Tissue Factor in Microvesicles Shed From U 87 MG Human Glioblastoma Cells Induces Coagulation , Platelet Aggregation

Microvesicles (diameter ca 200 nm) from the cell-free supernatant of U87MG human glioblastoma cell caused platelet aggregation and coagulation in a manner identical with that previously shown for the intact cells. Both activities were inhibited by dansylarginine-N-(3-ethyl-1 .5pentanediyl) amide (DAPA). confirming the thrombindependent nature of both activities. The specific activities per microgram of protein were 2-10 times greater in the microvesicles than in the plasma membrane fraction, suggesting localization in specific membrane domains. Sucrose density centrifugation gave a single protein peak (density 1 .14) with congruent procoagulant and platelet aggregating activities. Both activities required the extrinsic pathway, as shown by studies with factor-deficient plasmas, and both were inhibited by heating (60 min/lOOnC). by