Demethylation of the progesterone receptor CpG island is not required for progesterone receptor gene expression

Abstract

Progesterone receptor (PR) is an estrogen-stimulated gene which has a CpG island that is heavily methylated in a signi®cant fraction of estrogen receptor (ER)-negative/PR-negative human breast cancers and cell lines, including MDA-MB-231 cells. Treatment of MDA-MB-231 cells with the demethylating agent, 5-aza-2'-deoxycytidine (deoxyC) led to demethylation and expression of ER and PR. However, simultaneous treatment with antiestrogen prevented PR transcription, suggesting that demethylation of PR alone is not su cient to reactivate the PR gene. To examine the e ects of ER on the methylation status of the PR CpG island, we stably transfected MDA-MB-231 cells with an inducible expression vector for ER. Surprisingly, in two cell clones, we found that induction of PR gene expression by ligand-bound ER does not require demethylation of the PR CpG island. In contrast, induction of PR transcription was inhibited by blocking the interaction of ER with SRC-1A, a coactivator of ER function. For the ®rst time, we show that a transcription factor with the potential to remodel heterochromatin can activate gene expression without altering the methylation status of the CpG island. These results raise the possibility that demethylation and histone acetylation are distinct but complementary mechanisms for destabilizing heterochromatin and activating transcription.

Regulation of the NRSF/REST gene by methylation and CREB affects the cellular phenotype of small-cell lung cancer

“…Tumour phenotypes are influenced by both gene regulatory elements and the methylation state of the genome (Ferguson et al, 1995;Ekici et al, 2008). It has become apparent that NRSF/REST acts as an important determinant of cell differentiation in SCLC (Coulson et al, 2000;Gurrola-Diaz et al, 2003;Neumann et al, 2004;Onganer et al, 2005).…”

Evidence of epigenetic changes affecting the chromatin state of the retinoic acid receptor β2 promoter in breast cancer cells

“…Moreover, these studies are expected to shed light on the relation of histone acetylation and methylation of the RARb2 promoter. This issue is of particular interest since it is not yet completely clear whether DNA demethylation is indeed always required to restore transcription from genes with fully methylated promoters (Cameron et al, 1999;Ferguson et al, 1998;Razin, 1998;Ng and Bird, 1999).…”

Epigenetic Information and Estrogen Receptor Alpha Expression in Breast Cancer

“…Treatment of ER-negative human breast cancer cells with the methyltransferase inhibitor 5-aza-2ʹ-deoxycytidine (5-aza-dC) led to partial demethylation of the ER CpG island, re-expression of ER mRNA, and synthesis of functional ER protein [52,53]. Inhibition of DNMT1 by antisense oligonucleotides also caused ER gene re-expression and the restoration of estrogen responsiveness in ER-negative breast cancer cells [54].…”