Transcription factor E2F-1 is upregulated in response to DNA damage in a manner analogous to that of p53

The transcription factor E2F-1 directs the expression of genes that induce or regulate cell division, and a role for E2F-1 in driving cells into apopt osis is the subject of intense discussion. Recently it has been shown that E2F-1 binds and coprecipitates with the mouse double-minute chromosome 2 pr otein (Mdm2). A domain of E2F-1 (amino acids 390 to 406) shows striking sim ilarity to the Mdm2 binding domain of the tumor suppressor protein p53. It is known that interaction of Mdm2 with p53 through this domain is required for Mdm2-dependent degradation of p53. We show here that E2F-1 protein is u pregulated in response to DNA damage. The kinetics of induction are depende nt upon the source of DNA damage, i.e., fast and transient after irradiatio n with X rays and delayed and stable after irradiation with UVC, and thus m atch the kinetics of p53 induction in response to DNA damage. We show furth er that E2F-1 is also upregulated by treatment with the transcription inhib itor actinomycin D and with the kinase inhibitor DRB, as well as by high co ncentrations of the kinase inhibitor H7, all conditions which also upregula te p53. In our experiments we were not able to see an increase in E2F-1 RNA production but did find an increase in protein stability in WC-irradiated cells. Upregulation of E2F-1 in response to DNA damage seems to require the presence of wild-type p53, since we did not observe an increase in the lev el of E2F-1 protein in several cell lines which possess mutated p53. Previo us experiments showed that p53 is upregulated after microinjection of an an tibody which binds to a domain of Mdm2 that is required for the interaction of Mdm2 with p53. Microinjection of the same antibody also increases the e xpression of E2F-1 protein, while microinjection of a control antibody does not. Furthermore, microinjection of Mdm2 antisense oligonucleotides upregu lates E2F-1 protein, while microinjection of an unrelated oligonucleotide d oes not. These data suggest that E2F-1 is upregulated in a similar way to p 53 in response to DNA damage and that Mdm2 appears to play a major role in this pathway.