Pocket Protein-Independent Repression of Urokinase-Type Plasminogen Activator and Plasminogen Activator Inhibitor 1 Gene Expression by E2F1

Expression of genes of the plasminogen activator (PA) system declines at the G(0)/G(1)-S-phase boundary of the cell cycle. We found that overexpression of E2F1-3, which acts mainly in late G(1), inhibits promoter activity and endogenous expression of the urokinase-type PA (uPA) and PA inhibitor 1 (PAI-1) genes. This effect is dose dependent and conserved in evolution. Mutation analysis indicated that both the DNA-binding and transactivation domains of E2F1 are necessary for this regulation. Interestingly, an E2F1 mutant lacking the pRB-binding region strongly repressed the uPA and PAI-1 promoters. An E2F-mediated negative effect was also observed in pRB and p107/p130 knockout cell lines. This is the first report that E2F can act as a repressor independently of pocket proteins. Mutation of AP-1 elements in the uPA promoter abrogated E2F-mediated transcriptional inhibition, suggesting the involvement of AP-1 in this regulation. Results shown here identify E2F as an important component of transcriptional control of the PA system and thus provide new insights into mechanisms of cellular proliferation.