Cell surface lectins of transplantable human teratocarcinoma cells: purification of a new mannan-specific endogenous lectin.
Fractionation of detergent extracts of transplanted tumors of human teratocarcinoma cells by affinity chromatography yields one predominant protein with apparent molecular weight of 14,000 and further, for less abundant protein with apparent molecular weight of 35,000 from lactose-sepharose and one protein with apparent molecular weight of 68,000 from mannan-sepharose. No further carbohydrate-binding protein can be isolated on columns derivatized with asialofetuin, melibiose and L-fucose, to which the extract is applied successively. Both proteins agglutinate trypsinized, glutaraldehyde-fixed rabbit erythrocytes in the absence of Ca2+ and can thus be defined as endogenous human teratocarcinoma lectins. Inhibition of heterotypic and homotypic aggregation of human teratocarcinoma cells by D-mannose, D-galactose and glycoproteins rich in one of these sugars is consistent with a functional role of these Ca2+-independent lectins in cell aggregation. Visualization of these activities by fluorescent mannosylated and lactosylated markers on the cell surface further supports the cell surface localization of these detergent extractable lectins. The mannan-specific lectin, in particular, has so far not been detected in any mammalian tissue or tumor and is of potential value for a lectin-based diagnosis and therapy of embryonal carcinomas.