Eliminating epigenetic barriers induces transient hormone-regulated gene expression in estrogen receptor negative breast cancer cells.
In breast cancer, approximately one-third of tumors express neither the estrogen receptor (ERalpha) nor estrogen-regulated genes such as the progesterone receptor gene (PR). Our study provides new insights into the mechanism allowing hormone-activated expression of ERalpha target genes silenced in ERalpha-negative mammary tumor cells. In cell lines derived from ERalpha-negative MDA-MB231 cells, stable expression of different levels of ERalpha from a transgene did not result in transcription of PR. A quantitative comparative analysis demonstrates that inhibiting DNA methyltransferases using 5-aza-2'-deoxycytidine or specific disruption of DNMT1 by small interfering RNAs and treatment with the histone-deacetylase inhibitor trichostatin A enabled ERalpha-mediated hormone-dependent expression of endogenous PR. We show that demethylation of a CpG island located in the first exon of PR was a prerequisite for ERalpha binding to these regulatory sequences. Although not a general requirement, DNA demethylation is also necessary for derepression of a subset of ERalpha target genes involved in tumorigenesis. PR transcription did not subsist 4 days after removal of the DNA methyltransferase blocking agents, suggesting that hormone-induced expression of ERalpha target genes in ERalpha-negative tumor cells is transient. Our observations support a model where an epigenetic mark confers stable silencing by precluding ERalpha access to promoters.
Fleury
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L
Laboratoire de Biologie Moléculaire Eucaryote, Université de Toulouse, Toulouse, France.
Gerus
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M
Lavigne
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AC
Richard-Foy
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H
Bystricky
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K
D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D018899:CpG Islands / Q000235:genetics; D003568:Cytidine Monophosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D044127:Epigenesis, Genetic / Q000187:drug effects* / Q000235:genetics; D004958:Estradiol / Q000494:pharmacology*; D047628:Estrogen Receptor alpha; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D011980:Receptors, Progesterone / Q000096:biosynthesis*
D004791:Enzyme Inhibitors; D047628:Estrogen Receptor alpha; D004967:Estrogens; D006877:Hydroxamic Acids; D034741:RNA, Small Interfering; D011980:Receptors, Progesterone; C012201:5'-azacytidine 5'-monophosphate; C012589:trichostatin A; D004958:Estradiol; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human; D003568:Cytidine Monophosphate