ISOLATION OF A GLYCOPROTEIN RESPONSIBLE FOR THE ENHANCED CONCANAVALIN-A AGGLUTINABILITY OF ERYTHROCYTES IN YOSHIDA-ASCITES-SARCOMA-BEARING RATS - THE MECHANISM OF PARANEOPLASTIC SYNDROMES

As a model for the development of paraneoplastic syndromes, we have st udied the mechanism by which erythrocytes in the circulation of rats b earing intraperitoneal Yoshida ascites sarcoma acquire higher agglutin ability with concanavalin A (Con A). The in vitro incubation of erythr ocytes from normal animals with the cell-free ascites fluid or the pla sma of tumour-bearing animals is able to confer an enhanced agglutinab ility on the cells. Fractionation of the ascites fluid has yielded thr ee subfractions that are active in vitro. Two of these, occurring in s mall amounts, are a particulate fraction rich in plasma-membrane marke rs and a soluble fraction containing protein of molecular mass equal t o or less than 50 kDa. These two are, however, unable to affect the ag glutinability of erythrocytes in vivo, i.e. when injected intraperiton eally into normal rats. The third, and major, fraction consists of pro teins of molecular mass equal to or greater than 680 kDa, and is able to modify the erythrocyte agglutinability in vivo. From this fraction, by using a combination of Con A affinity chromatography, gel filtrati on, (NH4)2SO4 fractionation and DEAE-Sephadex chromatography, an activ e protein has been purified to apparent homogeneity. It yields a subun it of 310 kDa in the presence of SDS and further breaks down into a po lypeptide of 170 kDa when reduced with 2-mercaptoethanol. It has a pl of 5.35. The protein is rich in Glx, and appears to contain hybrid-typ e N-linked oligosaccharides. The protein is also present in the blood plasma of tumour-bearing, but not normal, rats. The radioiodinated pro tein binds to the erythrocyte surface adding about 7400 molecules/cell . The study unequivocally demonstrates that a protein from the tumour fluid can appear in the circulation, interact with host cells that are not in contact with the tumour and modify their properties.