Cell Surface Lectin Research Articles

Evidence for Involvement of β-Glucan-Binding Cell Surface Lectins in Human Natural Killer Cell Function

We have studied the effects of yeast cell wall derivatives (zymosan and particulate β-glucan), on the cytolytic effector function of human natural killer cells. Both zymosan and particulate β-glucan were found to inhibit the NK-cell-mediated killing of K562, Molt-4, U937, and HL60 tumor cells. Zymosan also inhibited the IL-2-dependent proliferation of NK cells, suggesting that some component of the yeast cell wall delivers a down-modulatory signal affecting multiple NK cell functions. NK cell surface molecules capable of binding both zymosan and Sepharose-immobilized pustulan (linear 1,6-β-D-glucan, a carbohydrate component of zymosan and particulate β-glucan) were identified in detergent lysates prepared from surface iodinated NK cells. Our results suggest that NK cells express cell surface β-glucan-binding lectins that may contribute to NK-cell-mediated natural cytotoxicity.

Characterization of oligomannoside binding to the surface of murine melanoma cells. Potential relationship to oligomannoside-initiated cell spreading.

The spreading of murine melanoma cells on unglycosylated laminin is initiated by soluble glycosylated laminins containing oligomannosides, or by mannan, and is inhibited by mannose (Chandrasekaran, S., Tanzer, M. L., and Giniger, M. S. (1994) J. Biol. Chem. 269, 3356-3366). In the present study, melanoma cell recognition of oligomannosides was explored by several different methods. Comparison of cell spreading, initiated by related branched oligomannosides, showed that micromolar concentrations of Man6 and Man9 were able to restore cell spreading maximally, whereas Man3 was ineffective. Man9 bound to the melanoma cells in a bimodal manner at micromolar concentrations, reaching saturation, whereas Man3 showed linear binding in the same and higher ranges. Comparison of Man9 binding with Man9-initiated cell spreading demonstrated that maximal spreading occurred at approximately half-saturation. Competition experiments showed that mannose or mannan effectively impaired Man9 binding to the cells, whereas galactose or fucose was ineffective. Mannan-conjugated fluorescent beads bound in a diffuse pattern to the surface of melanoma cells, whereas underivatized beads did not bind. The distribution of laminin-binding beta 1 integrin on the cell surface was compared with surface mannan binding. The beta 1 integrin staining pattern did not match the mannan staining pattern either in attached, nonspread cells or in attached, spread cells. The composite results support a model in which occupancy of both an integrin and a cell surface lectin is required for murine melanoma cells to spread on glycosylated laminin.

Sialylation and malignant potential in tumour cell glycosylation mutants.

Somatic mutations and drugs that either reduce beta 1-6GlcNAc-branching of N-linked oligosaccharides or block the addition of terminal sequences containing galactose and sialic acid have been shown to inhibit tumour growth and metastasis. In an attempt to further define the oligosaccharide sequences that contribute to the malignant phenotype, we have selected spontaneous wheat germ agglutinin-resistant (WGAR) mutants from highly metastatic murine lymphoid tumour cells and characterized four mutant phenotypes. Mutants were selected from VM4, a clone of the MDAY-D2 tumour cell line which had been transfected with the bacterial beta-galactosidase gene (LacZ). VM4 cells retained the malignant phenotype of MDAY-D2 and the cells expressed LacZ, which facilitated the counting of metastases as the tumour cells stained blue when incubated with 5-bromo-4-chloro-3-indolyl beta-D-galactopyranoside (X-gal). The most frequently isolated mutant was defective in the transport of UDP-Gal into the Golgi, and as previously observed for this mutation, the cells were non-metastatic and produced very slow-growing solid tumours. Mutants expressing CMP-SA hydroxylase, and consequently glycoconjugates with N-glycolylneuraminic acid (NeuNGc), remained highly metastatic, but grew more slowly than VM4 cells as s.c. tumours in mice. A novel WGAR mutant showing a large increase in Gal beta 1-4GlcNAc:alpha 2-6 sialyltransferase (SA-T) mRNA levels (ST6N) and enzyme activity was observed to be less metastatic and also grew more slowly at the s.c. site of inoculation. Finally, a fourth phenotypic class of WGAR mutants showed a complex phenotype including expression of a beta Gal-binding cell surface lectin and reduced sialylation of glycoconjugates. These results suggest that changes in either the amount, the type or linkage of sialic acid in tumour cell glycoconjugates can affect tumour growth and metastasis.

Structural analysis of the light subunit of the Entamoeba histolytica galactose-specific adherence lectin.

Adherence of Entamoeba histolytica trophozoites to colonic mucins and resistance to lysis by the membrane attack complex of complement are mediated by a galactose- and N-acetyl-D-galactosamine-specific cell-surface lectin. This lectin is a heterodimeric glycoprotein of heavy (170 kDa) and light (35/31 kDa) subunits. In this work, the amino acid sequence and membrane anchor of the light subunit were analyzed. The light subunit cDNA encoded a protein with a calculated molecular mass of 32 kDa containing two potential sites for N-linked glycosylation and putative amino- and carboxyl-terminal signal sequences characteristic of glycosylphosphatidylinositol (GPI)-anchored proteins. No classical carbohydrate-binding domains common to C- or S-type eukaryotic lectins were detected by sequence analysis of either the heavy or light subunits, leaving the location of the ligand-binding site of the lectin unknown. Analysis of restriction enzyme-digested E. histolytica DNA by Southern blotting was consistent with the presence of more than one light subunit gene. Two light subunit isoforms of 31 and 35 kDa were identified by SDS-polyacrylamide gel electrophoresis analysis of affinity-purified lectin, and the isoforms were shown on two-dimensional gel analysis to form distinct 170/35- and 170/31-kDa heterodimers. The amino acid compositions and cyanogen bromide peptide patterns of the two light subunit isoforms were nearly identical. The 35-kDa isoform labeled more efficiently than the 31-kDa isoform with [3H]glucosamine, while only the 31-kDa isoform labeled with [3H]myristate and [3H]palmitate. Nitrous acid deamination released lipid from the 31-kDa isoform, which co-migrated on thin layer chromatography with acylphosphatidylinositol, a component of some GPI anchors. Gas chromatography and mass spectrometry of the deamination product from the 31-kDa subunit identified both myo- and chiro-inositols, supporting the presence of a GPI membrane anchor. The covalent association of a transmembrane protein with a GPI-anchored protein, as suggested by the cDNA sequences of the lectin heavy and light subunits, is novel and suggests unique roles for the two subunits in the pathogenesis of amebiasis.

Cell surface lectins in the immune system

Emerging evidence establishes that the immune system employs carbohydrates as recognition determinants for various cellular interactions. The best understood case is provided by the selectin family (L-, E- and P-selectin), which are found on leukocytes or endothelial cells and mediate a variety of leukocyte-endothelial interactions. By virtue of C-type lectin domains, these receptors mediate adhesion by recognizing specific carbohydrate-based ligands on partner cells. This review will summarize current research on the selectins and their ligands. Additionally, several leukocyte receptors, for which lectin activity has been demonstrated or inferred to exist, will be considered briefly.

Characterization of glycoproteins fromChlamydia trachomatisusing lectins

Glycoproteins in Chlamydia trachomatis, serotype L1, elementary bodies were studied by lectin blotting. A panel of 23 lectins representing a variety of sugar specificities was used. The pattern of lectin-binding specificities at a peptide band was studied in order to determine the type and structure of its glycoconjugate. To establish chlamydial origin of the glycopeptide bands in the blot, control samples from non-infected host cell membranes were run in parallel. Terminal mannosidic structures were demonstrated in a 72 kDa glycopeptide (gp72) by its selective binding of Galanthus nivalis lectin (GNA). Sialic acids were found in two chlamydial glycopeptides, gp40 and gp64, which appear to carry O-linked glycoconjugates as they bound the peanut agglutinin (PNA, both gp40 and gp64) and jackfruit lectin (Jac, only gp40). Such structures were also present in other chlamydial glycopeptides. Lectins with specificities for fucose in different links, galactose and N-acetyl glucosamine bound to several chlamydial peptides. On the basis of our results we suggest an alternative mechanism for uptake of chlamydial elementary bodies into host cells, namely phagocytosis mediated by eukaryotic cell surface lectins.

Polysaccharides Influence the Aggregation of Dictyostelium discoideum Cells and Bind to Developmentally Regulated Cell Surface Proteins

Six of ten anionic polysaccharides studied were found to significantly reduce the adhesion of growth-phase Dictyostelium discoideum cells. However, only hyaluronic acid, chondroitin-4-sulfate and chondroitin-6-sulfate interfered with the adhesion of aggregation-competent cells. Neither EDTA-stable nor EDTA-sensitive adhesion of postaggregation cells were affected by the polyanions. The two chondroitin sulfates influenced the aggregation of cells in submerged cultures, long and broad aggregation streams being formed and the broad sheets of cells eventually building multilayered aggregates. Radioiodination of cell surface proteins followed by cellulose fiber affinity chromatography identified the same nine proteins bound by hyaluronic acid and the chondroitin sulfates, six of which were regulated during development. Protease-resistant anionic material isolated from cells bound the same surface proteins as the three glycosaminoglycans. Discoidin I bound to the uncoupled cellulose fibers, suggesting a structural role for the lectin in the extracellular slime sheath. Anionic polysaccharides and cell surface lectins that bind them may be involved in the cell recognition, cell aggregation, and the cell sorting that occurs during pattern formation.

Selectins: Cell surface lectins which mediate the binding of leukocytes to endothelial cells

The selectins are the most recently identified family of cell adhesion molecules. The three known members of this family (L-, E- and P-selectin) mediate the binding of leukocytes to endothelial cells and are involved in the homing of lymphocytes to lymph nodes, as well as the extravasation of neutrophilic granulocytes into inflamed tissues. The lectin character of these cell adhesion molecules (CAMs) makes the selectin protein family unique among all known CAM families. The review will summarize present knowledge about the structural organization, the ligands identified (carbohydrates and glycoproteins) and the different regulation mechanisms of the cell surface activity of the three selectins.

The 14 kDa beta-galactoside binding lectin in myoblast and myotube cultures: localization by confocal microscopy.

The endogenous 14 kDa beta-galactoside-specific lectin has been localised in myoblasts and myotubes by indirect immunofluorescence using confocal microscopy. The antibodies used in these experiments suggest that in myoblast cultures the lectin is abundant on the cell surface and concentrated at ruffled edges of migrating cells. The quantity and distribution of cell surface lectin is independent of the nature of the substratum and undiminished by brief trypsinisation or lactose-washing of the cell suspension. The lectin is also abundant intracellularly, apparently relatively free in the cytoplasm until the cells approach confluency, when the lectin is concentrated into particular areas of cytoplasm resulting in a 'patchy' appearance of stained cells. After fusion to form multinucleate myotubes, intracellular lectin is less abundant and concentrated at the periphery of myotubes, from where lectin appears to be released in vesicles packed with lectin which 'bud off' from the myotube surface. In recolonising cultures, lectin is apparently more abundant and lectin-packed vesicles can also be seen 'budding off' from myoblasts. In differentiated cultures, extracellular lectin is detected both on the myotube surface and in fibrillar arrays of extracellular material.

The mannose receptor and other macrophage lectins

The macrophage expresses a variety of cell surface lectins with activities that support specific functional roles and correspond to various differentiation states characteristic of this cell type. Recently, research has been carried out to investigate the mannose receptor, the advanced glycosylation end products receptor, the mannose-6-phosphate-receptor, the β-glucan receptor, sialoadhesin and several galactose-specific binding proteins.

Resistance of hamster bronchiolar epithelium to neutrophil elastase: investigation by cell surface lectin cytochemistry.

An intratracheal instillation of human neutrophil elastase (HNE) causes accumulation of an excess number of secretory granules in the epithelial secretory cells lining the hamster bronchus. This chronic lesion, which we refer to as secretory cell metaplasia (SCM), is not seen in the trachea or bronchioles. Because luminal cell surface lectin binding is much higher in the trachea than in the bronchus, we concluded that tracheal resistance may be due to a protective glycoconjugate coat. In the present ultrastructural study, we analyzed the lectin-binding capability of bronchiolar epithelial cells to determine whether their luminal cell surface glycoconjugate layer is similar to tracheal epithelial cells. None of the six ferritin-conjugated lectins showed higher binding in bronchioles compared to the bronchus, suggesting that a high level of surface oligosaccharides is not necessary for resistance to the metaplastic effects of HNE. HNE caused a significant reduction in bronchiolar surface binding of the gold-labeled, secretory cell-specific lectin, Helix pomatia agglutinin. The principal granulated secretory cell type in bronchioles was ultrastructurally similar to a form of bronchial Clara cell that converts to a mucous cell phenotype in response to HNE. The results suggest that absence of bronchiolar SCM is not attributable to a protective layer of cell surface oligosaccharides, a lack of cellular contact by HNE, or the presence of a morphologically distinct population of epithelial cells in bronchioles.

Hepatocyte adhesion to carbohydrate-derivatized surfaces. I. Surface topography of the rat hepatic lectin.

The rat hepatic lectins, galactose- and N-acetylgalactosamine-binding proteins found on the hepatocyte cell surface, mediate adhesion of isolated primary rat hepatocytes to artificial galactose-derivatized polyacrylamide gels. Biochemical and immunohistochemical techniques were used to examine the topographical redistribution of the rat hepatic lectins in response to galactose-mediated cell adhesion. Hepatocytes isolated from rat liver by collagenase perfusion had an average of 7 x 10(5) cell surface lectin molecules per cell, representing 30-50% of the total lectin molecules per cell, the remainder residing in intracellular pools. Hepatocytes incubated on galactose-derivatized surfaces, whether at 0-4 degrees C or 37 degrees C, rapidly lost greater than 80% of their accessible cell surface lectin binding sites into an adhesive patch of characteristic morphology. The kinetics of rat hepatic lectin disappearance were used to estimate a lateral diffusion coefficient greater than 9 x 10(-9) cm2/s at 37 degrees C, suggesting rapid and unimpeded lectin diffusion in the plane of the membrane. Indirect immunofluorescence labeling of adherent cells using antihepatic lectin antibody revealed a structured ring of receptors surrounding an area of exclusion (patch) of reproducible size and shape which represented approximately 8% of the hepatocyte cell surface. Notably, adherent cells, which had lost greater than 80% of their accessible surface binding sites, still endocytosed soluble galactose-terminated radioligand at greater than 50% of the rate of nonadherent control cells. No net movement of rat hepatic lectin from intracellular pools to the cell surface was found on cells recovered after adhesion to galactose-derivatized surfaces at 37 degrees C, suggesting that the physical size and/or lectin density of the patch was restricted by kinetic or topological constraints.

Dependence of mouse thymocyte‐erythrocyte rosette formation on complete identity at class‐l‐MHC

Mouse thymocytes and erythrocytes form rosettes when incubated together at 4 degrees C. The frequency is much higher when the thymocytes and erythrocytes are MHC-identical. If the indolizidine alkaloid swainsonine (SW) is present during rosette formation at concentrations of 1 microgram/ml (5.7 microM) or greater, rosette formation between MHC-identical pairs is inhibited to levels comparable to those observed for MHC-different pairs; rosette formation by MHC-different pairs is not affected. This was confirmed by examining 17 different MHC-identical combinations (9 completely syngeneic and 8 differing in non-MHC genes) and 13 MHC-different combinations (3 of these identical everywhere except at MHC). A SW-inhibitable component of rosette formation was observed only when thymocyte and erythrocyte were completely identical at MHC. Thus F1-parent pairs behaved as if allogeneic, although both F1-F1 and parent-parent had a SW-inhibitable rosetting component. Similarly, inbred strains only partially MHC-identical (B10.BR-B10.A, B10.D2-B10.A) behaved as if allogeneic. The SW-inhibitable component of rosetting could be partially but significantly blocked by including monoclonal antibodies against Thy-1, and anti-CD4 plus anti-CD8 (together but not separately); anti-class-I-MHC produced some inhibition of marginal significance. Monoclonal antibodies against class-I-MHC, LFA-1, and CD3 did not block. Pretreatment of erythrocytes with neuraminidase, greatly reduced the SW-inhibitable component of rosetting. The SW effect would appear to be due to a direct interaction of SW with a cell surface structure involved in syngeneic rosette formation rather than the known ability of SW to block the processing of N-linked sugar structures. The results are consistent with cell surface lectins and cell surface sugars playing a role in rosette formation.

Particle agglutination assays to identify fibronectin and collagen cell surface receptors and lectins in Aeromonas and Vibrio species

A rapid particle agglutination assay (PAA) utilizing latex beads coated with connective tissue and serum proteins was evaluated for its ability to identify fibronectin, collagen (types I and IV), fibrinogen, and transferrin cell surface receptors on Vibrio and Aeromonas strains isolated from diseased fish, human infections, and the environment. Similar tests were performed to screen for cell surface lectins. Vibrio as well as Aeromonas strains were found to bind connective tissue proteins (collagen types I, II, and IV and fibronectin), serum proteins (i.e., fibrinogen), and glycoproteins (bovine submaxillary mucin, hog gastric mucin, orosomucoid, and fetuin) immobilized on the latex particles. The specificity of the agglutination reaction was studied by particle agglutination inhibition assays performed by preincubating bacterial suspensions in solutions containing either gelatin (for the various connective tissue protein PAA reagents) or sialic acid-rich glycoproteins (for the various glycoprotein PAA reagents). Expression of cell surface receptors for connective tissue proteins was found to depend on culture methods.

Pathogenic and nonpathogenic strains of Entamoeba histolytica can be differentiated by monoclonal antibodies to the galactose-specific adherence lectin

Entamoeba histolytica infection results in either asymptomatic colonization or invasive colitis and liver abscess. E. histolytica isolates from patients with invasive disease have characteristic isoenzyme profiles (pathogenic zymodemes), suggesting a role for parasite factors in determining the severity of infection. A galactose-specific cell surface lectin from a pathogenic zymodeme was shown to mediate in vitro adherence to human colonic mucins and contact-dependent killing of target cells. Six nonoverlapping antigenic determinants were identified on the 170-kilodalton heavy subunit of the pathogenic lectin. Anti-lectin monoclonal antibodies (MAb) directed against epitopes 1 and 2 enhanced adherence whereas MAb to epitopes 3 through 6 either inhibited or had no effect on adherence. We tested 50 pathogenic and nonpathogenic strains for reactivity to these anti-lectin MAb by radioimmunoassay. MAb to epitopes 1 through 6 reacted in the radioimmunoassay with all 16 pathogenic zymodeme strains tested. In contrast, only MAb to epitopes 1 and 2 bound to the lectin from nonpathogenic strains. Western immunoblots with anti-lectin antibodies showed that the 170-kilodalton heavy subunit was present in the nonpathogenic amebae. Adherence of the nonpathogenic SAW 760 strain to human erythrocytes was enhanced by MAb to epitope 1 and blocked by galactose, confirming the presence of a functionally active lectin. A lectin radioimmunoassay based on MAb to epitopes 1 and 3 proved to be a simple and rapid method to distinguish pathogenic from nonpathogenic amebae in culture. Further exploration of the functional consequences of the antigenic differences demonstrated for the lectin may lead to a better understanding of its role in pathogenesis.

Cell surface lectins of human granulocytes: their expression is modulated by mononuclear cells and granulocyte/macrophage colony-stimulating factor

This paper presents the characterization of a sugar-specific receptor on the surface of human circulating polymorphonuclear cells. With the help of fluorescent neoglycoproteins and flow cytometry, a receptor was identified as being specific for alpha-L-rhamnosyl residues. The number of receptors was 55,000/cell and their affinity reached 2 x 10(8) l mol-1. This number changed as a function of the biological state of the cells. Indeed, receptor expression was modulated by the presence of other cells. T cells and B cells increased the number of receptors on the granulocyte surface. Expression of the alpha-L-rhamnose-specific lectin was dependent on lymphocyte derived soluble factor(s), which induce(s) growth and differentiation of polymorphonuclear phagocytes. Granulocyte/macrophage colony-stimulating factor (GM-CSF) specifically produced a significant increase in the number of receptors for alpha-L-rhamnose (2-10-fold/cell). This modulation was independent of protein kinase C activators such as phorbol ester, which produced no effect on alpha-L-rhamnose receptor expression. These findings demonstrate that GM-CSF may stimulate post differentiation functions and properties of mature granulocytes.

Endogenous lectin from cultured soybean cells: Exposure of the SB-1 lectin on the cell wall

Digestion of seed soybean agglutinin with V-8 protease yielded seven distinct fragments ( M r 10,000–20,000) that were well-resolved by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Each individual peptide (F 1 through F 7) was isolated; determination of the amino acid sequence at the NH 2-terminal portion of each peptide established its position in the intact polypeptide of soybean agglutinin. The isolated peptides were used as affinity adsorbents to obtain antibodies that bound individual fragments (anti-F 1 through anti-F 7). These antibody preparations were, in turn, used in immunofluorescence staining of intact cultured soybean (SB-1) cells. Only those antibody preparations that bind to the NH 2-terminal portion (residues 1–124) of the intact soybean agglutinin showed significant cell surface labeling. In contrast, the antibody preparations that bound to residues 125–253 failed to bind to intact SB-1 cells. These results suggest that the SB-1 lectin has the NH 2-terminal portion of the polypeptide chain exposed and accessible at the cell surface, while the COOH-terminal portion of the same molecule may be masked, either through protein folding or through embedding in the cell wall. Limited digestion of the cell wall polysaccharides by cellulase or pectinase released the majority of the cell surface lectin.

Poly[ N-acetyl-lactosamine]-type sugar chains in CD45 antigens of abnormal T cells of 1pr mice are different from those of normal T cells and B cells

The lymph node (LN) T cells from autoimmune MRL/MpJ-lpr/lpr (lpr) mice and control MRL/MpJ-+/+ (+/+) mice were compared as to their cell surface lectin binding sites and the glycoproteins responsible for the lectin binding. T cells from enlarged lymph nodes of lpr mice were found to express more binding sites for lectins which are reactive to poly[ N-acetyl-lactosamine]-type sugar chains than normal +/+ mouse lymph node T cells. Furthermore, we found that high mol. wt (180,000–220,000) glycoproteins on lpr T cells were strongly stained with these poly[ N-acetyl-lactosamine]-binding lectins on Western-blotting. These glycoproteins were found to belong to the CD45 family on immunoprecipitation and absorption with monoclonal anti-CD45 antibody. Thus, aberrant expression of high mol. wt CD45 (CD45R) antigens on lpr T cells may contribute greatly to the strong reaction of these cells with poly[ N-acetyl-lactosamine]-binding lectins. We also found that poly[ N-acetyl-lactosamine]-type sugar chains are more abundant on B cells than on lpr T cells, and that the molecular weights and the carbohydrate moieties of CD45R antigens on Ipr T cells are different from those of CD45R antigens on +/+ spleen B cells.

Membrane IL-1: IL-1 alpha precursor binds to the plasma membrane via a lectin-like interaction.

Although biologically active IL-1 associated with plasma membrane has been demonstrated in both mouse and man, a biochemical mechanism for membrane anchoring has not been described. We have analyzed the nature of membrane IL-1 in stimulated murine macrophages. We show that it consists of an IL-1 alpha precursor bound to the plasma membrane via a lectin-like interaction that is specifically dissociated with D-mannose. The dissociated IL-1 was detected as both a biological activity and, by immunoprecipitation and SDS-PAGE, as a 33 kDa IL-1 alpha precursor. Treatment of macrophages with D-mannose before fixation depleted detectable IL-1 biological activity associated with the membrane. Pro-IL-1 alpha was glycosylated in these cells, as shown by incorporation of D-[14C]mannose; thus it is likely that a cell surface lectin binds pro-IL-1 via these carbohydrate residues. In addition to anchoring IL-1 precursor to the plasma membrane, this lectin-like interaction may also be important in the overall regulation of IL-1 release.

Lectins in cancer cells.

Studies carried out over the last few years have demonstrated that tumor cells and malignant tissues contain lectins that are similar in sugar-binding specificity, molecular size, and antigenicity to the lectins found in normal cells and tissues. Lectins from tumor cells also share marked sequence homology with lectins from normal tissues. Lectins were purified from various tumor cells by affinity chromatography and monoclonal and polyclonal antilectin antibodies were prepared against them. These enabled us to establish the following: (1) Lectins are present on the surface of all the tumor cells that were examined, albeit at varying levels. (2) The level of cell surface lectins increases after normal cells are transformed by transfection with certain oncogenes or by retroviruses, or when cells transformed with a temperature-sensitive viral mutant are switched from growth at the nonpermissive to the permissive temperature. (3) Among tumor cells differing in metastatic propensity, those exhibiting a higher potential express higher levels of surface lectins. (4) Tumor cell surface lectins might be involved in cell-cell adhesion, cell attachment to substratum, the expression of the transformed phenotype (anchorage-independent growth), and blood-borne metastasis. (5) The levels of the lectins in tumor cells are modulated by agents that suppress the transformed phenotype (as represented by anchorage-independence) or enhance differentiation. Numerous studies by others have shown that cell surface carbohydrate-containing molecules are modified after transformation, and our findings demonstrate that the expression of cell surface carbohydrate-binding proteins is also altered by transformation. Obviously, any of these changes may result in alterations in cellular interactions. All the above findings implicate tumor cell lectins in cellular interactions (adhesion, attachment, possible binding of exogenous soluble glycoconjugates), cell growth and anchorage-independent growth, malignant transformation, tumor cell differentiation, and metastasis. It is clear that even if these lectins are involved in only a few of these fundamental processes, it is important to elucidate their functions and the mechanisms by which their expression is regulated during neoplastic transformation and tumor progression and the suppression of the transformed phenotype.