Selective binding of steroid hormone receptors to octamer transcription factors determines transcriptional synergism at the mouse mammary tumor virus promoter

PI3K Functions Downstream of Cdc42 to Drive Cancer phenotypes in a Melanoma Cell Line

Rho proteins are part of the Ras superfamily, which function to modulate cytoskeletal dynamics including cell adhesion and motility. Recently, an activating mutation in Cdc42, a Rho family GTPase, was found in a patient sample of melanoma. Previously, our work had shown the PI3K was important downstream of mutationally active Cdc42. Our present study sought to determine whether PI3K was a crucial downstream partner for Cdc42 in a melanoma cells line with a BRAF mutation, which is the most common mutation in cutaneous melanoma. In this work we were able to show that Cdc42 contributes to proliferation, anchorage-independent growth, cell motility and invasion. Treatment with a pan-PI3K inhibitor was able to effectively ameliorate all these cancer phenotypes. These data suggest that PI3K may be an important target downstream of Cdc42 in melanoma.

RNA binding by the glucocorticoid receptor attenuates dexamethasone-induced gene activation

The glucocorticoid receptor (GR) is a ligand-activated transcription factor that regulates a suite of genes through direct binding of GR to specific DNA promoter elements. GR also interacts with RNA, but the function of this RNA-binding activity remains elusive. Current models speculate that RNA could repress the transcriptional activity of GR. To investigate the function of the GR-RNA interaction on GR's transcriptional activity, we generated cells that stably express a mutant of GR with reduced RNA binding affinity and treated the cells with the GR agonist dexamethasone. Changes in the dexamethasone-driven transcriptome were quantified using 4-thiouridine labeling of RNAs followed by high-throughput sequencing. We find that while many genes are unaffected, GR-RNA binding is repressive for specific subsets of genes in both dexamethasone-dependent and independent contexts. Genes that are dexamethasone-dependent are activated directly by chromatin-bound GR, suggesting a competition-based repression mechanism in which increasing local concentrations of RNA may compete with DNA for binding to GR at sites of transcription. Unexpectedly, genes that are dexamethasone-independent instead display a localization to specific chromosomal regions, which points to changes in chromatin accessibility or architecture. These results show that RNA binding plays a fundamental role in regulating GR function and highlights potential functions for transcription factor-RNA interactions.

Identification of new octamer transcription factor 1-target genes upregulated in castration-resistant prostate cancer

Octamer transcription factor 1 (OCT1) is an androgen receptor (AR)‐interacting partner and regulates the expression of target genes in prostate cancer cells. However, the function of OCT1 in castration‐resistant prostate cancer (CRPC) is not fully understood. In the present study, we used 22Rv1 cells as AR‐positive CRPC model cells to analyze the role of OCT1 in CRPC. We showed that OCT1 knockdown suppressed cell proliferation and migration of 22Rv1 cells. Using microarray analysis, we identified four AR and OCT1‐target genes, disks large‐associated protein 5 (DLGAP5), kinesin family member 15 (KIF15), non‐SMC condensin I complex subunit G (NCAPG), and NDC80 kinetochore complex component (NUF2) in 22Rv1 cells. We observed that knockdown of DLGAP5 and NUF2 suppresses growth and migration of 22Rv1 cells. Furthermore, immunohistochemical analysis showed that positive expression of DLGAP5 in prostate cancer specimens is related to poor cancer‐specific survival rates of patients. Notably, enhanced expression of DLGAP5 was observed in CRPC tissues of patients. Thus, our findings suggest that these four genes regulated by the AR/OCT1 complex could have an important role in CRPC progression.

Exploiting sequence-based features for predicting enhancer-promoter interactions

Motivation

A large number of distal enhancers and proximal promoters form enhancer–promoter interactions to regulate target genes in the human genome. Although recent high-throughput genome-wide mapping approaches have allowed us to more comprehensively recognize potential enhancer–promoter interactions, it is still largely unknown whether sequence-based features alone are sufficient to predict such interactions.

Results

Here, we develop a new computational method (named PEP) to predict enhancer–promoter interactions based on sequence-based features only, when the locations of putative enhancers and promoters in a particular cell type are given. The two modules in PEP (PEP-Motif and PEP-Word) use different but complementary feature extraction strategies to exploit sequence-based information. The results across six different cell types demonstrate that our method is effective in predicting enhancer–promoter interactions as compared to the state-of-the-art methods that use functional genomic signals. Our work demonstrates that sequence-based features alone can reliably predict enhancer–promoter interactions genome-wide, which could potentially facilitate the discovery of important sequence determinants for long-range gene regulation.

Availability and Implementation

The source code of PEP is available at: https://github.com/ma-compbio/PEP.

Supplementary information

Supplementary data are available at Bioinformatics online.

The Oct1 transcription factor and epithelial malignancies: Old protein learns new tricks

The metazoan-specific POU domain transcription factor family comprises activities underpinning developmental processes such as embryonic pluripotency and neuronal specification. Some POU family proteins efficiently bind an 8-bp DNA element known as the octamer motif. These proteins are known as Oct transcription factors. Oct1/POU2F1 is the only widely expressed POU factor. Unlike other POU factors it controls no specific developmental or organ system. Oct1 was originally described to operate at target genes associated with proliferation and immune modulation, but more recent results additionally identify targets associated with oxidative and cytotoxic stress resistance, metabolic regulation, stem cell function and other unexpected processes. Oct1 is pro-oncogenic in multiple contexts, and several recent reports provide broad evidence that Oct1 has prognostic and therapeutic value in multiple epithelial tumor settings. This review focuses on established and emerging roles of Oct1 in epithelial tumors, with an emphasis on mechanisms of transcription regulation by Oct1 that may underpin these findings. This article is part of a Special Issue entitled: The Oct Transcription Factor Family, edited by Dr. Dean Tantin.

Regulatory roles of Oct proteins in the mammary gland

The expression of Oct-1 and -2 and their binding to the octamer motif in the mammary gland are developmentally and hormonally regulated, consistent with the expression of milk proteins. Both of these transcription factors constitutively bind to the proximal promoter of the milk protein gene β-casein and might be involved in the inhibition or activation of promoter activity via interactions with other transcription factors or cofactors at different developmental stages. In particular, the lactogenic hormone prolactin and glucocorticoids induce Oct-1 and Oct-2 binding and interaction with both the signal transducer and activator of transcription 5 (STAT5) and the glucocorticoid receptor on the β-casein promoter to activate β-casein expression. In addition, increasing evidence has shown the involvement of another Oct factor, Oct-3/4, in mammary tumorigenesis, making Oct-3/4 an emerging prognostic marker of breast cancer and a molecular target for the gene-directed therapeutic intervention, prevention and treatment of breast cancer. This article is part of a Special Issue entitled: The Oct Transcription Factor Family, edited by Dr. Dean Tantin.

Genetically engineered ERα-positive breast cancer mouse models

The majority of human breast cancers are estrogen receptor-positive (ER+), but this has proven challenging to model in genetically engineered mice. This review summarizes information on 21 mouse models that develop ER+ mammary cancer. Where available, information on cancer pathology and gene expression profiles is referenced to assist in understanding which histological subtype of ER+ human cancer each model might represent. ESR1, CCDN1, prolactin, TGFα, AIB1, ESPL1, and WNT1 overexpression, PIK3CA gain of function, as well as loss of P53 (Trp53) or STAT1 are associated with ER+ mammary cancer. Treatment with the PPARγ agonist efatutazone in a mouse with Brca1 and p53 deficiency and 7,12-dimethylbenz(a)anthracene exposure in combination with an activated myristoylated form of AKT1 also induce ER+ mammary cancer. A spontaneous mutant in nude mice that develops metastatic ER+ mammary cancer is included. Age of cancer development ranges from 3 to 26 months and the percentage of cancers that are ER+ vary from 21 to 100%. Not all models are characterized as to their estrogen dependency and/or response to anti-hormonal therapy. Strain backgrounds include C57Bl/6, FVB, BALB/c, 129S6/SvEv, CB6F1, and NIH nude. Most models have only been studied on one strain background. In summary, while a range of models are available for studies of pathogenesis and therapy of ER+ breast cancers, many could benefit from further characterization, and opportunity for development of new models remains.

Oct transcription factors in development and stem cells: insights and mechanisms

The POU domain family of transcription factors regulates developmental processes ranging from specification of the early embryo to terminal differentiation. About half of these factors display substantial affinity for an 8 bp DNA site termed the octamer motif, and are hence known as Oct proteins. Oct4 (Pou5f1) is a well-known Oct factor, but there are other Oct proteins with varied and essential roles in development. This Primer outlines our current understanding of Oct proteins and the regulatory mechanisms that govern their role in developmental processes and concludes with the assertion that more investigation into their developmental functions is needed.

Estrogen induced concentration dependent differential gene expression in human breast cancer (MCF7) cells: role of transcription factors

BACKGROUND

Breast cancer cells respond to estrogen in a concentration dependent fashion, resulting in proliferation or apoptosis. The mechanism of this concentration dependent differential outcome is not well understood yet.

METHODOLOGY

Meta-analysis of the expression data of MCF7 cells treated with low (1nM) or high (100nM) dose of estradiol (E2) was performed. We identified genes differentially expressed at the low or the high dose, and examined the nature of regulatory elements in the vicinity of these genes. Specifically, we looked for the difference in the presence, abundance and spatial distribution of binding sites for estrogen receptor (ER) and selected transcription factors (TFs) in the genomic region up to 25kb upstream and downstream from the transcription start site (TSS) of these genes.

RESULTS

It was observed that at high dose E2 induced the expression of stress responsive genes, while at low dose, genes involved in cell cycle were induced. We found that the occurrence of transcription factor binding regions (TFBRs) for certain factors such as Sp1 and SREBP1 were higher on regulatory regions of genes expressed at low dose. At high concentration of E2, genes with a higher frequency of Oct-1 binding regions were predominantly involved. In addition, there were differences in the spatial distribution pattern of the TFBRs in the genomic regions among the two sets of genes.

DISCUSSION

E2 induced predominantly proliferative/metabolic response at low concentrations; but at high concentration, stress-rescue responses were induced. At high E2 concentration, classical genomic pathway involving ER binding to the regulatory regions was reduced, and alternate or indirect activation of genes through Oct-1 became more prominent.

β-Estradiol-dependent activation of the JAK/STAT pathway requires p/CIP and CARM1

The steroid receptor coactivator p/CIP, also known as SRC-3, is an oncogene commonly amplified in breast and ovarian cancers. p/CIP is known to associate with coactivator arginine methyltransferase 1 (CARM1) on select estrogen responsive genes. We have shown, using a ChIP-on-chip approach, that in response to stimulation with 17β-estradiol (E2), the p/CIP/CARM1 complex is recruited to 204 proximal promoters in MCF-7 cells. Many of the complex target genes have been previously implicated in signaling pathways related to oncogenesis. Jak2, a member of the Jak/Stat signaling cascade, is one of the direct E2-dependent targets of the p/CIP/CARM1 complex. Following E2-treatment, histone modifications at the Jak2 promoter are reflective of a transcriptionally permissive gene, and modest changes in RNA and protein expression lead us to suggest that an additional factor(s) may be required for a more notable transcriptional and functional response. Bioinformatic examination of the 204 proximal promoter sequences of p/CIP/CARM1 targets supports the idea that transcription factor crosstalk is likely the favored mechanism of E2-dependent p/CIP/CARM1 complex recruitment. This data may have implications towards understanding the oncogenic role of p/CIP in breast cancer and ultimately allow for the identification of new prognostic indicators and/or viable therapeutic targets.

Interactions of the ubiquitous octamer-binding transcription factor-1 with both the signal transducer and activator of transcription 5 and the glucocorticoid receptor mediate prolactin and glucocorticoid-induced β-casein gene expression in mammary epithelial cells

Regulation of milk protein gene expression by lactogenic hormones (prolactin and glucocorticoids) provides an attractive model for studying the mechanisms by which protein and steroid hormones synergistically regulate gene expression. β-Casein is one of the major milk proteins and its expression in mammary epithelial cells is stimulated by lactogenic hormones. The signal transducer and activator of transcription 5 and glucocorticoid receptor are essential downstream mediators of prolactin and glucocorticoid signaling, respectively. Previous studies have shown that mutating the octamer-binding site of the β-casein gene proximal promoter dramatically reduces the hormonal induction of the promoter activity. However, little is known about the underlying molecular mechanisms. In this report, we show that lactogenic hormones rapidly induce the binding of octamer-binding transcription factor-1 to the β-casein promoter and this induction is not mediated by either increasing the expression of octamer-binding transcription factor-1 or inducing its translocation to the nucleus. Rather, lactogenic hormones induce physical interactions between the octamer-binding transcription factor-1, signal transducer and activator of transcription 5, and glucocorticoid receptor to form a ternary complex, and these interactions enhance or stabilize the binding of these transcription factors to the promoter. Abolishing these interactions significantly reduces the hormonal induction of β-casein gene transcription. Thus, our study indicates that octamer-binding transcription factor-1 may serve as a master regulator that facilitates the DNA binding of both signal transducer and activator of transcription 5 and glucocorticoid receptor in hormone-induced β-casein expression, and defines a novel mechanism of regulation of tissue-specific gene expression by the ubiquitous octamer-binding transcription factor-1.

Small-molecule hormones: molecular mechanisms of action

Small-molecule hormones play crucial roles in the development and in the maintenance of an adult mammalian organism. On the molecular level, they regulate a plethora of biological pathways. Part of their actions depends on their transcription-regulating properties, exerted by highly specific nuclear receptors which are hormone-dependent transcription factors. Nuclear hormone receptors interact with coactivators, corepressors, basal transcription factors, and other transcription factors in order to modulate the activity of target genes in a manner that is dependent on tissue, age and developmental and pathophysiological states. The biological effect of this mechanism becomes apparent not earlier than 30-60 minutes after hormonal stimulus. In addition, small-molecule hormones modify the function of the cell by a number of nongenomic mechanisms, involving interaction with proteins localized in the plasma membrane, in the cytoplasm, as well as with proteins localized in other cellular membranes and in nonnuclear cellular compartments. The identity of such proteins is still under investigation; however, it seems that extranuclear fractions of nuclear hormone receptors commonly serve this function. A direct interaction of small-molecule hormones with membrane phospholipids and with mRNA is also postulated. In these mechanisms, the reaction to hormonal stimulus appears within seconds or minutes.

Melanoma antigen-A11 (MAGE-A11) enhances transcriptional activity by linking androgen receptor dimers

Prostate cancer growth and progression depend on androgen receptor (AR) signaling through transcriptional mechanisms that require interactions with coregulatory proteins, one of which is the primate-specific steroid receptor coregulator melanoma antigen-A11 (MAGE-A11). In this report, we provide evidence how increased expression of MAGE-A11 during prostate cancer progression enhances AR signaling and prostate cancer growth. MAGE-A11 protein levels were highest in castration-recurrent prostate cancer. The cyclic AMP-induced increase in androgen-dependent and androgen-independent AR transcriptional activity correlated with an increase in MAGE-A11 and was inhibited by silencing MAGE-A11 expression. MAGE-A11 mediated synergistic AR transcriptional activity in LAPC-4 prostate cancer cells. The ability of MAGE-A11 to rescue transcriptional activity of complementary inactive AR mutants and promote coimmunoprecipitation between unlike forms of AR suggests that MAGE-A11 links transcriptionally active AR dimers. A model for the AR·MAGE-A11 multidimeric complex is proposed in which one AR FXXLF motif of the AR dimer engages in the androgen-dependent AR NH(2)- and carboxyl-terminal interaction, whereas the second FXXLF motif region of the AR dimer interacts with dimeric MAGE-A11. The AR·MAGE-A11 multidimeric complex accounts for the dual functions of the AR FXXLF motif in the androgen-dependent AR NH(2)- and carboxyl-terminal interaction and binding MAGE-A11 and for synergy between reported AR splice variants and full-length AR. We conclude that the increased expression of MAGE-A11 in castration-recurrent prostate cancer, which is enhanced by cyclic AMP signaling, increases AR-dependent growth of prostate cancer by MAGE-A11 forming a molecular bridge between transcriptionally active AR dimers.

Oct-1 acts as a transcriptional repressor on the C-reactive protein promoter

C-reactive protein (CRP), a plasma protein of the innate immune system, is produced by hepatocytes. A critical regulatory region (-42 to -57) on the CRP promoter contains binding site for the IL-6-activated transcription factor C/EBPβ. The IL-1β-activated transcription factor NF-κB binds to a κB site located nearby (-63 to -74). The κB site overlaps an octamer motif (-59 to -66) which is the binding site for the constitutively active transcription factor Oct-1. Oct-1 is known to function both as a transcriptional repressor and as an activator depending upon the promoter context. Also, Oct-1 can regulate gene expression either by binding directly to the promoter or by interacting with other transcription factors bound to the promoter. The aim of this study was to investigate the functions of Oct-1 in regulating CRP expression. In luciferase transactivation assays, overexpressed Oct-1 inhibited (IL-6+IL-1β)-induced CRP expression in Hep3B cells. Deletion of the Oct-1 site from the promoter drastically reduced the cytokine response because the κB site was altered as a consequence of deleting the Oct-1 site. Surprisingly, overexpressed Oct-1 inhibited the residual (IL-6+IL-1β)-induced CRP expression through the promoter lacking the Oct-1 site. Similarly, deletion of the Oct-1 site reduced the induction of CRP expression in response to overexpressed C/EBPβ, and overexpressed Oct-1 inhibited C/EBPβ-induced CRP expression through the promoter lacking the Oct-1 site. We conclude that Oct-1 acts as a transcriptional repressor of CRP expression and it does so by occupying its cognate site on the promoter and also via other transcription factors by an as yet undefined mechanism.

Androgen receptor repression of GnRH gene transcription

Alterations in androgen levels lead to reproductive defects in both males and females, including hypogonadotropic hypogonadism, anovulation, and infertility. Androgens have been shown to down-regulate GnRH mRNA levels through an androgen receptor (AR)-dependent mechanism. Here, we investigate how androgen regulates expression from the GnRH regulatory region in the GT1-7 cell line, a model of GnRH neurons. A synthetic androgen, R1881, repressed transcription from the GnRH promoter (GnRH-P) in an AR-dependent manner, and liganded AR associated with the chromatin at the GnRH-P in live GT1-7 cells. The three known octamer-binding transcription factor-1 (Oct-1) binding sites in GnRH-P were required for AR-mediated repression, although other sequences were also involved. Although a multimer of the consensus Oct-1 binding site was not repressed, a multimer of the cluster of Oct-1, Pre-B cell leukemia transcription factor (Pbx)/Prep, and NK2 homeobox 1 (Nkx2.1) binding sites, found at -106/-91 in GnRH-P, was sufficient for repression. In fact, overexpression of any of these factors disrupted the androgen response, indicating that a balance of factors in this tripartite complex is required for AR repression. AR bound to this region in EMSA, indicating a direct interaction of AR with DNA or with other transcription factors bound to GnRH-P at this sequence. Collectively, our data demonstrate that GnRH transcription is repressed by AR via multiple sequences in GnRH-P, including three Oct-1 binding sites, and that this repression requires the complex interaction of several transcription factors.

Systematic identification of conserved motif modules in the human genome

BACKGROUND

The identification of motif modules, groups of multiple motifs frequently occurring in DNA sequences, is one of the most important tasks necessary for annotating the human genome. Current approaches to identifying motif modules are often restricted to searches within promoter regions or rely on multiple genome alignments. However, the promoter regions only account for a limited number of locations where transcription factor binding sites can occur, and multiple genome alignments often cannot align binding sites with their true counterparts because of the short and degenerative nature of these transcription factor binding sites.

RESULTS

To identify motif modules systematically, we developed a computational method for the entire non-coding regions around human genes that does not rely upon the use of multiple genome alignments. First, we selected orthologous DNA blocks approximately 1-kilobase in length based on discontiguous sequence similarity. Next, we scanned the conserved segments in these blocks using known motifs in the TRANSFAC database. Finally, a frequent pattern mining technique was applied to identify motif modules within these blocks. In total, with a false discovery rate cutoff of 0.05, we predicted 3,161,839 motif modules, 90.8% of which are supported by various forms of functional evidence. Compared with experimental data from 14 ChIP-seq experiments, on average, our methods predicted 69.6% of the ChIP-seq peaks with TFBSs of multiple TFs. Our findings also show that many motif modules have distance preference and order preference among the motifs, which further supports the functionality of these predictions.

CONCLUSIONS

Our work provides a large-scale prediction of motif modules in mammals, which will facilitate the understanding of gene regulation in a systematic way.

Characterization of cis elements of the probasin promoter necessary for prostate-specific gene expression

BACKGROUND

The androgen-regulated probasin (PB) promoter has been used extensively to target transgenes to the prostate in transgenic mice; however, limited data exist on the mechanism that dictates prostate-specific gene expression. Tissue-specific gene expression involves synergistic effects among transcription factors associated in a complex bound to cis-acting DNA elements.

METHODS

Using comprehensive linker scan mutagenesis, enzyme mobility shift and supershift assays, chromatin immunoprecipitation, and transgenic animal studies, we have extensively characterized the prostate-specific PB promoter.

RESULTS

We identified a series of nonreceptor transcription factors that are bound to the prostate-specific rat PB promoter. These factors include several ubiquitously distributed proteins known to participate in steroid receptor-mediated transcription. In addition, we identified two tissue-specific DNA elements that are crucial in directing prostate-specific PB expression, and confirmed the functional importance of both elements in transgenic animal studies. These two elements are functionally interchangeable and can be bound by multiple protein complexes, including the forkhead transcription factor FoxA1, a "pioneer factor" that has a restricted distribution to some cells type that are ectoderm and endoderm in origin. Using transgenic mice, we further demonstrate that the minimal PB promoter region (-244/-96 bp) that encompasses these tissue-specific elements results in prostate-specific gene expression in transgenic mice, contains androgen receptor and FoxA1-binding sites, as well as ubiquitous transcription factor binding sites.

CONCLUSION

We propose that these sequence-specific DNA-binding proteins, including tissue-restricted and ubiquitous factors, create the first level of transcriptional control, which responds to intracellular pathways that directs prostate-specific gene expression.

The epigenetic landscape of mammary gland development and functional differentiation

Most of the development and functional differentiation in the mammary gland occur after birth. Epigenetics is defined as the stable alterations in gene expression potential that arise during development and proliferation. Epigenetic changes are mediated at the biochemical level by the chromatin conformation initiated by DNA methylation, histone variants, post-translational modifications of histones, non-histone chromatin proteins, and non-coding RNAs. Epigenetics plays a key role in development. However, very little is known about its role in the developing mammary gland or how it might integrate the many signalling pathways involved in mammary gland development and function that have been discovered during the past few decades. An inverse relationship between marks of closed (DNA methylation) or open chromatin (DnaseI hypersensitivity, certain histone modifications) and milk protein gene expression has been documented. Recent studies have shown that during development and functional differentiation, both global and local chromatin changes occur. Locally, chromatin at distal regulatory elements and promoters of milk protein genes gains a more open conformation. Furthermore, changes occur both in looping between regulatory elements and attachment to nuclear matrix. These changes are induced by developmental signals and environmental conditions. Additionally, distinct epigenetic patterns have been identified in mammary gland stem and progenitor cell sub-populations. Together, these findings suggest that epigenetics plays a role in mammary development and function. With the new tools for epigenomics developed in recent years, we now can begin to establish a framework for the role of epigenetics in mammary gland development and disease.

Inhibition of AR-mediated transcription by binding of Oct1 to a motif enriched in AR-occupied regions

BACKGROUND

The androgen receptor (AR) plays roles in prostate development and cancer (PCa). In response to androgens, the AR binds to androgen-response elements (AREs) to modulate gene transcription. The responses of such genes are dependent on the cellular milieu and on sequences around the AREs, which attract other transcription factors. Previously, bioinformatic analysis of 62 AR-occupied regions (ARORs) in PCa cells revealed enrichment for both AREs and a TTGGCAAATA-like motif. We undertook the present study to investigate the significance of the TTGGCAAATA-like motif.

METHODS

Prostate cancer cell lines, LNCaP and C4-2B, were analyzed by transient transfections of wild-type and mutant reporter constructs, electro-mobility shift assays (EMSAs), and RT-qPCR analysis of endogenous genes.

RESULTS

In two of six tested ARORs, point mutations in the TTGGCAAATA-like motif resulted in inhibition of DHT-mediated enhancer activity. EMSA revealed that Oct1 bound the motif, and that the mutations that abolished DHT responsiveness in the transfection assays augmented Oct1 binding. These results suggest a role for Oct1 as a context-dependent negative coregulator of AR. Consistent with this, siRNA knockdown of Oct1 increased the DHT-mediated enhancer activity of transfected reporters as well as an endogenous AR target gene, transglutaminase 2.

CONCLUSIONS

Oct1 negatively regulates DHT-mediated enhancer activity in a subset of ARORs. The enrichment of ARORs for the Oct-binding, TTGGCAAATA-like motif may reflect a mechanism that utilizes Oct1 to keep AR activity in check at some ARORs, while augmenting AR activity in other ARORs. Therefore, Oct1 may have regulatory functions in prostate development and cancer progression.

Expression of the muscle atrophy factor muscle atrophy F-box is suppressed by testosterone

The ubiquitin ligase muscle atrophy F-box (MAFbx; also called atrogin-1) is thought to play important roles in muscle loss. Conversely, testosterone reduces atrophy from glucocorticoids or denervation associated with repression of MAFbx. To characterize mechanisms of such repression, the effects of testosterone on MAFbx expression in C2C12 cells were tested. Testosterone reduced MAFbx mRNA levels as well as expression of a reporter gene under the control of 3.1 kb of the human MAFbx promoter. Repression required the androgen receptor (AR) as well as sequences within the first 208 bases upstream of the first codon of the MAFbx gene. This sequence is downstream of known forkhead transcription factor binding sites and testosterone did not alter Forkhead box O 3A phosphorylation. The AR associated with sequences conferring repression in a manner that was stimulated by testosterone and was independent of DNA binding. In gel shift studies, octamer binding transcription factor (Oct)-1 bound two predicted Oct-1 sites within these sequences. Deletion of Oct-1 sites from reporter genes prevented repression by testosterone. Gene knockdown of Oct-1 blocked repression of MAFbx reporter gene activity by testosterone and binding of AR to sequences conferring repression. In conclusion, testosterone represses MAFbx expression via interactions of the AR with Oct-1 that are associated with sequences within the 5' untranslated region of the MAFbx promotor located just upstream of the first codon. This action of testosterone may contribute to beneficial actions of testosterone on muscle.

Transactivation of a growth hormone (GH) promoter-luciferase construct in canine mammary cells

The gene encoding growth hormone (GH) is expressed not only in the pituitary but also in a variety of non-pituitary tissues. In the female dog, progestins are known to stimulate GH expression in the mammary gland. In order to investigate the regulation of the GH gene expression in the mammary gland, we transfected the canine mammary tumor cell line CMT-U229 with 3 different canine GH promoter-luciferase constructs. The constructs, varying in length between 252 bp and 673 bp, were transfected followed by an incubation for 4 h, 24 h and 48 h with cAMP, all-trans-retinoic acid (RA), 3,3',5-triiodothyronine (T3), 1,25-dihydroxy-vitamin D (VitD), progesterone and EGF. Promoter activity was stimulated by cAMP, T3 and RA whereas VitD clearly inhibited gene expression. However, despite the presence of nuclear and membrane receptors for progesterone, no direct effects of progesterone on promoter activity could be demonstrated. It is concluded that progesterone alone has no direct stimulatory effect on GH transcription. This finding is discussed in relation to the slow onset of progesterone-stimulated GH release in vivo and the absence of Pit-1 in canine mammary tissue.

Androgen receptor (AR) coregulators: a diversity of functions converging on and regulating the AR transcriptional complex

Androgens, acting through the androgen receptor (AR), are responsible for the development of the male phenotype during embryogenesis, the achievement of sexual maturation at puberty, and the maintenance of male reproductive function and behavior in adulthood. In addition, androgens affect a wide variety of nonreproductive tissues. Moreover, aberrant androgen action plays a critical role in multiple pathologies, including prostate cancer and androgen insensitivity syndromes. The formation of a productive AR transcriptional complex requires the functional and structural interaction of the AR with its coregulators. In the last decade, an overwhelming and ever increasing number of proteins have been proposed to possess AR coactivating or corepressing characteristics. Intriguingly, a vast diversity of functions has been ascribed to these proteins, indicating that a multitude of cellular functions and signals converge on the AR to regulate its function. The current review aims to provide an overview of the AR coregulator proteins identified to date and to propose a classification of these AR coregulator proteins according to the function(s) ascribed to them. Taken together, this approach will increase our understanding of the cellular pathways that converge on the AR to ensure an appropriate transcriptional response to androgens.

Association of IL-8 (−251)T/A polymorphism with susceptibility to and aggressiveness of nasopharyngeal carcinoma

Interleukin-8 (IL-8) is an angiogenic chemokine that plays a potent role in both development and progression of many human malignancies including nasopharyngeal carcinoma (NPC). In the present study, we evaluated the susceptibility and prognostic implications of the (-251) T/A genetic variation in IL-8 in NPC. We used the allele-specific polymerase chain reaction to characterize the variation of the IL-8 promoter region for 160 unrelated Tunisian patients with NPC and 169 healthy control subjects. There was a significant association between the homozygotes IL-8 (-251) AA genotype and nasopharyngeal carcinoma (OR = 2.46; P = 0.004). The presence of the IL-8 (-251) AA genotype was highly associated with elevated NPC risk for male patients. A significant association was demonstrated between the IL-8 (-251) AA genotype and the aggressive forms of NPC as defined by large tumor size, lymph node metastasis, and advanced stages. Moreover, the presence of the IL-8 (-251) AA genotype indicated a significant association with decreased overall survival. Our findings suggest that the IL-8 promoter polymorphism is associated with increased nasopharyngeal carcinoma risk, particularly in males, as well as disease progress, supporting our hypothesis for IL-8 involvement in NPC pathogenesis.

Gonadotropins affect Oct-4 gene expression during mouse oocyte growth

The transcription factor Oct-4 is required for the maintenance of stem cells pluripotency and is involved in the regulation of the expression of a number of developmental genes. Oct-4 is also expressed in the female gamete during folliculogenesis, but the role it plays is largely unknown. Its upstream and promoter regions have some characteristic features that make this gene a possible target of hormonal regulation. To further our understanding of Oct-4 gene expression during oocyte growth, we tested whether changes to the hormonal milieu of the ovary may affect its transcription. Using a semi-quantitative single-cell-sensitive reverse transcription-polymerase chain reaction (RT-PCR) assay, we investigated the pattern of Oct-4 expression during mouse oocyte growth in females intraperitoneally injected with pregnant mare serum gonadotropin (PMSG) alone or PMSG followed by human chorionic gonadotropin (hCG). The results of this study show that gonadotropins induced two major increases in Oct-4 expression during folliculogenesis: (1) 48 hr after PMSG injection, in oocytes isolated from primordial follicles; and (2) following a surge of hCG, in preovulatory antral oocytes. These results suggest a potential twofold role for this gene in the recruitment of oocytes for initiating growth and in the selection of oocytes for ovulation. Also, they may contribute to our knowledge of the molecular bases of oocyte growth, meiosis resumption, and acquisition of a developmental competence.

Expression of the Oct-2 transcription factor in mouse mammary gland and cloning and characterization of a novel Oct-2 isoform

Oct-2 is a member of the POU family of transcription factors, which specifically bind to the octamer DNA motif ATGCAAAT and its closely related sequences. Unlike its ubiquitous counterpart Oct-1, Oct-2 is thought to be expressed only in B lymphocytes and neuronal cells and is mainly involved in immunoglobulin gene expression. We show here that Oct-2 is also expressed in the epithelial cells of mouse mammary gland, and that this expression is developmentally regulated. Rapid amplification of cDNA ends and subsequent cDNA cloning indicate that the mammary gland expresses multiple Oct-2 isoforms, including a novel isoform, named Oct-2.7. Compared with Oct-2 (isoform 2.1), the deduced Oct-2.7 sequence has an additional 22 amino acids close to the N-terminus and a novel 76-amino-acid C-terminus resulting from alternative splicing, with retention of the last intron that is spliced out in all other isoforms. Although Oct-2.7 has intact POU-specific and POU-homeo domains, it is unable to bind to the octamer motif, unlike all other known isoforms. Like Oct-1, both Oct-2.1 and Oct-2.7 can activate basal beta-casein gene promoter activity. However, activation by Oct-2.7, which is independent of DNA binding, is significantly lower than that by Oct-2.1. Moreover, deletion of the first 114 amino acids at the N-terminus of Oct-2.1 has no effect on activation; this does not support previous reports of the presence of an inhibitory domain in this region.

Involvement of the ubiquitous Oct-1 transcription factor in hormonal induction of beta-casein gene expression

Transcription of the milk protein beta-casein gene is induced by the lactogenic hormones Prl (prolactin) and glucocorticoids. Multiple transcription factors involved in this induction have been identified, including the STAT5 (signal transducer and activator of transcription 5) and the GR (glucocorticoid receptor). Our previous studies have identified a binding site for the ubiquitous Oct-1 (octamer-binding transcription factor 1) protein in the lactogenic hormonal regulatory region of the mouse beta-casein promoter. In the present study, we report that Oct-1 is indeed expressed and binds to the beta-casein promoter in mammary epithelial cells. Oct-1 activates hormonally induced beta-casein promoter activity in a dose-dependent manner. Hormonal induction of promoter activity was decreased not only by mutating the Oct-1-binding site from ATTAGCAT to GCTAGCAT, which abolishes Oct-1 binding (50% decrease, P<0.01), but also by changing the site to the consensus Oct-1-binding motif ATTTGCAT (40% decrease, P<0.01). Reversing the Oct-1-binding site reduced hormonal induction by 70% (P<0.01), showing that orientation of Oct-1 binding is also critical in hormonal action. In transient transfection experiments, Oct-1 collaboratively transactivated the beta-casein gene promoter with STAT5 and/or GR in the presence of Prl receptor in cells treated with the lactogenic hormones. The C-terminus of Oct-1 was not essential to its function. The results of the present study provide biochemical evidence that the ubiquitous Oct-1 transcription factor may be involved in hormonally regulated, tissue-specific beta-casein gene expression.

Pdm and Castor specify late-born motor neuron identity in the NB7-1 lineage

Embryonic development requires generating cell types at the right place (spatial patterning) and the right time (temporal patterning). Drosophila neuroblasts undergo stem cell-like divisions to generate an ordered sequence of neuronal progeny, making them an attractive system to study temporal patterning. Embryonic neuroblasts sequentially express Hunchback, Krüppel, Pdm1/Pdm2 (Pdm), and Castor (Cas) transcription factors. Hunchback and Krüppel specify early-born temporal identity, but the role of Pdm and Cas in specifying temporal identity has never been addressed. Here we show that Pdm and Cas regulate late-born motor neuron identity within the NB7-1 lineage: Pdm specifies fourth-born U4 motor neuron identity, while Pdm/Cas together specify fifth-born U5 motor neuron identity. We conclude that Pdm and Cas specify late-born neuronal identity; that Pdm and Cas act combinatorially to specify a temporal identity distinct from either protein alone, and that Cas repression of pdm expression regulates the generation of neuronal diversity.

Genome-wide analysis of estrogen receptor binding sites

The estrogen receptor is the master transcriptional regulator of breast cancer phenotype and the archetype of a molecular therapeutic target. We mapped all estrogen receptor and RNA polymerase II binding sites on a genome-wide scale, identifying the authentic cis binding sites and target genes, in breast cancer cells. Combining this unique resource with gene expression data demonstrates distinct temporal mechanisms of estrogen-mediated gene regulation, particularly in the case of estrogen-suppressed genes. Furthermore, this resource has allowed the identification of cis-regulatory sites in previously unexplored regions of the genome and the cooperating transcription factors underlying estrogen signaling in breast cancer.

Stimulation of the novel estrogen receptor-alpha intronic TERP-1 promoter by estrogens, androgen, pituitary adenylate cyclase-activating peptide, and forskolin, and autoregulation by TERP-1 protein

The estrogen receptor-alpha (ERalpha) pituitary-specific variant, TERP-1, is regulated dramatically by physiological status. We examined hormonal regulation of the TERP-1 promoter in transient transfection assays in GH3 somatolactotrope cells. We found that 17beta-estradiol (E2), genistein, androgen, pituitary adenylate cyclase-activating peptide, and forskolin (FSK) all stimulated TERP-1 promoter activity, whereas progesterone had no effect. ERalpha bound to a palindromic estrogen response element (ERE) and two half-site EREs; mutation of any of these sites decreased basal expression and completely obliterated E2 stimulation. In contrast, mutation of an activator protein-1 site decreased basal and FSK-stimulated promoter activity, but not E2 or androgen stimulation. The pure antiestrogen ICI 182,780 suppressed E2 and genistein, but not FSK or androgen, stimulation. Similarly, mutation of the ERE palindrome or half-site EREs suppressed promoter stimulation by E2 and genistein, but not by androgen or FSK. Because TERP-1 levels regulate ERalpha function on model promoters, we tested TERP-1 modulation of its own and other physiological promoters. TERP-1 suppressed basal and E2-stimulated expression of its own promoter. TERP-1 suppression required the ERE regions of the promoter, and the dimerization domain of TERP-1. TERP-1 overexpression also suppressed E2 stimulation of the progesterone receptor and prolactin promoters. Thus, estrogens, androgen, and FSK can stimulate TERP-1 promoter activity, and increased TERP-1 expression modulates E2 stimulation of physiological promoters. These data suggest that TERP-1 regulation may play a significant role in modifying pituitary ERalpha responses.

A role for Runx2 in normal mammary gland and breast cancer bone metastasis

The transcription factor Runx2 is essential for the formation of the skeleton. It has therefore primarily been considered as a specific regulator of bone genes. However, mice containing a LacZ insertion at the Runx2 locus also revealed expression in the nascent mammary epithelium. Reports of Runx2 expression in breast cancer cell lines, combined with the fact that breast cancers preferentially metastasise to bone, have also hinted at a potential role for Runx2 in the formation of bone metastasese. These initial observations have prompted further analysis of Runx2 function in mammary epithelial cells and recent findings have demonstrated that Runx2 does indeed contribute to the ability of metastatic breast cancer cell lines to form osteolytic bone lesions. In addition, evidence is accumulating that Runx2 has a role in the regulation of normal mammary gland gene expression and recent data demonstrate that it regulates transcription of the mammary gland-specific gene, beta-casein. In this article I discuss recent advances that link Runx2 with normal mammary epithelial cell function and the development of bone metastasese in breast cancer.

Oct-1 counteracts autoinhibition of Runx2 DNA binding to form a novel Runx2/Oct-1 complex on the promoter of the mammary gland-specific gene beta-casein

The transcription factor Runx2 is essential for the expression of a number of bone-specific genes and is primarily considered a master regulator of bone development. Runx2 is also expressed in mammary epithelial cells, but its role in the mammary gland has not been established. Here we show that Runx2 forms a novel complex with the ubiquitous transcription factor Oct-1 to regulate the expression of the mammary gland-specific gene beta-casein. The Runx2/Oct-1 complex forms on a Runx/octamer element which is highly conserved in casein promoters. Chromatin immunoprecipitation, RNA interference, promoter mutagenesis, and transient expression analyses were used to demonstrate that the Runx2/Oct-1 complex contributes to the transcriptional regulation of the beta-casein gene. Analysis of the complex revealed autoinhibitory domains for DNA binding in both the N-terminal and the C-terminal regions of Runx2. Oct-1 stimulates the recruitment of Runx2 to the beta-casein promoter by interacting with the C-terminal region of Runx2, suggesting that Oct-1 stimulates Runx2 recruitment by relieving the autoinhibition of Runx2 DNA binding. These findings demonstrate that Runx2 collaborates with Oct-1 and contributes to the expression of a mammary gland-specific gene.

Modulatory effects of progesterone on inducible nitric oxide synthase expression in vivo and in vitro

Nitric oxide (NO) is produced in the CNS following injury-induced expression of inducible nitric oxide synthase (iNOS), yet its role as protective or damaging is unclear. Previous studies investigating the therapeutic potential of female sex steroids in stroke and trauma suggest that NO from this source is harmful, since oestradiol and progesterone decreased the level of iNOS expression in vitro and improved neurological outcome. We investigated the effects of progesterone on stroke-induced expression of iNOS in mice, as well as cytokine-induced expression of iNOS and its transcriptional activators in cells relevant to injury. We observed a significant reduction in stroke-induced iNOS transcript in progesterone-treated mice and in cultured macrophages. In contrast, progesterone significantly amplifed cytokine-induced iNOS mRNA in cultured primary astrocytes, although the expression of protein was decreased. We sequenced upstream of the 1.5 kb reported iNOS promoter region and identified a potential progesterone response element (PRE). Astrocytes transiently transfected with iNOS promoter/CAT reporter gene constructs containing the PRE displayed a significant increase in induction of CAT expression after progesterone treatment, and this was diminished in cells transfected with a construct containing a disrupted PRE. These observations suggest the involvement of iNOS in the neuroprotective effects of progesterone.

Glucocorticoid regulation of human BMP-6 transcription

Addition of dexamethasone (Dex) to human mesenchymal stem cells (hMSCs) resulted in a 16-fold increase in human bone morphogenetic protein-6 (hBMP-6) mRNA levels 24 h after treatment. Evaluation of luciferase expression after transfection of HeLa cells with hBMP-6 promoter/luciferase reporter constructs indicated that the hBMP-6 promoter activity was contained in a 268-bp region (-1051 to -784 where +1 is the translation start site) over 600 bases 5' to that previously published. It further showed that the promoter activity is regulated by glucocorticoid treatment. Analysis of RNA from hMSCs and HeLa cells by primer extension, RNase protection, and 5' RACE further narrowed the location of the transcription start site to an 84-bp region (-940 to -857). To determine whether this start site was regulated in hMSCs, hBMP-6 mRNA levels in control and Dex-treated cells were quantitated by RT-PCR using one primer set in the translated region of the gene and one located just 3' of the 84-bp region. Both primer sets showed hBMP-6 mRNA levels approximately 16- to 22-fold higher in the Dex-treated cells, demonstrating that hBMP-6 transcription is being regulated by glucocorticoids in the pluripotent hMSCs at the upstream transcription start site.

Update on glucocorticoid action and resistance

Glucocorticoids (GCs) are the most common group of medications used in the treatment of allergic and autoimmune disorders. They produce potent anti-inflammatory effects by inducing or repressing the expression of target genes. Although most patients with allergic diseases and autoimmune disorders respond to GC therapy, a small subset of patients demonstrate persistent tissue inflammation despite treatment with high doses of GCs. This condition results from an interaction between susceptibility genes, the host's environment, and immunologic factors. The treatment of these patients requires a systematic approach to rule out underlying conditions that lead to steroid resistance or treatment failure, as well as the use of alternative strategies to inhibit tissue inflammation.

Liganded androgen receptor interaction with beta-catenin: nuclear co-localization and modulation of transcriptional activity in neuronal cells

A yeast two-hybrid assay was employed to identify androgen receptor (AR) protein partners in gonadotropin-releasing hormone neuronal cells. By using an AR deletion construct (AR-(Delta371-485)) as a bait, beta-catenin was identified as an AR-interacting protein from a gonadotropin-releasing hormone neuronal cell library. Immunolocalization of co-transfected AR and FLAG-beta-catenin demonstrated that FLAG-beta-catenin was predominantly cytoplasmic in the absence of androgen. In the presence of 5alpha-dihydrotestosterone, FLAG-beta-catenin completely co-localized to the nucleus with AR. This effect was specific to AR because liganded progesterone, glucocorticoid, or estrogen alpha receptors did not translocate FLAG-beta-catenin to the nucleus. Agonist-bound AR was required because the AR antagonists casodex and hydroxyflutamide failed to translocate beta-catenin. Time course experiments demonstrated that co-translocation occurred with similar kinetics. Nuclear co-localization was independent of the glycogen synthase kinase-3beta, p42/44 ERK mitogen-activated protein kinase, and phosphatidylinositol 3-kinase pathways because inhibitors of these pathways had no effect. Transcription assays demonstrated that liganded AR repressed beta-catenin/T cell factor-responsive reporter gene activity. Conversely, co-expression of beta-catenin/T cell factor repressed AR stimulation of AR-responsive reporter gene activity. Our data suggest that liganded AR shuttles beta-catenin to the nucleus and that nuclear interaction of AR with beta-catenin may modulate transcriptional activity in androgen target tissues.

Androgen receptor interactions with Oct-1 and Brn-1 are physically and functionally distinct

POU domain proteins interact positively or negatively with steroid hormone receptors, depending on the precise array of these and other factors assembled on target gene promoters. Octamer transcription factor 1 (Oct-1), a ubiquitous POU factor, is implicated in androgen induction of the mouse sex-limited protein (Slp) gene based on protein-DNA interaction studies. However, direct evidence for a role of Oct-1 in the hormone response has been difficult to obtain. Brain 1 (Brn-1), another POU factor, is more tissue-specific, expressing in brain and also in kidney, which is a major site of Slp synthesis. We compared the interaction of the androgen receptor (AR) with Oct-1 and Brn-1 to reveal the more likely candidate for regulation of Slp. In transfection, addition of either Oct-1 or Brn-1 reduced AR activation, regardless of the presence of an octamer-like sequence in the enhancer, suggesting interference was indirect. However, when the octamer-like element was changed to a consensus octamer site, Brn-1, but not Oct-1, strongly enhanced androgen activation. This correlated with Brn-l's preference for the consensus octamer sequence in DNA binding assays. Direct interaction of AR with glutathione-S-transferase-(GST)-fused Oct-1 was DNA-dependent, while Brn-l-AR association was not. Chimeric Brn-1 and Oct-1 POU domains demonstrated that the DNA-dependent AR interaction relied on the origin of the POU homeodomain. However, in the context of full-length Brn-1 and Oct-1 chimeric proteins, the POU homedomain was not sufficient to confer the distinct behaviors of these factors in vivo, but instead revealed the importance of an N-terminal transactivation domain in Brn-1. These results demonstrate that functional interaction of Oct-1 and Brn-1 with AR is determined by the precise sequence of the octamer binding site, and by differential interaction of the POU factors with AR and other components of the transcriptional machinery.

Association between IL-1beta/TNF-alpha-induced glucocorticoid-sensitive changes in multiple gene expression and altered responsiveness in airway smooth muscle

The pleiotropic cytokines interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha have been implicated in the pathophysiology of asthma. To elucidate the role of these cytokines in the pro-asthmatic state, the effects of IL-1beta and TNF-alpha on airway smooth muscle (ASM) responsiveness and ASM expression of multiple genes, assessed by high-density oligonucleotide array analysis, were examined in the absence and presence of the glucocorticoid dexamethasone (DEX). Administration of IL-1beta/TNF-alpha increased ASM contractility to acetylcholine and impaired ASM relaxation to isoproterenol. These pro-asthmatic- like changes in ASM responsiveness were associated with IL-1beta/ TNF-alpha-induced mRNA expression of a host of proinflammatory genes that regulate transcription, cytokines and chemokines, cellular adhesion molecules, and various signal transduction molecules that regulate ASM responsiveness. In the presence of DEX, the changes induced in ASM responsiveness were abrogated, and most of the IL-1beta/TNF-alpha-mediated changes in proinflammatory gene expression were repressed, although mRNA expression of a small number of genes was enhanced by DEX. Collectively, the observations support the concept that, together with its role as a regulator of airway tone, in response to IL-1beta/TNF-alpha, the ASM expresses a host of glucocorticoid-sensitive genes that contribute to the altered structure and function of the airways in the pro-asthmatic state. We speculate that glucocorticoid-sensitive, cytokine-induced pathways involved in ASM cell signaling represent important targets for new therapeutic interventions.

17beta-estradiol, progesterone, and dihydrotestosterone suppress the growth of human melanoma by inhibiting interleukin-8 production

We studied the effects of 17beta-estradiol, progesterone, and dihydrotestosterone on in vitro growth of human metastatic melanoma. Each sex hormone inhibited the growth of melanoma receptor-dependently; 17beta-estradiol inhibited 3H-thymidine uptake of estrogen receptor-positive WM266-4 and NM26, but not that of the receptor-negative HS15. Progesterone inhibited 3H-thymidine uptake of progesterone receptor-positive WM266-4 and HS15, but not that of the receptor-negative NM26. Dihydrotestosterone inhibited 3H-thymidine uptake of androgen receptor-positive HS15 and NM26, but not that of the receptor-negative WM266-4. The growth inhibition by each hormone was counteracted by the respective hormone receptor antagonist. The combination of more than two hormones neither gave additive nor synergistic growth inhibition. The growth inhibition by each sex hormone was counteracted by interleukin-8 but not by the other growth factors. Each sex hormone reduced the constitutive interleukin-8 secretion and mRNA levels in the respective receptor-positive melanoma but not in the receptor-negative melanoma. Transient transfection showed that each sex hormone inhibited the constitutive chloramphenicol acetyltransferase expression driven by interleukin-8 promoter in the respective receptor-positive melanoma but not in the receptor-negative melanoma. Transfection with a series of 5'-deleted interleukin-8 promoter/chloramphenicol acetyltransferase reporter constructs demonstrated that the sequences between -98 and -63 bp on interleukin-8 promoter may be involved in the transcriptional repression. These data suggest that 17beta-estradiol, progesterone, and dihydrotestosterone suppress the growth of melanoma by inhibiting interleukin-8 production in a receptor-dependent manner.

Interleukin-2 inhibits glucocorticoid receptor transcriptional activity through a mechanism involving STAT5 (signal transducer and activator of transcription 5) but not AP-1

Cytokines and glucocorticoids (GCs) signaling pathways interfere with each other in the regulation of apoptosis and gene expression in the immune system. Interleukin-2 (IL-2), through the Janus kinase/signal transducers and activators of transcription (Jak/STAT) and mitogen-activated protein kinase (MAPK) pathways, activates STAT5 and activated protein-1 (AP-1) transcription factors, respectively, which are known to repress glucocorticoid receptor (GR) activity, at least in part, through protein-protein interactions. In this work, we have analyzed the mechanisms whereby IL-2 down-regulates the GC-induced transactivation of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) in murine CTLL-2 T lymphocytes. Mutagenesis studies revealed that the MMTV-LTR STAT5 binding site (-923/-914) was not required for IL-2-mediated inhibition but identified both glucocorticoid response elements (GREs) and the -104/+1 region as critical elements for this negative response. The DNA binding activities of transcription factors required for GC-mediated activation of the MMTV-LTR promoter and that bind to the -104/+1 region (nuclear factor-1, Oct-1) were not affected by IL-2 treatment. Overexpression of wild-type STAT5B enhanced the effect of IL-2 on MMTV-LTR activity, and a dominant negative form of STAT5B (Y699F) abolished the IL-2-mediated MMTV-LTR inhibition, whereas AP-1 activation had no effect in this system. Direct interaction between liganded GR and STAT5 was observed in CTLL-2 cells in a STAT5 phosphorylation-independent manner. Overexpression of nuclear coactivators CBP (CREB-binding protein) or SRC-1a (steroid receptor coactivator 1a) did not blunt IL-2 inhibitory effects. We suggest that the STAT5-repressive activity on the GC-dependent transcription may involve direct interaction of STAT5 with GR, is dependent on the promoter context and STAT5 activation level, and occurs independently of coactivators levels in T cells.

Structure of the human M(2) muscarinic acetylcholine receptor gene and its promoter

The M(2) muscarinic receptor inhibits the release of acetylcholine from cholinergic fibers in the lungs and elsewhere. In airway parasympathetic neurons, M(2) receptor expression is decreased by viral infections and by interferon-gamma, increasing actylcholine release. Dexamethasone increases M(2) receptor expression, decreasing acetylcholine release. We carried out 5' rapid amplification of cDNA ends beginning with mRNA from human heart and IMR32 human neuroblastoma cells. This demonstrated a 5' UTR of 100 BP, corresponding to two sequences on chromosome 7, separated by a 22.6 kB intron. The splice acceptor site is at -45 relative to the initiating atg. The 3000 BP upstream of 5' RACE product were subcloned into a pGL3 luciferase reporter vector. Deletional constructs were expressed in IMR32 cells. These demonstrated that 412 BP provided full expression of the reporter gene, and suggested a repressor element between -1848 and -1510.

Pou homeodomain protein OCT1 is implicated in the expression of the caudal-related homeobox gene Cdx-2

The caudal homeobox gene Cdx-2 is a transcriptional activator for approximately a dozen genes specifically expressed in pancreatic islets and intestinal cells. It is also involved in preventing the development of colorectal tumors. Studies using "knockout" approaches demonstrated that Cdx-2 is haplo-insufficient in certain tissues including the intestines but not the pancreatic islets. The mechanisms, especially transcription factors, which regulate Cdx-2 expression, are virtually unknown. We found previously that Cdx-2 expression could be autoregulated in a cell type-specific manner. In this study, we located an octamer (OCT) binding site within the mouse Cdx-2 gene promoter. This site, designated as Cdx-2(P)OCT, is involved in the expression of the Cdx-2 promoter. Both pancreatic and intestinal cell lines were found to express a number of POU (OCT binding) homeodomain proteins examined by electrophoretic mobility shift assay. However, it appears that Cdx-2(P)OCT interacts only with OCT1 in the nuclear extracts of the intestinal cell lines examined, although it interacts with OCT1 and at least two other POU proteins that are to be identified in the pancreatic InR1-G9 cell nuclear extract. Co-transfecting OCT1 cDNA but not five other POU gene cDNAs activates the Cdx-2 promoter in the pancreatic InR1-G9 and the intestinal Caco-2 cell lines. In contrast, Cdx-2(P)OCT cannot act as an enhancer element if it is fused to a thymidine kinase promoter. Furthermore, Cdx-2(P)OCT-thymidine kinase fusion promoters cannot be activated by OCT1 co-transfection. Cell type-specific expression, cell type-specific binding affinity of POU proteins to the cis-element Cdx-2(P)OCT, and the DNA content-dependent activation of Cdx-2 promoter via Cdx-2(P)OCT by OCT1 suggest that POU proteins play important and complicated roles in modulating Cdx-2 expression in cell type-specific manners.

Silencing mediator for retinoid and thyroid hormone receptors interacts with octamer transcription factor-1 and acts as a transcriptional repressor

Octamer transcription factor-1 (Oct-1) is a member of the POU (Pit-1, Oct-1, unc-86) family of transcription factors and is involved in the transcriptional regulation of a variety of gene expressions related to cell cycle regulation, development, and hormonal signals. It has been shown that Oct-1 acts not only as a transcriptional activator but also as a transcriptional repressor for certain genes. The mechanism of the repressive function of Oct-1 has not been well understood. Here we demonstrate by using the glutathione S-transferase pull-down assays and coimmunoprecipitation assays that the POU domain of Oct-1 directly interacts with a silencing mediator for retinoid and thyroid hormone receptors (SMRT). The interaction surfaces are located in the C-terminal region of SMRT, which are different from previously described silencing domains I and II or receptor interacting domains I and II. In transient transfection assays in COS1 cells, overexpression of SMRT attenuated the augmentation of Oct-1 transcriptional activity by OBF-1/OCA-B, activator for Oct-1. In pull-down assays, increasing amounts of SMRT could compete the binding of OCA-B to Oct-1 POU domain. The activity of Oct-1 could be determined by a regulated balance between SMRT and OCA-B. Furthermore, cotransfected unliganded thyroid hormone receptor enhanced the transactivation by Oct-1, and addition of 3,3',5-tri-iodo-l-thyronine obliterated the stimulatory effects. Consequently, in the presence of cotransfected thyroid hormone receptor, the octamer response element acts as an element negatively regulated by 3,3',5-tri-iodo-l-thyronine. The results suggest that the transcriptional activity of Oct-1 can be modulated by interaction through its POU domain by a silencing mediator SMRT resulting in the cross-talk between Oct-1 and nuclear receptors.

Oct-1 preferentially interacts with androgen receptor in a DNA-dependent manner that facilitates recruitment of SRC-1

Gene regulation by steroid hormone receptors depends on the particular character of the DNA response element, the array of neighboring transcription factors, and recruitment of coactivators that interface with the transcriptional machinery. We are studying these complex interactions for the androgen-dependent enhancer of the mouse sex-limited protein (Slp) gene. This enhancer has, in addition to multiple androgen receptor (AR)-binding sites, a central region (FPIV) with a binding site for the ubiquitous transcription factor Oct-1 that appears crucial for hormonal regulation in vivo. To examine the role of Oct-1 in androgen-specific gene activation, we tested the interaction of Oct-1 with AR versus glucocorticoid receptor (GR) in vivo and in vitro. Oct-1 coimmunoprecipitated from cell lysates with both AR and GR, but significant association with AR required both proteins to be DNA-bound. This was confirmed by sensitivity of the protein association to treatment with ethidium bromide or micrococcal nuclease. Addition of DNA to micrococcal nuclease-treated samples restored interaction, even when binding sites were on separate DNA molecules, suggesting association was due to direct protein-protein interaction and not indirect tethering via the DNA. AR/GR chimeras revealed that interaction of the N and C termini of AR was required to communicate the DNA-bound state that enhances interaction with Oct-1. Protease digestion assays of hormone-bound receptors revealed further conformational changes in the ligand binding domain of AR, but not GR, upon DNA binding. Furthermore, these conformational changes led to increased interaction with the coactivator SRC-1, via the NID 4 domain, suggesting DNA binding facilitates recruitment of SRC-1 by the AR-Oct-1 complex. Altogether, these results suggest that the precise arrangement of binding sites in the Slp enhancer ensures proper hormonal response by imposing differential interactions between receptors and Oct-1, which in turn contributes to SRC-1 recruitment to the promoter.

POU domain factors in the neuroendocrine system: lessons from developmental biology provide insights into human disease

POU domain factors are transcriptional regulators characterized by a highly conserved DNA-binding domain referred to as the POU domain. The structure of the POU domain has been solved, facilitating the understanding of how these proteins bind to DNA and regulate transcription via complex protein-protein interactions. Several members of the POU domain family have been implicated in the control of development and function of the neuroendocrine system. Such roles have been most clearly established for Pit-1, which is required for formation of somatotropes, lactotropes, and thyrotropes in the anterior pituitary gland, and for Brn-2, which is critical for formation of magnocellular and parvocellular neurons in the paraventricular and supraoptic nuclei of the hypothalamus. While genetic evidence is lacking, molecular biology experiments have implicated several other POU factors in the regulation of gene expression in the hypothalamus and pituitary gland. Pit-1 mutations in humans cause combined pituitary hormone deficiency similar to that found in mice deleted for the Pit-1 gene, providing a striking example of how basic developmental biology studies have provided important insights into human disease.

The classical progesterone receptor mediates Xenopus oocyte maturation through a nongenomic mechanism

Xenopus laevis oocytes are physiologically arrested at G(2) of meiosis I. Resumption of meiosis, or oocyte maturation, is triggered by progesterone. Progesterone-induced Xenopus oocyte maturation is mediated via an extranuclear receptor and is independent of gene transcription. The identity of this extranuclear oocyte progesterone receptor (PR), however, has remained a longstanding problem. We have isolated the amphibian homologue of human PR from a Xenopus oocyte cDNA library. The cloned Xenopus progesterone receptor (xPR) functioned in heterologous cells as a progesterone-regulated transcription activator. However, endogenous xPR was excluded from the oocyte nucleus and instead appeared to be a cytosolic protein not associated with any membrane structures. Injection of xPR mRNA into Xenopus oocytes accelerated the progesterone-induced oocyte maturation and reduced the required concentrations of progesterone. In enucleated oocytes, xPR accelerated the progesterone-induced mitogen-activated protein kinase activation. These data suggest that xPR is the long sought after Xenopus oocyte receptor responsible for progesterone-induced oocyte maturation.

Developmental effects of ectopic expression of the glucocorticoid receptor DNA binding domain are alleviated by an amino acid substitution that interferes with homeodomain binding

Steroid hormone receptors are distinguished from other members of the nuclear hormone receptor family through their association with heat shock proteins and immunophilins in the absence of ligands. Heat shock protein association represses steroid receptor DNA binding and protein-protein interactions with other transcription factors and facilitates hormone binding. In this study, we investigated the hormone-dependent interaction between the DNA binding domain (DBD) of the glucocorticoid receptor (GR) and the POU domains of octamer transcription factors 1 and 2 (Oct-1 and Oct-2, respectively). Our results indicate that the GR DBD binds directly, not only to the homeodomains of Oct-1 and Oct-2 but also to the homeodomains of several other homeodomain proteins. As these results suggest that the determinants for binding to the GR DBD are conserved within the homeodomain, we examined whether the ectopic expression of GR DBD peptides affected early embryonic development. The expression of GR DBD peptides in one-cell-stage zebra fish embryos severely affected their development, beginning with a delay in the epibolic movement during the blastula stage and followed by defects in convergence-extension movements during gastrulation, as revealed by the abnormal patterns of expression of several dorsal gene markers. In contrast, embryos injected with mRNA encoding a GR peptide with a point mutation that disrupted homeodomain binding or with mRNA encoding the DBD of the closely related mineralocorticoid receptor, which does not bind octamer factors, developed normally. Moreover, coinjection of mRNA encoding the homeodomain of Oct-2 completely rescued embryos from the effects of the GR DBD. These results highlight the potential of DNA-independent effects of GR in a whole-animal model and suggest that at least some of these effects may result from direct interactions with homeodomain proteins.