David Scott Calnek

Negative Regulation of Inducible Nitric-oxide Synthase Expression Mediated through Transforming Growth Factor-β-dependent Modulation of Transcription Factor TCF11

Inducible nitric-oxide synthase (iNOS) plays a central role in the regulation of vascular function and response to injury. A central mediator controlling iNOS expression is transforming growth factor-β (TGF-β), which represses its expression through a mechanism that is poorly understood. We have identified a binding site in the iNOS promoter that interacts with the nuclear heterodimer TCF11/MafG using chromatin immunoprecipitation and mutation analyses. We demonstrate that binding at this site acts to repress the induction of iNOS gene expression by cytokines. We show that this repressor is induced by TGF-β1 and by Smad6-short, which enhances TGF-β signaling. In contrast, the up-regulation of TCF11/MafG binding could be suppressed by overexpression of the TGF-β inhibitor Smad7, and a small interfering RNA to TCF11 blocked the suppression of iNOS by TGF-β. The binding of TCF11/MafG to the iNOS promoter could be enhanced by phorbol 12-myristate 13-acetate and suppressed by the protein kinase C inhibitor staurosporine. Moreover, the induction of TCF11/MafG binding by TGF-β and Smad6-short could be blocked by staurosporine, and the effect of TGF-β was blocked by the selective protein kinase C inhibitor calphostin C. Consistent with the in vitro data, we found suppression of TCF11 coincident with iNOS up-regulation in a rat model of endotoxemia, and we observed a highly significant negative correlation between TCF11 and nitric oxide production. Furthermore, treatment with activated protein C, a serine protease effective in septic shock, blocked the down-regulation of TCF11 and suppressed endotoxin-induced iNOS. Overall, our results demonstrate a novel mechanism by which iNOS expression is regulated in the context of inflammatory activation.

17β-Estradiol, But Not Raloxifene, Decreases Thrombomodulin in the Antithrombotic Protein C Pathway

Raloxifene is a nonsteroidal selective estrogen receptor modulator (SERM) that mimics the effects of estrogen on some plasma lipids and may have direct effects on the vascular wall. The objective of this study was to determine the effects of 17β-estradiol, raloxifene, and LY139,478 (a related benzothiophene SERM) on the anticoagulant protein C pathway. In human vascular endothelial cells activated with interleukin-1 (IL-1), we demonstrated decreased thrombomodulin-dependent protein C activation. 17β-estradiol reduced the anticoagulant properties of both unstimulated and IL-1-activated endothelial cells by decreasing thrombomodulin expression. In contrast, raloxifene and LY139,478 enhanced the anticoagulant properties of both unstimulated and IL-1-activated endothelial cells through upregulation of thrombomodulin. Regulation of the protein C pathway via thrombomodulin on vascular endothelium may be a novel mechanism by which SERMs could potentially confer cardioprotective effects and reduce the thrombotic ...