PROTEIN-S, AN ANTITHROMBOTIC FACTOR, IS SYNTHESIZED AND RELEASED BY NEURAL TUMOR-CELLS

Protein S, an anticoagulant factor in the protein C antithrombotic pat hway, was found to be synthesized and released by six tumor cell lines of neural origin by western blotting and ELISA. The rate of synthesis ranged from three- to 11-fold higher than that of a microvascular end othelial cell line and 36-144% that of a hepatoma cell line. The secre ted protein S displayed specific anticoagulant activity similar to tha t of purified plasma protein S, implying that it was fully gamma-carbo xylated. Ten primary brain tumor tissues also expressed protein S anti gen, as shown by western blot analysis. Expression of anticoagulantly active protein S by neural cells raises important questions concerning possible physiologic roles for this multidomain protein beyond its fu nction in control of thrombosis.