REST: a mammalian silencer protein that restricts sodium channel gene expression to neurons

Specification of skeletal muscle differentiation by repressor element-1 silencing transcription factor (REST)-regulated Kv7.4 potassium channels

K_v7.4-potassium channel expression plays a permissive role in skeletal muscle differentiation. The transcriptional repressor REST controls the changes in K_v7.4 levels during myogenesis by binding to regulatory regions in the K_v7.4 gene. This mechanism may be a target for intervention against abnormal repair and differentiation of skeletal muscle.

Changes in the expression of potassium (K⁺) channels is a pivotal event during skeletal muscle differentiation. In mouse C₂C₁₂ cells, similarly to human skeletal muscle cells, myotube formation increased the expression of K_v7.1, K_v7.3, and K_v7.4, the last showing the highest degree of regulation. In C₂C₁₂ cells, K_v7.4 silencing by RNA interference reduced the expression levels of differentiation markers (myogenin, myosin heavy chain, troponinT-1, and Pax3) and impaired myotube formation and multinucleation. In K_v7.4-silenced cells, the differentiation-promoting effect of the K_v7 activator N-(2-amino-4-(4-fluorobenzylamino)-phenyl)-carbamic acid ethyl ester (retigabine) was abrogated. Expression levels for the repressor element-1 silencing transcription factor (REST) declined during myotube formation. Transcript levels for K_v7.4, as well as for myogenin, troponinT-1, and Pax3, were reduced by REST overexpression and enhanced upon REST suppression by RNA interference. Four regions containing potential REST-binding sites in the 5′ untranslated region and in the first intron of the K_v7.4 gene were identified by bioinformatic analysis. Chromatin immunoprecipitation assays showed that REST binds to these regions, exhibiting a higher efficiency in myoblasts than in myotubes. These data suggest that K_v7.4 plays a permissive role in skeletal muscle differentiation and highlight REST as a crucial transcriptional regulator for this K⁺ channel subunit.

A REST derived gene signature stratifies glioblastomas into chemotherapy resistant and responsive disease

Background

Glioblastomas are the most common central nervous system neoplasia in adults, with 9,000 cases in the US annually. Glioblastoma multiformae, the most aggressive glioma subtype, has an 18% one-year survival rate, and 3% two year survival rate. Recent work has highlighted the role of the transcription factor RE1 Silencing Transcription Factor, REST in glioblastoma but how REST function correlates with disease outcome has not been described.

Method

Using a bioinformatic approach and mining of publicly available microarray datasets, we describe an aggressive subtype of gliomas defined by a gene signature derived from REST. Using this REST gene signature we predict that REST function is enhanced in advanced glioblastoma. We compare disease outcomes between tumors based on REST status and treatment regimen, and describe downstream targets of REST that may contribute to the decreased benefits observed with high dose chemotherapy in REM tumors.

Results

We present human data showing that patients with “REST Enhanced Malignancies” (REM) tumors present with a shorter disease free survival compared to non-REM gliomas. Importantly, REM tumors are refractory to multiple rounds of chemotherapy and patients fail to respond to this line of treatment.

Conclusions

This report is the first to describe a REST gene signature that predicts response to multiple rounds of chemotherapy, the mainline therapy for this disease. The REST gene signature may have important clinical implications for the treatment of glioblastoma.

Silencer-delimited transgenesis: NRSE/RE1 sequences promote neural-specific transgene expression in a NRSF/REST-dependent manner

BACKGROUND

We have investigated a simple strategy for enhancing transgene expression specificity by leveraging genetic silencer elements. The approach serves to restrict transgene expression to a tissue of interest - the nervous system in the example provided here - thereby promoting specific/exclusive targeting of discrete cellular subtypes. Recent innovations are bringing us closer to understanding how the brain is organized, how neural circuits function, and how neurons can be regenerated. Fluorescent proteins enable mapping of the 'connectome', optogenetic tools allow excitable cells to be short-circuited or hyperactivated, and targeted ablation of neuronal subtypes facilitates investigations of circuit function and neuronal regeneration. Optimally, such toolsets need to be expressed solely within the cell types of interest as off-site expression makes establishing causal relationships difficult. To address this, we have exploited a gene 'silencing' system that promotes neuronal specificity by repressing expression in non-neural tissues. This methodology solves non-specific background issues that plague large-scale enhancer trap efforts and may provide a means of leveraging promoters/enhancers that otherwise express too broadly to be of value for in vivo manipulations.

RESULTS

We show that a conserved neuron-restrictive silencer element (NRSE) can function to restrict transgene expression to the nervous system. The neuron-restrictive silencing factor/repressor element 1 silencing transcription factor (NRSF/REST) transcriptional repressor binds NRSE/repressor element 1 (RE1) sites and silences gene expression in non-neuronal cells. Inserting NRSE sites into transgenes strongly biased expression to neural tissues. NRSE sequences were effective in restricting expression of bipartite Gal4-based 'driver' transgenes within the context of an enhancer trap and when associated with a defined promoter and enhancer. However, NRSE sequences did not serve to restrict expression of an upstream activating sequence (UAS)-based reporter/effector transgene when associated solely with the UAS element. Morpholino knockdown assays showed that NRSF/REST expression is required for NRSE-based transgene silencing.

CONCLUSIONS

Our findings demonstrate that the addition of NRSE sequences to transgenes can provide useful new tools for functional studies of the nervous system. However, the general approach may be more broadly applicable; tissue-specific silencer elements are operable in tissues other than the nervous system, suggesting this approach can be similarly applied to other paradigms. Thus, creating synthetic associations between endogenous regulatory elements and tissue-specific silencers may facilitate targeting of cellular subtypes for which defined promoters/enhancers are lacking.

Microcephaly gene links trithorax and REST/NRSF to control neural stem cell proliferation and differentiation

Microcephaly is a neurodevelopmental disorder causing significantly reduced cerebral cortex size. Many known microcephaly gene products localize to centrosomes, regulating cell fate and proliferation. Here, we identify and characterize a nuclear zinc finger protein, ZNF335/NIF-1, as a causative gene for severe microcephaly, small somatic size, and neonatal death. Znf335 null mice are embryonically lethal, and conditional knockout leads to severely reduced cortical size. RNA-interference and postmortem human studies show that ZNF335 is essential for neural progenitor self-renewal, neurogenesis, and neuronal differentiation. ZNF335 is a component of a vertebrate-specific, trithorax H3K4-methylation complex, directly regulating REST/NRSF, a master regulator of neural gene expression and cell fate, as well as other essential neural-specific genes. Our results reveal ZNF335 as an essential link between H3K4 complexes and REST/NRSF and provide the first direct genetic evidence that this pathway regulates human neurogenesis and neuronal differentiation.

Neuron-restrictive silencer factor functions to suppress Sp1-mediated transactivation of human secretin receptor gene

In the present study, a functional neuron restrictive silencer element (NRSE) was initially identified in the 5' flanking region (-83 to -67, relative to ATG) of human secretin receptor (hSCTR) gene by promoter assays coupled with scanning mutation analyses. The interaction of neuron restrictive silencer factor (NRSF) with this motif was later indicated via gel mobility shift and ChIP assays. The silencing activity of NRSF was confirmed by over-expression and also by shRNA knock-down of endogenous NRSF. These studies showed an inverse relationship between the expression levels of NRSF and hSCTR in the cells. As hSCTR gene was previously shown to be controlled by two GC-boxes which are regulated by the ratio of Sp1 to Sp3, in the present study, the functional interactions of NRSF and Sp proteins to regulate hSCTR gene was investigated. By co-immunoprecipitation assays, we found that NRSF could be co-precipitated with Sp1 as well as Sp3 in PANC-1 cells. Interestingly, co-expressions of these factors showed that NRSF could suppress Sp1-mediated, but not Sp3-mediated, transactivation of hSCTR. Taken together, we propose here that the down-regulatory effects of NRSF on hSCTR gene expression are mediated via its suppression on Sp1-mediated transactivation.

Differential promoter methylation and histone modification contribute to the brain specific expression of the mouse Mbu-1 gene

Mbu-1 (Csrnp-3) is a mouse gene that was identified in our previous study as showing highly restricted expression to the central nervous system. In this study, to elucidate the regulatory mechanism for tissue specificity of the gene, epigenetic approaches that identify the profiles of CpG methylation, as well as histone modifications at the promoter region were conducted. Methylation-specific PCR revealed that the CpG sites in brain tissues from embryo to adult stages showed virtually no methylation (0.052-0.67%). Lung (9.0%) and pancreas (3.0%) also showed lower levels. Other tissues such as liver, kidney, and heart showed much higher methylation levels ranging from approximately 39-93%. Treatment of 5-aza-2'-deoxycytidine (5-Aza-dC) significantly decreased promoter methylation, reactivating Mbu-1 expression in NG108-15 and Neuro-2a neuronal cells. Chromatin immunoprecipitation assay revealed that 5-Aza-dC decreased levels of acetylated H3K9 and methylated H3K4, and increased methylated H3K9. This result indicates that CpG methylation converses with histone modifications in an opposing sense of regulating Mbu-1 expression.

Stem cell maintenance in the adult mammalian hippocampus: a matter of signal integration?

The continuous generation of new neurons from stem cells in the hippocampal dentate gyrus is considered an important contributor to hippocampal plasticity. A prerequisite for the life-long generation of new dentate granule neurons is the maintenance of the neural stem cell pool. A number of essential molecular regulators and signals for hippocampal neural stem cell maintenance have been identified, but how these pathways interact to prevent precocious differentiation or exhaustion of the stem cell pool is currently unknown. Here, we summarize the current knowledge on the molecular regulation of the hippocampal stem cell pool and discuss the possibility that signal integration through Notch signaling controls stem cell maintenance in the adult hippocampus.

Specific silencing of the REST target genes in insulin-secreting cells uncovers their participation in beta cell survival

The absence of the transcriptional repressor RE-1 Silencing Transcription Factor (REST) in insulin-secreting beta cells is a major cue for the specific expression of a large number of genes. These REST target genes were largely ascribed to a function of neurotransmission in a neuronal context, whereas their role in pancreatic beta cells has been poorly explored. To identify their functional significance, we have generated transgenic mice expressing REST in beta cells (RIP-REST mice), and previously discovered that REST target genes are essential to insulin exocytosis. Herein we characterized a novel line of RIP-REST mice featuring diabetes. In diabetic RIP-REST mice, high levels of REST were associated with postnatal beta cell apoptosis, which resulted in gradual beta cell loss and sustained hyperglycemia in adults. Moreover, adenoviral REST transduction in INS-1E cells led to increased cell death under control conditions, and sensitized cells to death induced by cytokines. Screening for REST target genes identified several anti-apoptotic genes bearing the binding motif RE-1 that were downregulated upon REST expression in INS-1E cells, including Gjd2, Mapk8ip1, Irs2, Ptprn, and Cdk5r2. Decreased levels of Cdk5r2 in beta cells of RIP-REST mice further confirmed that it is controlled by REST, in vivo. Using siRNA-mediated knock-down in INS-1E cells, we showed that Cdk5r2 protects beta cells against cytokines and palmitate-induced apoptosis. Together, these data document that a set of REST target genes, including Cdk5r2, is important for beta cell survival.

Zebrafish rest regulates developmental gene expression but not neurogenesis

The transcriptional repressor Rest (Nrsf) recruits chromatin-modifying complexes to RE1 'silencer elements', which are associated with hundreds of neural genes. However, the requirement for Rest-mediated transcriptional regulation of embryonic development and cell fate is poorly understood. Conflicting views of the role of Rest in controlling cell fate have emerged from recent studies. To address these controversies, we examined the developmental requirement for Rest in zebrafish using zinc-finger nuclease-mediated gene targeting. We discovered that germ layer specification progresses normally in rest mutants despite derepression of target genes during embryogenesis. This analysis provides the first evidence that maternal rest is essential for repression of target genes during blastula stages. Surprisingly, neurogenesis proceeds largely normally in rest mutants, although abnormalities are observed within the nervous system, including defects in oligodendrocyte precursor cell development and a partial loss of facial branchiomotor neuron migration. Mutants progress normally through embryogenesis but many die as larvae (after 12 days). However, some homozygotes reach adulthood and are viable. We utilized an RE1/NRSE transgenic reporter system to dynamically monitor Rest activity. This analysis revealed that Rest is required to repress gene expression in mesodermal derivatives including muscle and notochord, as well as within the nervous system. Finally, we demonstrated that Rest is required for long-term repression of target genes in non-neural tissues in adult zebrafish. Our results point to a broad role for Rest in fine-tuning neural gene expression, rather than as a widespread regulator of neurogenesis or cell fate.

Polyglutamine (polyQ) disorders: the chromatin connection

Polyglutamine (PolyQ)-related diseases are dominant late-onset genetic disorders that are manifested by progressive neurodegeneration, leading to behavioral and physical impairments. An increased body of evidence suggests that chromatin structure and epigenetic regulation are involved in disease pathology. PolyQ diseases often display an aberrant transcriptional regulation due to the disrupted function of histone-modifying complexes and altered interactions of the polyQ-extended proteins with chromatin-related factors. In this review we describe recent findings relating to the role of chromatin in polyQ diseases. We discuss the involvement of epigenetic-related factors and chromatin structure in genomic instability of CAG repeats; we describe changes in the expression and regulation of chromatin-related enzymes and in the levels and patterns of histone modifications in disease state; we illustrate the potential beneficial effects of different histone deacetylase (HDAC) inhibitors for the treatment of polyQ diseases, and we end by describing the potential use of human pluripotent stem cells and their differentiated derivatives for modeling polyQ diseases in vitro. Taken together, these accumulating studies strongly suggest that disrupted chromatin regulation may be directly involved with the pathophysiology of polyQ-related diseases.

Yeast one-hybrid assays: a historical and technical perspective

Since its development about two decades ago, the yeast one-hybrid (Y1H) assay has become an important technique for detecting physical interactions between sequence-specific regulatory transcription factor proteins (TFs) and their DNA target sites. Multiple versions of the Y1H methodology have been developed, each with technical differences and unique advantages. We will discuss several of these technical variations in detail, and also provide some ideas for how Y1H assays can be further improved.

REST is a novel prognostic factor and therapeutic target for medulloblastoma

Medulloblastoma is a malignant pediatric brain tumor. Current treatment following patient stratification into standard and high-risk groups using clinical features has improved survival. However, a subset of patients with standard risk features have unanticipated aggressive disease, underscoring the need for a better understanding of tumor biology and the development of novel treatments. Poor differentiation, a hallmark of medulloblastomas is associated with elevated expression levels of the repressor of neuronal differentiation called repressor element 1-silencing transcription factor (REST). Here, we assessed whether elevated REST expression levels had prognostic significance and whether its pharmacologic manipulation would promote neurogenesis and block tumor cell growth. REST levels in patient tumors were measured by immunohistochemistry and stratified into negative, low/moderate- (+/++/+++), and high-REST (+++++) groups. Kaplan-Meier curves revealed that patients with high-REST tumors had worse overall and event-free survival compared with patients with REST-negative or REST-low tumors. Because histone deacetylases (HDAC) are required for REST-dependent repression of neurogenesis, we evaluated a panel of HDAC inhibitors (HDACI) for their effects on growth and differentiation of established and primary REST-positive cell lines. MS-275, trichostatin-A (TSA), valproic acid (VPA), and suberoylanilide hydroxamic acid (SAHA) upregulated expression of the REST-target neuronal differentiation gene, Syn1, suggesting a potential effect of these HDACIs on REST function. Interestingly, VPA and TSA substantially increased histone acetylation at the REST promoter and activated its transcription, whereas SAHA unexpectedly promoted its proteasomal degradation. A REST-dependent decrease in cell growth was also observed following SAHA treatment. Thus, our studies suggest that HDACIs may have therapeutic potential for patients with REST-positive tumors. This warrants further investigation.

REST regulates the pool size of the different neural lineages by restricting the generation of neurons and oligodendrocytes from neural stem/progenitor cells

REST is a master repressor of neuronal genes; however, whether it has any role during nervous system development remains largely unknown. Here, we analyzed systematically the role of REST in embryonic stem cells and multipotent neural stem/progenitor (NS/P) cells, including neurogenic and gliogenic NS/P cells derived from embryonic stem (ES) cells or developing mouse embryos. We showed that REST-null ES cells remained pluripotent and generated teratomas consisting of the three germ layers. By contrast, multipotent NS/P cells lacking REST displayed significantly reduced self-renewal capacity owing to reduced cell cycle kinetics and precocious neuronal differentiation. Importantly, although early-born neurogenic NS/P cells that lack REST were capable of differentiating to neurons and glia, the neuronal and oligodendrocytic pools were significantly enlarged and the astrocytic pool was shrunken. However, gliogenic NS/P cells lacking REST were able to generate a normal astrocytic pool size, suggesting that the shrinkage of the astrocytic pool generated from neurogenic NS/P cells lacking REST probably occurs by default. Microarray profiling of early-born NS/P cells lacking REST showed upregulation of neuronal as well as oligodendrocytic genes, specifically those involved in myelination. Furthermore, chromatin immunoprecipitation analyses showed that some of the upregulated oligodendrocytic genes contain an RE1 motif and are direct REST targets. Together, our data support a central role for REST during neural development in promoting NS/P cell self-renewal while restricting the generation and maturation of neurons and oligodendrocytes.

Regulation of mGluR1 expression in human melanocytes and melanoma cells

We demonstrated that ectopic expression of metabotropic glutamate receptor 1 (mGluR1/Grm1) in mouse melanocytes was sufficient to induce melanoma development in vivo with 100% penetrance. We also showed that about 60% of human melanoma biopsies and cell lines, but not benign nevi or normal human melanocytes expressed mGluR1, suggesting that GRM1 may be involved in melanomagenesis. mGluR1 is expressed primarily in neurons. In various non-neuronal cells, mGluR1 expression is regulated via binding of Neuron-Restrictive-Silencer-Factor (NRSF) to a Neuron-Restrictive-Silencer-Element (NRSE). Here, we report on the possibility that aberrant mGluR1 expression in melanoma is due to alterations in NRSF and/or NRSE. We show that in human melanocytes, binding of NRSF to NRSE in the GRM1 promoter region is necessary for the suppression of mGluR1 expression. We also show that inhibiting the expression of the transcription factor Sp1 or interference with its ability to bind DNA can result in increased mGluR1 expression perhaps via its function as a negative regulator. In addition, we also provide evidence that demethylation within the promoter region of GRM1 may also be a mechanism for the derepression of mGluR1 expression in melanocytes that progress to cell transformation and tumor formation.

Binding of hnRNP H and U2AF65 to respective G-codes and a poly-uridine tract collaborate in the N50-5'ss selection of the REST N exon in H69 cells

The splicing of the N exon in the pre-mRNA coding for the RE1-silencing transcription factor (REST) results in a truncated protein that modifies the expression pattern of some of its target genes. A weak 3'ss, three alternative 5'ss (N4-, N50-, and N62-5'ss) and a variety of putative target sites for splicing regulatory proteins are found around the N exon; two GGGG codes (G2-G3) and a poly-Uridine tract (N-PU) are found in front of the N50-5'ss. In this work we analyzed some of the regulatory factors and elements involved in the preferred selection of the N50-5'ss (N50 activation) in the small cell lung cancer cell line H69. Wild type and mutant N exon/β-globin minigenes recapitulated N50 exon splicing in H69 cells, and showed that the N-PU and the G2-G3 elements are required for N50 exon splicing. Biochemical and knockdown experiments identified these elements as U2AF65 and hnRNP H targets, respectively, and that they are also required for N50 exon activation. Compared to normal MRC5 cells, and in keeping with N50 exon activation, U2AF65, hnRNP H and other splicing factors were highly expressed in H69 cells. CLIP experiments revealed that hnRNP H RNA-binding occurs first and is a prerequisite for U2AF65 RNA binding, and EMSA and CLIP experiments suggest that U2AF65-RNA recognition displaces hnRNP H and helps to recruit other splicing factors (at least U1 70K) to the N50-5'ss. Our results evidenced novel hnRNP H and U2AF65 functions: respectively, U2AF65-recruiting to a 5'ss in humans and the hnRNP H-displacing function from two juxtaposed GGGG codes.

Directing neuronal differentiation of primary neural progenitor cells by gene knockdown approach

Directing differentiation of neural stem/progenitor cells (NPCs) to produce functional neurons is a promising remedy for neural pathological conditions. The major challenge, however, lies in the effective and efficient generation of a sizable population of neurons. A potential strategy is to incorporate RNA interference (RNAi) during directed stem cell differentiation to recapitulate the complex cell-signaling cascades that often occurs during the process. In this study, in vitro silencing of RE1-silencing transcription factor (REST) was carried out using small-interfering RNAs (siRNAs) to evaluate the efficacy of combining REST knockdown with conventional differentiation approaches to enhance neurogenesis. While earlier studies have demonstrated enhanced neuronal lineage commitment from embryonic stem cells and mesenchymal stem cells upon REST knockdown, the effects of REST silencing during other stages of neural development have not been extensively evaluated. We hypothesize that REST knockdown would enhance NPC development to mature neurons and that induced REST silencing can serve as a potential biochemical approach to direct cell fate. Under nonspecific induction conditions, REST knockdown induced eightfold higher Tuj1 mRNA expression at day 14 compared with untransfected cells and cells subjected to scrambled-siRNA treatment (controls). Immunostaining also revealed greater percentage of Tuj1 positive cells with REST knockdown. Combined with neuronal induction, REST silencing enhanced the kinetics of neuronal differentiation and the rate of maturation of committed neuronal cells. Specifically, upregulation of MAP2 occurred as early as 3 days after induction with REST silencing and the expression was comparable to the controls at day 14. Likewise, downregulation of REST generated more than twice the percentage of Tuj1 and MAP2 positive cells compared with controls at day 5 (p<0.05). Morphologically, REST-silencing enhanced the number and length of neurite extensions from Tuj1 positive cells (p<0.05), which was not evaluated in previous differentiation studies with REST knockdown. Taken together, these results demonstrate the efficacy of combining REST silencing during directed NPC differentiation to enhance the rate of differentiation and subsequent maturation of NPCs. This study also highlights the potential of RNAi as a biomedical strategy for guided stem cell differentiation.

REST controls self-renewal and tumorigenic competence of human glioblastoma cells

The Repressor Element 1 Silencing Transcription factor (REST/NRSF) is a master repressor of neuronal programs in non-neuronal lineages shown to function as a central regulator of developmental programs and stem cell physiology. Aberrant REST function has been associated with a number of pathological conditions. In cancer biology, REST has been shown to play a tumor suppressor activity in epithelial cancers but an oncogenic role in brain childhood malignancies such as neuroblastoma and medulloblastoma. Here we examined REST expression in human glioblastoma multiforme (GBM) specimens and its role in GBM cells carrying self-renewal and tumorigenic competence. We found REST to be expressed in GBM specimens, its presence being particularly enriched in tumor cells in the perivascular compartment. Significantly, REST is highly expressed in self-renewing tumorigenic-competent GBM cells and its knock down strongly reduces their self-renewal in vitro and tumor-initiating capacity in vivo and affects levels of miR-124 and its downstream targets. These results indicate that REST contributes to GBM maintenance by affecting its self-renewing and tumorigenic cellular component and that, hence, a better understanding of these circuitries in these cells might lead to new exploitable therapeutic targets.

The genetic and epigenetic journey of embryonic stem cells into mature neural cells

Epigenetic changes occur throughout life from embryonic development into adulthood. This results in the timely expression of developmentally important genes, determining the morphology and identity of different cell types and tissues within the body. Epigenetics regulate gene expression and cellular morphology through multiple mechanisms without alteration in the underlying DNA sequences. Different epigenetic mechanisms include chromatin condensation, post-translational modification of histone proteins, DNA cytosine marks, and the activity of non-coding RNA molecules. Epigenetics play key roles in development, stem cell differentiation, and have high impact in human disease. In this review, we will discuss our current knowledge about these epigenetic mechanisms, with a focus on histone and DNA marks. We will then talk about the genetics and epigenetics of embryonic stem cell self-renewal and differentiation into neural stem cells, and further into specific neuronal cell types.

Ubiquitination and deubiquitination of REST and its roles in cancers

REST/NRSF (the RE-1 silencing transcription factor or neuron-restrictive silencer factor) was originally identified as a transcriptional repressor of a number of neuronal-specific genes in neural stem cells and non-neuronal cells. REST functions as a master regulator in the maintenance of neural stem cells. During tumorigenesis, REST shows opposing roles in different type of cells. In human epithelial cancers such as colon cancer, REST acts as a tumor suppressor. In contrast, REST plays an oncogenic role in the development of brain tumors and other cancers. Abnormal upregulation of REST has been found in medulloblastoma, neuroblastoma and glioblastoma (GBM). Recent studies in GBMs suggest that REST exerts its oncogenic function by maintaining self-renewal potential of glioma stem cells (GSCs).

NRSF/REST is required for gastrulation and neurogenesis during zebrafish development

Repressor element 1-silencing transcription factor (REST) was recognized as a transcription suppressor regulating nervous system differentiation. However, the role of REST during early development has not been clarified. We cloned the zebrafish homolog of human REST. Real-time polymerase chain reaction results showed that zebrafish REST mRNA was both maternal and zygotic with the higher expression level from blastula to the late segmentation period. Whole-mount in situ hybridization showed that REST was strongly expressed in the blastoderm since dome stage and dynamically expressed mainly in developing brain, especially in the border of the brain subdivisions in early segmentation period. Knockdown of REST using translation blocking morpholino (MO-tra) technique resulted in gastrulation delay or even blockage, and subsequently led to embryo lethality by early segmentation period with deficient neurogenesis. However, splicing blocking morpholino for REST did not show obviously abnormal phenotype until 48 hpf (hours post-fertilization), indicating that maternal REST was an important regulator for gastrulation. Further study revealed that the abnormal development in MO-tra morphants was at least partly due to the dysfunction of protein transportation from the yolk to the blastoderm. Our results showed that REST (especially maternal supplied REST) was required for gastrulation and neurogenesis during zebrafish early embryogenesis.

The joint association of REST and NFKB1 polymorphisms on the risk of colorectal cancer

Due to the high morbidity and mortality of colorectal cancer (CRC), this study aims to determine the joint association of RE-1-silencing transcription factor (REST) and nuclear factor-κB 1 (NFKB1) genes with CRC in a population-based study. A well-matched case-control study including 390 controls and 388 patients with CRC was enrolled in China. The selected single nucleotide polymorphisms (SNPs) in the REST and NFKB1 genes were genotyped by Illumina SnapShot Chip. After adjustment for important covariates, the associations of SNPs and joint association of REST and NFKB1 with CRC were evaluated by multiple logistic regression models. The subjects with the rs2228991 AA genotype of the REST gene had a decreased risk for CRC (OR = 0.38; 95%CI: 0.19-0.74), compared with the GG genotype. There were no significant associations between three SNPs in the NFKB1 gene, their haplotype and CRC risk. However, a significant combined effect of rs3774959 and rs3774964 in the NFKB1 gene with rs2228991 in the REST gene on CRC risk was observed. In conclusion, the present study found that mutation in the REST gene rather than the NFKB1 gene was associated with the risk of CRC. Furthermore, significant REST-NFKB1 joint association was observed for CRC, colon cancer and rectal cancer risk.

Induction of the RNA regulator LIN28A is required for the growth and pathogenesis of RESTless breast tumors

The transcription factor RE1 silencing transcription factor (REST) is lost in approximately 20% of breast cancers. Although it is known that these RESTless tumors are highly aggressive and include all tumor subtypes, the underlying tumorigenic mechanisms remain unknown. In this study, we show that loss of REST results in upregulation of LIN28A, a known promoter of tumor development, in breast cancer cell lines and human breast tumors. We found that LIN28A was a direct transcriptional target of REST in cancer cells and that loss of REST resulted in increased LIN28A expression and enhanced tumor growth both in vitro and in vivo, effects that were dependent on heightened LIN28A expression. Tumors lacking REST expression were locally invasive, consistent with the increased lymph node involvement observed in human RESTless tumors. Clinically, human RESTless breast tumors also displayed significantly enhanced LIN28A expression when compared with non-RESTless tumors. Our findings therefore show a critical role for the REST-LIN28A axis in tumor aggression and suggest a causative relationship between REST loss and tumorigenicity in vivo.

REST: transcriptional and epigenetic regulator

Acquisition and maintenance of cell fate and potential are dependent on the complex interplay of extracellular signaling, gene regulatory networks and epigenetic states. During embryonic development, embryonic stem cells become progressively more restricted along specific lineages, ultimately giving rise to the diversity of cell types in the adult mammalian organism. Recent years have seen major advances in our understanding of the mechanisms that regulate the underlying transcriptional programmes during development. In particular, there has been a significant increase in our knowledge of how epigenetic marks on chromatin can regulate transcription by generating more or less permissive chromatin conformations. This article focuses on how a single transcription factor, repressor element-1 silencing transcription factor, can function as both a transcriptional and epigenetic regulator, controlling diverse aspects of development. We will discuss how the elucidation of repressor element-1 silencing transcription factor function in both normal and disease conditions has provided valuable insights into how the epigenome and transcriptional regulators might cooperatively orchestrate correct development.

Regulation of gene expression during early neuronal differentiation: evidence for patterns conserved across neuron populations and vertebrate classes

Analysis of transcription factor function during neurogenesis has provided a huge amount of data on the generation and specification of diverse neuron populations in the central and peripheral nervous systems of vertebrates. However, an understanding of the induction of key neuron functions including electrical information processing and synaptic transmission lags seriously behind. Whereas pan-neuronal markers such as neurofilaments, neuron-specific tubulin and RNA-binding proteins have often been included in developmental analysis, the molecular players underlying electrical activity and transmitter release have been neglected in studies addressing gene expression during neuronal induction. Here, I summarize the evidence for a distinct accumulation pattern of mRNAs for synaptic proteins, a pattern that is delayed compared with pan-neuronal gene expression during neurogenesis. The conservation of this pattern across diverse avian and mammalian neuron populations suggests a common mechanism for the regulation of various sets of neuronal genes during initial neuronal differentiation. The co-regulation of genes coding for synaptic proteins from embryonic to postnatal development indicates that the expression of the players required for synaptic transmission shares common regulatory features. For the ion channels involved in neuronal electrical activity, such as voltage-gated sodium channels, the situation is less clear because of the lack of comparative studies early during neurogenesis. Transcription factors have been characterized that regulate the expression of synaptic proteins in vitro and in vivo. They currently do not explain the co-regulation of these genes across different neuron populations. The neuron-restrictive silencing factor NRSF/REST targets a large gene set, but not all of the genes coding for pan-neuronal, synaptic and ion channel proteins. The discrepancy between NRSF/REST loss-of-function and silencer-to-activator-switch studies leaves the full functional implications of this factor open. Together with microRNAs, splicing regulators, chromatin remodellers and an increasing list of transcriptional regulators, the factor is embedded in feedback circuits with the potential to orchestrate neuronal differentiation. The precise regulation of the coordinated expression of proteins underlying key neuronal functions by these circuits during neuronal induction is a major emerging topic.

Transformation by E1A oncoprotein involves ubiquitin-mediated proteolysis of the neuronal and tumor repressor REST in the nucleus

The adenovirus early region 1A (E1A) protein promotes cell immortalization and transformation by mediating the activities of key cellular regulators. The repressor element 1-silencing transcription factor (REST), which is a major neuronal and tumor suppressor, was previously found mainly in the cytoplasm rather than in the nuclei of adenovirus-transformed rodent cells (22). We now demonstrate that the loss of REST in the nucleus is due to its rapid degradation by the ubiquitin-proteasome system. Only nuclear REST, but not its cytoplasmic counterpart, was ubiquitinated and degraded. REST degradation was blocked by the ubiquitination inhibitor PYR-41 and the proteasome inhibitor MG-132 but not by the nuclear export inhibitor leptomycin B. REST degradation required both of its two C-terminal degrons that are recognized by the ubiquitin ligase SCF(β-TrCP), since deletion or mutation of either degron eliminated degradation. Importantly, E1A was shown to mediate REST ubiquitination and degradation by upregulating β-TrCP. Knockdown of E1A in virus-transformed cells reduced both β-TrCP and ubiquitination of nuclear REST. In contrast, when expressed in HeLa cells, E1A enhanced the degradation of nuclear REST. Reconstitution of REST in virus-transformed cells negatively affected E1A-mediated cell proliferation and anchorage-independent growth. These data strongly indicate that E1A stimulates ubiquitination and proteolysis of REST in the nucleus, thereby abolishing the tumor suppressor functions of REST.

Intronic miR-26b controls neuronal differentiation by repressing its host transcript, ctdsp2

Differentiation of neural stem cells (NSCs) to neurons requires the activation of genes controlled by the repressor element 1 (RE1) silencing transcription factor (REST)/neuron-restrictive silencer factor (NRSF) protein complex. Important components of REST/NRSF are phosphatases (termed RNA polymerase II C-terminal domain small phosphatases [CTDSPs]) that inhibit RNA polymerase II and suppress neuronal gene expression in NSCs. Activation of genes controlled by CTDSPs is required for neurogenesis, but how this is achieved is not fully understood. Here we show that ctdsp2 is a target of miR-26b, a microRNA that is encoded in an intron of the ctdsp2 primary transcript. This intrinsic negative feedback loop is inactive in NSCs because miR-26b biogenesis is inhibited at the precursor level. Generation of mature miR-26b is activated during neurogenesis, where it suppresses Ctdsp2 protein expression and is required for neuronal cell differentiation in vivo.

Dual transcriptional activator and repressor roles of TBX20 regulate adult cardiac structure and function

The ongoing requirement in adult heart for transcription factors with key roles in cardiac development is not well understood. We recently demonstrated that TBX20, a transcriptional regulator required for cardiac development, has key roles in the maintenance of functional and structural phenotypes in adult mouse heart. Conditional ablation of Tbx20 in adult cardiomyocytes leads to a rapid onset and progression of heart failure, with prominent conduction and contractility phenotypes that lead to death. Here we describe a more comprehensive molecular characterization of the functions of TBX20 in adult mouse heart. Coupling genome-wide chromatin immunoprecipitation and transcriptome analyses (RNA-Seq), we identified a subset of genes that change expression in Tbx20 adult cardiomyocyte-specific knockout hearts which are direct downstream targets of TBX20. This analysis revealed a dual role for TBX20 as both a transcriptional activator and a repressor, and that each of these functions regulates genes with very specialized and distinct molecular roles. We also show how TBX20 binds to its targets genome-wide in a context-dependent manner, using various cohorts of co-factors to either promote or repress distinct genetic programs within adult heart. Our integrative approach has uncovered several novel aspects of TBX20 and T-box protein function within adult heart. Sequencing data accession number (http://www.ncbi.nlm.nih.gov/geo): GSE30943.

Overexpression of either lysine-specific demethylase-1 or CLOCK, but not Co-Rest, improves long-term expression from a modified neurofilament promoter, in a helper virus-free HSV-1 vector system

Long-term expression from helper virus-free Herpes Simplex Virus (HSV-1) vectors is required for many specific neural gene therapies and studies on neuronal physiology. We previously developed a promoter that supports long-term, neuron-specific expression by fusing the chicken ß-globin insulator (INS), followed by an upstream enhancer from the rat tyrosine hydroxylase (TH) promoter, to a neurofilament heavy gene (NFH) promoter. Here, we examined the capability of specific transcription factors to further improve long-term expression from this promoter. Following a HSV-1 virus infection, the virus genome is localized to promyelocytic leukemia protein (PML) nuclear bodies (NB). At these sites, specific cellular transcription factors interact with HSV-1 encoded transcription factors, and together regulate HSV-1 gene expression. Importantly, lysine-specific demethylase-1 (LSD1), CLOCK, and Co-Rest each activate HSV-1 gene expression. However, gene expression from HSV-1 vectors differs in a number of important aspects from the virus, including no HSV-1 genes are expressed. Nonetheless, these observations raise the possibility that specific transcription factors may improve long-term expression from specific promoters in HSV-1 vectors. Here, we show that overexpression of either LSD1 or CLOCK improves long-term expression from the INS-TH-NFH promoter, but overexpression of Co-Rest supports levels of long-term expression similar to those supported by a control vector. Further, overexpression of LSD1 is compatible with neuron-specific expression. Thus, overexpressing specific transcription factors can improve long-term expression from specific cellular promoters in HSV-1 vectors, and the chromatin structure of the vector has an important role in enabling expression.

Genetic ablation of Rest leads to in vitro-specific derepression of neuronal genes during neurogenesis

Rest (RE1-silencing transcription factor, also called Nrsf) is involved in the maintenance of the undifferentiated state of neuronal stem/progenitor cells in vitro by preventing precocious expression of neuronal genes. However, the function of Rest during neurogenesis in vivo remains to be elucidated because of the early embryonic lethal phenotype of conventional Rest knockout mice. In the present study, we have generated Rest conditional knockout mice, which allow the effect of genetic ablation of Rest during embryonic neurogenesis to be examined in vivo. We show that Rest plays a role in suppressing the expression of neuronal genes in cultured neuronal cells in vitro, as well as in non-neuronal cells outside of the central nervous system, but that it is dispensable for embryonic neurogenesis in vivo. Our findings highlight the significance of extrinsic signals for the proper intrinsic regulation of neuronal gene expression levels in the specification of cell fate during embryonic neurogenesis in vivo.

Cross-regulation between an alternative splicing activator and a transcription repressor controls neurogenesis

Neurogenesis requires the concerted action of numerous genes that are regulated at multiple levels. However, how different layers of gene regulation are coordinated to promote neurogenesis is not well understood. We show that the neural-specific Ser/Arg repeat-related protein of 100 kDa (nSR100/SRRM4) negatively regulates REST (NRSF), a transcriptional repressor of genes required for neurogenesis. nSR100 directly promotes alternative splicing of REST transcripts to produce a REST isoform (REST4) with greatly reduced repressive activity, thereby activating expression of REST targets in neural cells. Conversely, REST directly represses nSR100 in nonneural cells to prevent the activation of neural-specific splicing events. Consistent with a critical role for nSR100 in the inhibition of REST activity, blocking nSR100 expression in the developing mouse brain impairs neurogenesis. Our results thus reveal a fundamental role for direct regulatory interactions between a splicing activator and transcription repressor in the control of the multilayered regulatory programs required for neurogenesis.

Form of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A nonphosphorylated at tyrosine 145 and 147 is enriched in the nuclei of astroglial cells, adult hippocampal progenitors, and some cholinergic axon terminals

Compelling lines of evidence indicate that overexpression of dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) in subjects with trisomy 21 (Down syndrome[DS]) contributes to the abnormal structure and function of the DS brain. In the present study, we used a novel, phospho-dependent antibody recognizing DYRK1A only with nonphosphorylated tyrosine 145 and 147 (DYRK1A Tyr-145/147P(-)), to investigate the expression pattern of this DYRK1A species in trisomic and disomic human and mouse brains. Immunoblotting and dephosphorylation experiments demonstrated higher levels of DYRK1A Tyr-145/147P(-) in postnatal trisomic brains in comparison with controls (by ∼40%) than those of the DYRK1A visualized by three other N- and C-terminally directed antibodies to DYRK1A. By immunofluorescence, the immunoreactivity to DYRK1A Tyr-145/147P(-) was the strongest in the nuclei of astroglial cells, which contrasted with the predominantly neuronal localization of DYRK1A visualized by the three other antibodies to DYRK1A we used. In addition, DYRK1A Tyr-145/147P(-) was enriched in the nuclei of neuronal progenitors and newly born neurons in the adult hippocampal proliferative zone and also occurred in some cholinergic axonal terminals. Our data show a distinctive expression pattern of DYRK1A forms nonphosphorylated at Tyr-145 and Tyr-147 in the brain tissue and suggest that DS subjects may exhibit not only upregulation of total DYRK1A, but also more subtle differences in phosphorylation levels of this kinase in comparison with control individuals.

Plasmids containing NRSE/RE1 sites enhance neurite outgrowth of retinal ganglion cells via sequestration of REST independent of NRSE dsRNA expression

Repressor element-1 silencing transcription factor (REST) is a transcriptional repressor of neuron-specific genes that binds to a conserved DNA element, the neuron restrictive silencer element (NRSE/RE1). Interestingly, increased REST activity is found in several neurological diseases like Huntington's disease and cerebral ischemia. Recently, it was shown that NRSE dsRNA, a double-stranded non-coding RNA can bind to REST during a defined period of neuronal differentiation, and thereby changes REST from a transcriptional repressor to an activator of neuron-specific genes. Here, we analyzed the effects of NRSE dsRNA expression in primary retinal ganglion cells. We found that NRSE dsRNA expression vectors significantly enhance neurite outgrowth even when axonal degeneration is induced by neurotrophin deprivation. Transfection of HEK cells with NRSE dsRNA-expressing vectors altered their morphology leading to the formation of thin processes and induced the expression of neurofilament-68. Surprisingly, control vectors containing REST-binding sites, but not expressing NRSE dsRNA, resulted in the same effects, also in the retinal ganglion cell model. Reporter assays and retention of REST in the cytoplasm with a labeled NRSE/RE1-containing plasmid incapable of entering the nucleus suggest that sequestration of REST in the cytoplasm is the reason for the observed effects. No evidence for a biological function of NRSE dsRNA could be found in these models. We conclude that sequestration of REST leads to enhanced neurite outgrowth in retinal ganglion cells and that an increased activity of REST, as it is found in several neurodegenerative diseases, can be effectively modulated by sequestration of REST with plasmids containing NRSE/RE1 sites.

Epigenetic (de)regulation of adult hippocampal neurogenesis: implications for depression

Adult neurogenesis represents a dynamic level of modulation upon the neuroplastic properties of the mature nervous system, that is essential to the homeostatic brain function. The adult neurogenic process comprises several sequential steps, all of which subjected to an assortment of cell-intrinsic and neurogenic-niche complex regulatory mechanisms. Among these, epigenetic regulation is now emerging as a crucial regulator of several neurogenesis steps. In particular, the active regulation of hippocampal neurogenesis and its repercussions in global hippocampal function are of special interest for the biomedical field, since imbalances at this level have been strongly related to the precipitation of several neuropsychyatric disorders, such as depression. Indeed, growing evidence supports that the detrimental effects on adult hippocampal neurogenesis, that have been associated with depression, might be epigenetically-mediated. Therefore, understanding the epigenetic regulation of the neurogenic process may provide a link between neurogenesis imbalances and the deterioration of the behavioural and cognitive domains frequently affected in depression, thus contributing to unravel the complex pathophysiology of this disorder.

Here, we outline some of the major epigenetic mechanisms contributing to the regulation of hippocampal neurogenesis and discuss several lines of evidence supporting their involvement on the development of imbalances in the neurogenic process, often correlated to behavioural and cognitive deficits commonly observed in major depressive disorder.

Connexins: key mediators of endocrine function

The appearance of multicellular organisms imposed the development of several mechanisms for cell-to-cell communication, whereby different types of cells coordinate their function. Some of these mechanisms depend on the intercellular diffusion of signal molecules in the extracellular spaces, whereas others require cell-to-cell contact. Among the latter mechanisms, those provided by the proteins of the connexin family are widespread in most tissues. Connexin signaling is achieved via direct exchanges of cytosolic molecules between adjacent cells at gap junctions, for cell-to-cell coupling, and possibly also involves the formation of membrane "hemi-channels," for the extracellular release of cytosolic signals, direct interactions between connexins and other cell proteins, and coordinated influence on the expression of multiple genes. Connexin signaling appears to be an obligatory attribute of all multicellular exocrine and endocrine glands. Specifically, the experimental evidence we review here points to a direct participation of the Cx36 isoform in the function of the insulin-producing β-cells of the endocrine pancreas, and of the Cx40 isoform in the function of the renin-producing juxtaglomerular epithelioid cells of the kidney cortex.

Regulatory elements required for the activation and repression of the protocadherin-alpha gene cluster

The mouse protocadherin (Pcdh) -α, -β, and -γ gene clusters encode more than 50 protein isoforms, the combinatorial expression of which generates vast single-cell diversity in the brain. At present, the mechanisms by which this diversity is expressed are not understood. Here we show that two transcriptional enhancer elements, HS5-1 and HS7, play a critical role in Pcdhα gene expression in mice. We show that the HS5-1 element functions as an enhancer in neurons and a silencer in nonneuronal cells. The enhancer activity correlates with the binding of zinc finger DNA binding protein CTCF to the target promoters, and the silencer activity requires the binding of the REST/NRSF repressor complex in nonneuronal cells. Thus, the HS5-1 element functions as a neuron-specific enhancer and nonneuronal cell repressor. In contrast, the HS7 element functions as a Pcdhα cluster-wide transcription enhancer element. These studies reveal a complex organization of regulatory elements required for generating single cell Pcdh diversity.

Genome wide gene expression regulation by HIP1 Protein Interactor, HIPPI: prediction and validation

Background

HIP1 Protein Interactor (HIPPI) is a pro-apoptotic protein that induces Caspase8 mediated apoptosis in cell. We have shown earlier that HIPPI could interact with a specific 9 bp sequence motif, defined as the HIPPI binding site (HBS), present in the upstream promoter of Caspase1 gene and regulate its expression. We also have shown that HIPPI, without any known nuclear localization signal, could be transported to the nucleus by HIP1, a NLS containing nucleo-cytoplasmic shuttling protein. Thus our present work aims at the investigation of the role of HIPPI as a global transcription regulator.

Results

We carried out genome wide search for the presence of HBS in the upstream sequences of genes. Our result suggests that HBS was predominantly located within 2 Kb upstream from transcription start site. Transcription factors like CREBP1, TBP, OCT1, EVI1 and P53 half site were significantly enriched in the 100 bp vicinity of HBS indicating that they might co-operate with HIPPI for transcription regulation. To illustrate the role of HIPPI on transcriptome, we performed gene expression profiling by microarray. Exogenous expression of HIPPI in HeLa cells resulted in up-regulation of 580 genes (p < 0.05) while 457 genes were down-regulated. Several transcription factors including CBP, REST, C/EBP beta were altered by HIPPI in this study. HIPPI also interacted with P53 in the protein level. This interaction occurred exclusively in the nuclear compartment and was absent in cells where HIP1 was knocked down. HIPPI-P53 interaction was necessary for HIPPI mediated up-regulation of Caspase1 gene. Finally, we analyzed published microarray data obtained with post mortem brains of Huntington's disease (HD) patients to investigate the possible involvement of HIPPI in HD pathogenesis. We observed that along with the transcription factors like CREB, P300, SREBP1, Sp1 etc. which are already known to be involved in HD, HIPPI binding site was also significantly over-represented in the upstream sequences of genes altered in HD.

Conclusions

Taken together, the results suggest that HIPPI could act as an important transcription regulator in cell regulating a vast array of genes, particularly transcription factors and at least, in part, play a role in transcription deregulation observed in HD.

Repressor element 1 silencing transcription factor (REST) controls radial migration and temporal neuronal specification during neocortical development

Neurogenesis requires mechanisms that coordinate early cell-fate decisions, migration, and terminal differentiation. Here, we show that the transcriptional repressor, repressor element 1 silencing transcription factor (REST), regulates radial migration and the timing of neural progenitor differentiation during neocortical development, and that the regulation is contingent upon differential REST levels. Specifically, a sustained presence of REST blocks migration and greatly delays--but does not prevent--neuronal differentiation, resulting in a subcortical band heterotopia-like phenotype, reminiscent of loss of doublecortin. We further show that doublecortin is a direct gene target of REST, and that its overexpression rescues, at least in part, the aberrant phenotype caused by persistent presence of REST. Our studies support the view that the targeted down-regulation of REST to low levels in neural progenitors, and its subsequent disappearance during neurogenesis, is critical for timing the spatiotemporal transition of neural progenitor cells to neurons.

The master negative regulator REST/NRSF controls adult neurogenesis by restraining the neurogenic program in quiescent stem cells

Transcriptional regulation is a critical mechanism in the birth, specification, and differentiation of granule neurons in the adult hippocampus. One of the first negative-acting transcriptional regulators implicated in vertebrate development is repressor element 1-silencing transcription/neuron-restrictive silencer factor (REST/NRSF)--thought to regulate hundreds of neuron-specific genes--yet its function in the adult brain remains elusive. Here we report that REST/NRSF is required to maintain the adult neural stem cell (NSC) pool and orchestrate stage-specific differentiation. REST/NRSF recruits CoREST and mSin3A corepressors to stem cell chromatin for the regulation of pro-neuronal target genes to prevent precocious neuronal differentiation in cultured adult NSCs. Moreover, mice lacking REST/NRSF specifically in NSCs display a transient increase in adult neurogenesis that leads to a loss in the neurogenic capacity of NSCs and eventually diminished granule neurons. Our work identifies REST/NRSF as a master negative regulator of adult NSC differentiation and offers a potential molecular target for neuroregenerative approaches.

Mediator and human disease

Since the identification of a metazoan counterpart to yeast Mediator nearly 15 years ago, a convergent body of biochemical and molecular genetic studies have confirmed their structural and functional relationship as an integrative hub through which regulatory information conveyed by signal activated transcription factors is transduced to RNA polymerase II. Nonetheless, metazoan Mediator complexes have been shaped during evolution by substantive diversification and expansion in both the number and sequence of their constituent subunits, with important implications for the development of multicellular organisms. The appearance of unique interaction surfaces within metazoan Mediator complexes for transcription factors of diverse species-specific origins extended the role of Mediator to include an essential function in coupling developmentally coded signals with precise gene expression output sufficient to specify cell fate and function. The biological significance of Mediator in human development, suggested by genetic studies in lower metazoans, is emphatically illustrated by an expanding list of human pathologies linked to genetic variation or aberrant expression of its individual subunits. Here, we review our current body of knowledge concerning associations between individual Mediator subunits and specific pathological disorders. When established, molecular etiologies underlying genotype-phenotype correlations are addressed, and we anticipate that future progress in this critical area will help identify therapeutic targets across a range of human pathologies.

Involvement of REST corepressor 3 in prognosis of human hepatitis B

AIM

To examine the potential correlation between serum REST corepressor 3 (RCOR3) level and the outcome of patients with hepatitis B.

METHODS

Concanavalin A (ConA)-induced mouse hepatitis model was used. The mRNA level of RCOR3 in mouse liver was measured using GeneChip array and real-time PCR. One hundred seventy-seven patients with hepatitis B and 34 healthy individuals were categorized into six groups including mild chronic hepatitis, moderate chronic hepatitis B, severe hepatitis B (SHB), cirrhosis, hepatocellular carcinoma (HCC) and healthy control. Serum levels of human RCOR3 were measured using ELISA.

RESULTS

In the mouse hepatitis model, the mRNA level of RCOR3 in liver was reduced early after exposure to ConA, then increased after 6 h of exposure. There was no significant difference in the serum RCOR3 level between the mild chronic hepatitis B and the control groups. The serum RCOR3 level was significantly increased in the moderate chronic hepatitis B group, but significantly reduced in SHB, cirrhosis and HCC groups, as compared with the control group. Moreover, the serum RCOR3 levels in SHB, cirrhosis and liver cancer patients were significantly lower than those in the patients with moderate chronic hepatitis B and with mild chronic hepatitis B. Rank correlation analysis revealed a significant correlation between serum RCOR3 level and total bilirubin (r=-0.305, P<0.01). There was no significant correlation between RCOR3 on one hand, and alanine transaminase (r=0.014, P>0.05) or aspartate transaminase (r=-0.079, P>0.05) on the other hand.

CONCLUSION

Serum RCOR3 level may reflect the degree of liver damage, which might be a potential biomarker for the outcome of patients with hepatitis B.

Transcriptional up-regulation of cell surface Na V 1.7 sodium channels by insulin-like growth factor-1 via inhibition of glycogen synthase kinase-3β in adrenal chromaffin cells: enhancement of 22Na+ influx, 45Ca2+ influx and catecholamine secretion

Insulin-like growth factor-1 (IGF-1) plays important roles in the regulation of neuronal development. The electrical activity of Na(+) channels is crucial for the regulation of synaptic formation and maintenance/repair of neuronal circuits. Here, we examined the effects of chronic IGF-1 treatment on cell surface expression and function of Na(+) channels. In cultured bovine adrenal chromaffin cells expressing Na(V)1.7 isoform of voltage-dependent Na(+) channels, chronic IGF-1 treatment increased cell surface [(3)H]saxitoxin binding by 31%, without altering the Kd value. In cells treated with IGF-1, veratridine-induced (22)Na(+) influx, and subsequent (45)Ca(2+) influx and catecholamine secretion were augmented by 35%, 33%, 31%, respectively. Pharmacological properties of Na(+) channels characterized by neurotoxins were similar between nontreated and IGF-1-treated cells. IGF-1-induced up-regulation of [(3)H]saxitoxin binding was prevented by phosphatydil inositol-3 kinase inhibitors (LY204002 or wortmannin), or Akt inhibitor (Akt inhibitor IV). Glycogen synthase kinase-3 (GSK-3) inhibitors (LiCl, valproic acid, SB216763 or SB415286) also increased cell surface [(3)H]saxitoxin binding by ∼ 33%, whereas simultaneous treatment of IGF-1 with GSK-3 inhibitors did not produce additive increasing effect on [(3)H]saxitoxin binding. IGF-1 (100 nM) increased Ser(437)-phosphorylated Akt and Ser(9)-phosphorylated GSK-3β, and inhibited GSK-3β activity. Treatment with IGF-1, LiCl or SB216763 increased protein level of Na(+) channel α-subunit; it was prevented by cycloheximide. Either treatment increased α-subunit mRNA level by ∼ 48% and accelerated α-subunit gene transcription by ∼ 30% without altering α-subunit mRNA stability. Thus, inhibition of GSK-3β caused by IGF-1 up-regulates cell surface expression of functional Na(+) channels via acceleration of α-subunit gene transcription.

REST is a key regulator in brain-specific homeobox gene expression during neuronal differentiation

Brain-specific homeobox (Bsx) is specifically expressed at the early embryonic stages during brain development. Several studies show that Bsx plays important roles in brain development; however, the mechanisms of its transcriptional regulation remain to be established. In this study, we show that binding of repressor element silencing transcription factor (REST) to the neuron restrictive silencer element (NRSE) represses Bsx transcription in non-neuronal P19 cells. The Bsx promoter contains several putative binding sites for transcription factors, including NRSE for REST and the GC box for the transcriptional activator, Sp1. Upon neuronal differentiation of P19 cells with retinoic acid, Bsx gene expression increased, whereas that of the REST gene decreased. Electrophoretic mobility shift analyses demonstrated that recombinant REST proteins bound the NRSE region of the Bsx promoter. In neuronal NS20Y cells, transcriptional activity of the Bsx promoter was decreased upon expression of REST. Moreover, dominant-negative REST derepressed Bsx transcription in P19 cells. Sp1-mediated transcriptional activity of the Bsx promoter was attenuated by treatment with mithramycin A, a GC box-binding drug, but was enhanced upon mutation of NRSE. Co-immunoprecipitation and chromatin immunoprecipitation assays showed that the Bsx promoter appeared to be modulated by direct interactions between REST and Sp1. The CpG sites of NRSE and GC box were completely unmethylated, signifying no interference of DNA methylation. Our results suggest that binding of REST to NRSE suppresses the Sp1-mediated activation of Bsx in non-neuronal cells.