Tissue factor: a vitamin K-dependent clotting factor?

Procoagulant activity of gastric, colorectal, and renal cancer is factor VII-dependent

The PA of GC, CC, and RC extracts was assayed by the recalcification of human normal or F VII-DP, and the PA of normal tissue was also determined. The PA of normal tissue was higher than that of the cancer tissues in all groups of specimens. Substitution of normal plasma by F VII-DP resulted in significant depression of the PA and the differences in the PA between the normal and cancer tissue samples disappeared. Preincubation of normal and cancer tissue extracts with the cysteine proteinase inhibitors, mercuric chloride and iodoacetamide, did not affect the PA of these extracts. We conclude that the PA of the investigated cancer extracts is factor VII-dependent and can be related to the presence of tissue factor within cancer tissue.

Evidence for a warfarin-sensitive serum factor that participates in factor X activation by Lewis lung tumor cells

Mouse Lewis lung (LL) carcinoma cells possess a factor X activator (procoagulant) that is inhibited in vivo by warfarin treatment or diet-induced vitamin K deficiency. This inhibition suggests that vitamin-K-dependent proteins are involved in LL cell activation of factor X. A LL primary tumor clone (LL13) was isolated which contained a warfarin-sensitive vitamin-K cycle of metabolism and expressed factor X procoagulant activity. LL13 cells exposed to media containing warfarin or deficient in vitamin K grew as well as cells in normal media, and activated factor X to similar extents. In contrast, administration of warfarin to mice bearing LL13 cells inhibited factor X procoagulant activity as well as the vitamin K cycle of metabolism in the primary tumors. In relation to LL13 cells grown in media containing fetal bovine serum, those incubated for 20 hr in media containing mouse serum or the sera from LL13-bearing mice exhibited 9- to 10-times higher levels of factor X procoagulant activity. However, LL13 cells exposed to media containing the sera of warfarin-treated LL-13-bearing mice or to barium-sulfate-adsorbed normal mouse serum activated factor X much less efficiently. Collectively, these data suggest that inhibition of vitamin K function in LL cells does not affect the extent of factor X activation and thus the intrinsic factor X procoagulant is not a vitamin-K-dependent protein. They further suggest that both a warfarin-sensitive (vitamin-K-dependent) protein present in normal mouse serum and a LL13 cell component participate in factor X procoagulant activity.

Monocyte tissue factor activity in anticoagulant-treated patients

The tissue factor coagulant activity of peripheral blood monocytes was measured in 20 patients on long-term anticoagulant treatment with warfarin and in 21 healthy individuals. Contrary to expectations, tissue factor activity was not reduced in the warfarin-treated group and was, in fact, elevated in several patients. No relationship existed between the daily warfarin dose or the degree of prolongation of the prothrombin time and the monocyte tissue factor activity. These results indicate that monocyte tissue factor activity is not necessarily reduced to below normal levels with warfarin treatment.