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Valproate (VPA) and trichostatin A (TSA), inhibitors of zinc-dependent deacetylase activity, induce reduction in the levels of mRNA encoding oestrogen receptor-alpha (ERalpha), resulting in subsequent clearance of ERalpha protein from breast and ovarian cell lines. Inhibition of oestrogen signalling may account for the endocrine disorders, menstrual abnormalities, osteoporosis and weight gain that occur in a proportion of women treated with VPA for epilepsy or for bipolar mood disorder. Transcriptome profiling revealed that VPA and TSA also modulate the expression of, among others, key regulatory components of the cell cycle. Meta-analysis of genes directly responsive to oestrogen indicates that VPA and TSA have a generally antioestrogenic profile in ERalpha positive cells. Concomitant treatment with cycloheximide prevented most of these changes in gene expression, including downregulation of ERalpha mRNA, indicating that a limited number of genes signal a hyperacetylated state within cells. Three members of the NAD-dependent deacetylases, the sirtuins, are upregulated by VPA and by TSA and sirtuin activity contributes to loss of ERalpha expression. However, prolonged inhibition of the sirtuins by sirtinol also induces loss of ERalpha from cells. Mechanistically, we show that VPA invokes reversible promoter shutoff of the ERalpha, pS2 and cyclin D1 promoters, by inducing recruitment of methyl cytosine binding protein 2 (MeCP2) with concomitant exclusion of the maintenance methylase DNMT1. Furthermore, we demonstrate that, in the presence of VPA, local DNA methylation, deacetylation and demethylation of activated histones and recruitment of inhibitory complexes occurs on the pS2 promoter.

Unliganded (apo-) estrogen receptor alpha (ERalpha, NR3A1) is classically considered as transcriptionally unproductive. Reassessing this paradigm demonstrated that apo-human ERalpha (ERalpha66) and its N-terminally truncated isoform (ERalpha46) are both predominantly nuclear transcription factors that cycle on the endogenous estrogen-responsive pS2 gene promoter in vivo. Importantly, isoform-specific consequences occur in terms of poising the promoter for transcription, as evaluated by determining (i) the engagement of several cofactors and the resulting nucleosomal organization; and (ii) the CpG methylation state of the pS2 promoter. Although transcriptionally unproductive, cycling of apo-ERalpha66 prepares the promoter to respond to ligand, through sequentially targeting chromatin remodeling complexes and general transcription factors. Additionally, apo-ERalpha46 recruits corepressors, following engagement of cofactors identical to those recruited by apo-ERalpha66. Together, these data describe differential activities of ERalpha isoforms. Furthermore, they depict the maintenance of a promoter in a repressed state as a cyclical process that is intrinsically dependent on initial poising of the promoter.

The role of estrogens in the development and physiology of the male reproductive tract remains provocative, with a growing body of evidence suggesting that estrogens are able to influence normal testis development and physiology, through their classical receptors, estrogen receptor (ER)-alpha and ER-beta. We describe the identification and characterization of a new promoter that is involved in the expression of ER-alpha in the epididymis and in testis. This promoter lies on chromosome 6q25.1, approximately 16 kb upstream of the first coding exon of ER-alpha. Sequence analysis indicates that this promoter has a conventional TATA box and GC box but no upstream CAAT sequence. Alternative splicing results in at least two species of mRNA encoding ER-alpha being synthesized from this promoter. Transcription profiling of human tissues shows that, among those tested, this promoter is predominantly active only in testis and epididymal tissues. Transient transfection assays using this new promoter in a number of cell lines indicate that the region we have identified functions as a promoter and that tissue-specific regulation is likely to be dependent on inhibitory sequences greater than 1 kb upstream of the transcription start site.

The beneficial influence of E2 in the maintenance of healthy bone is well recognized. However, the way in which the actions of this hormone are mediated is less clearly understood. Western blot analysis of ERα in osteoblasts clearly demonstrated that the well characterized 66-kDa ERα was only one of the ERα isoforms present. Here we describe a 46-kDa isoform of ERα, expressed at a level similar to the 66-kDa isoform, that is also present in human primary osteoblasts. This shorter isoform is generated by alternative splicing of an ERα gene product, which results in exon 1 being skipped with a start codon in exon 2 used to initiate translation of the protein. Consequently, the transactivation domain AF-1 of this ERα isoform is absent. Functional analysis revealed that human (h)ERα46 is able to heterodimerize with the full-length ERα and also with ERβ. Further, a DNA-binding complex that corresponds to hERα46 is detectable in human osteoblasts. We have shown that hERα46 is a strong inhibitor of hERα66 when they are coexpressed in the human osteosarcoma cell line SaOs. As a functional consequence, proliferation of the transfected cells is inhibited when increasing amounts of hERα46 are cotransfected with hERα66. In addition to human bone, the expression of the alternatively spliced ERα mRNA variant is also detectable in bone of ERα knockout mice. These data suggest that, in osteoblasts, E2 can act in part through an ERα isoform that is markedly different from the 66-kDa receptor. The expression of two ERα protein isoforms may account, in part, for the differential action that estrogens and estrogen analogs have in different tissues. In particular, the current models of the action of estrogens should be reevaluated to take account of the presence of at least two ERα protein isoforms in bone and perhaps in other tissues.

The focus of this study is on the expression and regulation of the estrogen-regulated breast cancer and salivary gland expression (BASE) gene that may function as a breast cancer marker. In MCF7 cells, BASE is repressed by estrogen in an estrogen receptor α (ERα)-dependent manner. Promoter analysis of the BASE gene led to the identification of a 2-kb upstream enhancer that harbors binding sites for ERα and FoxA1. The recruitment of both ERα and FoxA1 to this region was shown by chromatin immunoprecipitation analysis. Furthermore, mutation studies and knockdown experiments show a clear separation between gene expression mediated by FoxA1 and ERα-dependent gene regulation. Additionally, we provide information on BASE expression in human breast tumor samples. [Cancer Res 2008;68(1):106–14]

Estradiol (E2) is believed to modulate physiological functions relevant to osteoblast biology through the actions of estrogen receptors (ERs) that in turn regulate the expression of target genes. The molecular effects of estrogen action in bone remain to be fully elucidated. This study reports a genome-wide molecular and computational analysis of the interaction between ER and regulatory elements on the DNA of target genes in human primary osteoblasts. Of approximately 54,000 gene probes surveyed in this study, a total of 375 genes were up-regulated and 418 genes were down-regulated on exposure to E2, with only 46 of these being direct target genes after 24 h, as determined by concomitant cycloheximide treatment. Computational analysis discovered several pathways where E2 co-regulates multiple functionally linked components. Examination of the genomic sequence of IGF binding protein 4 located ER response elements within the first intron. Using by chromatin immunoprecipitation, we show a site- and cell-specific recruitment of transcription factors to this newly identified regulatory region. Transient transfection studies revealed that this intronic region acts as a functional promoter in human osteoblasts. Taken together, this analysis provides a comprehensive gene transcription profile and identifies several genes of potential physiological importance in controlling estrogen-mediated signaling in primary osteoblasts.

The functional interplay between different domains of estrogen receptor-alpha (ERalpha, NR3A1) is responsible for the overall properties of the full-length protein. We previously identified an interaction between the N-terminal A and C-terminal domains, which we demonstrate here to repress ligand-independent transactivation and transrepression abilities of ERalpha. Using targeted mutations based on ERalpha structural models, we determine the basis for this interaction that defines a regulatory interplay between ERalpha A domain, corepressors, and ERalpha Helix 12 for binding to the same C-terminal surface. We propose a dynamic model where binding of different ligands influences the A/D-F domain interaction and results in specific functional outcomes. This model gives insights into the dynamic properties of full-length ERalpha and into the structure of unliganded ERalpha.

The human estrogen receptor-alpha (hER alpha) gene is a complex genomic unit exhibiting alternative splicing and promoter usage in a tissue-specific manner. During the investigation of new hER alpha mRNA variants by rapid amplification of 5' cDNA ends, we identified a cDNA in which the acceptor site of exon 1A, into which the different leader exons are normally alternatively spliced, was spliced accurately the 3' extremity of exon 1A (scrambled 1A--1A hER alpha cDNA). Reverse transcription-PCR and S1 nuclease mapping analysis revealed that 1A--1A hER alpha transcripts were not circular RNAs constituted by exon 1A only but corresponded to linear polyadenylated hER alpha RNAs composed of the eight coding exons of the hER alpha gene and characterized by a duplication of exon 1A. Genomic Southern blot experiments excluded the hypothesis of duplication of hER alpha exon 1A in the human genome. Therefore, these data suggested that 1A--1A hER alpha transcripts were likely generated by trans-splicing. The production of such transcripts by trans-splicing of pre-mRNAs generated from a chimeric gene formed by a single hER alpha exon 1A, exon 2, and their flanking intronic regions was demonstrated in transient transfection experiments. Therefore, in addition to the alternative cis-splicing, the hER alpha gene is also subject to natural trans-splicing.

A new isoform of the human estrogen receptor-alpha (hER-alpha) has been identified and characterized. This 46 kDa isoform (hERalpha46) lacks the N-terminal 173 amino acids present in the previously characterized 66 kDa isoform (hERalpha66). hERalpha46 is encoded by a new class of hER-alpha transcript that lacks the first coding exon (exon 1A) of the ER-alpha gene. We demonstrated that these Delta1A hER-alpha transcripts originate from the E and F hER-alpha promoters and are produced by the splicing of exon 1E directly to exon 2. Functional analysis of hERalpha46 showed that, in a cell context sensitive to the transactivation function AF-2, this receptor is an effective ligand-inducible transcription factor. In contrast, hERalpha46 is a powerful inhibitor of hERalpha66 in a cell context where the transactivating function of AF-1 predominates over AF-2. The mechanisms by which the AF-1 dominant-negative action is exerted may involve heterodimeri zation of the two receptor isoforms and/or direct competition for the ER-alpha DNA-binding site. hERalpha66/hERalpha46 ratios change with the cell growth status of the breast carcinoma cell line MCF7, suggesting a role of hERalpha46 in cellular proliferation.

Transcriptional activation of a gene involves an orchestrated recruitment of components of the basal transcription machinery and intermediate factors, concomitant with an alteration in local chromatin structure generated by posttranslational modifications of histone tails and nucleosome remodeling. We provide here a comprehensive picture of events resulting in transcriptional activation of a gene, through evaluating the estrogen receptor-α (NR3A1) target pS2 gene promoter in MCF-7 cells. This description integrates chromatin remodeling with a kinetic evaluation of cyclical networks of association of 46 transcription factors with the promoter, as determined by chromatin immunoprecipitation assays. We define the concept of a "transcriptional clock" that directs and achieves the sequential and combinatorial assembly of a transcriptionally productive complex on a promoter. Furthermore, the unanticipated findings of key roles for histone deacetylases and nucleosome-remodeling complexes in limiting transcription implies that transcriptional activation is a cyclical process that requires both activating and repressive epigenetic processes.