Regulation Of The Downstream Genes And Biological Function By Transcriptional Factor E2F1

The cellular important transcriptional factor E2F1,the first cloned gene in the E2F family, plays a key role in the cellular proliferation, differentiation, and apoptosis.E2F1 take part in the cell cycle transition from the G1 phase to the S phase. In the G1 prophase, E2F1 was inhibited by the protein Rb.When the Rb was phosphorylated by the cell cycle dependent kinase (CDK), the heterodimer of E2F1/DP-1 was released from the Rb, and then binds the genomic DNA for activating the downstream genes, letting the cell cycle change from the G1 phase to the S phase. At the same time, E2F1 have the pro-apoptosis ability to activate the proteins, such as Bcl-2 homology3 (BH3)-only proteins PUMA, Noxa, Bim, Hrk/DP5,Bik and Caspase-3,-9, and so on, through the p53-dependent and p53-independent pathways.Besides, E2F1 blocks the cellular survival factors NF-κB and Mcl-1.What we have known of the E2F1 from the two sides contributes to the cellular apoptosis. Therefore, E2F1,as a new therapeutic target, has a close relationship with tumors.Because of the importance of the transcriptional factor E2F1,we decide to do some researches on the regulation of the downstream genes of the E2F1,making use of the H1299 cell line that constitutively expresses an estrogen receptor-E2F1 fusion protein (ER-E2F1).Then, the fusion protein will stay out of the cellular nuclear, for its binding on the cytomembrane ligand. However, the fusion protein will entry into the nuclear to play an important role in the activities of cell cycle and apoptosis, when the estrogen receptor inhibitor (4-OHT) was added. In the present work, first of all, we construct the H1299 stable cell line that constitutively expresses an estrogen receptor-E2F1 fusion protein (ER-E2F1).Secondly, we found that ER-E2F1 potently activates the endogenous proteins of DP-1 and B-Raf upon treatment with 4-hydroxytamoxifen (100nM).Once more, western blot and immunofluorescence assays demonstrate that transient transfection of HA-E2F1 is associated with the up-regulation of the proteins of DP-1 and B-Raf in H1299 and Hela cell lines. Finally, E2F1 potently activates DP-1 on the transcriptional level by the Rt-PCR assay.In our study, the fusion protein ER-E2F1 was pre-expressed in the H1299 stable cell line. The localization of the fusion protein was changed, when the cell line was treated with the estrogen receptor inhibitor (4-OHT). In conclusion, we discovered the novel relationship between transcription factor E2F1 and the downstream protein DP-1.This is helpful on the study of E2F1/DP-1 heterodimer to regulate the cellular transcriptional function. At the same time, the new relationship between E2F1 and B-Raf is meaningful for the study of cell cycle transition and cellular tumorgenesis.