A
lectin isolated from Rana catesbeiana eggs preferentially agglutinates a large variety of human and animal
tumor cells but not normal red blood cells, lymphocytes, or fibroblasts. The phenomenon correlates with a higher binding activity of the
lectin with
tumor cells. Chemical and physical analysis of the purified
lectin indicates that the
lectin is a low molecular weight basic
polypeptide with five intrachain
disulfide bonds. Its agglutination of
tumor cells was abolished by blocking the amino group. The
lectin strongly binds with a large variety of
tumor cells but binds only minimally with fibroblasts, lymphocytes, and erythrocytes.
Tumor cell agglutination induced by this
lectin was strongly inhibited by submaxillary
mucin, to a lesser degree by
fetuin and
keratan sulfate, and not at all by less-sialylated
glycoproteins, such as
transferrin. Inhibition by
mucin or
fetuin was greatly reduced by desialylation of
glycoprotein with
sialidase. Treatment of
tumor cells with
sialidase greatly reduced the
lectin-dependent agglutination, and the
sialidase-dependent reduction of
tumor cell agglutination was inhibited by the
sialidase inhibitor
2,3-dehydro-2-deoxy-N-acetylneuraminic acid. However,
tumor cell agglutination was not inhibited by
chondroitin sulfates or
hyaluronic acid. Thus, the
lectin-dependent
tumor cell agglutination is due to a high density of
sialic acid at the cell surface. The receptor
glycoprotein that interacts with this
lectin was demonstrated in the
detergent-insoluble fraction of a variety of
tumor cells by
sodium dodecyl sulfate:
polyacrylamide gel electrophoresis, followed by Western blotting with
lectin and anti-
lectin antibodies. The presence of a common high molecular weight
lectin-binding
glycoprotein in various
tumor cells was demonstrated.