Synergistic induction of plasminogen activator inhibitor type-1 in HEP G2 cells by thrombin and transforming growth factor-beta.
Plasminogen activator inhibitor type-1 (PAI-1) is a physiologic modulator of the fibrinolytic system. Its activity in plasma increases in diverse thrombotic states. The large synthetic capacity of the liver make it a source of potentially large amounts of PAI-1. Because thrombin activity increases in association with thrombotic disorders and because specific binding sites for thrombin have been identified on hepatocytes, we characterized the effect of thrombin on hepatocyte PAI-1 production. Incubation of Hep G2 cells with human alpha-thrombin resulted in a dose- and time-dependent increase in the concentration of PAI-1 in conditioned media. This effect was inhibited completely by hirudin and by antithrombin III. Steady-state levels of both the 3.2-kb and 2.2-kb forms of PAI-1 mRNA increased after stimulation of the cells with thrombin, indicating that thrombin influences PAI-1 expression in Hep G2 cells at the pretranslational level. Incubation of Hep G2 cells with alpha-thrombin and either platelet lysates or purified transforming growth factor-beta (TGF-beta), both previously shown to augment hepatocyte PAI-1 expression, resulted in a synergistic increase in the concentration of PAI-1 in conditioned media. PAI-1 mRNA appeared to be synergistically increased as well. Thus, thrombin increases expression of both PAI-1 protein and mRNA in Hep G2 cells and exerts synergistic effects with TGF-beta. These results underscore the potential importance of inhibition of thrombin under conditions in which thrombolysis is induced pharmacologically.
Hopkins
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WE
Cardiovascular Division, Washington University School of Medicine, St Louis, MO 63110.
Fujii
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Sobel
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BE
D000990:Antithrombin III / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism; D015152:Blotting, Northern; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D004357:Drug Synergism; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008113:Liver Neoplasms / Q000378:metabolism; D015849:Plasminogen Inactivators / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D006629:Hirudins; D015849:Plasminogen Inactivators; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D000990:Antithrombin III; D013917:Thrombin