The high mobility group protein 1 enhances binding of the estrogen receptor DNA binding domain to the estrogen response element

HMGB1/STAT3/p65 axis drives microglial activation and autophagy exert a crucial role in chronic Stress-Induced major depressive disorder

INTRODUCTION

Neuroinflammation and autophagy are implicated in stress-related major depressive disorder (MDD), but the underlying molecular mechanisms remain largely unknown.

OBJECTIVES

Here, we identified that MDD regulated by HMGB1/STAT3/p65 axis mediated microglial activation and autophagy for the first time. Further investigations were performed to uncover the effects of this axis on MDD in vivo and in vitro.

METHODS

Bioinformatics analyses were used to re-analysis the transcriptome data from the dorsolateral prefrontal cortex (dlPFC) of post-mortem male MDD patients. The expression level of HMGB1 and its correlation with depression symptoms were explored in MDD clinical patients and chronic social defeat stress (CSDS)-induced depression model mice. Specific adeno-associated virus and recombinant (r)HMGB1 injection into the medial PFC (mPFC) of mice, and pharmacological inhibitors with rHMGB1 in two microglial cell lines exposed to lipopolysaccharide were used to analyze the effects of HMGB1/STAT3/p65 axis on MDD.

RESULTS

The differential expression of genes from MDD patients implicated in microglial activation and autophagy regulated by HMGB1/STAT3/p65 axis. Serum HMGB1 level was elevated in MDD patients and positively correlated with symptom severity. CSDS not only induced depression-like states in mice, but also enhanced microglial reactivity, autophagy as well as activation of the HMGB1/STAT3/p65 axis in mPFC. The expression level of HMGB1 was mainly increased in the microglial cells of CSDS-susceptible mice, which also correlated with depressive-like behaviors. Specific HMGB1 knockdown produced a depression-resilient phenotype and suppressed the associated microglial activation and autophagy effects of CSDS-induced. The effects induced by CSDS were mimicked by exogenous administration of rHMGB1 or specific overexpression of HMGB1, while blocked by STAT3 inhibitor or p65 knockdown. In vitro, inhibition of HMGB1/STAT3/p65 axis prevented lipopolysaccharide-induced microglial activation and autophagy, while rHMGB1 reversed these changes.

CONCLUSION

Our study established the role of microglial HMGB1/STAT3/p65 axis in mPFC in mediating microglial activation and autophagy in MDD.

Admixture mapping of uterine fibroid size and number in African American women

OBJECTIVE

To evaluate the relationship between genetic ancestry and uterine fibroid characteristics.

DESIGN

Cross-sectional study.

SETTING

Not applicable.

PATIENT(S)

A total of 609 African American participants with image- or surgery-confirmed fibroids in a biorepository at Vanderbilt University electronic health record biorepository and the Coronary Artery Risk Development in Young Adults studies were included.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Outcome measures include fibroid number (single vs. multiple), volume of largest fibroid, and largest fibroid dimension of all fibroid measurements.

RESULT(S)

Global ancestry meta-analyses revealed a significant inverse association between percentage of European ancestry and risk of multiple fibroids (odds ratio: 0.78; 95% confidence interval 0.66, 0.93; P=6.05 × 10-3). Local ancestry meta-analyses revealed five suggestive (P<4.80 × 10-3) admixture mapping peaks in 2q14.3-2q21.1, 3p14.2-3p14.1, 7q32.2-7q33, 10q21.1, 14q24.2-14q24.3, for number of fibroids and one suggestive admixture mapping peak (P<1.97 × 10-3) in 10q24.1-10q24.32 for volume of largest fibroid. Single variant association meta-analyses of the strongest associated region from admixture mapping of fibroid number (10q21.1) revealed a strong association at single nucleotide polymorphism variant rs12219990 (odds ratio: 0.41; 95% confidence interval 0.28, 0.60; P=3.82 × 10-6) that was significant after correction for multiple testing.

CONCLUSION(S)

Increasing African ancestry is associated with multiple fibroids but not with fibroid size. Local ancestry analyses identified several novel genomic regions not previously associated with fibroid number and increasing volume. Future studies are needed to explore the genetic impact that ancestry plays into the development of fibroid characteristics.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Expanding the paradigm for estrogen receptor binding and transcriptional activation

Estrogen receptor (ER) binds to a spectrum of functional estrogen response elements (ERE) within the human genome, including ERE half-sites (HERE), inverted and direct repeats. This has been confounding, because ER has been reported to bind weakly, if at all, to these sites in vitro. We show that ER binds strongly to these nonconventional EREs, and the binding is enhanced by the presence of high-mobility group protein B1 (HMGB1). Collectively, these and previous findings reinforce the notion of the plasticity of strong ER/ERE interactions, consistent with their broader range of observed binding specificity. In addition, transient transfection studies using luciferase reporter gene assays show that these EREs drive luciferase activity, and HMGB1 enhances transcriptional activity. Furthermore, HMGB1 gene expression knockdown results in a precipitous drop in luciferase activity, suggesting a prominent role for HMGB1 in activation of estrogen/ER-responsive genes. Therefore, these data advocate that the minimal target site for ER is a cHERE (consensus HERE) that occurs in many different contexts and that HMGB1 enhances both the binding affinity and transcriptional activity. This challenges the current paradigm for ER binding affinity and functional activity and suggests that the paradigm requires significant reevaluation and modification. These findings also suggest a possible mechanism for a cross talk between genes regulated by ER and class II nuclear receptors.

Modulation of the DNA-binding activity of Saccharomyces cerevisiae MSH2-MSH6 complex by the high-mobility group protein NHP6A, in vitro

DNA mismatch repair corrects mispaired bases and small insertions/deletions in DNA. In eukaryotes, the mismatch repair complex MSH2–MSH6 binds to mispairs with only slightly higher affinity than to fully paired DNA in vitro. Recently, the high-mobility group box1 protein, (HMGB1), has been shown to stimulate the mismatch repair reaction in vitro. In yeast, the closest homologs of HMGB1 are NHP6A and NHP6B. These proteins have been shown to be required for genome stability maintenance and mutagenesis control. In this work, we show that MSH2–MSH6 and NHP6A modulate their binding to DNA in vitro. Binding of the yeast MSH2–MSH6 to homoduplex regions of DNA significantly stimulates the loading of NHP6A. Upon binding of NHP6A to DNA, MSH2–MSH6 is excluded from binding unless a mismatch is present. A DNA binding-impaired MSH2–MSH6F337A significantly reduced the loading of NHP6A to DNA, suggesting that MSH2–MSH6 binding is a requisite for NHP6A loading. MSH2–MSH6 and NHP6A form a stable complex, which is responsive to ATP on mismatched substrates. These results suggest that MSH2–MSH6 binding to homoduplex regions of DNA recruits NHP6A, which then prevents further binding of MSH2–MSH6 to these sites unless a mismatch is present.

A progesterone receptor co-activator (JDP2) mediates activity through interaction with residues in the carboxyl-terminal extension of the DNA binding domain

Progesterone receptor (PR) belongs to the nuclear receptor family of ligand-dependent transcription factors and mediates the major biological effects of progesterone. Transcriptional co-activators that are recruited by PR through the carboxyl-terminal ligand binding domain have been studied extensively. Much less is known about co-activators that interact with other regions of receptors. Jun dimerization protein 2 (JDP2) is a PR co-activator that enhances the transcriptional activity of the amino-terminal domain by increasing the alpha-helical content and stability of the intrinsically disordered amino-terminal domain. To gain insights into the mechanism of JDP2 co-activation of PR, the structural basis of JDP2-PR interaction was analyzed using NMR. The smallest regions of each protein needed for efficient protein interaction were used for NMR and included the basic region plus leucine zipper (bZIP) domain of JDP2 and the core zinc modules of the PR DNA binding domain plus the intrinsically disordered carboxyl-terminal extension (CTE) of the DNA binding domain. Chemical shift changes in PR upon titration with JDP2 revealed that most of the residues involved in binding of JDP2 reside within the CTE. The importance of the CTE for binding JDP2 was confirmed by peptide competition and mutational analyses. Point mutations within CTE sites identified by NMR and a CTE domain swapping experiment also confirmed the functional importance of JDP2 interaction with the CTE for enhancement of PR transcriptional activity. These studies provide insights into the role and functional importance of the CTE for co-activator interactions.

Isolation of novel coregulatory protein networks associated with DNA-bound estrogen receptor alpha

Background

DNA-bound transcription factors recruit an array of coregulatory proteins that influence gene expression. We previously demonstrated that DNA functions as an allosteric modulator of estrogen receptor α (ERα) conformation, alters the recruitment of regulatory proteins, and influences estrogen-responsive gene expression and reasoned that it would be useful to develop a method of isolating proteins associated with the DNA-bound ERα using full-length receptor and endogenously-expressed nuclear proteins.

Results

We have developed a novel approach to isolate large complexes of proteins associated with the DNA-bound ERα. Purified ERα and HeLa nuclear extracts were combined with oligos containing ERα binding sites and fractionated on agarose gels. The protein-DNA complexes were isolated and mass spectrometry analysis was used to identify proteins associated with the DNA-bound receptor. Rather than simply identifying individual proteins that interact with ERα, we identified interconnected networks of proteins with a variety of enzymatic and catalytic activities that interact not only with ERα, but also with each other. Characterization of a number of these proteins has demonstrated that, in addition to their previously identified functions, they also influence ERα activity and expression of estrogen-responsive genes.

Conclusion

The agarose gel fractionation method we have developed would be useful in identifying proteins that interact with DNA-bound transcription factors and should be easily adapted for use with a variety of cultured cell lines, DNA sequences, and transcription factors.

High mobility group box 1 (HMGB1) is implicated in preimplantation embryo development in the mouse

High mobility group box 1 (HMGB1) regulates multiple cell functions, including transcription, DNA repair, differentiation, and apoptosis. In order to obtain insight into the role of HMGB1 in embryo development, we first evaluated its gene expression levels in mouse preimplantation embryos. Quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) revealed high expression levels in zygotes, and expression steadily increased after zygotic genome activation when normalized to the rabbit Globin mRNA. Indirect immunocytochemistry showed that the HMGB1 protein was also produced in mouse embryos. Injection of a small interfering RNA (siRNA) specific for HMGB1 into zygotes specifically reduced both mRNA expression (P < 0.001) and protein synthesis of HMGB1 in early embryos developed in vitro. Injection of siRNA into the zygote did not affect development to the blastocyst stage, but significantly decreased cell numbers (P < 0.01) in the blastocyst and increased caspase3 (Casp3, P < 0.05) gene expression and apoptosis (P < 0.005). Addition of recombinant HMGB1 (Sigma, H-4652) into the culture medium enhanced the development of zygote stage mouse embryos to blastocysts, in the absence of BSA supplementation. These findings suggest that endogenous and exogenous HMGB1 are implicated in preimplantation embryo development in the mouse.

High mobility group box-1 protein acts as a coactivator of nuclear factor of activated T cells-2 in promoting interleukin-2 transcription

High mobility group box-1 protein, an abundant and conserved constituent of vertebrate nuclei, has recently been reported to be an endogenous immune signal [Rovere-Querini P, Capobianco A, Scaffidi P, Valentinis B, Catalanotti F, Giazzon M, et al. HMGB1 is an endogenous immune adjuvant released by necrotic cells. EMBO Reports 2004;5:825-30]. High mobility group box-1 protein can trigger the release of interleukin-2 and interleukin-12 from lymphocytes. However, at present the underlying mechanism remains unknown. It has been clarified that nuclear factor of activated T cells-2 transduces most immunological signals in T cells and modulates the production of interleukin-2. So it is natural that we asked whether high mobility group box-1 protein could promote production of interleukin-2 in a nuclear factor of activated T cells-2-dependent way. Our experiments firstly showed that high mobility group box-1 protein could bind to nuclear factor of activated T cells-2 in vivo and in vitro. High mobility group box-1 protein cotransfection markedly upregulated the transcription activity of nuclear factor of activated T cells-2 in promoting interleukin-2 reporter gene transcription, which was demonstrated to be dose-dependent. Cotransfection of high mobility group box-1 protein and nuclear factor of activated T cells-2 induced an 18.4-time increase of interleukin-2 activity in 293T cells and a 117.7-time increase in Hela cells. Moreover, inhibition of either high mobility group box-1 protein or nuclear factor of activated T cells -2 expression by sRNAi led to significant decrease of transcription activity of interleukin-2 reporter gene, suggesting that high mobility group box-1 protein and nuclear factor of activated T cells-2 both take important roles in facilitating interleukin-2 transcription, and high mobility group box-1 protein could act as a coactivator for nuclear factor of activated T cells-2 in enhancing transcription of interleukin-2. This discovery has not been reported elsewhere, and helps to understand the newly highlighted immunological role of high mobility group box-1 protein.

Mechanism of high-mobility group protein B enhancement of progesterone receptor sequence-specific DNA binding

The DNA-binding domain (DBD) of progesterone receptor (PR) is bipartite containing a zinc module core that interacts with progesterone response elements (PRE), and a short flexible carboxyl terminal extension (CTE) that interacts with the minor groove flanking the PRE. The chromosomal high-mobility group B proteins (HMGB), defined as DNA architectural proteins capable of bending DNA, also function as auxiliary factors that increase the DNA-binding affinity of PR and other steroid receptors by mechanisms that are not well defined. Here we show that the CTE of PR contains a specific binding site for HMGB that is required for stimulation of PR-PRE binding, whereas the DNA architectural properties of HMGB are dispensable. Specific PRE DNA inhibited HMGB binding to the CTE, indicating that DNA and HMGB-CTE interactions are mutually exclusive. Exogenous CTE peptide increased PR-binding affinity for PRE as did deletion of the CTE. In a PR-binding site selection assay, A/T sequences flanking the PRE were enriched by HMGB, indicating that PR DNA-binding specificity is also altered by HMGB. We conclude that a transient HMGB-CTE interaction alters a repressive conformation of the flexible CTE enabling it to bind to preferred sequences flanking the PRE.

What are comparative studies telling us about the mechanism of ERbeta action in the ERE-dependent E2 signaling pathway?

Estrogen hormone (E2) signaling is primarily conveyed by the estrogen receptors (ER) alpha and beta. ERs are encoded by two distinct genes and share varying degrees of domain-specific structural/functional similarities. ERs mediate a complex array of nuclear and non-nuclear events critical for the homeodynamic regulation of various tissue functions. The canonical nuclear signaling involves the interaction of ERalpha and ERbeta with specific DNA sequences, the so-called estrogen responsive elements (EREs). This interaction constitutes the initial step in ERE-dependent signaling in which ERbeta is a weaker transcription factor than ERalpha in response to E2. However, it remains unclear why transactivation potencies of ER subtypes differ. Studies suggest that the amino-terminus, the least conserved structural region, of ERbeta, but not that of ERalpha, impairs the ability of the receptor to bind to ERE independent of E2. Although the impaired ERbeta-ERE interaction contributes, it is not sufficient to explain the weak transactivation potency of the receptor. It appears that the lack of transactivation ability and of the capability of the amino-terminus of ERbeta, as opposed to that of ERalpha, to functionally interact with the carboxyl-terminal hormone-dependent activation domain is also critical for the receptor-specific activity. Thus, the structurally distinct amino-termini of ERs are important determinants in defining the function of ER-subtypes in the ERE-dependent pathway. This could differentially affect the physiology and pathophysiology of E2 signaling.

Effects of Cu/Zn superoxide dismutase on estrogen responsiveness and oxidative stress in human breast cancer cells

The effects of estrogen on gene expression in mammary cells are mediated by interaction of the estrogen receptor (ER) with estrogen response elements in target DNA. Whereas the ER is the primary initiator of transcription, the recruitment of coregulatory proteins to the DNA-bound receptor influences estrogen responsiveness. To better understand how estrogen alters gene expression, we identified proteins associated with the DNA-bound ERalpha. Surprisingly, the antioxidant enzyme Cu/Zn superoxide dismutase (SOD1), which is known primarily as a scavenger of superoxide, was associated with the DNA-bound receptor. We have now demonstrated that SOD1 interacts with ERalpha from MCF-7 cell nuclear extracts and with purified ERalpha and that SOD1 enhances binding of ERalpha to estrogen response element-containing DNA. Although SOD1 decreases transcription of an estrogen-responsive reporter plasmid in transiently transfected U2 osteosarcoma cells, RNA interference assays demonstrate that SOD1 is required for effective estrogen responsiveness of the endogenous pS2, progesterone receptor, cyclin D1, and Cathepsin D genes in MCF-7 breast cancer cells. Furthermore, ERalpha and SOD1 are associated with regions of the pS2 and progesterone receptor genes involved in conferring estrogen-responsive gene expression. Interestingly, when MCF-7 cells are exposed to 17beta-estradiol and superoxide generated by addition of potassium superoxide (KO2) to the cell medium, SOD1 levels are increased and tyrosine nitration, which is an indicator of oxidative stress-induced protein damage, is significantly diminished. Our studies have identified a new role for SOD1 in regulating estrogen-responsive gene expression and suggest that the 17beta-estradiol- and KO2-induced increase in SOD1 may play a role in the survival of breast cancer cells and the progression of mammary tumors.

Interaction of the tumor metastasis suppressor nonmetastatic protein 23 homologue H1 and estrogen receptor alpha alters estrogen-responsive gene expression

Metastasis of cancer cells from the primary tumor is associated with poor prognosis and decreased overall survival. One protein implicated in inhibiting metastasis is the tumor metastasis suppressor nonmetastatic protein 23 homologue 1 (NM23-H1). NM23-H1 is a multifunctional protein, which, in addition to limiting metastasis, has DNase and histidine protein kinase activities. We have identified new functions for NM23-H1 in influencing estrogen receptor alpha (ER alpha)-mediated gene expression. Using a battery of molecular and biochemical techniques, we show that NM23-H1 interacts with ER alpha and increases the ER alpha-estrogen response element (ERE) interaction. When NM23-H1 expression is increased in U2 osteosarcoma and MDA-MB-231 breast cancer cells, transcription of a transiently transfected, estrogen-responsive reporter plasmid is decreased. More importantly, when endogenous NM23-H1 expression is knocked down in MCF-7 human breast cancer cells using small interfering RNA, estrogen responsiveness of the progesterone receptor (PR), Bcl-2, cathepsin D, and cyclin D1 genes, but not the pS2 gene, is enhanced. Furthermore, NM23-H1 associates with the region of the PR gene containing the +90 activator protein 1 site, but not with the ERE-containing region of the pS2 gene, indicating that NM23-H1 mediates gene-specific effects by association with endogenous chromatin. Our studies suggest that the capacity of NM23-H1 to limit the expression of estrogen-responsive genes such as cathepsin D and Bcl-2, which are involved in cell migration, apoptosis, and angiogenesis, may help to explain the metastasis-suppressive effects of this protein. The complementary abilities of ER alpha and NM23-H1 together to influence gene expression, cell migration, and apoptosis could be key factors in helping to determine tumor cell fate.

Interaction of estrogen receptor alpha with proliferating cell nuclear antigen

The ability of estrogen receptor alpha (ERalpha) to modulate gene expression is influenced by the recruitment of a host of co-regulatory proteins to target genes. To further understand how estrogen-responsive genes are regulated, we have isolated and identified proteins associated with ERalpha when it is bound to DNA containing the consensus estrogen response element (ERE). One of the proteins identified in this complex, proliferating cell nuclear antigen (PCNA), is required for DNA replication and repair. We show that PCNA interacts with ERalpha in the absence and in the presence of DNA, enhances the interaction of ERalpha with ERE-containing DNA, and associates with endogenous estrogen-responsive genes. Interestingly, rather than altering hormone responsiveness of endogenous, estrogen-responsive genes, PCNA increases the basal expression of these genes. Our studies suggest that in addition to serving as a platform for the recruitment of DNA replication and repair proteins, PCNA may serve as a platform for transcription factors involved in regulating gene expression.

The deoxyribonucleic acid repair protein flap endonuclease-1 modulates estrogen-responsive gene expression

The ligand-occupied estrogen receptor alpha (ERalpha) initiates changes in gene expression through its interaction with target DNA. The capacity of ERalpha to modulate gene expression is influenced by the association of the receptor with a variety of coregulatory proteins. To further understand the role of these coregulatory proteins in ERalpha-mediated transcription, we have isolated and identified proteins associated with ERalpha when it is bound to the consensus estrogen response element. One of the proteins identified in this complex, flap endonuclease-1 (FEN-1), is required for DNA replication and repair. We show that FEN-1 interacts directly with ERalpha and enhances the interaction of ERalpha with estrogen response element-containing DNA. More importantly, chromatin immunoprecipitation and RNA interference assays demonstrate that endogenously expressed FEN-1 associates with the native pS2 gene in MCF-7 cells and influences estrogen-responsive gene expression. Interestingly, estrogen differentially regulates expression of FEN-1 in mouse uterine epithelial, stromal, and myometrial cells. Together, our studies help to elucidate the functional consequence of the ERalpha-FEN-1 interaction and increase our understanding of the elaborate regulatory mechanisms that drive estrogen-responsive gene expression and DNA repair.

Structure of the progesterone receptor-deoxyribonucleic acid complex: novel interactions required for binding to half-site response elements

The DNA binding domain (DBD) of nuclear hormone receptors contains a highly conserved globular domain and a less conserved carboxyl-terminal extension (CTE). Despite previous observations that the CTEs of some classes of nuclear receptors are structured and interact with DNA outside of the hexanucleotide hormone response element (HRE), there has been no evidence for such a CTE among the steroid receptors. We have determined the structure of the progesterone receptor (PR)-DBD-CTE DNA complex at a resolution of 2.5 A, which revealed binding of the CTE to the minor groove flanking the HREs. Alanine substitutions of the interacting CTE residues reduced affinity for inverted repeat HREs separated by three nucleotides, and essentially abrogated binding to a single HRE. A highly compressed minor groove of the trinucleotide spacer and a novel dimerization interface were also observed. A PR binding site selection experiment revealed sequence preferences in the trinucleotide spacer and flanking DNA. These results, taken together, support the notion that sequences outside of the HREs influence the DNA binding affinity and specificity of steroid receptors.

[Immunohistochemical characterization of salivary gland tumors with tissue micro-arrays]

Systematic analysis of gene expression in salivary gland tumors is necessary to identify genes associated with specific tumor types. From the salivary gland register of the University Hospital Hamburg-Eppendorf sufficient samples of various tumors were available to generate Tissue Micro-Arrays (TMA). In light of the considerable heterogeneity of salivary gland tumors, this study was aimed at evaluating the suitability of TMA in salivary gland diagnostics and research. Epithelial antigens are not sufficient for a tumor-type-specific characterization. Myoepithelial markers are suitable for distinguishing biphasic tumor types from purely epithelial tumors. The detection of amylase in acinic cell carcinomas, and the detection of steroid hormone receptors in these and other malignant salivary gland tumors particularly in combination with the expression of transcription factors, oncogenes and proliferation associated antigens result in characteristic expression profiles. These may prove to be valuable for further investigations, especially on the molecular level.

Binding of estrogen receptor beta to estrogen response element in situ is independent of estradiol and impaired by its amino terminus

The functions of 17beta-estradiol (E2) are mediated by estrogen receptor (ER) alpha and beta. ERs display similar DNA- and ligand-binding properties in vitro. However, ERbeta shows lower transcriptional activity than ERalpha from the estrogen response element (ERE)-dependent signaling. We predicted that distinct amino termini contribute to differences in transcription efficacies of ERs by affecting in situ ER-ERE interactions. We used chromatin immunoprecipitation and a novel in situ ERE competition assay, which is based on the ability of ER to compete for ERE binding with a designer activator that constitutively induces transcription from an ERE-driven reporter construct. Interference of activator-mediated transcription by unliganded or liganded ERs was taken as an indication of ER-ERE interaction. Results revealed that ERs interacted with ERE similarly in the absence of E2. However, E2 enhanced the ERE binding of ERalpha but not that of ERbeta. The removal of the amino terminus increased the ERbeta-ERE interaction independent of E2. The ERbeta amino terminus also prevented E2-mediated enhancement of the chimeric ERalpha-ERE interaction. Thus, the amino terminus of ERbeta impairs the binding of ERbeta to ERE. The abrogation of ligand-dependent activation function 2 of the amino-terminally truncated ERbeta resulted in the manifestation of E2 effect on ERbeta-ERE interaction. This implies that E2-mediated enhancement of ERbeta-ERE interaction is masked by the activation function 2, whereas the intact amino terminus is a dominant region that decreases the binding of ERbeta to ERE. Thus, ERbeta-ERE interaction is independent of E2 and is impaired by its amino terminus. These findings provide an additional explanation for differences between ERalpha and ERbeta functions that could differentially affect the physiology and pathophysiology of E2 signaling.

A Novel Estrogen Receptor α-Associated Protein Alters Receptor-Deoxyribonucleic Acid Interactions and Represses Receptor-Mediated Transcription

Estrogen receptor α (ERα) serves as a ligand-activated transcription factor, turning on transcription of estrogen-responsive genes in target cells. Numerous regulatory proteins interact with the receptor to influence ERα-mediated transactivation. In this study, we have identified pp32, which interacts with the DNA binding domain of ERα when the receptor is free, but not when it is bound to an estrogen response element. Coimmunoprecipitation experiments demonstrate that endogenously expressed pp32 and ERα from MCF-7 breast cancer cells interact. Although pp32 substantially enhances the association of the receptor with estrogen response element-containing DNA, overexpression of pp32 in MCF-7 cells decreases transcription of an estrogen-responsive reporter plasmid. pp32 Represses p300-mediated acetylation of ERα and histones in vitro and inhibits acetylation of ERα in vivo. pp32 Also binds to other nuclear receptors and inhibits thyroid hormone receptor β-mediated transcription. Taken together, our studies provide evidence that pp32 plays a role in regulating transcription of estrogen-responsive genes by modulating acetylation of histones and ERα and also influences transcription of other hormone-responsive genes as well.

Metastasis-associated protein 1 interacts with NRIF3, an estrogen-inducible nuclear receptor coregulator

The transcriptional activity of estrogen receptor alpha (ER-alpha) is modified by regulatory action and interactions of coactivators and corepressors. Recent studies have shown that the metastasis-associated protein 1 (MTA1) represses estrogen receptor element (ERE)-driven transcription in breast cancer cells. With a yeast two-hybrid screen to clone MTA1-interacting proteins, we identified a known nuclear receptor coregulator (NRIF3) as an MTA1-binding protein. NRIF3 interacted with MTA1 both in vitro and in vivo. NRIF3 bound to the C-terminal region of MTA1, while MTA1 bound to the N-terminal region of NRIF3, containing one nuclear receptor interaction LXXLL motif. We showed that NRIF3 is an ER coactivator, hyperstimulated ER transactivation functions, and associated with the endogenous ER and its target gene promoter. MTA1 repressed NRIF3-mediated stimulation of ERE-driven transcription and interfered with NRIF3's association with the ER target gene chromatin. In addition, NRIF3 deregulation enhanced the responsiveness of breast cancer cells to estrogen-induced stimulation of growth and anchorage independence. Furthermore, we found that NRIF3 is an estrogen-inducible gene and activated ER associated with the ER response element in the NRIF3 gene promoter. These findings suggest that NRIF3, an MTA1-interacting protein, is an estrogen-inducible gene and that regulatory interactions between MTA1 and NRIF3 might be important in modulating the sensitivity of breast cancer cells to estrogen.

Synthesis, Characterization, and Cytotoxicity of a Series of Estrogen-Tethered Platinum(IV) Complexes

Several estrogen-tethered platinum(IV) complexes were prepared and characterized by ESI-MS and (1)H NMR spectroscopy. Their design was inspired by the observation that estrogen receptor-positive cells exposed to the hormone are sensitized to cisplatin. Intracellular reduction of bis-estrogen-cis-diamminedichloroplatinum(IV), BEP(n) (where n = 1-5 methylene groups between Pt and estrogen), occurs to afford cisplatin and two equivalents of the linker-modified estrogen. The ability of BEP(n) to induce overexpression of HMGB1 was established by immunofluorescence microscopy. The cytotoxicity of the compounds was evaluated in ER(+) MCF-7 and ER(-) HCC-1937 human breast cancer cell lines. BEP3 selectively induces overexpression of HMGB1 in MCF-7 cells, compared to HCC-1937 cells, and enhances their sensitivity (IC(50) = 2.1 +/- 0.4 microM versus 3.7 +/- 0.9 microM, respectively) to the compound. The difference in compound activities and the potential of compounds of this class for treating breast and ovarian cancer are discussed.

The functional interaction between HMGA1 and the estrogen receptor requires either the N- or the C-terminal domain of the receptor

We have previously shown that HMGA1 enhances the transcriptional activity of promoters containing the estrogen response element (ERE) and increases binding of the estrogen receptor (ER) to ERE. Herein, we have assessed the transcriptional activity and ERE-binding ability of deleted ER fragments in absence or in presence of HMGA1. The HMGA1 protein stimulated binding and transcriptional activity by a factor of about 2-fold compared to the wild-type ER and both the N- and C-terminal ER deleted domains, but had no effect when both domains were deleted. These data show that HMGA1 cooperates with either the N- or the C-terminal transcriptional activation domain of the ER.

Uterine leiomyoma in the Eker rat: A unique model for important diseases of women

Eker rats carry a defect in the Tsc-2 tumor suppressor gene and female Eker rats develop uterine leiomyoma with a high frequency. The presentation, response to hormones and molecular alterations in these mesenchymal smooth muscle tumors, closely resembles their cognate human disease. Female rats and tumor-derived cell lines from Eker rat leiomyomas (ELT lines) have been developed as an in vivo/in vitro model system for preclinical studies to identify novel therapeutic agents for this disease and for studying disease pathogenesis. In addition to serving as a model for uterine leiomyoma, Eker rats have proven valuable for studying lymphangioleiomyomatosis, a related proliferative smooth muscle disease of women.

A direct beta-catenin-independent interaction between androgen receptor and T cell factor 4

T cell factor (Tcf) proteins bind beta-catenin and are downstream effectors of Wnt/beta-catenin signals. A recently demonstrated interaction between beta-catenin and the androgen receptor (AR) ligand binding domain has suggested that AR may be a Tcf-independent Wnt/beta-catenin effector. This study demonstrates that there is a direct interaction between the AR DNA binding domain (DBD) and Tcf4. Tcf4 bound specifically to a glutathione S-transferase-ARDBD fusion protein and could be coimmunoprecipitated with beta-catenin and transfected AR or endogenous AR in prostate cancer cells. Transfected Tcf4 repressed the transcriptional activity of full-length AR and a VP16-ARDBD fusion protein, and this repression was only partially reversed by transfected beta-catenin. AR activation by cyproterone acetate, a partial agonist that did not support beta-catenin binding to the AR, was also repressed by Tcf4, further indicating that repression was not due to beta-catenin sequestration. Tcf4 could recruit beta-catenin to the AR DBD in vitro and to the cyproterone acetate-liganded AR in vivo. Chromatin immunoprecipitation experiments in LNCaP prostate cancer cells showed that endogenous AR was bound to a Tcf4-responsive element in the c-myc promoter. These findings indicate that AR and Tcf4 can interact directly and that this interaction may occur on the promoters or enhancers of particular genes. The direct AR-Tcf4 interaction, in conjunction AR- and Tcf4-beta-catenin binding, provides a mechanism for cooperative and selective gene regulation by AR and the Wnt/beta-catenin-Tcf pathway that may contribute to normal and neoplastic prostate growth.

The C-terminal extension (CTE) of the nuclear hormone receptor DNA binding domain determines interactions and functional response to the HMGB-1/-2 co-regulatory proteins

Previously, we and others reported that the high mobility group proteins, HMGB-1/-2, enhance DNA binding in vitro and transactivation in situ by the steroid hormone subgroup of nuclear receptors but did not influence these functions of class II receptors. We show here that the DNA binding domain (DBD) is sufficient to account for the selective influence of HMGB-1/-2 on the steroid class of receptors. Furthermore, the use of chimeric DBDs reveals that this selectivity is dependent on the C-terminal extension (CTE), amino acid sequences adjacent to the zinc finger core DBD. HMGB-1/-2 interact directly with the DBDs of steroid but not class II receptors, and this interaction requires the CTE. This in vitro interaction correlates with a requirement of the CTE for maximal HMGB-1/-2 enhancement of DNA binding in vitro and transcriptional activation in cells. Finally, class II receptor DBDs have a much higher intrinsic affinity for DNA than steroid receptor DBDs, and this affinity difference is also dependent on the CTE. These results reveal the importance of the steroid receptor CTE for DNA binding affinity and functional response to HMGB-1/-2.

Identification and characterization of a tissue-specific coactivator, GT198, that interacts with the DNA-binding domains of nuclear receptors

Gene activation mediated by nuclear receptors is regulated in a tissue-specific manner and requires interactions between nuclear receptors and their cofactors. Here, we identified and characterized a tissue-specific coactivator, GT198, that interacts with the DNA-binding domains of nuclear receptors. GT198 was originally described as a genomic transcript that mapped to the human breast cancer susceptibility locus 17q12-q21 with unknown function. We show that GT198 exhibits a tissue-specific expression pattern in which its mRNA is elevated in testis, spleen, thymus, pituitary cells, and several cancer cell lines. GT198 is a 217-amino-acid nuclear protein that contains a leucine zipper required for its dimerization. In vitro binding and yeast two-hybrid assays indicated that GT198 interacted with nuclear receptors through their DNA-binding domains. GT198 potently stimulated transcription mediated by estrogen receptor alpha and beta, thyroid hormone receptor beta1, androgen receptor, glucocorticoid receptor, and progesterone receptor. However, the action of GT198 was distinguishable from that of the ligand-binding domain-interacting nuclear receptor coactivators, such as TRBP, CBP, and SRC-1, with respect to basal activation and hormone sensitivity. Furthermore, protein kinase A, protein kinase C, and mitogen-activated protein kinase can phosphorylate GT198 in vitro, and cotransfection of these kinases regulated the transcriptional activity of GT198. These data suggest that GT198 is a tissue-specific, kinase-regulated nuclear receptor coactivator that interacts with the DNA-binding domains of nuclear receptors.

SRY interacts with and negatively regulates androgen receptor transcriptional activity

This study investigated interactions between SRY, the Y chromosome encoded male sex determining factor, and the androgen receptor (AR). Coexpression of AR and SRY caused marked repression of AR transcriptional activity on a series of androgen-responsive reporter genes. Mammalian one- and two-hybrid experiments demonstrated an AR-SRY interaction mediated by the AR DNA binding domain. Precipitations with glutathione S-transferase fusion proteins indicated that AR-SRY interactions were direct and mediated by the AR DNA binding domain and the SRY high mobility group box DNA binding domain. Transient expression of SRY in LNCaP prostate cancer cells repressed expression of an androgen-dependent prostate-specific antigen (PSA) reporter gene and stable SRY expression repressed the endogenous PSA gene. SRY protein expression was increased by proteosome inhibitors and by the androgen-liganded AR in transient and stable transfectants. AR transcriptional activity was also repressed by DAX1, and the effects of SRY and DAX1 on the AR were additive. These findings indicate that interactions between the AR, SRY, and DAX1 contribute to normal male development and function and suggest a general role for protein-protein interactions between high mobility group box proteins and steroid hormone receptors in regulating tissue-specific gene expression.

Proteomic analysis of apoptosis initiation induced by all-trans retinoic acid in human acute promyelocytic leukemia cells

The irreversible destiny of apoptosis in its early stage might play a critical role in the apoptosis of human acute promyelocytic leukemia (APL) cell line induced by all-trans retinoic acid (ATRA). To characterize protein alterations during the apoptosis-initiation phase and to understand the metabolic status at that time, we investigated the protein profiles in the apoptosis-initiation phase of APL cell line HL-60 by proteomic analysis. ATRA-withdrawal was conducted to demonstrate that there was committed initiation phase of apoptosis triggered by 10(-6) M ATRA at day 3. Only after that time point, ATRA-treated cells irreversibly went to apoptosis. Also at that time point, the positive regulators of apoptosis such as STAT3 increased at protein level, whereas negative regulators (Bcl-2 and p-STAT3) decreased. In addition, caspase-3 also increased after that time. Furthermore, comparative proteomic analysis was utilized to examine the protein expression profiles during the initiation stage of apoptosis. Our results showed 12 upregulated and 7 downregulated proteins experiencing twofold alteration, including key regulators of signal transduction such as G-proteins and nucleic receptors, proteins related with metabolism, oxidation and reduction, proteins associated with the nucleus and cytoskeleton-related proteins. Some of them could be positive modulators to trigger apoptosis, whereas others could contribute to intracellular defense against apoptosis induced by exogenous triggers. The results above suggest that there is a subtle balance between apoptosis and the intracellular defense against apoptosis. Once the balance is disturbed, cells would irreversibly initiate to undergo the execution of apoptosis.

Estrogen receptor interaction with estrogen response elements

The estrogen receptor (ER) is a ligand-activated enhancer protein that is a member of the steroid/nuclear receptor superfamily. Two genes encode mammalian ER: ERalpha and ERbeta. ER binds to specific DNA sequences called estrogen response elements (EREs) with high affinity and transactivates gene expression in response to estradiol (E(2)). The purpose of this review is to summarize how natural and synthetic variations in the ERE sequence impact the affinity of ER-ERE binding and E(2)-induced transcriptional activity. Surprisingly, although the consensus ERE sequence was delineated in 1989, there are only seven natural EREs for which both ERalpha binding affinity and transcriptional activation have been examined. Even less information is available regarding how variations in ERE sequence impact ERbeta binding and transcriptional activity. Review of data from our own laboratory and those in the literature indicate that ERalpha binding affinity does not relate linearly with E(2)-induced transcriptional activation. We suggest that the reasons for this discord include cellular amounts of coactivators and adaptor proteins that play roles both in ER binding and transcriptional activation; phosphorylation of ER and other proteins involved in transcriptional activation; and sequence-specific and protein-induced alterations in chromatin architecture.

BAG-1 p50 isoform interacts with the vitamin D receptor and its cellular overexpression inhibits the vitamin D pathway

Human BAG-1 is an anti-apoptotic protein with four protein isoforms (BAG-1 p50, p46, p33, and p29). BAG-1 p46 was originally isolated in a screen for proteins binding to the glucocorticoid receptor; it binds and modulates the action of several members of the nuclear steroid hormone receptor superfamily. The vitamin D receptor (VDR) is another member of this superfamily, and the vitamin D pathway is important for prevention and therapy of osteoporosis, renal failure, cancer, and psoriasis. Therefore, we investigated the effect of the recently isolated BAG-1 p50 on the vitamin D pathway. By use of Far Western blot analysis and glutathione S-transferase BAG-1 p50 binding assays, BAG-1 p50 was demonstrated to interact with the VDR, and the BAG-1 p50 N-terminus was required. In U87 cells that were stably transfected with BAG-1 p50, binding of the VDR to its response element in electrophoretic mobility shift assays was blocked, enhancement of transcriptional activation was inhibited, cell growth rate was enhanced, cell growth inhibition induced by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] was blocked, and 1,25(OH)2D3-mediated VDR induction was inhibited. These results suggest that BAG-1 p50 is a novel regulator of the vitamin D signaling pathway, and its overexpression may lead to cellular resistance to 1,25(OH)2D3 therapy.

The role of trans-acting factors and DNA-bending in the silencing of human beta-globin gene expression

The molecular mechanisms which govern the develop-mental specificity of human beta-globin gene transcription have been studied in K562 cells, a human eyrthroleukemia line that expresses minimal beta-globin. Protein-binding analysis reveals that the 5' region contains three elements bound by trans-acting factors, beta-protein 1 (BP1) and beta-protein 2 (BP2). In vitro mutagenesis of each individual element in a beta-globin vector containing chloramphenicol acetyl-transferase (pCAT) followed by transient transfection into K562 cells increased levels of CAT activity 5. 5-fold higher than wild-type (wt) betaCAT, consistent with their silencing role. Mutagenesis of all three elements, however, resulted in activity significantly lower than wt betaCAT. BP1 and BP2 motifs have overlapping binding sites for high mobility group proteins (HMG1+2), DNA-bending factors, shown here to extrinsically bend the beta-globin promoter. Theoretically, mutations in all beta-protein binding sites could affect the binding of HMG1+2 sufficiently to impede DNA-protein and/or protein-protein interactions needed to facilitate constitutive gene expression. Placing two turns of DNA between BP1 and BP2 motifs also increased expression 3-fold, indicative of spatial constraints required for optimal silencing. However, insertion of the HMG1+2 DNA-bending motif (also equivalent to two turns) facilitates beta-silencing by re-establishment of BP1-BP2 proximity. Thus a combination of general DNA-bending and specific transcriptional factors appear to be involved in beta-globin silencing in the embryonic/fetal erythroid stage.

Role of estrogen receptor ligand and estrogen response element sequence on interaction with chicken ovalbumin upstream promoter transcription factor (COUP-TF)

Estrogen-responsive genes are regulated by altering the balance of estrogen receptor (ER) interaction with transcription activators and inhibitors. Here we examined the role of ER ligand on ER interaction with the Chicken Ovalbumin Upstream Promoter Transcription Factor (COUP-TF) orphan nuclear receptor. COUP-TF binding to half-site estrogen response elements (EREs) was increased by the addition of estradiol (E2) -liganded ER (E2-ER), but not by ER liganded with the antiestrogens 4-hydroxytamoxifen (4-OHT-ER) or tamoxifen aziridine (TAz-ER). ER did not bind to single half-sites. Conversely, COUP-TF enhanced the ERE binding of purified E2-ER, but did not affect TAz-ER-ERE binding. In contrast, only antiestrogens enhanced direct interaction between ER and COUP-TF as assessed by GST pull-down assays. Identical results were obtained using either purified bovine or recombinant human ERalpha. Co-immunoprecipitation assays showed that ER and COUP-TF interact in extracts from MCF-7 and ERalpha-transfected MDA-MB-231 cells. Here we document that ER ligand impacts COUP-TF-ER interaction. COUP-TF interaction is mediated by the DNA binding and ligand-binding domains of ER. We suggest that changes in ER conformation induced by DNA binding reduce ER-COUP-TF interaction. Transient transfection of human MCF-7 breast cancer cells with a COUP-TFI expression vector repressed E2-induced luciferase reporter gene expression from single or multiple tandem copies of a consensus ERE. COUP-TFI stimulated 4-OHT-induced luciferase activity from a minimal ERE. Alone, COUP-TFI increased transcription from ERE half-sites or a single ERE in a sequence-dependent manner. These data provide evidence that the ERE sequence and its immediate flanking regions influence whether COUP-TF enhances, inhibits, or has no effect on ER ligand-induced ERE reporter gene expression and that COUP-TFI activates gene transcription from ERE half-sites. We suggest that COUP-TFI plays a role in mitigating estrogen-responsive gene expression.

Characterization of the mouse alpha1D-adrenergic receptor gene

Alpha1-adrenergic receptors (alpha1-ARs) play critical roles in the regulation of a variety of physiological processes. Increasing evidence suggests that multiple receptor subtypes of alpha1-ARs regulate these physiological processes. Molecular cloning has identified three distinct cDNAs encoding alpha1-AR subtypes (alpha1A, alpha1B and alpha1D) that are structurally homologous. Among the alpha1-AR subtypes, the function of the alpha1D-AR remains unclear. In order to examine the physiological role of alpha1D-AR, we cloned and characterized a gene for the mouse alpha1D-AR. Using a mouse alpha1D-AR cDNA as a probe, we isolated the gene for the mouse alpha1D-AR from a mouse genomic library. The alpha1D-AR consists of two exons and an intron that interrupts the coding region of the putative sixth transmembrane domain. The 5'-flanking region of exon 1 contains neither a TATA box nor a CAAT box but is high in GC content and contains several Sp1 binding sites (GC boxes). This pattern is similar to promoters described for other members of alpha1-ARs. The untranslated region also contains putative cyclic AMP response elements. Isolation of this gene will allow further investigation, via gene knock-outs and deletion mutants, of the mechanisms of transcriptional regulation and a greater understanding of the physiological role of alpha1D-AR.

High-mobility group chromatin proteins 1 and 2 functionally interact with steroid hormone receptors to enhance their DNA binding in vitro and transcriptional activity in mammalian cells

We previously reported that the chromatin high-mobility group protein 1 (HMG-1) enhances the sequence-specific DNA binding activity of progesterone receptor (PR) in vitro, thus providing the first evidence that HMG-1 may have a coregulatory role in steroid receptor-mediated gene transcription. Here we show that HMG-1 and the highly related HMG-2 stimulate DNA binding by other steroid receptors, including estrogen, androgen, and glucocorticoid receptors, but have no effect on DNA binding by several nonsteroid nuclear receptors, including retinoid acid receptor (RAR), retinoic X receptor (RXR), and vitamin D receptor (VDR). As highly purified recombinant full-length proteins, all steroid receptors tested exhibited weak binding affinity for their optimal palindromic hormone response elements (HREs), and the addition of purified HMG-1 or -2 substantially increased their affinity for HREs. Purified RAR, RXR, and VDR also exhibited little to no detectable binding to their cognate direct repeat HREs but, in contrast to results with steroid receptors, the addition of HMG-1 or HMG-2 had no stimulatory effect. Instead, the addition of purified RXR enhanced RAR and VDR DNA binding through a heterodimerization mechanism and HMG-1 or HMG-2 had no further effect on DNA binding by RXR-RAR or RXR-VDR heterodimers. HMG-1 and HMG-2 (HMG-1/-2) themselves do not bind to progesterone response elements, but in the presence of PR they were detected as part of an HMG-PR-DNA ternary complex. HMG-1/-2 can also interact transiently in vitro with PR in the absence of DNA; however, no direct protein interaction was detected with VDR. These results, taken together with the fact that PR can bend its target DNA and that HMG-1/-2 are non-sequence-specific DNA binding proteins that recognize DNA structure, suggest that HMG-1/-2 are recruited to the PR-DNA complex by the combined effect of transient protein interaction and DNA bending. In transient-transfection assays, coexpression of HMG-1 or HMG-2 increased PR-mediated transcription in mammalian cells by as much as 7- to 10-fold without altering the basal promoter activity of target reporter genes. This increase in PR-mediated gene activation by coexpression of HMG-1/-2 was observed in different cell types and with different target promoters, suggesting a generality to the functional interaction between HMG-1/-2 and PR in vivo. Cotransfection of HMG-1 also increased reporter gene activation mediated by other steroid receptors, including glucocorticoid and androgen receptors, but it had a minimal influence on VDR-dependent transcription in vivo. These results support the conclusion that HMG-1/-2 are coregulatory proteins that increase the DNA binding and transcriptional activity of the steroid hormone class of receptors but that do not functionally interact with certain nonsteroid classes of nuclear receptors.