Gene expression profiling reveals that the regulation of estrogen-responsive element-independent genes by 17 beta-estradiol-estrogen receptor beta is uncoupled from the induction of phenotypic changes in cell models

Modulation of neural gene networks by estradiol in old rhesus macaque females

The postmenopausal decrease in circulating estradiol (E2) levels has been shown to contribute to several adverse physiological and psychiatric effects. To elucidate the molecular effects of E2 on the brain, we examined differential gene expression and DNA methylation (DNAm) patterns in the nonhuman primate brain following ovariectomy (Ov) and subsequent subcutaneous bioidentical E2 chronic treatment. We identified several dysregulated molecular networks, including MAPK signaling and dopaminergic synapse response, that are associated with ovariectomy and shared across two different brain areas, the occipital cortex (OC) and prefrontal cortex (PFC). The finding that hypomethylation (p = 1.6 × 10-51) and upregulation (p = 3.8 × 10-3) of UBE2M across both brain regions provide strong evidence for molecular differences in the brain induced by E2 depletion. Additionally, differential expression (p = 1.9 × 10-4; interaction p = 3.5 × 10-2) of LTBR in the PFC provides further support for the role E2 plays in the brain, by demonstrating that the regulation of some genes that are altered by ovariectomy may also be modulated by Ov followed by hormone replacement therapy (HRT). These results present real opportunities to understand the specific biological mechanisms that are altered with depleted E2. Given E2's potential role in cognitive decline and neuroinflammation, our findings could lead to the discovery of novel therapeutics to slow cognitive decline. Together, this work represents a major step toward understanding molecular changes in the brain that are caused by ovariectomy and how E2 treatment may revert or protect against the negative neuro-related consequences caused by a depletion in estrogen as women approach menopause.

Modulation of neural gene networks by estradiol in old rhesus macaque females

The postmenopausal decrease in circulating estradiol (E2) levels has been shown to contribute to several adverse physiological and psychiatric effects. To elucidate the molecular effects of E2 on the brain, we examined differential gene expression and DNA methylation (DNAm) patterns in the nonhuman primate brain following ovariectomy (Ov) and subsequent E2 treatment. We identified several dysregulated molecular networks, including MAPK signaling and dopaminergic synapse response, that are associated with ovariectomy and shared across two different brain areas, the occipital cortex (OC) and prefrontal cortex (PFC). The finding that hypomethylation (p=1.6×10-51) and upregulation (p=3.8×10-3) of UBE2M across both brain regions, provide strong evidence for molecular differences in the brain induced by E2 depletion. Additionally, differential expression (p=1.9×10-4; interaction p=3.5×10-2) of LTBR in the PFC, provides further support for the role E2 plays in the brain, by demonstrating that the regulation of some genes that are altered by ovariectomy may also be modulated by Ov followed by hormone replacement therapy (HRT). These results present real opportunities to understand the specific biological mechanisms that are altered with depleted E2. Given E2's potential role in cognitive decline and neuroinflammation, our findings could lead to the discovery of novel therapeutics to slow cognitive decline. Together, this work represents a major step towards understanding molecular changes in the brain that are caused by ovariectomy and how E2 treatment may revert or protect against the negative neuro-related consequences caused by a depletion in estrogen as women approach menopause.

Molecular mechanism of estrogen-estrogen receptor signaling

17β‐Estradiol (E2), as the main circulating estrogen hormone, regulates many tissue and organ functions in physiology. The effects of E2 on cells are mediated by the transcription factors and estrogen receptor (ER)α and ERβ that are encoded by distinct genes. Localized at the peri‐membrane, mitochondria, and the nucleus of cells that are dependent on estrogen target tissues, the ERs share similar, as well as distinct, regulatory potentials. Different intracellular localizations of the ERs result in dynamically integrated and finely tuned E2 signaling cascades that orchestrate cellular growth, differentiation, and death. The deregulation of E2–ER signaling plays a critical role in the initiation and progression of target tissue malignancies. A better understanding of the complex regulatory mechanisms that underlie ER actions in response to E2 therefore holds a critical trajectory for the development of novel prognostic and therapeutic approaches with substantial impacts on the systemic management of target tissue diseases.

Estradiol-Estrogen Receptor α Mediates the Expression of the CXXC5 Gene through the Estrogen Response Element-Dependent Signaling Pathway

17β-estradiol (E2), the primary circulating estrogen hormone, mediates physiological and pathophysiological functions of breast tissue mainly through estrogen receptor α (ERα). Upon binding to E2, ERα modulates the expression of target genes involved in the regulation of cellular proliferation primarily through interactions with specific DNA sequences, estrogen response elements (EREs). Our previous microarray results suggested that E2-ERα modulates CXXC5 expression. Because of the presence of a zinc-finger CXXC domain (ZF-CXXC), CXXC5 is considered to be a member of the ZF-CXXC family, which binds to non-methylated CpG dinucleotides. Although studies are limited, CXXC5 appears to participate as a transcription factor, co-regulator and/or epigenetic factor in the regulation of cellular events induced by various signaling pathways. However, how signaling pathways mediate the expression of CXXC5 is yet unclear. Due to the importance of E2-ERα signaling in breast tissue, changes in the CXXC5 transcription/synthesis could participate in E2-mediated cellular events as well. To address these issues, we initially examined the mechanism whereby E2-ERα regulates CXXC5 expression. We show here that CXXC5 is an E2-ERα responsive gene regulated by the interaction of E2-ERα with an ERE present at a region upstream of the initial translation codon of the gene.

Modulation of Estrogen Response Element-Driven Gene Expressions and Cellular Proliferation with Polar Directions by Designer Transcription Regulators

Estrogen receptor α (ERα), as a ligand-dependent transcription factor, mediates 17β-estradiol (E2) effects. ERα is a modular protein containing a DNA binding domain (DBD) and transcription activation domains (AD) located at the amino- and carboxyl-termini. The interaction of the E2-activated ERα dimer with estrogen response elements (EREs) of genes constitutes the initial step in the ERE-dependent signaling pathway necessary for alterations of cellular features. We previously constructed monomeric transcription activators, or monotransactivators, assembled from an engineered ERE-binding module (EBM) using the ERα-DBD and constitutively active ADs from other transcription factors. Monotransactivators modulated cell proliferation by activating and repressing ERE-driven gene expressions that simulate responses observed with E2-ERα. We reasoned here that integration of potent heterologous repression domains (RDs) into EBM could generate monotransrepressors that alter ERE-bearing gene expressions and cellular proliferation in directions opposite to those observed with E2-ERα or monotransactivators. Consistent with this, monotransrepressors suppressed reporter gene expressions that emulate the ERE-dependent signaling pathway. Moreover, a model monotransrepressor regulated DNA synthesis, cell cycle progression and proliferation of recombinant adenovirus infected ER-negative cells through decreasing as well as increasing gene expressions with polar directions compared with E2-ERα or monotransactivator. Our results indicate that an ‘activator’ or a ‘repressor’ possesses both transcription activating/enhancing and repressing/decreasing abilities within a chromatin context. Offering a protein engineering platform to alter signal pathway-specific gene expressions and cell growth, our approach could also be used for the development of tools for epigenetic modifications and for clinical interventions wherein multigenic de-regulations are an issue.

The ligand-mediated nuclear mobility and interaction with estrogen-responsive elements of estrogen receptors are subtype specific

17β-Estradiol (E(2)) plays important roles in functions of many tissues. E(2) effects are mediated by estrogen receptor (ER) α and β. ERs regulate transcriptions through estrogen-responsive element (ERE)-dependent and ERE-independent modes of action. ER binding to ERE constitutes the basis of the ERE-dependent pathway. Direct/indirect ER interactions with transcription complexes define ERE-independent signaling. ERs share functional features. Ligand-bound ERs nevertheless induce distinct transcription profiles. Live cell imaging indicates a dynamic nature of gene expressions by highly mobile ERs. However, the relative contribution of ER mobility at the ERE-independent pathway to the overall kinetics of ER mobility remains undefined. We used fluorescent recovery after a photo-bleaching approach to assess the ligand-mediated mobilities of ERE binding-defective ERs, ER(EBD). The decrease in ERα mobility with E(2) or the selective ER modulator 4-hydroxyl-tamoxifen (4HT) was largely due to the interaction of the receptor with ERE. Thus, ERα bound to E(2) or 4HT mediates transcriptions from the ERE-independent pathway with remarkably fast kinetics that contributes fractionally to the overall motility of the receptor. The antagonist Imperial Chemical Industries 182 780 immobilized ERαs. The mobilities of ERβ and ERβ(EBD) in the presence of ligands were indistinguishable kinetically. Thus, ERβ mobility is independent of the nature of ligands and the mode of interaction with target sites. Chimeric ERs indicated that the carboxyl-termini are critical regions for subtype-specific mobility. Therefore, while ERs are highly mobile molecules interacting with target sites with fast kinetics, an indication of the hit-and-run model of transcription, they differ mechanistically to modulate transcriptions.

Estrogen receptors similarly mediate the effects of 17β-estradiol on cellular responses but differ in their potencies

17β-estradiol (E2), as the main circulating estrogen hormone, plays critical roles in the physiology and pathophysiology of various tissues. The E2 information is primarily conveyed by the transcription factors, estrogen receptors (ERs) α and β. ERs share similar structural and functional features. Experimental studies indicate that upon binding to E2, ERs directly or indirectly interact with DNA and regulate gene expressions with ERα being more potent transregulator than ERβ. However, studies also showed that ERβ induces alterations in phenotypic features of cancer cell lines independent of E2. These observations suggested that the manner in which the unliganded ERβ induces phenotypic alterations in cancer cell models differs from that of ERα. Studies demonstrated that while requiring E2 for function at low levels of synthesis, the unliganded ERα at augmented concentrations modulates gene expressions and cellular growth. We, therefore, anticipated that heightened levels of ERβ synthesis could similarly circumvent the dependency on E2 leading to gene transcriptions and cellular proliferation. To test this prediction, we used adenovirus-infected cancer cell lines in which ERs were shown to induce genomic and cellular responses. We found that while ERβ at low levels of synthesis was dependent upon E2 for function, the receptor at high levels regulated gene expression and cellular proliferation independent of E2. We then addressed whether ERs at comparable levels that require E2 for function differentially alter gene expressions and cellular responses. We found that ERs mediate the effects of E2 on gene expression, cellular proliferation, apoptosis, and motility with an overlapping pattern. However, ERα was more potent regulator than ERβ in inducing cellular responses. Our results suggest that differences in potencies to regulate the expression of genes are a critical feature of the ER subtypes in mediating E2 signaling in cancer cell lines.

Designer monotransregulators provide a basis for a transcriptional therapy for de novo endocrine-resistant breast cancer

The main circulating estrogen hormone 17beta-estradiol (E2) contributes to the initiation and progression of breast cancer. Estrogen receptors (ERs), as transcription factors, mediate the effects of E2. Ablation of the circulating E2 and/or prevention of ER functions constitute approaches for ER-positive breast cancer treatments. These modalities are, however, ineffective in de novo endocrine-resistant breast neoplasms that do not express ERs. The interaction of E2-ERs with specific DNA sequences, estrogen responsive elements (EREs), of genes constitutes one genomic pathway necessary for cellular alterations. We herein tested the prediction that specific regulation of ERE-driven genes by an engineered monomeric and constitutively active transcription factor, monotransregulator, provides a basis for the treatment of ER-negative breast cancer. Using adenovirus infected ER-negative MDA-MB-231 cells derived from a breast adenocarcinoma, we found that the monotransregulator, but not the ERE-binding defective counterpart, repressed cellular proliferation and motility, and induced apoptosis through expression of genes that required ERE interactions. Similarly, the monotransregulator suppressed the growth of ER-negative BT-549 cells derived from a breast-ductal carcinoma. Moreover, the ERE-binding monotransregulator repressed xenograft tumor growth in a nude mice model. Thus, specific regulation of genes bearing EREs could offer a therapeutic approach for de novo endocrine-resistant breast cancers.

Genomic responses from the estrogen-responsive element-dependent signaling pathway mediated by estrogen receptor alpha are required to elicit cellular alterations

Estrogen (E2) signaling is conveyed by the transcription factors estrogen receptor (ER) alpha and beta. ERs modulate the expression of genes involved in cellular proliferation, motility, and death. The regulation of transcription by E2-ERalpha through binding to estrogen-responsive elements (EREs) in DNA constitutes the ERE-dependent signaling pathway. E2-ERalpha also modulates gene expression by interacting with transregulators bound to cognate DNA-regulatory elements, and this regulation is referred to as the ERE-independent signaling pathway. The relative importance of the ERE-independent pathway in E2-ERalpha signaling is unclear. To address this issue, we engineered an ERE-binding defective ERalpha mutant (ERalpha(EBD)) by changing residues in an alpha-helix of the protein involved in DNA binding to render the receptor functional only through the ERE-independent signaling pathway. Using recombinant adenovirus-infected ER-negative MDA-MB-231 cells derived from a breast adenocarcinoma, we found that E2-ERalpha(EBD) modulated the expression of a subset of ERalpha-responsive genes identified by microarrays and verified by quantitative PCR. However, E2-ERalpha(EBD) did not affect cell cycle progression, cellular growth, death, or motility in contrast to E2-ERalpha.ERalpha(EBD) in the presence of E2 was also ineffective in inducing phenotypic alterations in ER-negative U-2OS cells derived from an osteosarcoma. E2-ERalpha, on the other hand, effectively repressed growth in this cell line. Our findings suggest that genomic responses from the ERE-dependent signaling pathway are required for E2-ERalpha to induce alterations in cellular responses.