NOVEL EXPRESSION AND LOCALIZATION OF ACTIVE THROMBOMODULIN ON THE SURFACE OF MOUSE-BRAIN ASTROCYTES

Thrombin's potent effects on astrocytes are mediated by a specific rec eptor and inhibited by a serpin, protease nexin I (PNI). Thrombomoduli n (TM), a membrane protein that forms complexes with thrombin, changin g its enzymatic specificity, has not been studied in astrocytes. In pr imary astrocyte cultures, using Western blotting and immunocytochemist ry, we found a 70 kDa TM band and TM localized to the surface with an anti-mouse TM monoclonal antibody. By reverse transcriptase coupled wi th polymerase chain reaction (RT-PCR), we found the correct sequence f or mouse TM mRNA in astrocytes. Finally, we documented calcium-depende nt activation of protein C by a thrombin:TM complex with thrombin adde d to the astrocytes. These results indicate the presence of functional ly active Till at the astrocyte surface and add support to a role for thrombin signaling in the nervous system. (C) 1997 Wiley-Liss, Inc.