Collectively, these results suggest that, in response to 4OHT, ER regulates E2F1 expression to mediate both cellular growth selleck Ganetespib and anti oestrogen resist ance. Since the 4OHT ER complex usually weakly binds to any promoter, these results also indicated that 4OHT might promote the ER ligand independent pathway in which phosphorylated ER may control the expression of several genes, including E2F1. Designing a combined therapy to enhance the E2F1 pro apoptotic signalling in 4OHT treated ER negative breast cancer cells The E2F family of transcription factors plays a key role in the regulation of cell growth, apoptosis, and oncogenic transformation by mediating the timely expression of genes involved in these processes.

Although the over expression of E2F1 has been directly correlated with its pro apoptotic activity, more recent data indicated that the control of E2F1 dependent cell growth or pro apoptotic pathways is more related to the posttranslational processing of this transcription factor. Recently, negative crosstalk between methylation and other post translational modifications of E2F1, such as acetylation and phosphorylation, has been described. Thus, methyl ated E2F1 is prone to ubiquitination and degradation, whereas the demethylation of E2F1 favours its P/CAF dependent acetylation at lysine residues 117, 120, and 125. Whether acetylated E2F1 binds to the promoter of genes required for S phase or to the promoters of proapoptotic genes may depend on its subsequent phosphorylation by specific kinases.

Thus, in response to severe DNA damage, the hyperacetylated E2F1 protein is stabilised through direct phosphorylation by Chk2 at Ser364 or ATM kinase at Ser31. AV-951 Although 4OHT induced the ER mediated expression of E2F1, the treatment of MDA MB 231 cells with this drug did not result in visible DNA double strand breaks. Therefore, consistent with these results, 4OHT did not increase the phosphoryl ation of E2F1 at Serines 31 and 364. Tryp sin digests of E2F1 immunoprecipitated from untreated and 4OHT treated MDA MB 231 cells primary yielded the peptides LLDSSQIVIISAAQDASAPPAPTGPAA PAAGPC DPDLLLFATPQAPRPTPSAP RPALGRPPVK and MGSLRAPVDEDR, which correspond to the non phosphorylated Ser31 and Ser364 containing peptides, respectively. Taken together, these data strongly agree with the results showing the resistance of MDA MB 231 cells to 4OHT, which resulted in an enhancement of cell growth but not visible apoptosis. Recently, we observed that the TMCG/DIPY combin ation acted as an epigenetic treatment that reactivated RASSF1A expression and induced apoptosis in breast cancer cells. In addition to modulating DNA methyla tion and chromatin remodelling, this combination also induced the demethylation of the E2F1 transcription factor.