A re-examination of the isolectin components of the fucose-binding proteins of Lotus tetragonolobus

Fucose-binding lectins: purification, characterization and potential biomedical applications

The property of lectins to specifically recognize and bind carbohydrates makes them an excellent candidate in biomedical research. Among them are fucose-binding lectins possessing the capacity to bind fucose are taxonomically, evolutionarily and ecologically significant class of lectins that are identified in a wide range of taxa. Purification of fucose-binding lectins dates back to 1967 when L-fucose binding protein from Lotus tetragonolobus was isolated using a dye that contained three α-L-fucopyranosyl residues. Beginning with that, several FBLs were purified from various animals as well as plant sources that were structurally and functionally characterised. This review focuses on fucose-binding lectins, their occurrence and purification with special emphasis on various strategies adopted to purify them followed by molecular and functional characterization. The exclusive ability to recognize and bind to fucose-containing glycans endows these lectins with the potential to act as anti-cancer agents, diagnostic markers and mitogens for immune cells. Though they have been in research focus for more than half a century with their occurrence reported in various taxa, they still need to be explored for their prospective functions to develop them as a biological tool in biomedical research.

A metastasis-associated antigen is present on a 60 kDa glycoprotein in transitional cell carcinoma of the human urinary bladder

We have previously shown that the degree of expression of Lex-related carbohydrate epitopes, namely, Lotus tetragonolobus agglutinin (LTA) receptors, SSEA-1 and FH6, correlates with the metastatic potential of transitional cell carcinoma of the human urinary bladder. In an effort to obtain a better reagent with which to detect a metastasis-associated epitope, monoclonal antibodies were produced against LTA receptors from BOY bladder carcinoma cells. One antigen defined by such a monoclonal antibody, MM4, indeed showed better correlation with the metastatic potential of the tumour than did other carbohydrate markers. In the LTA receptors, MM4 antigen was located only on a 60 kDa glycoprotein. In extracts from primary carcinomas and lymph node metastases, the 60 kDa glycoprotein was the principal carrier of MM4 antigen. LTA receptors from these sources were composed of arrays of glycoproteins, while the 60 kDa one was invariably present. Metastasis-associated carbohydrate epitopes on the 60 kDa glycoprotein may promote metastasis by interaction with carbohydrate-recognizing proteins such as selectins on host cells.

Expression of SSEA-1 carbohydrate antigen correlates with stage, grade and metastatic potential of transitional cell carcinoma of the bladder

Expression of stage-specific embryonic antigen-1 (SSEA-1) was immunohistochemically analyzed in primary cancerous regions from transitional cell carcinoma of the bladder. Lymph node metastasis occurred in 14 (50%) of 28 patients with high expression of SSEA-1 antigen, but in only one (4%) of 23 patients with low or no expression. Of 36 invasive bladder carcinoma patients with no metastasis at operation, 8 (57%) of 14 with high expression of SSEA-1 antigen died of cancer or had metastasis, whereas 4 (18%) of 22 with low or no expression had progression of the disease. In addition, stage pT3b-4 tumors more frequently reacted with SSEA-1 MAb than stage pT1 tumors (p less than 0.01). Grade 2 or 3 tumors were also more reactive than grade 1 tumors, which were all unreactive except for one (p less than 0.01, respectively). Our data suggest that SSEA-1, which is a Le(x) antigen, correlates with stage and grade as well as metastatic phenotype of transitional cell carcinoma of the bladder.

Reactivity to Fucose-Binding Proteins of Lotus Tetragonolobus Correlates with Metastatic Phenotype of Transitional Cell Carcinoma of the Bladder

Expression of binding sites for fucose binding proteins (FBP) of Lotus tetragonolobus were immunohistochemically analyzed in surgically extirpated specimens from patients with transitional cell carcinoma of the bladder. The degree of expression of FBP binding sites in the primary cancerous region correlated with the occurrence of lymph node metastasis. Thus, lymph node metastases occurred in 15 of 34 cases with high expression of FBP binding sites, but did not in 17 cases with low or no FBP binding site expression. All metastatic lymph nodes strongly reacted with FBP. In addition, primary lesions at the pT3b or pT4 stage more frequently reacted with FBP as compared with those at the pTa, pT1 or pT2 stage. Although FBP is known to react both with Gal beta 1----4(Fuc alpha 1----3)GlcNAc and Fuc alpha 1----2Gal sequences, comparative staining of other carbohydrate markers revealed that the latter structure is not related with metastatic potential and stages.

Expression of blood group antigens and lectin binding in adenocarcinomas of the endometrium

To investigate cytoplasmic alterations in cancers of the endometrium, monoclonal antibodies against H, A and B blood group substances and related lectins such as Ulex europaeus agglutinin 1 (UEA-1), Lotus tetragonolobus agglutinin (LTA), and Griffonia simplicifolia 1 (GS1-A4, -B4) were applied to 42 cases of endometrial adenocarcinoma (EAC) and 11 adenomyoses. The control specimens consisted of normal endometria with leiomyoma or adenomyosis from patients of known blood group type. The brightest and most consistent staining was obtained with GS1-A4, showing 98% positivity in EAC in contrast to 18% in normal endometria. In contrast, expression of A antigen was seen in only 24% of EAC and in 13% of normal endometria, UEA-1 binding was seen in 81% of EAC and in 10% of normal endometria, whereas H antigen was seen in 60% of EAC and 0% of normal endometria. In adenocarcinomas, staining was seen not only along the luminal border of glands but also in the cytoplasm and the lateral or basal cell membranes, whereas in the normal endometrium staining was mostly along the luminal border. Thus, a difference in the positivity and localization of glycoconjugates was observed in neoplastic and non-neoplastic endometrium.

Correlation between glycoconjugate expression and fucosyltransferase activity in human colorectal carcinoma

Using the surgically extirpated specimens from 9 patients with colorectal carcinoma, fucosyltransferase activities in the carcinoma tissue and the normal mucosa were measured and were compared with the histochemical findings of glycoconjugates which were shown by staining with lectins reacting with blood group antigens and related substances. The fucosyltransferase activities of the carcinoma tissue were well correlated with the overall findings of lectin stainings after neuraminidase treatment. The more intense the carcinoma tissue was stained, the higher the fucosyltransferase activity was shown. However, there were marked differences in the fucosyltransferase activities by the portions measured, depending upon the relative amount of carcinoma tissue and interstitial tissue; in the invasive portion with less carcinoma tissue, the activity was generally low in comparison with that in the surface area where carcinoma tissue was rather abundant. Thus, the morphological and lectin histochemical finding are of paramount importance for the evaluation of glycosyltransferase activity in human colorectal carcinoma.

Receptors for fucose-binding proteins of Lotus tetragonolobus isolated from mouse embryonal carcinoma cells. Structural characteristics of the poly(N-acetyllactosamine)-type glycan

Receptors for fucose-binding proteins of Lotus tetragonolobus were isolated from N4-1 and F9 embryonal carcinoma cells. They were glycoproteins, whose major components had apparent relative molecular masses of more than 100,000. Carbohydrates released from the receptors of N4-1 cells by hydrazinolysis were separated into three fractions by gel filtration. Binding activity to the lectin was detected in the high-molecular-mass fraction. The composition of the large glycan was characteristic of the poly (N-acetyllactosamine)-type, and glucosamine was identified as the sugar involved in the protein-carbohydrate linkage. The glycan has one fucosyl residue per four N-acetyllactosamine units. Most of the fucose was linked to the C-3 hydroxyl group of N-acetylglucosamine. No Fuc alpha 1----2Gal or Fuc alpha 1----4GlcNAc linkage was detected. The glycan had a relative molecular mass of 9000 or more and the poly(N-acetyllactosamine) units were branched. N-Acetylgalactosamine residues were detected in non-reducing ends of at least a part of the glycan. Therefore, the glycan has a more complex structure than the related one from human granulocytes, although both of them have Fuc alpha 1----3GlcNAc termini.

Differential distribution of receptors for two fucose-binding lectins in embryos and adult tissues of the mouse

Ulex europaeus agglutinin-I (UEA-I) recognizes the Fuc alpha 1----2 Gal linkage. Receptors for UEA-I were not detected in mouse embryos until the 13th day of embryo-genesis, except for their temporary expression in early trophectoderm cells. In adult mice, UEA-I receptors were detected at various sites, including cells of the digestive tracts, the bronchial epithelium, Hassall's corpuscle of the thymus, and the skin. The fucose-binding protein of Lotus tetragonolobus (FBP) is another lectin that recognizes fucosyl residues. The distribution of FBP receptors was significantly different from that of UEA-I receptors. FBP receptors were first detected in late 8-cell embryos and were expressed in the embryonic ectoderm, visceral endoderm, and trophoblastic giant cells in egg-cylinders. At later stages, the distribution of FBP receptors became restricted to certain parts of the embryo. In the adult, the distribution of FBP receptors was more restricted than that of UEA-I receptors. Particularly in embryos before the 11th day of gestation, the distribution of FBP receptors resembled that of SSEA-1, which is defined by the Gal beta 1----4(Fuc alpha 1----3) GlcNAc linkage. From the specificity of FBP, we inferred that the disappearance of SSEA-1 and FBP receptors during embryogenesis is not the result of alpha 1----2 fucosylation of the terminal galactosyl residue in the determinant. The fact that the expression of two fucose-related cell-surface markers, i.e., UEA-I receptors and SSEA-1 (or FBP receptors), is developmentally regulated in an entirely different fashion is an excellent example illustrating the precise control of differentiation-dependent alterations in cell-surface carbohydrates.