PROCOAGULANT ACTIVITY IN CANCER-CELLS IS DEPENDENT ON TISSUE FACTOR EXPRESSION

Procoagulant activity of pairs of cell lines, which were derived from the same original cell type but which possess different growth charact eristics and metastatic properties, was examined. The following charac teristics were considered suggestive of a greater likelihood of metast atic potential: high histological grade; establishment of the line fro m a metastatic rather than a nonmetastatic cancer; increased tumorigen icity in nude mice; and/or estrogen receptor-negative mammary cancer. Procoagulant activity was evaluated by a two stage clotting assay. Pro coagulant activity was highly variable, with up to a 1,300-fold differ ence, among the cancer cell lines examined. The rate of clot formation was factor VII dependent and was totally inhibited by an anti tissue factor monoclonal antibody, indicating that tissue factor was the only significant procoagulant present in these cancer cells. Tissue factor antigen expression, evaluated by ELISA, correlated with procoagulant activity. In all pairs of cancer cell lines, those with characteristic s of increased proliferative potential had increased tissue factor lev els compared to cell lines that originated from the same cell type, bu t which possess less aggressive characteristics. Tissue factor activit y in these cancer cells was increased by cell lysis or by exposure of intact cells to a calcium ionophore, similar to results previously obt ained in fibroblasts. Tissue factor mRNA was evaluated by northern blo t analysis using a specific probe complementary to tissue factor mRNA. The previously described predominant tissue factor mRNA species of 2. 2 kb was identified in the majority of cancer cell lines examined, but tissue factor mRNA species of 3.2 to 3.4 kb were also identified. The larger tissue factor mRNA species was predominant compared to the mat ure 2.2-kb species in those cell lines, which expressed low tissue fac tor activity. Procoagulant activity in these cancer cell lines was als o due only to tissue factor. Thus, tissue factor expression is regulat ed at both the molecular and cellular level and is inherently higher i n cancer cell lines established from aggressive tumors compared to les s aggressive tumors.