Modification of the erythrocyte surface in rats bearing Yoshida ascites sarcoma is brought about by a tumour variant of α2-macroglobulin

Abstract

Erythrocytes from the circulation of rats bearing Yoshida ascites sarcoma exhibit higher concanavalin A (ConA)-mediated agglutinability than those from normal animals. A tetrameric glycoprotein of subunit molecular mass 170 kDa, purified from the cell-free ascites fluid, was found to confer higher ConA-mediated agglutinability on erythrocytes in vitro. An antiserum to this tumour-derived protein failed to detect any cross-reactive component in normal rat plasma or in any of the normal tissues examined. An immunoreactive protein was, however, detected in blood plasma when the acute-phase reaction was stimulated by injection of turpentine. The cross-reactive acute-phase protein was purified by ConA-affinity, gel-filtration and ion-exchange chromatography, and identified as alpha2-macroglobulin. The acute-phase protein and the protein obtained from the ascites fluid have identical or very similar native and subunit molecular masses, subunit arrangement and pI. They both are able to inhibit trypsin and, as a consequence, acquire greater mobility in native PAGE. In addition, the two proteins bind to rat erythrocytes non-specifically, and in similar amounts. However, despite these similarities, the acute-phase protein is unable to enhance the agglutinability of erythrocytes. The two proteins differ in their carbohydrate content, but this differential glycosylation is not the cause of the difference in their surface modification activity. The chemically deglycosylated proteins show a small but consistent difference in the size of their polypeptides. Their tryptic peptide maps, although largely similar, show some differences, as do their amino acid compositions. It is probable that the proteins are independent members of the same (alpha-macroglobulin) family. The rat embryo is also found to express a soluble protein consisting of a 170 kDa polypeptide that cross-reacts with the antibody to the tumour-derived protein. The purified embryo protein is able to alter the ConA-mediated agglutinability of erythrocytes in vitro, and also yields a tryptic peptide map that is identical to that of the tumour-derived protein. The modification of the host cell surface in the tumour-bearing rats is thus caused by what appears to be a tumour (oncofetal?) variant of alpha2-macroglobulin.

Cancer‐related anemia in a rat model: α2‐macroglobulin from Yoshida sarcoma shortens erythrocyte survival

“…From our earlier work, ascites fluid‐derived α 2 ‐macroglobulin was found to modify membrane properties of erythrocytes, as reflected in their acquisition of high Con A‐agglutinability (12, 13). Since the survival of erythrocytes in the circulation is also determined by cell membrane characteristics (see ), the effect of α 2 M on the survival of the cells was tested.…”

“…During the acute phase reaction, a protein appears in the blood that is very similar to the tumor‐derived α 2 M (13). When erythrocytes from the acute phase‐primed rats were isolated, labeled with 51 Cr and injected in normal animals, their survival was found to be normal (not shown).…”

“…The sources of reagents and other material used in the study have been described earlier (13, 14) except sodium ( 51 Cr)chromate, which was purchased from Amersham International plc, Little Chafont, Bucks., UK.…”

“…The preparation of erythrocyte ghosts, sodium dodecyl sulfate – polyacrylamide gel electrophoresis (SDS‐PAGE) with Coomassie blue staining, and Western blotting have been described earlier (13).…”

“…We found that a 170‐kDa subunit glycoprotein, secreted by the tumor cells, enters the circulation, binds to erythrocytes (11) and increases their agglutinability by reducing the charge on the cell surface (12). The protein was identified as an oncofetal variant of the rat acute‐phase plasma protein, α 2 ‐macroglobulin (13). During these studies it was repeatedly observed that, following transplantation of the tumor, the yield of erythrocytes from the blood of the rats decreased progressively.…”