Transcriptional activation of urokinase by the Krüppel-like factor Zf9/COPEB activates latent TGF-β1 in vascular endothelial cells

Abstract

Understanding the regulation of genes controlling fibrinolysis and matrix homeostasis is essential for elucidating the basis of tissue repair. A recently described novel Krüppel-like factor, Zf9, is up-regulated in acute liver injury in activated hepatic stellate cells. Because Zf9 can be induced widely, its activity was examined in vascular endothelium, a key cell in vascular injury. Zf9 is induced as an immediate-early response gene in bovine aortic endothelial cells (BAECs) following treatment with serum or phorbol ester. Zf9 transcriptionally activates urokinase plasminogen activator (uPA). Recombinant Zf9-GST binds to wild-type but not mutated 'GC-box' motifs within the human uPA promoter (-63 to -32), with greatest affinity to the middle of 3 contiguous GC boxes. Transient transfection of Zf9 drives transactivation of a full-length uPA promoter- and GC box-construct, but not a uPA promoter-construct devoid of GC boxes. Transactivation of uPA by Zf9 is also supported in Drosophila S2 cells. Most importantly, transiently transfected Zf9 up-regulates endogenous uPA messenger RNA and activity in BAECs, resulting in increased bioactive transforming growth factor-beta (TGF-beta) via enhancement of proteolytic activation of the latent molecule. Furthermore, concomitant expression of Zf9 and uPA proteins was observed in arterial endothelial cells after balloon injury in rats, suggesting a potential role of Zf9 in uPA expression not only in vitro but also in vivo. These findings suggest a role of Zf9 in the injury response by enhancing uPA synthesis and subsequent activation of latent TGF-beta. (Blood. 2000;95:1309-1316)