Endoglin is an endothelial membrane glycoprotein involved in cardiovascular morphogenesis and vascular remodeling. It associates with transforming growth factor-␤ (TGF-␤) signaling receptors to bind TGF-␤ family members, forming a functional receptor complex. Arterial injury leads to up-regulation of endoglin, but the underlying regulatory events are unknown. The transcription factor KLF6, an immediate-early response gene induced in endothelial cells during vascular injury, transactivates TGF-␤, TGF-␤ signaling receptors, and TGF-␤-stimulated genes. KLF6 and, subsequently, endoglin were colocalized to vascular endothelium (ie, expressed in the same cell type) following carotid balloon injury in rats. After endothelial denudation, KLF6 was induced and translocated to the nucleus; this was followed 6 hours later by increased endoglin expression. Transient overexpression of KLF6, but not Egr-1, stimulated endogenous endoglin mRNA and transactivated the endoglin promoter. This transactivation was dependent on a GC-rich tract required for basal activity of the endoglin promoter driven by the related GC box binding protein, Sp1. In cells lacking Sp1 and KLF6, transfected KLF6 and Sp1 cooperatively transactivated the endoglin promoter and those of collagen ␣1(I), urokinase-type plasminogen activator, TGF-␤1, and TGF-␤ receptor type 1. Direct physical interaction between Sp1 and KLF6 was documented by coimmunoprecipitation, pull-down experiments, and the GAL4 one-hybrid system, mapping the KLF6 interaction to the Cterminal domain of Sp1. These data provide evidence that injury-induced KLF6 and preexisting Sp1 may cooperate in regulating the expression of endoglin and related members of the TGF-␤ signaling complex in vascular repair. IntroductionCoordinated gene expression is a crucial requirement in the response to tissue injury. Extracellular matrix proteins, 1-3 growth factors such as transforming growth factor-␤ (TGF-␤), 1,4,5 and proteases such as urokinase-type plasminogen activator (uPA) 6,7 are jointly regulated. In particular, the TGF-␤ family plays a central role in the injury response based on the following: (1) TGF-␤1 expression is up-regulated after injury; 8,9 (2) infusion of TGF-␤ polypeptide or transfection of cDNA into injured arteries increases extracellular matrix production; 1,10 and (3) antibodies to TGF-␤ reduce intimal hyperplasia. 11 Members of the TGF-␤ superfamily exert their biologic functions through membrane receptors known as type 1 (T␤RI) and type 2 (T␤RII) serine/threonine kinases. After ligand binding, T␤RII recruits and phosphorylates T␤RI, which initiates the signaling pathway by phosphorylating the Smad family of proteins. 12,13 Endoglin is a homodimeric membrane glycoprotein that functions, in association with T␤RI and T␤RII, as an auxiliary receptor for TGF-␤1, TGF-␤3, activin, bone morphogenetic protein 2 (BMP-2), and BMP-7. [14][15][16] It is highly expressed by endothelial cells 17,18 and, at lower levels, by activated monocytes/ macrophages 19 and by mesenchymal cells, including...

Host factors involved in viral replication are potentially attractive antiviral targets that are complementary to specific inhibitors of viral enzymes, since resistant mutations against the latter are likely to emerge during long-term treatment. It has been reported recently that cyclosporine, which binds to a family of cellular proteins, cyclophilins, inhibits hepatitis C virus (HCV) replication in vitro. Here, the activities of various cyclosporine derivatives were evaluated in the HCV replicon system. There was a strong correlation between the anti-HCV activity and cyclophilin-binding affinity of these compounds. Of these, NIM811 has been selected as a therapeutic candidate for HCV infection, since it binds to cyclophilins with higher affinity than cyclosporine but is devoid of the significant immunosuppressive activity associated with cyclosporine. NIM811 induced a concentration-dependent reduction of HCV RNA in the replicon cells with a 50% inhibitory concentration of 0.66 M at 48 h. Furthermore, a greater than three-log 10 viral RNA reduction was achieved after treating the cells with as little as 1 M of NIM811 for 9 days. In addition, the combination of NIM811 with alpha interferon significantly enhanced anti-HCV activities without causing any increase of cytotoxicity. Taken together, these promising in vitro data warrant clinical investigation of NIM811, an inhibitor of novel mechanism, for the treatment of hepatitis C.

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