Functional Cooperation Between Smad Proteins and Activator Protein-1 Regulates Transforming Growth Factor-beta-mediated Induction of Endothelin-1 Expression

Endothelin-1 (ET-1) is a 21-amino-acid potent vasoconstrictor peptide that is mainly produced by vascular endothelial cells. Expression of the ET-1 gene is subject to complex regulation by numerous factors, among which transforming growth factor-beta (TGF-beta) is one of the most important. It has been widely documented that TGF-beta increases ET-1 mRNA and peptide levels. We have explored the mechanism by which TGF-beta upregulates ET-1 expression in endothelial cells. Transcriptional activation of the ET-1 promoter accounted for the TGF-beta-induced increase in ET-1 mRNA levels. We have identified within the ET-1 promoter two DNA elements indispensable for TGF-beta-mediated induction of ET-1: an activator protein-1 (AP-1) site at -108/-102, known to be important for constitutive and induced expression, and a novel regulatory sequence located at -193/-171, which constitutes a specific binding site for Smad transcription factors. Mutation of both elements abolished TGF-beta responsiveness. Binding of Smad3/Smad4 and c-Jun to their corresponding DNA elements was evidenced by electrophoretic mobility shift assays. Furthermore, the coactivator CREB-binding protein (CBP)/p300 was found to play an essential role in the induction of the gene. The simultaneous requirement for two distinct and independent DNA elements suggests that Smads and activator protein-1 functionally cooperate through CBP/p300 to mediate TGF-beta-induced transcriptional activation of the ET-1 gene.