FOXM1 is a transcriptional target of ERalpha and has a critical role in breast cancer endocrine sensitivity and resistance.
In this study, we investigated the regulation of FOXM1 expression by estrogen receptor alpha (ERalpha) and its role in hormonal therapy and endocrine resistance. FOXM1 protein and mRNA expression was regulated by ER-ligands, including estrogen, tamoxifen (OHT) and fulvestrant (ICI182780; ICI) in breast carcinoma cell lines. Depletion of ERalpha by RNA interference (RNAi) in MCF-7 cells downregulated FOXM1 expression. Reporter gene assays showed that ERalpha activates FOXM1 transcription through an estrogen-response element (ERE) located within the proximal promoter region. The direct binding of ERalpha to the FOXM1 promoter was confirmed in vitro by mobility shift and DNA pull-down assays and in vivo by chromatin immunoprecipitation (ChIP) analysis. Our data also revealed that upon OHT treatment ERalpha recruits histone deacetylases to the ERE site of the FOXM1 promoter, which is associated with a decrease in histone acetylation and transcription activity. Importantly, silencing of FOXM1 by RNAi abolished estrogen-induced MCF-7 cell proliferation and overcame acquired tamoxifen resistance. Conversely, ectopic expression of FOXM1 abrogated the cell cycle arrest mediated by the anti-estrogen OHT. OHT repressed FOXM1 expression in endocrine sensitive but not resistant breast carcinoma cell lines. Furthermore, qRT-PCR analysis of breast cancer patient samples revealed that there was a strong and significant positive correlation between ERalpha and FOXM1 mRNA expression. Collectively, these results show FOXM1 to be a key mediator of the mitogenic functions of ERalpha and estrogen in breast cancer cells, and also suggest that the deregulation of FOXM1 may contribute to anti-estrogen insensitivity.
Millour
J
J
Department of Surgery and Cancer, Imperial College London, London W12 0NN, UK.
Constantinidou
D
D
Stavropoulou
A V
AV
Wilson
M S C
MS
Myatt
S S
SS
Kwok
J M-M
JM
Sivanandan
K
K
Coombes
R C
RC
Medema
R H
RH
Hartman
J
J
Lykkesfeldt
A E
AE
Lam
E W-F
EW
D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D019008:Drug Resistance, Neoplasm; D024202:Electrophoretic Mobility Shift Assay; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000502:physiology*; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors / Q000235:genetics* / Q000378:metabolism; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
C506487:ESR1 protein, human; D004965:Estrogen Antagonists; D047628:Estrogen Receptor alpha; D004967:Estrogens; C107585:FOXM1 protein, human; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors; D012333:RNA, Messenger; D000077267:Fulvestrant; D004958:Estradiol