Activation of extrinsic coagulation on tumor cell

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We have studied the binding of radioiodinated human factors VII and VIIa to a human bladder carcinoma cell line (J82) that expresses functional cell surface tissue factor. The binding of factors VII and VIIa was found to be time-, temperature-, and calcium-dependent. The binding isotherms for factors VII and VIIa were hyperbolic, Kd values were 3.20 and 3.25 nM, respectively. Binding of factor VIIa to the cells was completely blocked by preincubation of the cells with anti-tissue factor IgG. Functional studies revealed that factor X activation by increasing amounts of cell-bound factor VII or VIIa was hyperbolic. Half maximal rates occurred at factor VII and VIIa concentrations of 3.7 and 3.2 nM, respectively. The offered ^<125>I-factor VII was progressively converted to two-chain factor VIIa upon binding to the cells. Specific binding of factor VIIa lacking the gamma-carboxyglutamic acid domain (GD-VIIa) to J82 was neither influenced by calcium nor blocked by prior incubation of the cells with anti-tissue factor IgG. These results indicate that the gamma-carboxyglutamic acid domain of factor VIIa is essential for its interaction with cell surface tissue factor. We have next examined the ability of four human tumor cell lines to augment the conversion of prothrombin to thrombin by factor Xa and calcium. The order of effectiveness was COLO 205>HepG2>J82>CAPAN-2. Furthermore, factor Xa bound specifically to J82 and HepG2 cells, whereas no significant specific binding of factor X to either cell was observed. Kd values were 1.66nM(HepG2) and 1.64nM(J82). Thrombin formation by cell-bound factor Xa was hyperbolic and saturable at 5nM factor Xa on each cell line. Our results indicate that these tumor cells can readily assemble a functional cell surface prothrombinase complex that may be important in fibrin deposition associated with the growth and metastatic progression of these, and perhaps, other tumors.