ABSTRACT: We explored the combinatorial interactions between p53, estrogen receptors and NFkB using the breast adenocarcinoma-derived MCF7 cells. Recently, we have established that p53 can modulate transcription also through non-canonical response elements (REs), consisting of half-sites and ¾ sites. In particular, we identified a half-site p53 response element in the promoter of FLT1/VEGFR-I gene that was required but not sufficient for the p53 responsiveness of the promoter. The transcriptional control required also estrogen receptor (ER) half-sites (EREs) located in close proximity to the p53 RE. Further studies led us to establish that p53-mediated transcription from the FLT1 half site RE is dependent on ER binding at the EREs and strongly influenced by the level of ER proteins, and the specific nature of the p53-inducing stress as well as ER ligand. In another study we found an enrichment of NFkB REs nearby p53 REs in p53 target genes, suggesting an additional mode of functional interactions between these two transcription factors. To identify at a genome scale the transcriptional network that selectively responds to the concomitant activation of p53, ER and/or NFkB, we measured gene expression upon treatment with specific chemotherapeutic agents combined with 17-β estradiol (E2) and/or the inflammatory cytokine TNFα. Firstly we measured using MCF7 cells growing in estrogen-depleted media the transcriptome changes induced by doxorubicin (doxo) and 5-fluorouracil (5FU), two different drugs both able to stabilize and activate the p53 protein. We next obtained the expression profiles in the presence of E2 with or without doxo or 5FU. We also measured transcriptome changes in response to TNFαalone or in combination with doxo and/or E2. All these analyses were conducted using the same batch of MCF7 cells (wild type for p53, ERα, ERβ -weakly-, and NFkB positive) that we had previously used to characterize the cis-mediated transcriptional cooperation between p53 and ER at the FLT1 gene. Keywords: transcription factor, transcriptional networks, p53, ER, NFkB, p53-ER-NFkB crosstalk, doxorubicin, 5-fluorouracil, 17-β estradiol, TNFα, combined genotoxic, estrogenic and inflammatory responses, composite DNA binding site signatures, MCF7. The cooperation at the transcriptional level among p53, ERs and NFkB was analyzed by transcriptome analysis in response to different stimuli (doxo or 5FU, E2, TNFα). To identify mRNA molecules that would be modulated by the coordinated activity of the three TFs, gene expression signals derived from the combinatorial treatment were compared by microarrays analyses to those obtained from each drug when individually administered. Total RNA was isolated from MCF7 cells grown in estrogen-depleted medium and treated so as to stimulate the activity of the three different transcription factors (p53, ERs and NFkB). Cells lysates were collected after 10 hours from the treatments. All experiments were run from triplicate to septuples.
