THE SAME SEQUENCE MEDIATES ACTIVATION OF THE HUMAN UROKINASE PROMOTERBY CAMP IN MOUSE SERTOLI CELLS AND BY SV40 LARGE T-ANTIGEN IN COS CELLS

Cell-specific activation by follicle-stimulating hormone and its intra cellular mediator, cAMP, of the human urokinase promoter in mouse Sert oli cells requires overlapping purine-rich and GC-rich sequences betwe en -54 and -42 from the transcriptional start site. We have previously shown that binding of unidentified nuclear factors to these sequences is induced by cAMP stimulation, and that sequences from the enhancerl ess SV40 replication origin can interfere with the binding, whereas co nsensus Sp1 binding sites are ineffective. We now show that sequences within the SV40 origin able to compete for the formation of cAMP-induc ed DNA-protein complexes in Sertoli cell nuclear extracts are binding sites for the SV40 large T antigen. Large T antigen expressed in COS c ells binds the cAMP-responsive sequences of the human urokinase gene a nd transactivates the proximal promoter, thus mimicking the effect of nuclear factors induced by cAMP in Sertoli cells. We show that Egr-1 i s one of the factors present in cAMP-induced DNA-protein complexes for med between the human urokinase promoter and Sertoli cell nuclear extr acts. However, Egr-1 levels are similar in unstimulated and cAMP-treat ed Sertoli cells, suggesting that this factor interacts with a differe nt GC-box binding factor; that we have previously shown to be strongly induced by cAMP treatment of Sertoli cells. We propose that SV40 larg e T antigen in COS cells can mimick the action of heterodimers formed in cAMP stimulated Sertoli cells between Egr-1 and a cell specific cAM P-induced GC-box binding factor.