IDENTIFICATION OF A MULTIHORMONE RESPONSIVE ENHANCER FAR UPSTREAM FROM THE HUMAN TISSUE-TYPE PLASMINOGEN-ACTIVATOR GENE

A 2.4-kilobase (kb) DNA fragment, located 7.1 kb up-stream from the hu man tissue-type plasminogen activator (t-PA) gene (t-PA2.4), acts as a n enhancer which is activated by glucocorticoids, progesterone, androg ens, and mineralocorticoids. Transient expression of t-PA-chlorampheni col acetyltransferase reporter constructs in HT1080 human fibrosarcoma cells identified a glucocorticoid responsive unit with four functiona l binding sites for the glucocorticoid receptor, located between bp -7 ,501 and -7,974. The region from bp -7,145 to -9,578 (t-PA2.4) was fou nd to confer a cooperative induction by dexamethasone and all-trans-re tinoic acid (RA) to its homologous and a heterologous promoter, irresp ective of its orientation. The minimal enhancer, defined by progressiv e deletion analysis, comprised the region from -7.1 to -8.0 kb (t-PA0. 9) and encompassed the glucocorticoid responsive unit and the previous ly identified RA-responsive element located at -7.3 kb (Bulens, F., Ib anez-Tallon, I., Van Acker, P., De Vriese, A., Nelles, L., Belayew, A. , and Collen, D. (1995) J. Biol. Chem. 270, 7167-7175). The amplitude of the synergistic response to dexamethasone and RA increased by reduc ing the distance between the enhancer and the proximal t-PA promoter. The synergistic interaction was also observed between the aldosterone and the RA receptors. It is postulated that the t-PA0.9 enhancer might play a role in the hormonal regulation of the expression of human t-P A in vivo.