Platelet aggregating material in mouse tumor cells. Removal and regeneration

The platelet aggregating principle of two mouse ascites tumors and of their cell-free supernatants released spontaneously has been studied. It was found that the principle disappeared from the cells after trypsin digestion and that part of it was recovered in the cell-free trypsinate. Digested cells regenerated the principle during subsequent incubation by a process requiring protein synthesis. The principle was found to be spontaneously released by intact cells into the medium and sensitive to proteolytic attack. The principle was not present in five varieties of nonneoplastic cells. Since previous work by the authors indicates that the principle is present in numerous other tumor cell lines, its study might reveal it to be an indicator of malignant transformation or malignant progression.