Identification of Tissue Factor in Two Human Pancreatic Cancer Cell Lines1

We have studied the effects of two human pancreatic cancer and two human small cell lung cancer cell lines on clotting and platelet aggrega tion. Both pancreatic lines markedly shortened recalcification times and induced platelet aggregation. The lung cancer lines produced little short ening of recalcification times and no platelet aggregation. The clotting and aggregation activities of the pancreatic lines were further character ized. Recalcification times following the addition of cancer cell line material to plasmas deficient in factors VII and X were markedly pro longed, suggesting that the activity is due to tissue factor. Hirudin, an inhibitor of thrombin from the saliva of leeches, and rabbit polyclonal immunoglobulin G anti-bovine brain tissue factor inhibited both procoagulant and aggregation activities. Apyrase (an enzyme degrading ADP), diisopropylfluorophosphate (a serine protease inhibitor) and L-transepoxysuccinylleucylantido(4-guanidino)butane (a cysteine protease inhib itor) failed to inhibit these activities. Increasing concentrations of heparin inhibited platelet aggregation. Subcellular fractionation studies showed these activities to be localized to the plasma membrane. The association between nuicin and the acceleration of clotting has been well described. The absence of inucin in electron micrographs of these pancreatic whole cells, membrane fractions, and shed microvesicles, as well as the failure of chaotropic agents (i.e., agents stripping material extrinsic to the cell membrane such as mucin) to abrogate this activity support these activities being intrinsic to the plasma membrane. These data strongly suggest that these activities are due to tissue factor which appears to be released as microvesicles in vitro. The release of tissue factor via microvesicles in vivo is one possible mechanism for the coagulopathy sometimes seen in patients with pancreatic carcinoma.