ICI182,780 Induces p21 Gene Transcription through Releasing Histone Deacetylase 1 and Estrogen Receptor α from Sp1 Sites to Induce Cell Cycle Arrest in MCF-7 Breast Cancer Cell Line

Abstract

We used the estrogen-responsive MCF-7 breast cancer cell line as a relevant model to study the anti-proliferative effects of ICI182,780 and identified the negative cell cycle regulator p21Waf1 as a specific target of ICI182,780. Furthermore, silencing of the p21 Waf1 expression by small interfering RNA overcame the G 0 /G 1 cell cycle arrest induced by ICI182,780, suggesting that the induction of p21Waf1 expression has a direct role in mediating the ICI182,780-induced G 0 /G 1 arrest. We further demonstrated that the induction of p21Waf1 by ICI182,780 is mediated at transcriptional and gene promoter levels through the proximal Sp1 sites located near the transcription start site. Co-immunoprecipitation, DNA "pulldown," and chromatin immunoprecipitation experiments together showed that in cycling cells, estrogen receptor ␣ and histone deacetylase 1 (HDAC1) are recruited to the proximal Sp1 sites of the promoter to repress p21 Estradiol (E 2 ) 1 is the principle steroid mitogen for normal breast epithelial cells and has been shown to be important for the development and progression of de novo breast cancers. E 2 exerts its effect on target cells predominantly through binding to and activating the estrogen receptor ␣ (ER␣), which is a member of the steroid/thyroid hormone superfamily of liganddependent transcription factors. The ligand-bound receptor binds to promoter regions of estrogen-regulated genes, where it recruits co-activators or co-repressors as well as the transcriptional machinery necessary to modulate gene expression. The recruitment of ligand-bound ER to the promoter regions of target genes can occur directly through binding to specific DNA sequences in target genes known as estrogen response elements (EREs) or indirectly through interaction with other DNA-binding transcription factors, such as AP1 and Sp1 (1). In addition to estradiol, the transcription activity of ER can also be modulated by a group of ligands called selective estrogen receptor modulators (SERMs), which have agonist and/or antagonist functions depending on the target promoters and tissues. Some of these SERMs, including tamoxifen, raloxifene, and ICI182,780 (also clinically termed faslodex or fulvestrant), have been employed to antagonize estrogen actions in order to treat breast cancer and protect high risk individuals against breast cancer (2). However, SERMs, such as tamoxifen and raloxifene, also behave as agonists in certain tissues. In fact, the modes of action of SERMs are often promoter context-and cell type-specific. For example, whereas tamoxifen is an effective adjuvant treatment for breast cancer, it can also promote endometrial cancer. Recent gene array data showed that antiestrogens, such as tamoxifen, raloxifene, and ICI182,780, function by either partially or completely antagonizing the actions of estrogen on most genes in breast cancer cells (3). Although it was initially believed that anti-estrogens function merely by competing with endogenous estrogens for receptor binding, previous studies using mutated ERs and re...

Lithium Down-regulates Histone Deacetylase 1 (HDAC1) and Induces Degradation of Mutant Huntingtin

“…p21 is a classic target gene of HDAC1 (43,44), and HDAC1 represses p21 transcription by associating with the transcription factor SP1 on the p21 promoter (45,46). We found that lithium significantly up-regulated p21 mRNA levels based on qPCR analysis (Fig.…”

Tamoxifen-stimulated growth of breast cancer due to p21 loss

“…Similarly, sequencing of the two coding exons of p21 in the metastatic lesions revealed only wild-type alleles. This result was expected because p21 is rarely mutated in human breast cancers (19), and epigenetic silencing of the p21 gene through promoter methylation and histone modifications has been described as a mechanism for p21 loss of expression in human cancers and cell lines (20)(21)(22)(23)(24)(25).…”

Modulating Estrogen Receptor-related Receptor-α Activity Inhibits Cell Proliferation

“…The behavior of XCT790 is thus reminiscent of that of the antiestrogen ICI182,780 in several features. Indeed, both compounds induce a proteasome-dependent degradation of their cognate receptor (15,37), repress the expression of the pS2 promoter in a receptor-dependent manner, yet activate the expression of the p21 promoter (6). However, the main difference is that ER␣ represses this promoter, and ERR␣ moderately activates it.…”

“…waf/cip1 (hereafter referred to as p21) (6). This protein blocks the activity of the cyclin D-cdk complexes leading to hypophosphorylation of Rb and arrest in the G 1 phase of the cell cycle (4).…”