Introduction to the Symposium and Studies on the Surfaces of Separated and Synchronized Tumor and Embryonic Cell Populations
Tumor and embryonic cell surfaces are examined in this symposium with respect to their roles in cell-cell interactions and in early development and malignancy. Three sets of studies have been recently performed in my laboratory to help elucidate the nature of tumor and embryonic cell surfaces and the means by which these cells adhere to each other. We separated an in vivo 129/J ascites mouse teratoma into specific subpopuladons of cells by velocity sedimentation in shallow density gradients. The teratoma consistently separated into two major populations: "large" and "small" cells. Only the large cells displayed "malignant-like" surface characteristics in terms of their agglutinability with carbohydrate binding lectins. The teratoma cells were also synchronized in culture with thymidine plus colcemid. In these synchronized cultures, cellular adhesiveness and glutamine synthetase specific activity displayed oscillatory patterns with peaks of glutamine synthetase specific activity occurring just prior to peaks of adhesivenesss. Also, both glutamine synthetase specific activity and cellular adhesiveness were enhanced by two compounds: actinomycin D and hydrocortisone. Based upon previous work that implicates L-glutamine in intercellular adhesion, it is not unreasonable to speculate that glutamine synthetase specific activity and cellular adhesiveness may be causally related. The problem of altered tumor cell adhesiveness is important because it seems, in part, to be responsible for tumor spread. Finally, the sea urchin embryo system was utilized to identify specific cell surface carbohydrates that may be involved in intercellular adhesion. In 15 separate experiments with each sugar and with 15 different saccharides, D-galactose and N-acetyl-D-galactosamine were the best inhibitors of rotation-medicated reaggregation of 24-hr sea urchin embryo cells dissociated by removal of divalent cations. ?-galactosidase also inhibited reaggregation of these cells. These results implicate galactopyranosyl-like residues in the adhesion of 24-hr sea urchin embryo cells with each other.