New plasma membrane proteins expressed by a high metastatic variant of a chemically induced tumor

The composition of plasma membrane proteins of related low and high metastatic tumor cells were compared in order to elucidate possible genetic changes which may occur during progression of tumor cells towards metastatic capacity. For this purpose a procedure was worked out which allows the purification of mouse plasma membrane (PM) proteins from biosynthetically labeled cells. PM isolated from the two related T lymphoma lines Eb and ESb, which differ greatly in metastatic capacity, as well as from Con A-activated T cell blasts displayed similar degrees of purification as shown by marker enzyme analysis. When [35S]-methionine-labeled proteins of such PM preparations from cloned Eb and ESb cells were compared by 2-D gel electrophoresis it was found that maps of the highly metastatic variant ESb cells permitted detection of about 50 new protein spots which were not found on the 2-D gel maps of the parental Eb cells. Approximately 80% of these new spots were also found on maps derived from syngeneic splenic Con A blasts. This observation indicated that most of the newly expressed membrane proteins of ESb cells were possible differentiation or cell activation-related and not tumor cell-specific.