The regulation of the synthesis of the endothelial-derived vasoconstrictor endothelin-1 (ET-1) is a complex process encompassing transcriptional as well as mRNA stability mechanisms. We have described recently the existence of a mechanism for the control of ET-1 expression based on the mRNA-destabilizing capacity of specific cytosolic proteins through interaction with AU-rich elements (AREs) present in the 3 untranslated region of the gene. We now identify glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a protein which binds to the AREs and is responsible for the destabilization of the mRNA. Oxidant stress alters the binding of GAPDH to the mRNA and its capacity to modulate ET-1 expression, a phenomenon occurring through specific S glutathionylation of the catalytically active residue Cys 152. Finally, we provide data consistent with a role for GAPDH in mRNA unwinding, yielding this molecule more prone to degradation. In contrast, S-thiolated GAPDH appears unable to modify mRNA unwinding, thus facilitating enhanced stability. Taken together, these results describe a novel, redox-based mechanism regulating mRNA stability and add a new facet to the panoply of GAPDH cellular homeostatic actions.The endothelium contributes greatly to vascular homeostasis by functioning as a sensor of physical and chemical stimuli and responding to them with specific signals. Vascular tone and blood pressure are regulated by endothelial cells through a tight balance of the levels of vasodilator and vasoconstrictor substances, the most important being nitric oxide (NO) and endothelin-1 (ET-1), respectively. In addition to its constrictor action, ET-1 has been shown to be involved in normal tissue repair and also in the pathogenesis of fibrotic diseases (38). All of these ET-1 biological actions can lead to pathophysiological processes under certain circumstances. In this respect, elevated circulating and tissue ET-1 levels have been measured in patients suffering from certain vascular diseases, such as atherosclerosis, pulmonary hypertension, or skin and lung fibrosis (2, 32). Therefore, ET-1 production and secretion by vascular endothelial cells must be tightly regulated. Endothelial cells synthesize ET-1 as a propeptide of 212 residues, preproendothelin-1, which is then subjected to specific proteolysis to yield the bioactive ET-1 peptide of 21 amino acids. The regulation of the expression is a complex process that occurs mainly at the mRNA level and involves both transcriptional and posttranscriptional mechanisms (26,27,31,45). Although the analysis of the transcription of the gene has attracted most of the attention, posttranscriptional mechanisms have recently been revealed as essential steps in the regulation of the biosynthesis (37, 43).Generally speaking, many of the processes dealing with specific regulatory mechanisms at the posttranscriptional level take place within genetic elements present in the 3Ј untranslated region (3Ј UTR) of the genes (10,17,20). Adenine-and uridine-rich elements (AREs), which are often found in...

Objective. To characterize the pathways induced by transforming growth factor ␤1 (TGF␤1) that lead to the expression of endothelin 1 (ET-1) in human dermal fibroblasts, and to study the effects of TGF␤1 and ET-1 on the acquisition of a profibrotic phenotype and assess the contribution of the TGF␤1/ET-1 axis to skin wound healing and fibrosis in vivo.Methods. The mechanism of induction of ET-1 expression by TGF␤1 and its effect on the expression of ␣-smooth muscle actin and type I collagen were studied in human dermal fibroblasts, in experiments involving the TGF␤ receptor inhibitor GW788388 and the ET receptor antagonist bosentan, by real-time reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay, immunofluorescence, Western blotting, and promoter/reporter transient transfection analyses. Experiments assessing dermal wound healing in mice were performed with adenovirus-driven overexpression of active TGF␤1 and ET-1, with or without treatment with bosentan. The contributions of TGF␤1 and ET-1 to the fibrotic response were also assessed in a mouse model of bleomycin-induced skin fibrosis, by histologic, immunohistochemical, RT-PCR, and protein analyses.Results. TGF␤1 induced ET-1 expression in human dermal fibroblasts through Smad-and activator protein 1/JNK-dependent signaling. The ability of TGF␤1 to induce the expression of profibrotic genes was dependent on ET-1. Adenovirus-mediated overexpression of TGF␤1 and ET-1 in mouse skin was associated with accelerated wound closure, increased fibrogenesis, and excessive scarring. Treatment with bosentan prevented the effects of TGF␤1. In the bleomycin-induced fibrosis model, treatment with GW788388 and bosentan prevented the fibrotic response.Conclusion. Our results strongly support the notion that the TGF␤1/ET-1 axis has a role in wound repair and skin fibrosis. ET-1 receptor antagonists, such as bosentan, may represent a useful therapeutic tool in the treatment of excessive scarring and fibrosisrelated diseases.

to the regulation of the endothelial cell migration and proliferation capacity. Our experiments indicate that TGF-␤ induces ET-1 expression preferentially through the ALK5/Smad3 pathway. Specific ALK5 inhibition totally blocked the anti-angiogenic effect of TGF-␤. Antagonism of ET receptors partially reverted the effect of TGF-␤, indicating that a significant portion of the anti-migratory and anti-proliferative actions of this cytokine is mediated by ET-1 acting in an autocrine manner on endothelial cells.