Ligand-induced Redistribution of Concanavalin a Receptors on Normal, Trypsinized and Transformed Fibroblasts

Abstract

WHEN normal fibroblasts or fibroblast-derived cells are stably transformed by oncogenic viruses they acquire a number of new properties, some of which involve the cell surface^1,2. Transformed cells are agglutinated by plant lectins, such as cancanavalin A (con A), at concentrations where normal cells are unaffected^3–6. Increased agglutination can also be induced in normal cells by low concentrations of trypsin^8,7. The reasons for these differences in agglutinability are unclear. As enhanced agglutination cannot be accounted for by an increase in the number of lectin receptors resulting from either new synthesis or “unmasking” of hidden sites^8–10, it has been suggested that it may result from changes in the arrangement of cell surface lectin receptors¹¹. This hypothesis has been supported by the observation that receptors labelled with con A-ferritin appear randomly dispersed on isolated membranes from normal 3T3 cells, but are clustered on the membranes of transformed or trypsinized 3T3 cells^11,12. Similar observations, with some notable exceptions, were made on labelling intact cells on glass with con A and peroxidase¹³. Several studies, however, have now demonstrated that cell surface macro-molecules are mobile in the plane of the membrane and that their distribution can be altered by the binding of multivalent ligands^14–18. It is therefore possible that the clustered distribution of con A receptors was secondarily induced by the binding of the multivalent con A. We have tested this hypothesis and tried to correlate the pattern of induced redistribution and agglutinability in normal, trypsinized and transformed cells, using thin section electron microscopy.