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Genome-wide mapping of FOXM1 binding reveals co-binding with oestrogen receptor alpha in breast cancer cells (expression)

ABSTRACT: The forkhead transcription factor FOXM1 is a key regulator of the cell cycle and is overexpressed in cancer. Increased levels of FOXM1 are associated with both poor prognosis and oestrogen receptor (ERalpha) status in primary breast cancer. In this study, we map FOXM1 binding genome wide in both ERalpha-positive (MCF-7) and -negative (MDA-MB-231) breast cancer cells. We identify a common set of FOXM1 binding events at cell cycle-regulating genes, but in addition, in MCF-7 cells we find a high level of concordance with ERalpha-binding regions. FOXM1 binding at these co-binding sites is dependent on ERalpha binding, as depletion of ER protein levels reduced FOXM1 binding. FOXM1 interacts directly with both ERalpha co-activator CARM1 and is required for H3 arginine methylation at the ERalpha complex. Inhibition of FOXM1 activity with the ligand thiostrepton resulted in decreased FOXM1 binding at cca. 1400 sites genome wide and reduced expression of genes correlated with poor prognosis in ERalpha-positive tumour samples. These data demonstrate a novel role for the forkhead protein FOXM1 as an ERalpha cofactor and provide insight into the role of FOXM1 in ERalpha-positive breast cancer.

ORGANISM(S): Homo sapiens

PROVIDER: GSE40766 | GEO | 2013/01/07

SECONDARY ACCESSION(S): PRJNA174828

REPOSITORIES: GEO

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Project description:The transcription factor FOXM1 coordinates the expression of cell cycle-related genes and plays a pivotal role in tumorigenesis and cancer progression. We have previously shown that FOXM1 acts downstream of 14-3-3ζ signaling, which correlates with a more aggressive tumor phenotype. However, the role that FOXM1 might play in engendering the resistance to endocrine treatments in estrogen receptor-positive (ER+) patients when tumor FOXM1 is high, has not been clearly defined. To understand the role of FOXM1 in endocrine resistance and cancer aggressiveness, we analyzed FOXM1 protein expression by IHC in 501 ER-positive breast cancers; this revealed high FOXM1 expression in 20% of the tumors and a significantly reduced survival in these patients (p=0.003, log rank Mantel-Cox). We also mapped genome-wide FOXM1 binding events by chromatin immunoprecipitation, followed by high-throughput sequencing (ChIP-seq), in hormone-sensitive and resistant breast cancer cells after tamoxifen treatment. FOXM1 binding sites were enriched at the transcription start site of genes involved in cell cycle progression, maintenance of stem cell properties, and invasion and metastasis, all of which are correlated with the worst prognosis in ERα-positive patients treated with tamoxifen. Binding profiles were also integrated with gene expression data from cells before and after FOXM1 knockdown to highlight specific FOXM1 transcriptional networks. By modulating the levels of FOXM1 and newly discovered FOXM1-regulated genes [in breast cancer cells], we demonstrate that increased expression of FOXM1 was associated with an expansion of the cancer stem-like cell population and with increased cell invasiveness and resistance to endocrine treatments. Use of a selective FOXM1 inhibitor proved very effective in restoring endocrine therapy sensitivity and decreasing breast cancer aggressiveness. Collectively, our findings uncover novel roles for FOXM1 and FOXM1-regulated genes in promoting cancer stem-like cell properties and therapy resistance, and highlight the relevance of FOXM1 as a therapeutic target to be considered for reducing invasiveness and enhancing breast cancer response to endocrine treatments. MCF-7 human breast adenocarcinoma cells were tranfected with control, and FOXM1 siRNA for 72 hours and treated with 0.1% EtOH (Vehicle) or 1 uM TOT for 24 hours, and cDNA microarray analyses were carried out using Affymetrix [HG-U133A_2] Affymetrix Human Genome U133A 2.0 Array.

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Genome-wide mapping of FOXM1 binding reveals co-binding with oestrogen receptor alpha in breast cancer cells (expression)

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