Transcriptional activation of urokinase by the Kruppel-like factor Zf9/COPEB activates latent TGF-beta 1 in vascular endothelial cells

Understanding the regulation of genes controlling fibrinolysis and matrix h omeostasis is essential for elucidating the basis of tissue repair. A recen tly described novel Kruppel-like factor, Zf9, is up-regulated in acute live r injury in activated hepatic stellate cells. Because Zf9 can be induced wi dely, its activity was examined in vascular endothelium, a key cell in vasc ular injury. Zf9 is induced as an immediate-early response gene in bovine a ortic endothelial cells (BAECs) following treatment with serum or phorbol e ster, Zf9 transcriptionally activates urokinase plasminogen activator (uPA) , Recombinant Zf9-GST binds to wild-type but not mutated 'GC-box' motifs wi thin the human uPA promoter (-63 to -32), with greatest affinity to the mid dle of 3 contiguous GC boxes. Transient transfection of Zf9 drives transact ivation of a full-length uPA promoter- and cc box-construct, but not a uPA promoter-construct devoid of GC boxes. Transactivation of uPA by Zf9 is als o supported in Drosophila S2 cells. Most importantly transiently transfecte d Zf9 up-regulates endogenous uPA messenger RNA and activity in BAECs, resu lting 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 en dothelial cells after balloon injury in rats, suggesting a potential role o f 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-S. (C) 2000 by The American Society of Hematology.