Cooperative coactivation of estrogen receptor alpha in ZR-75 human breast cancer cells by SNURF and TATA-binding protein

Altered methylation of imprinted genes in neuroblastoma: implications for prognostic refinement

BACKGROUND

Neuroblastoma (NB) is a complex disease, and the current understanding of NB biology is limited. Deregulation in genomic imprinting is a common event in malignancy. Since imprinted genes play crucial roles in early fetal growth and development, their role in NB pathogenesis could be suggested.

METHODS

We examined alterations in DNA methylation patterns of 369 NB tumours at 49 imprinted differentially methylated regions (DMRs) and assessed its association with overall survival probabilities and selected clinical and genomic features of the tumours. In addition, an integrated analysis of DNA methylation and allele-specific copy number alterations (CNAs) was performed, to understand the correlation between the two molecular events.

RESULTS

Several imprinted regions with aberrant methylation patterns in NB were identified. Regions that underwent loss of methylation in > 30% of NB samples were DMRs annotated to the genes NDN, SNRPN, IGF2, MAGEL2 and HTR5A and regions with gain of methylation were NNAT, RB1 and GPR1. Methylation alterations at six of the 49 imprinted DMRs were statistically significantly associated with reduced overall survival: MIR886, RB1, NNAT/BLCAP, MAGEL2, MKRN3 and INPP5F. RB1, NNAT/BLCAP and MKRN3 were further able to stratify low-risk NB tumours i.e. tumours that lacked MYCN amplification and 11q deletion into risk groups. Methylation alterations at NNAT/BLCAP, MAGEL2 and MIR886 predicted risk independently of MYCN amplification or 11q deletion and age at diagnosis. Investigation of the allele-specific CNAs demonstrated that the imprinted regions that displayed most alterations in NB tumours harbor true epigenetic changes and are not result of the underlying CNAs.

CONCLUSIONS

Aberrant methylation in imprinted regions is frequently occurring in NB tumours and several of these regions have independent prognostic value. Thus, these could serve as potentially important clinical epigenetic markers to identify individuals with adverse prognosis. Incorporation of methylation status of these regions together with the established risk predictors may further refine the prognostication of NB patients.

Allelic to genome wide perspectives of swine genetic variation to litter size and its component traits

Litter size is a complex and sex limited trait that depends on various biological, managemental and environmental factors. Owing to its low heritability it is inefficaciously selected by traditional methods. However, due to higher heritability of ovulation rate and embryo survival, selection based on component traits of litter size is advocated. QTL analysis and candidate gene approach are among the various supplementary/alternate strategies for selection of litter size. QTL analysis is aimed at identifying genomic regions affecting trait of interest significantly. Candidate gene approach necessitates identification of genes potentially affecting the trait. There are various genes that significantly affect litter size and its component traits viz. ESR, LEP, BF, IGFBP, RBP4, PRLR, CTNNAL1, WNT10B, TCF12, DAZ, and RNF4. These genes affect litter size in a complex interacting manner. Lately, genome wide association study (GWAS) have been utilized to unveil the genetic and biological background of litter traits, and elucidate the genes governing litter size. Favorable SNPs in these genes have been identified and offers a scope for inclusion in selection programs thereby increasing breeding efficiency and profit in pigs. The review provides a comprehensive coverage of investigations carried out globally to unravel the genetic variation in litter size and its component traits in pigs, both at allelic and genome wide level. It offers a current perspective on different strategies including the profiling of candidate genes, QTLs, and genome wide association studies as an aid to efficient selection for litter size and its component traits.

From the Evasion of Degradation to Ubiquitin-Dependent Protein Stabilization

A hallmark of cancer is dysregulated protein turnover (proteostasis), which involves pathologic ubiquitin-dependent degradation of tumor suppressor proteins, as well as increased oncoprotein stabilization. The latter is due, in part, to mutation within sequences, termed degrons, which are required for oncoprotein recognition by the substrate-recognition enzyme, E3 ubiquitin ligase. Stabilization may also result from the inactivation of the enzymatic machinery that mediates the degradation of oncoproteins. Importantly, inactivation in cancer of E3 enzymes that regulates the physiological degradation of oncoproteins, results in tumor cells that accumulate multiple active oncoproteins with prolonged half-lives, leading to the development of "degradation-resistant" cancer cells. In addition, specific sequences may enable ubiquitinated proteins to evade degradation at the 26S proteasome. While the ubiquitin-proteasome pathway was originally discovered as central for protein degradation, in cancer cells a ubiquitin-dependent protein stabilization pathway actively translates transient mitogenic signals into long-lasting protein stabilization and enhances the activity of key oncoproteins. A central enzyme in this pathway is the ubiquitin ligase RNF4. An intimate link connects protein stabilization with tumorigenesis in experimental models as well as in the clinic, suggesting that pharmacological inhibition of protein stabilization has potential for personalized medicine in cancer. In this review, we highlight old observations and recent advances in our knowledge regarding protein stabilization.

Analysis of H3K4me3-ChIP-Seq and RNA-Seq data to understand the putative role of miRNAs and their target genes in breast cancer cell lines

Breast cancer is one of the leading causes of cancer in women all over the world and accounts for ~25% of newly observed cancers in women. Epigenetic modifications influence differential expression of genes through non-coding RNA and play a crucial role in cancer regulation. In the present study, epigenetic regulation of gene expression by in-silico analysis of histone modifications using chromatin immunoprecipitation sequencing (ChIP-Seq) has been carried out. Histone modification data of H3K4me3 from one normal-like and four breast cancer cell lines were used to predict miRNA expression at the promoter level. Predicted miRNA promoters (based on ChIP-Seq) were used as a probe to identify gene targets. Five triple-negative breast cancer (TNBC)‒specific miRNAs (miR153-1, miR4767, miR4487, miR6720, and miR-LET7I) were identified and corresponding 13 gene targets were predicted. Eight miRNA promoter peaks were predicted to be differentially expressed in at least three breast cancer cell lines (miR4512, miR6791, miR330, miR3180-3, miR6080, miR5787, miR6733, and miR3613). A total of 44 gene targets were identified based on the 3′-untranslated regions of downregulated mRNA genes that contain putative binding targets to these eight miRNAs. These include 17 and 15 genes in luminal-A type and TNBC respectively, that have been reported to be associated with breast cancer regulation. Of the remaining 12 genes, seven (A4GALT, C2ORF74, HRCT1, ZC4H2, ZNF512, ZNF655, and ZNF608) show similar relative expression profiles in large patient samples and other breast cancer cell lines thereby giving insight into predicted role of H3K4me3 mediated gene regulation via the miRNA-mRNA axis.

Effect of RNF4-SacII gene polymorphism on reproductive traits of Landrace × Large White crossbred sows

The aim of the present study was to investigate whether and to what extent the RNF4-SacII gene polymorphism influences reproduction performances in hyperprolific sow lines. The study involved 101 Landrace x Large White crossbred sows, with 461 records collected on the following reproductive traits: Total Number of piglets Born per litter (TNB), Number of piglets Born Alive per litter (NBA), Number of StillBorn piglets per litter (NSB), piglet Pre-Weaning Mortality (PWM) and Number of piglets at Weaning per litter (NW). The least square method with the GLM procedure in SAS with eight effects was used to pursue the data analysis. Study results revealed that TT homozygotes and TC heterozygotes had a significantly higher (p < .05) NW than CC homozygotes for the life-span performance in all parities and first parity analysed. In the fourth parity analysed, TNB and NBA in TC genotype were significantly higher (p < .05) as compared with TT genotype. Based on the life-span performance, significant effect (p < .05) was recorded for order of parity on TNB, NBA and NW, for farrowing season on TNB and NSB, and for lactation length on PWM. In the second parity, significant effect (p < .05) was recorded for sire of boar on NSB and for gestation length on TNB. Only in the fourth parity, significant effect (p < .05) of RNF4 gene was observed on NBA. There was significant additive effect (p < .05) of the RNF4 gene polymorphism identified on NW in all parities analysed, and significant additive and dominance effects (p < .05) on NSB in the third parity analysed. In conclusion, additional research on related production pig genotypes is necessary to elucidate the effect of RNF4 gene mutation on reproductive traits.

Screening of Prognosis-Related Genes in Primary Breast Carcinoma Using Genomic Expression Data

This study aimed at exploring the genes that may be related to the prognosis of primary breast cancer (BC) patients. The gene expression microarray data, together with sample survival data were acquired from The Cancer Genome Atlas database. The top 20% genes according to expression value variance were subjected to hierarchical cluster analysis. Bootstrap methods were utilized to assess the stability of cluster. Cox regression was applied to screen genes related to the survival time of patients with BC, and the Beta-Uniform Mixture model was applied to adjust the significance of numerous tests. Further, ingenuity pathway analysis (IPA) was carried out to analyze the functions of the potential prognostic genes. Cluster analysis revealed that there were at least five stable BC subtypes, each with specific gene expression. Further, 42 survival time-associated genes were found (p-value = 0.0006, false discovery rate = 0.2) by Cox regression analysis. According to Gene Ontology (GO) functional annotation, genes in clusters A, B, C, D, and E separately were implicated in cell adhesion cooperation, cell stress response, cell cycle, the assembly of nucleosome and chromosome, and immune regulation. IPA results showed that prognosis-related genes mainly participated in the pathways of cell apoptosis, and cell communication and morphology. Genes such as JAK2, TBP, PTGES3, and RYBP may be promising prognostic biomarkers for BC patients.

Ubiquitylation of nuclear receptors: new linkages and therapeutic implications

The nuclear receptor (NR) superfamily is a group of transcriptional regulators that control multiple aspects of both physiology and pathology and are broadly recognized as viable therapeutic targets. While receptor-modulating drugs have been successful in many cases, the discovery of new drug targets is still an active area of research, because resistance to NR-targeting therapies remains a significant clinical challenge. Many successful targeted therapies have harnessed the control of receptor activity by targeting events within the NR signaling pathway. In this review, we explore the role of NR ubiquitylation and discuss how the expanding roles of ubiquitin could be leveraged to identify additional entry points to control receptor function for future therapeutic development.

STUbLs in chromatin and genome stability

Chromatin structure and function is based on the dynamic interactions between nucleosomes and chromatin-associated proteins. In addition to the other post-translational modifications considered in this review issue of Biopolymers, ubiquitin and SUMO proteins also have prominent roles in chromatin function. A specialized form of modification that involves both, referred to as SUMO-targeted ubiquitin ligation, or STUbL [Perry, Tainer, and Boddy, Trends Biochem Sci, 2008, 33, 201-208], has significant effects on nuclear functions, ranging from gene regulation to genomic stability. Intersections between SUMO and ubiquitin in protein modification have been the subject of a recent comprehensive review [Praefcke, Hofmann, and Dohmen, Trends Biochem Sci, 2012, 37, 23-31]. Our goal here is to focus on features of enzymes with STUbL activity that have been best studied, particularly in relation to their nuclear functions in humans, flies, and yeasts. Because there are clear associations of disease and development upon loss of STUbL activities in metazoans, learning more about their function, regulation, and substrates will remain an important goal for the future.

Interactions between IGF-I, estrogen receptor-α (ERα), and ERβ in regulating growth/apoptosis of MCF-7 human breast cancer cells

Understanding of the interactions between estradiol (E₂) and IGF-I is still incomplete. Cell lines derived from the MCF-7 breast cancer cells were generated with suppressed expression of the IGF-I receptor (IGF-IR), termed IGF-IR.low cells, by stable transfection using small interfering RNA (siRNA) expression vector. Vector for control cells carried sequence generating noninterfering RNA. Concomitant with reduction in the IGF-IR levels, the IGF-IR.low cells also showed a reduction in estrogen receptor α (ERα) and progesterone receptor expressions, and an elevation in the expression of ERβ. The number of the IGF-IR.low cells was reduced in response to IGF-I and human GH plus epidermal growth factor, but E₂ did not cause an increase in the number of the IGF-IR.low cells compared to controls. The proliferation rate of IGF-IR.low cells was only reduced in response to E₂ compared to controls, whereas their basal and hormone-stimulated apoptosis rate was increased. Phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) was increased in the IGF-IR.low cells after treatment with E₂, without affecting control cells. Furthermore, phosphorylation of the tumor suppressor protein p53 was elevated in the IGF-IR.low cells compared to the controls. In conclusion, suppressing IGF-IR expression decreased the level of ERα but increased the level of ERβ. Overall growth rate of the IGF-IR.low cells was reduced mostly through an increase in apoptosis without affecting proliferation substantially. We hypothesize that a decreased ERα:ERβ ratio triggered a rapid phosphorylation of p38 MAPK, which in turn phosphorylated the p53 tumor suppressor and accelerated apoptosis rate.

Genome stability roles of SUMO-targeted ubiquitin ligases

Post-translational modification of the cell's proteome by ubiquitin and ubiquitin-like proteins provides dynamic functional regulation. Ubiquitin and SUMO are well-studied post-translational modifiers that typically impart distinct effects on their targets. The recent discovery that modification by SUMO can target proteins for ubiquitination and proteasomal degradation sets a new paradigm in the field, and offers insights into the roles of SUMO and ubiquitin in genome stability.

Estrogen receptor beta isoform-specific induction of transforming growth factor beta-inducible early gene-1 in human osteoblast cells: an essential role for the activation function 1 domain

The estrogen receptors (ER) alpha and beta are important ligand-mediated transcription factors known to play significant biological roles in numerous tissues including bone. Despite the high homology shared by these receptors, recent studies have suggested that their function is largely unique. Although these receptors have been studied in detail for more than a decade, little data exist concerning the mechanisms by which these two proteins regulate distinct sets of genes. Using the TGFbeta-inducible early gene-1 (TIEG) as a model, we demonstrate that TIEG is rapidly induced in response to estrogen in osteoblasts by ERbeta, but not ERalpha. We have identified the regulatory elements utilized by ERbeta and have demonstrated that ERbeta recruits steroid receptor coactivator (SRC)1 and SRC2 to this regulatory region. Additionally, deletion of the ERbeta-activation function 1 (AF1) domain drastically decreases the estrogen induction of TIEG. Through the use of chimeric receptors, we have demonstrated that the AF1 domain of ERbeta is responsible for recruiting SRC1 and SRC2 and inducing the expression of TIEG in osteoblasts. Finally, SRC1, but not SRC2, is essential for TIEG induction by ERbeta. Overall, these data demonstrate that the estrogen induction of TIEG is ERbeta specific and that the AF1 domain of ERbeta confers this specificity. Finally, a novel and important role for ERbeta's AF1 is implicated in the recruitment of specific coactivators, suggesting that the AF1 may play a significant role in conferring the differences in regulation of gene expression by these two receptors.

Identification of polymorphism and association analysis with reproductive traits in the porcine RNF4 gene

The ring finger protein 4 gene (RNF4), which might play a role in fetal germ cell development as well as in oocyte and granulosa cell maturation, was one of the potential candidate genes for reproductive traits. In the present work, we isolated the complete coding sequence of porcine RNF4 gene, identified a single nucleotide polymorphism (SNP: T/C) in intron5, and developed a PCR-SacII-RFLP genotyping assay. Association of this SNP with reproductive traits was assessed in three populations with diverse genetic backgrounds. One was Chinese Qingping sows. Another was consisted of crossbred sows derived from Landrace, Large White, Chinese Tongcheng and/or Chinese Meishan (Line DIV). The third is Large White x Meishan (LW x M) F(2) slaughtered population. Statistical analysis demonstrated that, in the first parity, the difference between RNF4 genotypes and reproductive traits of both Qingping and Line DIV sows was not significant. In the second and subsequent litters, CC animals in Qingping population had more piglets born (+1.74 piglets) and piglets born alive (+2.02 piglets) than sows with the TT genotype (P<0.05). Line DIV sows inheriting the CC genotype had additional 0.69 piglets born compared to the TC animals (P<0.05) in second and subsequent litters. No significant difference was observed between genotypes and reproductive tracts components in F(2) animals. In addition, we found RNF4 gene has a significant additive effect on both piglet born and piglet born alive in Qingping animals (P<0.05). Results here suggested that the RNF4 SNP was significantly associated with litter size in two populations and could be useful in selection for increasing litter size in pigs. Further studies were needed to confirm these preliminary researches.

Fission yeast Rnf4 homologs are required for DNA repair

We describe two RING finger proteins in the fission yeast Schizosaccharomyces pombe, Rfp1 and Rfp2. We show that these proteins function redundantly in DNA repair. Rfp1 was isolated as a Chk1-interacting protein in a two-hybrid screen and has high amino acid sequence similarity to Rfp2. Deletion of either gene does not cause a phenotype, but a double deletion (rfp1Deltarfp2Delta) showed poor viability and defects in cell cycle progression. These cells are also sensitive to DNA-damaging agents, although they maintained normal checkpoint signaling to Chk1. Rfp1 and Rfp2 are most closely related to human Rnf4, and we showed that Rnf4 can substitute functionally for Rfp1 and/or Rfp2. The double mutants also showed significantly increased levels of protein SUMOylation, and we identified an S. pombe Ulp2/Smt4 homolog that, when overexpressed, reduced SUMO levels and suppressed the DNA damage sensitivity of rfp1Delta rfp2Delta cells.

Estrogen Receptor Isoform-specific Regulation of the Retinoblastoma-binding Protein 1 (RBBP1) Gene

Estrogen (E2) is involved in mediating many important functions relevant to osteoblast biology through the actions of the estrogen receptors (ER) alpha and beta. To further understand the mechanisms of ER-specific regulation, we used microarray and reverse transcription-PCR analyses of E2-treated U2OS-ERalpha or -ERbeta cells and identified retinoblastoma-binding protein 1 (RBBP1) as a major E2-regulated gene. RBBP1 is a retinoblastoma cofactor involved in the control of osteoblastic proliferation. Although RBBP1 mRNA levels rapidly increased after 2 h of E2 treatment in both U2OS-ER-expressing lines, a sustained induction was only observed in U2OS-ERalpha cells. Examination of the RBBP1 genomic sequence revealed an ER response element and a Sp1 site located within the first intron. Chromatin immunoprecipitation analyses demonstrated that E2-dependent ERalpha binding to the intron 1 enhancer region was constitutive, whereas ERbeta binding was transient, consistent with the mRNA time course. Interestingly, transient transfection and receptor mutational studies revealed that RBBP1 induction by ERalpha only requires the Sp1 site, whereas ERbeta utilizes both the Sp1 and estrogen response elements binding sites for maximal E2-dependent activation. Stable U2OS transfectants containing a deletion of the ERalpha activation function 1 (AF1) resulted in a temporal mRNA induction profile similar to that of wild type ERbeta. Further, overexpression and chromatin immunoprecipitation analyses also demonstrated that E2-dependent RBBP1 induction is SRC2-dependent for both ER isoforms. These results describe an E2-dependent, ER isoform-specific transcriptional activation of the RBBP1 gene, which in part, is explained by the differential activity of ER AF1 and enhancer element binding.

Transcription of gonadotropin beta subunit genes involves cross-talk between the transcription factors and co-regulators that mediate actions of the regulatory hormones

The gonadotropins LH and FSH have distinct temporal patterns of expression as a result of differential regulation by hormones such as GnRH, steroids and activin. This specific regulation is due to diverse sets of transcription factors that are recruited to the promoters of these genes, and recruit specific co-activator complexes which function to stabilize interactions with the general transcription factors and RNA polymerase II, and also to induce covalent modifications of the histone tails at these gene loci. As these molecular mechanisms are elucidated, the nature of nuclear cross-talk between the various hormonally induced pathways is becoming evident, revealing both negative and positive effects of interacting transcription factors and co-regulators. This paper will review current knowledge on the transcriptional regulation of gonadotropin beta subunit gene expression in the chromatin setting, and will present new data pertaining to nuclear cross-talk between the various endocrine-induced pathways regulating gonadotropin gene transcription.

Gender difference in the activity but not expression of estrogen receptors alpha and beta in human lung adenocarcinoma cells

The higher frequency of lung adenocarcinoma in women smokers than in men smokers suggests a role for gender-dependent factors in the etiology of lung cancer. We evaluated estrogen receptor (ER) alpha and beta expression and activity in human lung adenocarcinoma cell lines and normal lung fibroblasts. Full-length ERalpha and ERbeta proteins were expressed in all cell lines with higher ERbeta than ERalpha. Although estradiol (E(2)) binding was similar, E(2) stimulated proliferation only in cells from females, and this response was inhibited by anti-estrogens 4-hydroxytamoxifen (4-OHT) and ICI 182,780. In contrast, E(2) did not stimulate replication of lung adenocarcinoma cells from males and 4-OHT or ICI did not block cell proliferation. Similarly, transcription of an estrogen response element-driven reporter gene was stimulated by E(2) in lung adenocarcinoma cells from females, but not males. Progesterone receptor (PR) expression was increased by E(2) in two out of five adenocarcinoma cell lines from females, but none from males. E(2) decreased E-cadherin protein expression in some of the cell lines from females, as it did in MCF-7 breast cancer cells, but not in the cell lines from males. Thus, ERalpha and ERbeta expression does not correlate with the effect of ER ligands on cellular activities in lung adenocarcinoma cells. On the other hand, coactivator DRIP205 expression was higher in lung adenocarcinoma cells from females versus males and higher in adenocarcinoma cells than in normal human bronchial epithelial cells. DRIP205 and other ER coregulators may contribute to differences in estrogen responsiveness between lung adenocarcinoma cells in females and males.

Cross talk in hormonally regulated gene transcription through induction of estrogen receptor ubiquitylation

Estrogen tightly regulates the levels of circulating gonadotropins, but a direct effect of estrogen receptor alpha (ERalpha) on the mammalian LHbeta gene has remained poorly defined. We demonstrate here that ERalpha can associate with the LHbeta promoter through interactions with Sf-1 and Pitx1 without requiring an estrogen response element (ERE). We show that gonadotropin-releasing hormone (GnRH) promotes ERalpha ubiquitylation and also degradation while stimulating expression of ubc4. GnRH also increases the association and lengthens the cycling time of ERalpha on the LHbeta promoter. The ERalpha association and transactivation of the LHbeta gene, as well as ERalpha degradation, are increased following ubc4 overexpression, while the effects of GnRH are abated following ubc4 knockdown. Our results indicate that ERalpha ubiquitylation and subsequent transactivation of the LHbeta gene can be induced by increasing the levels of the E2 enzyme as a result of signaling by an extracellular hormone, thus providing a new form of cross talk in hormonally stimulated regulation of gene expression.

The molluscan RING-finger protein L-TRIM is essential for neuronal outgrowth

The tripartite motif proteins TRIM-2 and TRIM-3 have been put forward as putative organizers of neuronal outgrowth and structural plasticity. Here, we identified a molluscan orthologue of TRIM-2/3, named L-TRIM, which is up-regulated during in vitro neurite outgrowth of central neurons. In adult animals, L-Trim mRNA is ubiquitously expressed at low levels in the central nervous system and in peripheral tissues. Central nervous system expression of L-Trim mRNA is increased during postnatal brain development and during in vitro and in vivo neuronal regeneration. In vitro double-stranded RNA knock-down of L-Trim mRNA resulted in a >70% inhibition of neurite outgrowth. Together, our data establish a crucial role for L-TRIM in developmental neurite outgrowth and functional neuronal regeneration and indicate that TRIM-2/3 family members may have evolutionary conserved functions in neuronal differentiation.

SPBP is a phosphoserine-specific repressor of estrogen receptor alpha

Multiple signaling pathways stimulate the activity of estrogen receptor alpha (ERalpha) by direct phosphorylation within its N-terminal activation function 1 (AF1). How phosphorylation affects AF1 activity remains poorly understood. We performed a phage display screen for human proteins that are exclusively recruited to the phosphorylated form of AF1 and found the stromelysin-1 platelet-derived growth factor-responsive element-binding protein (SPBP). In a purified system, SPBP bound only the in vitro-phosphorylated form of the ERalpha AF1 or the phosphoserine mimic S118E, and the interaction domain could be mapped to a 42-amino-acid fragment of SPBP. In cells, SPBP preferentially interacted with liganded and phosphorylated ERalpha. Functionally, SPBP behaved as a repressor of activated ERalpha, which extends its previously demonstrated roles as a DNA binding transactivation factor and coactivator of other transcription factors. By targeting the phosphorylated form of AF1, SPBP may contribute to attenuating and fine-tuning ERalpha activity. A functional consequence is that SPBP inhibits the proliferation of ERalpha-dependent but not ERalpha-independent breast cancer cell lines, mirroring a reported negative correlation with the ERalpha status of breast tumors.

DRIP150 coactivation of estrogen receptor alpha in ZR-75 breast cancer cells is independent of LXXLL motifs

Vitamin D receptor-interacting protein 150 (DRIP150) has been identified as part of mediator-like complexes that enhance transcriptional activation of the estrogen receptor (ER) and other nuclear receptors (NRs). DRIP150 coactivates ligand-dependent ERalpha-mediated transactivation in ZR-75 and MDA-MB-231 breast cancer cells transfected with a (luciferase) reporter construct (pERE3) regulated by three tandem estrogen-responsive elements. Coactivation of ERalpha by DRIP150 in ZR-75 cells was activation function 2-dependent and required an intact helix 12 that typically interacts with LXXLL motifs (NR box) in p160 steroid receptor coactivators. DRIP150 contains C- and N-terminal NR boxes (amino acids 1182-1186 and 69-73, respectively), and deletion analysis of DRIP150 showed that regions containing these sequences were not necessary for coactivation of ERalpha. Analysis of multiple DRIP150 deletion mutants identified a 23-amino-acid sequence (789-811) required for coactivation activity. Analysis of the protein crystal structure data base identified two regions at amino acids 789-794 and 795-804, which resembled alpha-helical motifs in Lanuginosa lipase/histamine N-methyltransferase and hepatocyte nuclear factor 1, respectively. By using a squelching assay and specific amino acid point mutations within each alpha-helix, the NIFSEVRVYN (795-804) region was identified as the critical sequence required for the activity of DRIP150. These results demonstrate that coactivation of ERalpha by DRIP150 in ZR-75 cells is NR box-independent and requires a novel sequence with putative alpha-helical structure.

Estrogen receptor mutations in human disease

As early as the 1800s, the actions of estrogen have been implicated in the development and progression of breast cancer. The estrogen receptor (ER) was identified in the late 1950s and purified a few years later. However, it was not until the 1980s that the first ER was molecularly cloned, and in the mid 1990s, a second ER was cloned. These two related receptors are now called ERalpha and ERbeta, respectively. Since their discovery, much research has focused on identifying alterations within the coding sequence of these receptors in clinical samples. As a result, a large number of naturally occurring splice variants of both ERalpha and ERbeta have been identified in normal epithelium and diseased or cancerous tissues. In contrast, only a few point mutations have been identified in human patient samples from a variety of disease states, including breast cancer, endometrial cancer, and psychiatric diseases. To elucidate the mechanism of action for these variant isoforms or mutant receptors, experimental mutagenesis has been used to analyze the function of distinct amino acid residues in the ERs. This review will focus on ERalpha and ERbeta alterations in breast cancer.

Coordinate transcription of the ADAMTS-1 gene by luteinizing hormone and progesterone receptor

ADAMTS-1 (a disintegrin and metalloproteinase with thrombospondin-like motifs) is a multifunctional protease that is expressed in periovulatory follicles. Herein we show that induction of ADAMTS-1 message in vivo and transcription of the ADAMTS-1 promoter in cultured granulosa cells are dependent on separable but coordinate actions of LH and the progesterone receptor (PR). To analyze the molecular mechanisms by which LH and PR regulate this gene, truncations and site-specific mutants of ADAMTS-1 promoter-luciferase reporter constructs (ADAMTS-1-Luc) were generated and transfected into rat granulosa cell cultures. Three regions of the promoter were found to be important for basal activity, two of which were guanine cytosine-rich binding sites for specificity proteins Sp1/Sp3 and the third bound a nuclear factor 1-like factor. Despite the absence of a consensus PR DNA response element in the proximal ADAMTS-1 promoter, cotransfection of a PRA (or PRB) expression vector stimulated ADAMTS-1 promoter activity, a response that was reduced by the PR antagonist ZK98299. Forskolin plus phorbol myristate acetate also increased promoter activity and, when added to cells cotransfected with PRA, ADAMTS-1 promoter activity increased further. Activation of the ADAMTS-1 promoter by PRA involves functional CAAT enhancer binding protein beta, nuclear factor 1-like factor, and three Sp1/Sp3 binding sites as demonstrated by transfection of mutated promoter constructs. In summary, LH and PRA/B exert distinct but coordinate effects on transactivation of the ADAMTS-1 gene in granulosa cells in vivo and in vitro with PR acting as an inducible coregulator of the ADAMTS-1 gene.

Transcriptional coregulator SNURF (RNF4) possesses ubiquitin E3 ligase activity

SNURF/RNF4 has been implicated in transcriptional regulation and growth inhibition in a RING finger-dependent fashion. In this work, we show that SNURF mediates its own ubiquitination in vitro in a ubiquitin-conjugating enzyme (E2)-selective manner: SNURF acts as an E3 ligase with UbcH5A and B, HHR6B (RAD6B), E2-25K, MmUbc7 and UbcH13, but not with UbcH3, UbcM4, MmUbc6 or E2-20K. In contrast, the well-characterized RING E3, AO7, functions only with members of the UbcH5 family. Furthermore, depending on the E2 used, the ubiquitin modification manifests as mono- or multi-ubiquitination. Mutation of conserved cysteine residues within the RING finger motif of SNURF abolishes the ubiquitination in vitro and in intact cells. Size fractionation of murine embryonal carcinoma F9 cell proteins shows that the majority of endogenous SNURF resides in salt-resistant > or =500-kDa complexes, suggesting that SNURF functions as a RING component in a multiprotein complex. Taken together, SNURF/RNF4 functions as an E3 ligase and this activity is closely linked to its transcription regulatory functions.

Small nuclear RING finger protein stimulates the rat luteinizing hormone-beta promoter by interacting with Sp1 and steroidogenic factor-1 and protects from androgen suppression

GnRH controls expression of the LH subunit genes, alpha and LHbeta, with the LHbeta subunit regulated most dramatically. Two enhancer regions, distal and proximal, on the rat LHbeta gene promoter cooperate for full basal expression and GnRH stimulation. It has been hypothesized that the transcription factors binding to these regions, Sp1, Egr-1, and steroidogenic factor 1 (SF-1), may interact directly or indirectly via a coactivator. One such coactivator may be small nuclear RING finger protein (SNURF), which is expressed in pituitary tissue and the LbetaT2 gonadotrope cell line. In transfection experiments in LbetaT2 cells, SNURF stimulated basal expression of LHbeta and increased overall GnRH stimulation. SNURF specifically stimulated LHbeta, with no effect on the alpha-subunit promoter. SNURF interacts with Sp1 and SF-1, but not Egr-1, in pull-down experiments. Point mutations or deletions of SNURF functional domains demonstrated that Sp1 and SF-1 interactions with SNURF are required for SNURF stimulatory effects on the LHbeta promoter. Endogenous SNURF is associated with the LHbeta promoter on native chromatin, suggesting that it plays a physiological role in LHbeta gene expression. SNURF also binds the androgen receptor, and SNURF overexpression overcomes androgen suppression of GnRH-stimulated LHbeta but not alphasubunit promoter activity. SNURF mutations that disrupt Sp1 or SF-1 binding eliminate rescue by SNURF. We conclude that SNURF may mediate interactions between the distal and proximal GnRH response regions of the LHbeta promoter to stimulate transcription and can also protect the promoter from androgen suppression.

Activator protein-2gamma (AP-2gamma) expression is specifically induced by oestrogens through binding of the oestrogen receptor to a canonical element within the 5'-untranslated region

The activator protein 2 (AP-2) transcription factors are essential proteins for oestrogenic repression of the ERBB2 proto-oncogene in breast cancer cells. In the present study, we have examined the possible oestrogenic regulation of AP-2 genes themselves in breast-tumour-derived lines. As early as 1 h after oestrogen treatment, AP-2gamma mRNA was markedly increased, whereas AP-2alpha was down-regulated, but with slower kinetics, and AP-2beta was not affected at all. Addition of anti-oestrogens ablated these effects. Modulation of the protein levels corresponded to changes in the transcript levels, thus suggesting that in oestrogen-treated cells, an inversion of the balance between AP-2alpha and AP-2gamma isoforms occurs. The 5'-untranslated region (5'-UTR) of the human AP-2gamma gene contains one consensus and one degenerate oestrogen-responsive element (ERE). Reporter constructs carrying the AP-2gamma promoter and the 5'-UTR were up-regulated by oestrogens in transient transfection assays. Deletion of the most conserved (but not of the degenerate) ERE from reporter constructs abrogated the oestrogenic response, although both ERE-containing segments were footprinted in DNaseI protection assays. In vitro binding assays demonstrated the ability of oestrogen receptor alpha (ERalpha) to bind to this site, and chromatin immunoprecipitation analysis of the endogenous gene showed that ERalpha occupies this region in response to oestrogens. We conclude that AP-2gamma is a primary oestrogen-responsive gene and suggest that AP-2 proteins may mediate some oestrogenic responses.

Down-Regulation of Estrogen Receptor β and Transcriptional Coregulator SNURF/RNF4 in Testicular Germ Cell Cancer

OBJECTIVE

The role of estrogens and androgens in the etiology and progression of testicular germ cell cancer is poorly understood. To gain insight into the role of sex steroid action in testicular tumorigenesis, we have measured mRNAs encoding estrogen receptor beta (ERbeta), androgen receptor (AR), and their coregulators SNURF/RNF4, PIASx, and PIAS1 in testicular germ cell tumors.

METHODS

We used real-time quantitative reverse transcription-PCR assay to compare the steroid receptor and coregulator mRNA levels in 12 matched samples of testicular tumors and adjacent normal tissues (seminomas n=8, nonseminomas n=4). In addition, ERbeta and SNURF/RNF4 protein immunoreactivity was analyzed from paraffin-embedded normal testis and tumor specimens.

RESULTS

ERbeta mRNA levels were down-regulated by 59% in seminomas (p=0.017), and those of AR and SNURF/RNF4 mRNAs were decreased by 75% and 67%, respectively, in seminomas and teratocarcinomas compared to paired normal samples (p=0.034 for both, Wilcoxon signed rank test), whereas the PIASx and PIAS1 mRNA were unaltered. ERbeta and SNURF/RNF4 were also clearly down-regulated at the protein level in testicular tumors.

CONCLUSIONS

Expression of ERbeta and SNURF/RNF4 was significantly lower in cancerous than in noncancerous testis tissue. Down-regulation of the ERbeta and the coregulator SNURF/RNF4 genes may play a role in testicular tumorigenesis.

Advances in estrogen receptor biology: prospects for improvements in targeted breast cancer therapy

Estrogen receptor (ER) has a crucial role in normal breast development and is expressed in the most common breast cancer subtypes. Importantly, its expression is very highly predictive for response to endocrine therapy. Current endocrine therapies for ER-positive breast cancers target ER function at multiple levels. These include targeting the level of estrogen, blocking estrogen action at the ER, and decreasing ER levels. However, the ultimate effectiveness of therapy is limited by either intrinsic or acquired resistance. Identifying the factors and pathways responsible for sensitivity and resistance remains a challenge in improving the treatment of breast cancer. With a better understanding of coordinated action of ER, its coregulatory factors, and the influence of other intracellular signaling cascades, improvements in breast cancer therapy are emerging.

Ini, a small nuclear protein that enhances the response of the connexin43 gene to estrogen

This article describes the structural and functional characterization of Ini (AF495522), a novel highly conserved zinc-finger protein that had been identified by screening an estrogen-induced rat myometrial expression library. Ini localizes to the nucleus of HeLa cells and binds to the proximal connexin43 (cx43) promoter, as demonstrated by EMSA. In addition, transient transfection experiments performed with estrogen receptor alpha (ERalpha) cDNA show that overexpression of Ini enhances, in a dose-dependent fashion, the up-regulation of the cx43 gene by estrogen. On binding to the cx43 promoter, Ini stimulates the transcriptional activating function (AF)-1, but not the AF-2, of the ERalpha. This makes Ini one of the few known coactivators specific for AF-1. Because estrogen up-regulates Ini mRNA in the myometrium, it is likely that Ini's physiological role in this tissue is to modulate the response of the cx43 gene to estrogen. Transfection studies with an Ini antisense construct seem to indicate that Ini plays an additional role in the cellular response to estrogen affecting both AF-1 and AF-2 activities of the ERalpha. This broader effect may be associated with cell cycle progression that in yeast has been shown to require Ini.

17Beta-estradiol inhibits MCP-1 production in human keratinocytes

A chemokine, monocyte chemoattractant protein 1 (MCP-1), attracts macrophages. The production of MCP-1 is enhanced in keratinocytes of psoriatic lesions, which may contribute to macrophage infiltration into the lesions. It is known that estrogen regulates the course of psoriasis. We examined in vitro effects of 17beta-estradiol (E2) on MCP-1 production by human keratinocytes. E2 inhibited constitutive and 12-O-tetradecanoylphorbol-13-acetate-induced MCP-1 secretion, mRNA expression, and promoter activity in keratinocytes, and these effects of E2 were counteracted by estrogen receptor antagonist ICI 182 780. GC-rich Sp1 element and activator protein 1 (AP-1) element on MCP-1 promoter were required for constitutive and 12-O-tetradecanoylphorbol-13-acetate-induced transcription, respectively, and involved in transrepression by E2. E2 inhibited constitutive Sp1 and 12-O-tetradecanoylphorbol-13-acetate-induced AP-1 transcriptional activities whereas it did not inhibit DNA binding of Sp1 or AP-1 c-Fos/c-Jun. E2 inhibited Sp1 and AP-1 transcriptional activities and MCP-1 promoter activity in estrogen receptor beta (ERbeta) transfected SKBR3 cells. Deletion of the A/B region or mutation of activation function 2 in ERbeta abrogated E2-dependent transcriptional inhibition by ERbeta whereas mutation of DNA-binding domain retained the inhibitory effects. Transfection of ERbeta enhanced the inhibitory effects of E2 on Sp1 and AP-1 transcriptional activities and MCP-1 promoter activities in nontransfected keratinocytes. Coimmunoprecipitation studies showed an E2-dependent association of ERbeta with Sp1 or AP-1 in ERbeta-transfected keratinocytes. These results suggest that E2-bound ERbeta may inhibit MCP-1 gene expression by inhibiting Sp1 and AP-1 transcriptional activities in keratinocytes. A/B region and intact activation function 2 of ERbeta may be responsible for the effects of E2.

Domains of estrogen receptor alpha (ERalpha) required for ERalpha/Sp1-mediated activation of GC-rich promoters by estrogens and antiestrogens in breast cancer cells

Estrogen receptor alpha (ERalpha)/Sp1 activation of GC-rich gene promoters in breast cancer cells is dependent, in part, on activation function 1 (AF1) of ERalpha, and this study investigates contributions of the DNA binding domain (C) and AF2 (DEF) regions of ERalpha on activation of ERalpha/Sp1. 17Beta-estradiol (E2) and the antiestrogens 4-hydroxytamoxifen and ICI 182,780 induced reporter gene activity in MCF-7 and MDA-MB-231 cells cotransfected with human or mouse ERalpha (hERalpha or MOR), but not ERbeta and GC-rich constructs containing three tandem Sp1 binding sites (pSp13) or other E2-responsive GC-rich promoters. Estrogen and antiestrogen activation of hERalpha/Sp1 was dependent on overlapping and different regions of the C, D, E, and F domains of ERalpha. Antiestrogen-induced activation of hERalpha/Sp1 was lost using hERalpha mutants deleted in zinc finger 1 [amino acids (aa) 185-205], zinc finger 2 (aa 218-245), and the hinge/helix 1 (aa 265-330) domains. In contrast with antiestrogens, E2-dependent activation of hERalpha/Sp1 required the C-terminal F domain (aa 579-595), which contains a beta-strand structural motif. Moreover, in peptide competition experiments overexpression of a C-terminal (aa 575-595) F domain peptide specifically blocked E2-dependent activation of hERalpha/Sp1, suggesting that F domain interactions with nuclear cofactors are required for ERalpha/Sp1 action.

Estrogen up-regulation of p53 gene expression in MCF-7 breast cancer cells is mediated by calmodulin kinase IV-dependent activation of a nuclear factor kappaB/CCAAT-binding transcription factor-1 complex

This study investigates the mechanism of hormonal regulation of p53 gene expression in MCF-7 human breast cancer cells. 17beta-Estradiol (E2) induced a 2-fold increase in p53 mRNA levels and a 2- to 3-fold increase in p53 protein. Analysis of the p53 gene promoter has identified a minimal E2-responsive region at -106 to -40, and mutation/deletion analysis of the promoter showed that motifs that bind CCAAT-binding transcription factor-1 (CTF-1) and nuclear factor kappaB (NFkappaB) proteins are required for hormone responsiveness. The p65 subunit of NFkappaB was identified in both nuclear and cytosolic fractions of untreated MCF-7 cells; however, formation of the nuclear NFkappaB complex was E2 independent. Hormonal activation of constructs containing p53 promoter inserts (-106 to -40) and the GAL4-p65 fusion proteins was inhibited by the intracellular Ca2+ ion chelator EGTA-AM and Ca2+/calmodulin-dependent protein kinase (CaMK) inhibitor KN-93. Constitutively active CaMKIV but not CaMKI activated p65, and treatment of MCF-7 cells with E2 induced phosphorylation of CaMKIV but not CaMKI. The results indicate that hormonal activation of p53 though nongenomic pathways was CaMKIV-dependent and involved cooperative p65-CTF-1 interactions.