Yu Koyama

Apoptosis Induction by Lectin Isolated from the Mushroom Boletopsis leucomelas in U937 Cells

A 15-kDa lectin was isolated from the edible mushroom Kurokawa by affinity chromatography using N,N′-diacetylchitobiose-Sepharose 4B. The results of microsequencing analysis indicated that the lectin has a partial amino acid sequence similar to the mushroom lectin, Agaricus bisporus agglutinin (ABA). We found that the Kurokawa lectin inhibited proliferation of human monoblastic leukemia U937 cells dose-dependently. Several lines of evidence indicated that this inhibition was due to its apoptosis induction. We observed that the lectin induced apoptotic bodies formation, chromatin condensation, and DNA ladder formation, features of apoptosis. The DNA ladder formation was inhibited by a general inhibitor of caspases, which are known to play essential roles in apoptosis. In contrast, ABA did not have cell growth-inhibiting or apoptosis-inducing activities. Thus, the Kurokawa lectin is the first mushroom lectin with apoptosis-inducing activity.

Carbohydrate Specificity of Lectins from Boletopsis leucomelas and Aralia cordate

The carbohydrate specificity of three novel lectins, Boletopsis leucomelas lectin (BLL), Aralia cordate lectin (ACL), and Wasabia japonica lectin (WJL), was examined by frontal affinity chromatography using a panel of fluorescently labeled 47 oligosaccharides. The results indicate that BLL recognizes an agalacto structure of the biantennary chain and its bisecting structure. ACL showed strong affinity for triantennary oligosaccharides, but no affinity for tetraantennary structure. WJL showed no appreciable affinity for any of the 47 glycans examined. These lectins with a unique affinity specificity might be useful for examining alterations in the glycan structures of the glycoconjugates in association with development and various diseases.

Isolation of Lectins by Affinity Chromatography with Porcine Plasma Proteins Immobilized on Agarose

To develop a convenient method to isolate lectins, we prepared an affinity gel by coupling plasma proteins with agarose beads under conditions where the pH did not exceed 7.5. The validity of the use of this affinity gel in combination with elution using a hapten saccharide was confirmed by isolation of concanavalin A from Jack bean meal. Successful application of the method was demonstrated by isolation of two novel vegetable lectins from udo (Aralia cordate) and wasabi (Wasabia japonica). The method would be useful to isolate new lectins from various sources including plant and animal tissues.

Stimulation of IL-8 production by Aralia cordate lectin in human colon carcinoma Caco-2 cells.

Some lectins are known to stimulate interleukin-8 (IL-8) productions in human colon carcinoma Caco-2 cells. Since IL-8 may cause deleterious effects, we examined this stimulatory activity of Aralia cordate lectin (ACL) and Wasabia japonica lectin (WJL), both of which we isolated recently. The results indicate that ACL exhibited strong stimulatory activity for IL-8 protein production, while WJL showed marginal activity. The activity of ACL was associated with high enhancement of IL-8 gene expression. The effect of ACL was abolished almost completely in the presence of brefeldin A, indicating that internalization into cells is necessary for ACL to exert activity. The findings suggest that ingestion of a large amount of raw vegetable Aralia cordate might cause unfavorable effects on the colon.