Regulation of endothelial cell coagulant properties. Modulation of tissue factor, plasminogen activator inhibitors, and thrombomodulin by phorbol 12-myristate 13-acetate and tumor necrosis factor.

The procoagulant response of endothelium to many stimuli alters the expression of tissue factor, thrombomodulin, and plasminogen activator inhibitors (PAI) PAI-1 and PAI-2. The regulation of these proteins was examined in cultured human endothelial cells treated with phorbol myristate acetate (PMA) or tumor necrosis factor (TNF). Unstimulated cells contained approximately 670 PAI-1 and approximately 100 thrombomodulin mRNA molecules/cell, whereas tissue factor and PAI-2 mRNAs were not detectable. By 3-5 h, PMA or TNF induced both tissue factor and PAI-2 to approximately 150-420 mRNA molecules/cell and both mRNAs declined to basal levels within several hours; however, PAI-1 and thrombomodulin mRNA levels did not change. Nuclear runoff assays showed that PMA, TNF, or cycloheximide induced transcription of the tissue factor gene, whereas the genes for thrombomodulin, PAI-1, and PAI-2 apparently were transcribed at the same relative rate in the presence or absence of these agents. Treatment of cells with cycloheximide stabilized tissue factor and PAI-2 mRNAs and increased their induction by PMA or TNF. The synthesis of tissue factor, PAI-1, and PAI-2 proteins paralleled their mRNA levels. The effects of TNF were similar to those of PMA with one exception. In contrast to PMA, TNF reduced thrombomodulin activity approximately 80% with no change in thrombomodulin mRNA levels. Thus, PAI-2 may be induced by inhibiting mRNA degradation. Tissue factor can be induced by stimulating transcription and potentially by inhibiting mRNA degradation. Thrombomodulin can be repressed by a translational or posttranslational mechanism. PAI-1 was not regulated under the conditions studied. The different effects of PMA and TNF on thrombomodulin expression indicate that some effects of TNF are not mediated solely by protein kinase C.