Cell cycle dependent agglutinability, distribution of concanavalin A binding sites and surface morphology of normal and transformed fibroblasts

In studies on phenotypic reversion of transformed cells to normal growth patterns, we investigated the effect of dibutyryl cyclic AMP (dbc-AMP) and a protease inhibitor (TLCK) on growth of SV40-transformed mouse fibroblasts (3T3). The results did not support the hypothesis that transformed cells grown with dbc-AMP or TLCK are induced to contact-mediated growth control. The growth rate of SV-3T3 cells grown with the drugs was strongly reduced, due to accumulation of the cells in the G2 phase of the cell cycle. In addition, decreased agglutinability with concanavalin A (Con A) of those SV-3T3 cells was not caused by a direct effect of the drugs on the cell surface, but by partial synchronization of the cells in the G2 phase of the cycle. In synchronized cultures agglutinability of transformed cells reached a minimum in G2 and was maximal in mitosis and G1. Normal cells agglutinated only in mitosis. This suggested that agglutinability of cells is somehow cell cycle dependent. Cytochemical investigations on normal and transformed 3T3 cells had shown that Con A-induced redistribution of binding sites on the surface of these cells is not correlated with agglutinability. The present work on replicas confirmed this, but indicated also that normal 3T3 cells have more extended lamellipodia with less Con A binding sites than SV-3T3 cells. Preliminary scanning electron microscope data showed cell cycle dependent changes in 3T3 cells and also showed that confluent 3T3 and SV-3T3 cells suspended for agglutination tests had a different surface morphology. These results may represent additional factors important for differences in cell agglutinability by Con A.