concanavalin-a and Paraneoplastic-Syndromes

As a model for the development of paraneoplastic syndromes, we have studied the mechanism by which erythrocytes in the circulation of rats bearing intraperitoneal Yoshida ascites sarcoma acquire higher agglutinability with concanavalin A (Con A). The in vitro incubation of erythrocytes from normal animals with the cell-free ascites fluid or the plasma of tumour-bearing animals is able to confer an enhanced agglutinability on the cells. Fractionation of the ascites fluid has yielded three subfractions that are active in vitro. Two of these, occurring in small amounts, are a particulate fraction rich in plasma-membrane markers and a soluble fraction containing protein of molecular mass equal to or less than 50 kDa. These two are, however, unable to affect the agglutinability of erythrocytes in vivo, i.e. when injected intraperitoneally into normal rats. The third, and major, fraction consists of proteins 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 filtration, (NH4)2SO4 fractionation and DEAE-Sephadex chromatography, an active protein has been purified to apparent homogeneity. It yields a subunit of 310 kDa in the presence of SDS and further breaks down into a polypeptide of 170 kDa when reduced with 2-mercaptoethanol. It has a pI of 5.35. The protein is rich in Glx, and appears to contain hybrid-type N-linked oligosaccharides. The protein is also present in the blood plasma of tumour-bearing, but not normal, rats. The radioiodinated protein 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.

Topics: Agglutination; Animals; Chromatography, Gel; Chromatography, Ion Exchange; Concanavalin A; Electrophoresis, Polyacrylamide Gel; Erythrocytes; Glycoproteins; Paraneoplastic Syndromes; Rats; Rats, Wistar; Sarcoma, Yoshida

A not well-appreciated but clinically important aspect of malignant tumours is their effects on distantly located host cells. The effects, termed paraneoplastic syndromes, also pose an intriguing mechanistic problem: how do malignant cells influence properties of host cells not in contact with them? Erythrocytes from the circulation of rats bearing intraperitoneal Yoshida ascites sarcoma exhibit higher agglutinability with concanavalin A (Con A) than the cells from normal animals. Since the tumour and the red cells are not in contact, the enhanced agglutinability of the latter is a paraneoplastic effect. The mechanism by which the tumour brings about this effect is investigated as a model for paraneoplastic syndromes. The cell-free ascites fluid is able to impart high agglutinability on cells from normal animals in vitro. Also, when injected intraperitoneally in normal animals, the ascites fluid is able to enhance the agglutinability of erythrocytes in circulation. Apparently the tumour produces a substance(s) that appears in the ascites fluid and is able to diffuse into circulation, explaining the mechanism by which it can reach distant sites. From the cell-free ascites fluid three fractions have been isolated that are active in vitro. Of these, only one showed activity in vivo. From this fraction, a glycoprotein has been purified to homogeneity that confers maximal Con A-agglutinability on normal erythrocytes at 8 x 10(-7)M, at which concentration 6,400 molecules bind per cell. The protein has a molecular weight of 600 kDa in the native state and a pI of 5.35. It is made up of 4 identical subunits of Mr 170,000. It is detected in the plasma of tumour-bearing but not normal rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: alpha-Macroglobulins; Animals; Ascitic Fluid; Concanavalin A; Disease Models, Animal; Electrophoresis, Polyacrylamide Gel; Erythrocyte Aggregation; Erythrocyte Membrane; Erythrocytes; Glycoproteins; Neoplasm Proteins; Paraneoplastic Syndromes; Rats; Sarcoma, Yoshida