CHARACTERIZATION OF PLATELET-AGGREGATION INDUCED BY THE HUMAN CARCINOSARCOMA COLO-526 - ROLE OF PLATELET ACTIVATION, TUMOR-CELL CYTOSKELETON AND TUMOR-CELL PLASMA-MEMBRANE

Tumor cell-platelet interactions have been shown to be involved in the process of metastasis. This study characterizes the aggregation of wa shed platelets induced by the human uterine carcinosarcoma Cole 526. U ltrastructural studies revealed a two-stage process in which the earli est events were the adhesion and degranulation of individual platelets in contact with the tumor cell membrane. The second stage consisted o f a wave of aggregation involving all residual platelets. We found tha t the first stage was initiated by a factor integral to the tumor cell plasma membrane which acted independently of the tumor cell cytoskele ton or metabolic processes. This factor was found to be a glycoprotein or glycolipid with functionally important sialic acid and N-linked ca rbohydrate residues, The initial stage was not dependent on platelet a ctivation as neither aspirin nor prostacyclin prevented adhesion or de granulation, The second stage was found to be dependent on platelet ac tivation. These results suggest that platelet aggregation induced by C ole 526 involves a distinctive primary stage which is initiated by a f actor on the tumor cell plasma membrane resulting in the degranulation and lysis of individual platelets, This process can occur independent ly of platelet activation or aggregation and thus may have some releva nce to the clinical use of platelet antagonists as antimetastatic agen ts.