic and therapeutic tools for cancer

Within the past few years, lectins have become a well-established means for understanding varied aspects of cancer and metastasis. Evidence is now emerging that lectins are dynamic contributors to tumor cell recognition (surface markers), cell adhesion and localization, signal transduction across membranes, mitogenic stimulation, augmentation of host immune defense, cytotoxicity, and apoptosis. To advance understanding of these lectin-dependent processes, attempts are being made to discover new lectins that have one or more of these functions and to develop lectin- (or glycoconjugate-) based tools that could be used to home in on tumor cells. This review will summarize current research on the lectins and recent advances in the development of lectin-based diagnostic and therapeutic tools for cancer. Additionally, the future potential of lectin-based diagnosis and therapy is discussed.

Murine tumor cells metastasizing selectively in the liver: ability to produce hepatocyte-activating cytokines interleukin-1 and/or -6

Increasing evidence suggests that an intimate correlation may exist between the production of a cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF) and the ability to metastasize spontaneously in the lungs in murine transplantable tumors. In the present study, we further examined the cytokine production by tumor cells with the ability to metastasize in the liver. Four out of 8 test tumors, which produced metastasis in the lungs but not in the liver, exhibited the ability to produce GM-CSF activity in culture. Three other tumors produced metastasis in the liver but not in the lungs. These tumor cells exhibited no ability to produce GM-CSF, but two of them expressed an interleukin-6 (IL-6) mRNA and also produced IL-6 activity in the culture fluids. One of the two IL-6-producing tumors and the remaining liver metastatic tumor produced interleukin-1 (IL-1) as revealed by bioassay and neutralization test. In the tumor cells producing pulmonary metastasis, neither IL-6 gene expression nor IL-1 production could be detected. The last test tumor, which produced no metastasis either in the lungs or liver, produced neither GM-CSF, IL-1 nor IL-6. Furthermore, injection of antisera reactive to recombinant murine IL-6 caused a marked decrease of the number of liver metastases of an IL-6-producing tumor, but not lung metastases of a GM-CSF-producing tumor, which could be markedly inhibited by injection of anti-recombinant murine GM-CSF sera. These results suggest the possibility that there may be a correlation between the cytokines produced by tumor cells and their organ specificity in spontaneous metastasis, and also indicate that these tumor models may provide a useful tool for studies on the role of cytokines in tumor metastasis.

Malignant transformation in hepatocytes is associated with the general increase of glycoprotein ligands specifically binding to the endogenous lectin CSL

Several hepatoma cell lines and hepatic ascite tumour cells were studied for the presence of glycoprotein ligands of an endogenous lectin, the "Cerebellar Soluble Lectin" (CSL). This lectin is also present in hepatocytes in vivo and in vitro and can be detected biochemically and immunologically. In transformed cells, the level of CSL glycoprotein ligands is increased 50-fold as compared to the control cells. Such an increase is not observed for the ligands of the plant lectin, concanavalin A, which is, as CSL, a D-mannose-binding lectin. These results indicated that the changes in glycans during malignant transformation, in these cells, is specifically important for minor glycans binding to CSL.

A correlation between GM-CSF gene expression and metastases in murine tumors

Using 14 transplantable murine tumors, we investigated a possible correlation between their ability to produce the cytokine GM-CSF and the spontaneous metastatic potential when mice were subcutaneously inoculated. The following results were obtained: (1) seven tumors, which produced severe pulmonary metastases and metastatic swelling of lymph nodes, exhibited the ability to produce GM-CSF activity in culture. The cell population analysis revealed that the cells producing GM-CSF were tumor cells themselves, but that contaminating macrophages/granulocytes and T lymphocytes did not produce GM-CSF. The mRNA for GM-CSF was also found in all of these highly metastatic tumors tested. In mice inoculated with a highly metastatic tumor, the GM-CSF mRNA was also found in lungs; (2) in 3 other tumors, which produced histological but not macroscopical pulmonary metastases, no GM-CSF activity could be detected in the culture fluids. GM-CSF mRNA was, however, detected in the tumor cells in the presence of an mRNA-stabilizing agent, cycloheximide, suggesting the possibility that the tumor cells of this type were transcribing GM-CSF gene, and secreting it in undetectable levels; (3) in culture of the 4 remaining poorly or non-metastatic tumors, neither CSF activity nor GM-CSF mRNA could be detected even in the presence of cycloheximide. GM-CSF mRNA was also not found in lungs of tumor-bearing mice. Our results indicate that there may be a correlation between GM-CSF gene expression in tumor cells and spontaneous metastases.

Analysis of cell-surface sugar receptor expression by neoglycoenzyme binding and adhesion to plastic-immobilized neoglycoproteins for related weakly and strongly metastatic cell lines of murine tumor model systems

Recognition of the carbohydrate part of cellular glycoconjugates by cell-surface sugar receptors may contribute to interactions, essential to the establishment of metastases. Comparison of the properties of strongly metastatic variants to their related, less metastatic counterparts offers a generally accepted approach to the discovery of metastasis-associated characteristics. The chemically induced murine lymphoma line Eb and its spontaneously arising variant ESb with increased potential for lung and liver colonization, the virally induced lymphosarcoma cell line RAW117-P and its in vivo selected variant H10 with increased potential for liver colonization, and the B16-F1 melanoma line and its in vivo selected variant F10 with increased potential for lung colonization, were chosen. A panel of 12 types of chemically glycosylated E. coli beta-galactosidase, exposing the pivotal carbohydrate residues for specific carbohydrate-dependent cell binding, was employed to study the expression of respective cell-surface sugar receptors on these cell lines. Specific binding occurred in a non-uniform manner for the individual probes. Systematic measurements at a non-saturating ligand concentration revealed quantitative differences between the 2 cell lines of each system. However, there were no consistent changes associated with the metastatic phenotype. A similar result was obtained employing Scatchard analyses for quantitative evaluation of binding characteristics in several cases. Surface receptor expression was responsive to chemical induction of differentiation in the lymphosarcoma model. Analyses of sugar-inhibitable cell adhesion to neoglycoprotein-coated plastic wells for the lymphoma and lymphosarcoma cells revealed that the presence of cell-surface sugar receptors, even at similar densities to those defined by neoglycoenzyme binding, will not necessarily translate into an identical adhesive response. Several carbohydrates, especially N-acetyl-D-galactosamine, can differentially affect this interaction at a non-toxic concentration in both model systems.

Expression of endogenous receptors for neoglycoproteins in Dunning R3327 rat prostatic carcinoma

An important animal model for human prostatic adenocarcinoma is the Dunning R3327 rat carcinoma. In the present study this tumor was further characterized by analyzing the expression of endogenous sugar-binding proteins using glycohistochemistry and immunocytochemistry as well as affinity chromatography and gel electrophoresis. Our glycohistochemical and glycobiochemical results provide evidence for the presence of specific receptors for various carbohydrate moieties. Remarkably, basal cells of the Dunning tumor contain an endogenous lectin with specificity for beta-galactosides that is not found in basal cells of the normal rat prostate. This finding was corroborated using polyclonal antibodies against an immunologically related beta-galactoside-specific lectin from bovine heart. Basal cells of prostatic carcinoma may therefore behave different from normal basal cells. This difference could have a significant impact on the development of prostatic cancer.

Site-associated expression of endogenous tumor lectins

The expression of endogenous lectins was compared in mouse Lewis lung carcinomas growing in the kidney or subcutaneously. A panel of carbohydrates coupled to a biotinylated carrier molecule (bovine serum albumin), biotinylated desialylated glycoproteins and sulfated polysaccharides were used in histochemical assays to detect the presence and distribution of carbohydrate receptors. Heterogeneous staining patterns were observed with most carbohydrates in sections of tumor tissue from both anatomic sites, and staining intensities also varied within each section. At least 2 populations of cells were identified at each site, of which one had receptors for all carbohydrates, while the other had no receptors for melibiose, sialic acid, or alpha-glucosides (maltose and glucose). There were quantitative differences in expression of endogenous lectins by tumors growing s.c. or in the kidney; 3LL cells growing in the kidney bound 6 out of 10 carbohydrates to a greater extent than 3LL cells in s.c. tumors. Conversely, 3LL cells in s.c. tumors bound heparin and asialofetuin to greater extents than cancer cells in kidney tumors. Biochemical analyses of detergent extracts of tissues subjected to affinity chromatography and subsequent SDS-PAGE revealed quantitative and also qualitative differences in lectins between tumors growing in the 2 anatomic sites.

Identification of a cell cycle-dependent gene product as a sialic acid-binding protein

A Ca2+-dependent sialic acid-binding protein was purified on fetuin-Sepharose from various types of human tissue. The molecular mass was determined to be 10,315 Da by laser desorption mass spectrometry. Partial sequence analysis after cyanogen bromide cleavage that yielded one N-terminus accessible for Edman degradation revealed an identity to an internal stretch following the only methionine residue within a putative amino acid sequence (Mr 10,048), deduced from the cDNA of a cell cycle-specific gene. The reported biochemical identification is a prerequisite to infer the biological role of the so far undetected gene product. Initial glycohistochemical studies with sialic acid-(BSA-biotin) raised evidence for nuclear localization of sialic acid-binding sites that might reflect, at least in part, detection of this protein.

Lineage- and differentiation-dependent alterations in the expression of receptors for glycoconjugates (lectins) in different human hematopoietic cell lines and low grade lymphomas

Important biological functions and cellular recognition phenomena are supposedly governed by specific sugar-protein interactions. Human hematopoietic cell lines offer an excellent model for the study of the expression of endogenous receptors for the carbohydrate part of glycoconjugates with respect to cell lineage and modulation by differentiation. Initially, a panel of fluorescent (neo)glycoproteins was successfully employed to demonstrate cytologically the actual presence of such receptors on different cell lines: the B lymphoblast line, Daudi; the T cell lymphoblastic leukemia line, P12; the multipotent leukemic line, K562 and the promyelocytic line, HL060. Biochemical analyses were performed using affinity chromatography on supports with immobilized lactose and asialofetuin (simple or complex beta-galactosides), melibiose (alpha-galactoside), fucose, N-acetyl-D-galactosamine, maltose (alpha-glucoside), the mannose-rich yeast glycoprotein, mannan, glycopeptides containing sialic acid residues and heparin. Subsequently, sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis was used to detect cell lineage-dependent changes in theses parameters. Differentiation-dependent changes in the expression of receptors with specificity to galactose, N-acetylgalactosamine, maltose and heparin were similarly uncovered upon dimethyl sulfoxide-induced differentiation of HL60 cells. Differences in this type of cellular characteristic were also apparent for lymphoma cells from patients with various histological subtypes of lowgrade lymphomas. This initial description of lineage- and differentiation-dependent differences in various human hematopoietic cell lines and in cells from patients with lowgrade lymphomas suggests that advances in the knowledge of the composition of endogenous sugar receptors (lectins) may aid in understanding aspects of the biological behavior of hematopoietic cells and their related malignancies via participation of sugar-protein (lectin) interactions.

Is the profile of binding of a panel of neoglycoproteins useful as a diagnostic marker in human lung cancer?

Histomorphological evaluation of the profile of carbohydrate-binding proteins with specificities to alpha- and beta-glucosides (maltose, cellobiose), alpha-L-fucosides (L-fucose), alpha-D-mannosides (D-mannose), a N-acetylated sugar, present in natural glycoconjugates (N-acetyl-D-glucosamine), two negatively charged sugars (glucuronic acid and sialic acid), rhamnose (6-deoxy-L-mannose) or to heparin has been assessed. 133 cases of formalin fixed, paraffin embedded human lung carcinoma specimens (45 cases of epidermoid carcinoma, 24 cases of small cell anaplastic carcinoma, 48 cases of adenocarcinoma, and 16 cases of large cell anaplastic carcinoma) as well as 14 cases with epithelial or biphasic mesothelioma and 7 cases of pleuritis carcinomatosa were incubated with biotinylated, suitably modified neoglycoproteins or heparin for detecting the corresponding endogenous sugar receptors (lectins). Histochemical reaction was demonstrated by use of the avidin-biotin-method. Significant differences were obtained between the different markers used for each cell type as well as between the different cell types. For separating small cell anaplastic carcinoma from non small cell anaplastic carcinoma the markers carrying the histochemically crucial maltose, fucose, and mannose residues are useful, showing a positive reaction to only 4-8% of the small cell anaplastic carcinoma cases compared to 60-80% of the non small cell carcinoma cases. For separation of mesothelioma from pleuritis carcinomatosa a carrier, modified by attachment of N-acetylglucosamine moieties is the most useful marker being negative in all cases of the analyzed mesothelioma cases and being positive in 62-80% of the adenocarcinoma cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Malignant and normally developing trophoblastic cells of human placenta display different characteristics defined by histochemical and biochemical mapping of endogenous lectins

Trophoblastic cells with their strictly controlled propensity for invasive growth hereby bear limited resemblance to malignant cells. Therefore, detailed description of molecular characteristics of this cell type in comparison to histologically related tumor cells may aid in defining physiologically relevant differences. In view of the potential importance of selective protein-carbohydrate interactions in recognitive processes, labelled neoglycoproteins were employed to evaluate systematically the presence and distribution of sugar receptors in tumor cells of chorionepithelioma and in trophoblastic cells of an early stage of gestation. Control reactions in glycohistochemistry, involving prolonged incubation, pH variation and use of nucleotides excluded the possibility that glycosidases or glycosyltransferases govern the sugar-specific binding to the tissue sections. Pronounced differences were detected in the expression of receptors (lectins) for alpha- and beta-glucosides as well as for N-acetylgalactosamine and N-acetylglucosamine. Further differences were revealed by probing both types of tissue with lactosylated, fucosylated, xylosylated and sialylated carrier protein. Upon developmental maturation of the normal cells in placenta the extent of binding of the neoglycoproteins decreased. The glycohistochemical differences between malignant and normally developing trophoblastic cells were found to be reflected in the alteration of expression of certain endogenous lectins, as ascertained by affinity chromatography and gel electrophoretic analysis. Consequently, we assume that the transient presence of certain endogenous lectins during early stages of gestation and their differential expression in relation to tumor cells of chorionepithelioma may be relevant for the special invasive and adhesive behavior of human trophoblastic cells.

Endogenous sugar receptor pattern in human glioblastomas and gangliocytomas studied by histochemical application of biotinylated (neo)glycoproteins and affinity chromatography

Biotinylation of chemically glycosylated bovine serum albumin, yielding a panel of neoglycoproteins, and of desialylated, naturally occurring glycoproteins allowed to systematically evaluate presence and distribution of various types of endogenous sugar receptors in the sections of human glioblastomas and gangliocytomas by a routine histochemical procedure. Pronounced cytoplasmic staining with markers, carrying constituents of natural glycoconjugates, e.g. for beta-galactoside-specific receptors, contrasted with the different intensities, noticed for alpha- and beta-glucoside-specific receptors. Significant qualitative differences between the two tumor types were detected with N-acetyl-D-galactosamine- and sialic acid-carrying probes. Nuclear staining with only a part of the applied panel underscored the specificity of the protein-carbohydrate interaction. Fine structural features of the synthetic neoglycoproteins, e.g. the mode of coupling of the carbohydrate moiety to the protein, were found to exert a significant influence on their suitability as histochemical markers. On the basis of the histochemical results, exemplary biochemical analysis of certain classes of endogenous sugar receptors by affinity chromatography and subsequent gel electrophoresis, namely of beta-galactoside-, alpha-fucoside-, alpha-mannoside- and alpha-glucoside-specific proteins, revealed presence and characteristics of respective sugar receptors that can contribute to the histochemical staining. Similar extent of histochemical staining with the respective probes notwithstanding, the different tumor types exhibited qualitative differences in the expression of individual endogenous sugar receptors. The combined histochemical and biochemical analysis is supposed to be of conspicuous value for biological and clinical investigations on endogenous sugar receptors.

Endogenous sugar-binding proteins in human breast tissue and benign and malignant breast lesions

Binding of carbohydrate moieties was detected in tissue sections of human breast by employing two types of labeled ligands: neoglycoproteins (chemically glycosylated, histochemically inert carrier protein) and desialylated naturally occurring glycoproteins. Paraffin-embedded, formalin-fixed sections from 40 benign and malignant breast lesions were examined for the presence and distribution of endogenous sugar receptors, employing a panel of 13 biotinylated neoglycoproteins, representing carbohydrates commonly found in naturally occurring glycoconjugates, and four biotinylated glycoproteins. Benign and malignant breast lesions revealed staining with mannosylated carrier neoglycoprotein in comparison to normal breast. A mixed pattern of staining localization and intensity was seen for different types of malignancy with this neoglycoprotein. Similarly, receptors for lactose and N-acetylglucosamine could only be detected within the cytoplasm for certain types of malignancy. Their nuclear localization, however, could also be seen in normal breast specimens. The extent of staining with different glycoproteins, containing different types of galactoside-terminal sugar chains, also appeared to differ between various types of breast cancer. The detection of endogenous sugar receptors by neoglycoproteins is proposed to contribute to an understanding of malignancy-associated alterations in the structure of their potential physiological ligands, the glycoconjugates. Changes in the structure and abundance of such glycoconjugates have commonly been detected with the use of plant lectins in histopathologic studies.

Inhibition of liver tumor cell colonization in two animal tumor models by lectin blocking with D-galactose or arabinogalactan

Repeated administration of the hepatic lectin blocking agents D-galactose or arabinogalactan completely prevented the settling of metastatic cells of sarcoma L-1 tumor in the liver of Balb/c mice and greatly reduced the colonization process of highly metastatic ESb lymphoma cells of the liver of DBA/2 mice. Therefore, when hepatic lectins were blocked with competitive glycoconjugates, tumor cell colonization of the liver could be prevented in two different model systems.

Evidence for the involvement of protein-carbohydrate interaction in hematopoietic, multipotential colony-stimulating factor-dependent stem cell proliferation

Immunologically important mediators have been shown to exhibit ability to specifically bind distinct carbohydrates. This type of protein-carbohydrate interaction is one mechanism how to explain involvement of glycochemical interactions in regulatory processes. Interference of certain saccharides with murine multipotential colony-stimulating factor (multi-CSF)-dependent colony formation from progenitor cells in semisolid agar raised evidence for similar potential involvement of protein-carbohydrate interactions. Affinity depletion of conditioned WEHI-3B-medium on resins, bearing saccharides that have been elucidated to be effective inhibitors (mannose and lactose), resulted in preparations with significantly reduced capability to sustain development and proliferation. Sequence comparison of multi-CSF to carbohydrate-binding proteins (lectins) with this specificity failed to uncover extended homologies in diagonal plots. But detailed sequence alignments revealed confined, high-scoring stretches of homology between various lectins and two types of CSF. These results prove the importance of protein-carbohydrate interactions in stem cell proliferation.

Preparation of neoglycoprotein-enzyme conjugate using a heterobifunctional reagent and its use in solid-phase assays and histochemistry

A conjugate of a neoglycoprotein (chemically lactosylated bovine serum albumin) and an enzyme (horseradish peroxidase) has been prepared in solution using a heterobifunctional reagent, N-succinimidyl-3-(2-pyridyldithio)propionate, and has been purified by gel filtration on an Ultrogel AcA-44 column. To preclude any carbohydrate-dependent binding to the sugar residues on the glycoprotein peroxidase, the enzyme has to be treated with sodium periodate and sodium cyanoborohydride prior to coupling, which results in oxidative cleavage of the carbohydrates and reduction of the aldehydes thus formed to primary alcohols. Lactosylated bovine serum albumin-peroxidase conjugate has been employed to detect plastic-bound Ricinus communis agglutinin with dependence of the concentration of the lectin and with dependence of the presence of specific inhibitors. Enzyme-labeled conjugates with unmodified bovine serum albumin are completely ineffective in this assay. Localization of beta-galactoside-specific sugar receptors in connective tissue is used to demonstrate the feasibility of application of such neoglycoprotein-enzyme conjugates in histochemistry with a minimum number of steps.