Eliminating epigenetic barriers induces transient hormone-regulated gene expression in estrogen receptor negative breast cancer cells

Abstract

In breast cancer, approximately one-third of tumors express neither the estrogen receptor (ERa) nor estrogen-regulated genes such as the progesterone receptor gene (PR). Our study provides new insights into the mechanism allowing hormone-activated expression of ERa target genes silenced in ERa-negative mammary tumor cells. In cell lines derived from ERa-negative MDA-MB231 cells, stable expression of different levels of ERa from a transgene did not result in transcription of PR. A quantitative comparative analysis demonstrates that inhibiting DNA methyltransferases using 5-aza-2 0 -deoxycytidine or specific disruption of DNMT1 by small interfering RNAs and treatment with the histone-deacetylase inhibitor trichostatin A enabled ERa-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 ERa binding to these regulatory sequences. Although not a general requirement, DNA demethylation is also necessary for derepression of a subset of ERa 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 ERa target genes in ERa-negative tumor cells is transient. Our observations support a model where an epigenetic mark confers stable silencing by precluding ERa access to promoters.

HDAC inhibition does not induce estrogen receptor in human triple-negative breast cancer cell lines and patient-derived xenografts

“…Moreover, certain publications proposed that HDACis reduced ERa-target gene expression such as PGR, only in ERa-positive cell lines [24], or reduced HER2 mRNA level and stability in ERa-positive cell lines resistant to letrozole which is MCF7Ca [26]. Others showed that E2-sensitive Arbitrary units 2 DDCt 9 100 as previously described (11); Average expression level of 5 independent xenografts per series C Control, A Abexinostat-treated xenografts, NP Not performed genes could be activated by HDACis only in cells who stably express functional ERa from a transgene [25]. Hence, we have also analyzed PGR and HER2 regulation in TNBC PDXs in vivo treated for various times with abexinostat.…”

“…This was also reported by Biçaku et al who found minimal or no changes in ERa or in ERb mRNA and protein in ERa-negative BC cell lines (MDA-MB231 and SKBR3) treated by vorinostat or valproic acid for 48 h, whereas these compounds down-regulate ERa expression in ERa-positive cells (MCF7 and T47D cell lines) [24]. Similarly, treatment of MDA-MB231 cells with Trichostatin A did not induce ERa expression nor did it stimulate any of its downstream target genes, including TFF1 or PGR [25]. Moreover, certain publications proposed that HDACis reduced ERa-target gene expression such as PGR, only in ERa-positive cell lines [24], or reduced HER2 mRNA level and stability in ERa-positive cell lines resistant to letrozole which is MCF7Ca [26].…”

The faah gene is the first direct target of estrogen in the testis: role of histone demethylase LSD1

“…Thus, we suggest that the absence of the latter histone demethylase could contribute to the loss of E 2 inducibility of FAAH promoter at this age. In mammary tumor cell lines it has been demonstrated that ERa binding to target regulatory sequences is impaired by DNA hypermethylation of CpGs, and that the first step needed to stimulate E 2 -regulated gene expression is to eliminate epigenetic barriers, thus allowing ERa access to regulatory sequences [39]. DNA cytosine methyltransferase 1 (DNMT1) is the most abundant and catalytically active DNA methyltransferase, and is able to induce covalent addition of a methyl group to the 5 0 position of cytosine, predominantly within CpG dinucleotides, which are generally localized in promoter regions [40].…”

Fetal programming and fetal psychology

“…Breast and reproductive tract cancers and osteoporosis have drawn considerable attention as candidates for the effects of fetal programming (Barbieri, 2008;Michels, Xue, Terry, and Willett, 2006;Zhou, Dowdy, Podratz, and Jiang, 2007). This in turn suggests that the expression patterns of steroid receptor genes may also be subject to epigenetic regulation (Fleury, Gerus, Lavigne, Richard-Foy, and Bystricky, 2008;Jordan, 2007;Leader, Wang, Fu, and Pestell, 2006;Wu, Strawn, Basir, Halverson, and Guo, 2006). Non-pathological correlates of birth size have also been reported, including variation in adult patterns of ovarian steroid production Jasienska, Ziomkiewicz, Lipson, Thune, and Ellison, 2006).…”