[Endogenous tumor lectins: new tumor markers and targets in cancer therapy?].
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Biomarkers, Tumor↗
Biomedical subjects
S Gabius
Publications and source records attributed to S Gabius.
Conjugation of p-aminophenyl glycosides with squaric acid diester to a carrier protein and the use of neoglycoprotein in the histochemical detection of lectins.
The coupling of p-aminophenyl 2-acetamido-2-deoxy-3-O-beta-D- galactopyranosyl-beta-D-galactopyranoside (gal-beta 1,3-galNAc) to bovine serum albumin (BSA) was achieved by using 1,2-diethoxycyclobutene-3,4-dione (squaric acid diester) as a new coupling reagent. Two selective consequential steps afforded the desired neoglycoprotein: reaction of the p-aminophenyl group of gal-beta 1,3-galNAc with squaric acid diester gave the corresponding squaric acid amide ester, which was transformed into the BSA conjugate by coupling with the lysyl epsilon-amino group of BSA through formation of a squaric acid 1,2-bisamide. The experimental conditions for the reactions and the optimization of average were performed by using p-anisidine as model substance, the methyl group substituting for the carbohydrate part of a p-aminophenylglycoside. Neoglycoproteins have proven to be valuable tools for lectin detection. To evaluate the properties of this type of probe, the obtained neoglycoprotein with the histochemically crucial T-antigen structure was used for glycocytological and glycohistochemical studies. Three cultured human tumor cell lines and tissue sections from human breast carcinomas were chosen. Its efficiency was similar in comparison to measurements with a probe, derived by diazotization with the p-aminophenyl glycosides of gal-beta 1,3-galNAc and already shown to be a reliable marker for lectin localization in tissue sections and cultured cells.
Antigens, Tumor-Associated, Carbohydrate↗
The immunomodulatory beta-galactoside-specific lectin from mistletoe: partial sequence analysis, cell and tissue binding, and impact on intracellular biosignalling of monocytic leukemia cells.
Nanogram quantities of the beta-galactoside-specific lectin from mistletoe (ML-I) that is composed of two different types of subunits exhibit immunomodulatory potency and enhance cytokine secretion in vitro and in vivo. Partial sequence analysis of the carbohydrate-binding B chain revealed a ragged N-terminus and overall homologies to the B subunit of Ricin D and Ricin E. Two evolutionarily neutral substitutions were apparent in the otherwise identical N-terminal sequences of the two toxic chains within the lectin preparation. On the basis of the influence of chemical modification by group-specific reagents on ligand binding, the lectin was biotinylated with biotinyl-N-hydroxysuccinimide ester to allow monitoring of cell binding. Monocytic leukemia cells (THP-1) specifically bound the lectin with positive cooperativity at low lectin concentrations. Radiolabelled lectin could be found in several organs and in an experimental solid tumor in biodistribution in mice. Its presence in a notable amount in spleens is especially noteworthy with respect to the already reported immunomodulation. To determine intracellular responses that precede the lectin-dependent augmentation of cytokine secretion, phosphorylation of proteins and phospholipids as well as Ca(2+)-mobilization were assessed in THP-1 cells. Quantitative increases of [32P]-phosphate incorporation were determined for a 28 kDa protein and for phosphatidylinositol-4,5-biphosphate. Similarly, the fluorescence activity of the intracellular Ca(2+)-indicator fluo-3 is elevated by approximately 25% after lectin treatment. Apparently, cell binding of the lectin is followed by modulation of biosignalling processes.
Amino Acid Sequence↗
Establishment, characterization and determination of cell surface sugar receptor (lectin) expression by neoglycoenzymes of a human myeloid marker-expressing B lymphoblastoid cell line.
Mediation of cellular interactions by protein (lectin)-carbohydrate recognition presupposes the expression of respective surface determinants. Due to the importance of cellular contacts between bone marrow stromal cells, recently shown to express cell surface lectins, and tumor or normal progenitor cells for biosignaling and marrow egress, quantitation of cell surface sugar receptor expression by a panel of chemically glycosylated enzymes (tetrameric E. coli beta-galactosidase) for human leukemia/lymphoma cells was initiated. Cells of the new B lymphoblastoid line Croco II that are partially positive for the CD15-specific epitope expressed receptors for various sugar specificities on their surface, fulfilling an indispensable prerequisite for establishment of glycobiological interactions. Binding studies with increasing neoglycoenzyme concentrations up to saturation in four cases disclosed values for apparent affinity constants in the range of 25-200 nM with 0.25-3 x 10(5) bound probes per cell. The presence of receptors for constituents of carbohydrate chains of cellular glycoconjugates was also ascertained biochemically, namely for beta-galactosides, alpha-mannosides, alpha-fucosides and N-acetylgalactosaminides. Expression of this property was modulated by changes in the culture conditions, as revealed by binding studies with cells, derived from growth in medium containing different serum concentrations. These findings indicate that cell surface sugar receptors of tumor cells warrant further attention with respect to recognitive interactions.
Antigens, CD↗
Regulation of distribution, amount and ligand affinity of sugar receptors in human colon carcinoma cells by treatment with sodium butyrate, retinoic acid and phorbol ester.
Human colon carcinoma cells were treated with non-toxic levels of sodium butyrate, retinoic acid or phorbol ester, eliciting characteristic growth inhibition and morphological changes. Since protein-carbohydrate interactions are supposedly involved in regulatory processes and can serve within targeted drug delivery, the capacity to bind components of the carbohydrate chains of cellular glycoconjugates was monitored for such cells in relation to the type of the medium additive. The pattern of binding of a panel of neoglycoproteins was significantly altered for fixed cells, depending on the type of putative maturation factor. Quantitation of cell surface sugar receptors at a non-saturating concentration of neoglycoenzyme, employed as carbohydrate ligand-exposing probe, led to a similar conclusion. Up to six-fold increases were determined for individual probes. Binding studies with varying concentrations of neoglycoenzymes in the case of four ligands revealed that the receptor density, but not the affinity was significantly affected. Biochemical analyses corroborated this result by demonstrating mainly quantitative differences after affinity chromatography of detergent extracts from the four types of cell pellet. By showing the inhibitory potency of neoglycoprotein-conjugated liposomes in the cell binding assay with neoglycoenzymes, a perspective is indicated, of how the different effects of the differentiation-inducing agents might be beneficially exploited in targeted drug delivery.
Adenocarcinoma↗