TISSUE FACTOR IN MICROVESICLES SHED FROM U87MG HUMAN GLIOBLASTOMA CELLS INDUCES COAGULATION, PLATELET-AGGREGATION, AND THROMBOGENESIS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 64  (1) , 177-184
Abstract
Microvesicles (diameter .apprx. 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-1,5-pentanediyl) amide (DAPA), confirming the thrombin-dependent nature of both activities. The specific activities/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/100.degree. C), by reduction and alkylation, and by incubation of the microvesicles with rabbit anti-bovine brain tissue factor antibody. These observations were confirmed using microvesicles from the HL-60 human promyelocytic leukemia cells, which are known to contain tissue factor activity. Both procoagulant and proaggregating activities apparently are causally related through the presence of tissue factor in the mcirovesicles. Studies with the Baumgartner perfusion apparatus showed that U87MG microvesicles increased the size of adherent thrombi nearly 10-fold and that these thrombi were associated with nucleated cells from the blood. The increase in adherent thrombi did not occur if perfusion was carried out in the presence of DAPA, confirming the role of thrombin in their formation.