Transcriptional modulation of mouse mu-opioid receptor distal promoter activity by Sox18

H3.3 Barcoding of Nucleus Accumbens Transcriptional Activity Identifies Novel Molecular Cascades Associated with Cocaine Self-administration in Mice

Although numerous epigenetic modifications have been associated with addiction, little work has explored the turnover of histone variants. Uniquely, the H3.3 variant incorporates stably and preferentially into chromatin independently of DNA replication at active sites of transcription and transcription factor binding. Thus, genomic regions associated with H3.3-containing nucleosomes are particularly likely to be involved in plasticity, such as following repeated cocaine exposure. A recently developed mouse line expressing a neuron-specific hemagglutinin (HA)-tagged H3.3 protein was used to track transcriptionally active sites cumulatively across 19 d of cocaine self-administration. RNA-seq and H3.3-HA ChIP-seq analyses were performed on NAcc tissue collected following cocaine or food self-administration in male mice. RNA sequencing revealed five genes upregulated in cocaine relative to food self-administering mice: Fosb, Npas4, Vgf, Nptx2, and Pmepa1, which reflect known and novel cocaine plasticity-associated genes. Subsequent ChIP-seq analysis confirmed increased H3.3 aggregation at four of these five loci, thus validating H3.3 insertion as a marker of enhanced cocaine-induced transcription. Further motif recognition analysis of the ChIP-seq data showed that cocaine-associated differential H3.3 accumulation correlated with the presence of several transcription factor binding motifs, including RBPJ1, EGR1, and SOX4, suggesting that these are potentially important regulators of molecular cascades associated with cocaine-induced neuronal plasticity. Additional ontological analysis revealed differential H3.3 accumulation mainly near genes involved in neuronal differentiation and dendrite formation. These results establish the H3.3-HA transgenic mouse line as a compelling molecular barcoding tool to identify the cumulative effects of long-term environmental perturbations, such as exposure to drugs of abuse.SIGNIFICANCE STATEMENT Histone H3.3 is a core histone variant that is stably incorporated at active sites of transcription. We used a tagged version of H3.3 expressed exclusively in neurons to delineate active transcription sites following extended cocaine self-administration in mice. This approach revealed the cumulative list of genes expressed in response to cocaine taking over the course of several weeks. We combined this technique with RNA sequencing of tissue collected from the same animals 24 h after the last cocaine exposure. Comparing these datasets provided a full picture of genes that respond to chronic cocaine exposure in NAcc neurons. These studies revealed novel transcription factors that are likely involved in cocaine-induced plasticity and addiction-like behaviors.

Opposite Epigenetic Associations With Alcohol Use and Exercise Intervention

Alcohol use disorder (AUD) is a devastating public health problem in which both genetic and environmental factors play a role. Growing evidence supports that epigenetic regulation is one major mechanism in neuroadaptation that contributes to development of AUD. Meanwhile, epigenetic patterns can be modified by various stimuli including exercise. Thus, it is an intriguing question whether exercise can lead to methylation changes that are opposite to those related to drinking. We herein conducted a comparative study to explore this issue. Three cohorts were profiled for DNA methylation (DNAm), including a longitudinal exercise intervention cohort (53 healthy participants profiled at baseline and after a 12-months exercise intervention), a cross-sectional case-control cohort (81 hazardous drinkers and 81 healthy controls matched in age and sex), and a cross-sectional binge drinking cohort (281 drinkers). We identified 906 methylation sites showing significant DNAm differences between drinkers and controls in the case-control cohort, as well as, associations with drinking behavior in the drinking cohort. In parallel, 341 sites were identified for significant DNAm alterations between baseline and follow-up in the exercise cohort. Thirty-two sites overlapped between these two set of findings, of which 15 sites showed opposite directions of DNAm associations between exercise and drinking. Annotated genes of these 15 sites were enriched in signaling pathways related to synaptic plasticity. In addition, the identified methylation sites significantly associated with impaired control over drinking, suggesting relevance to neural function. Collectively, the current findings provide preliminary evidence that exercise has the potential to partially reverse DNAm differences associated with drinking at some CpG sites, motivating rigorously designed longitudinal studies to better characterize epigenetic effects with respect to prevention and intervention of AUD.

TNFα-induced down-regulation of Sox18 in endothelial cells is dependent on NF-κB

The transcription factor Sox18 plays a role in angiogenesis, including lymphangiogenesis, where it is upregulated by growth factors and directs the expression of genes encoding, e.g., guidance molecules and a matrix metalloproteinase. Conversely, we found that in human umbilical vein endothelial cells (HUVEC) Sox18 is repressed by the pro-inflammatory mediator TNFα (as well as IL-1 and LPS). Since a common feature of these mediators is the activation of the NF-κB signaling pathway, we investigated whether Sox18 downregulation is dependent on this transcription factor. Transduction of HUVEC with an adenoviral vector directing the expression of the NF-κB inhibitor IκBα prevented the downregulation of Sox18. Transient transfections of Sox18 promoter reporter genes revealed that the downregulation takes place on the level of transcription, and that the p65/RelA subunit of NF-κB was operative. Furthermore, the responsible promoter region of Sox18 is located within -1.0kb from the transcriptional start site. The repression of Sox18 and its target genes may lead to altered formation of vessels in inflamed settings.

Epigenetics: a promising paradigm for better understanding and managing pain

Epigenetic regulation of gene expression is a rapidly growing area of research. Considering the longevity and plasticity of neurons, the studies on epigenetic pathways in the nervous system should be of special interest for both epigeneticists and neuroscientists. Activation or inactivation of different epigenetic pathways becomes more pronounced when the cells experience rapid changes in their environment, and such changes can be easily caused by injury and inflammation, resulting in pain perception or distortion of pain perception (eg, hyperalgesia). Therefore, in this regard, the field of pain is at an advantage to study the epigenetic pathways. More importantly, understanding pain from an epigenetics point of view would provide a new paradigm for developing drugs or strategies for pain management. In this review, we introduce basic concepts of epigenetics, including chromatin dynamics, histone modifications, DNA methylation, and RNA-induced gene silencing. In addition, we provide evidence from published studies suggesting wide implication of different epigenetic pathways within pain pathways.

PERSPECTIVE

This article provides a brief overview of epigenetic pathways for gene regulation and highlights their involvement in pain. Our goal is to expose the readers to these concepts so that pain-related phenotypes can be investigated from the epigenetic point of view.

Inhibition of c-Jun NH2-terminal kinase stimulates mu opioid receptor expression via p38 MAPK-mediated nuclear NF-κB activation in neuronal and non-neuronal cells

Despite its potential side effects of addiction, tolerance and withdrawal symptoms, morphine is widely used for reducing moderate and severe pain. Previous studies have shown that the analgesic effect of morphine depends on mu opioid receptor (MOR) expression levels, but the regulatory mechanism of MOR is not yet fully understood. Several in vivo and in vitro studies have shown that the c-Jun NH2-terminal kinase (JNK) pathway is closely associated with neuropathic hyperalgesia, which closely resembles the neuroplastic changes observed with morphine antinociceptive tolerance. In this study, we show that inhibition of JNK by SP600125, its inhibitory peptide, or JNK-1 siRNA induced MOR at both mRNA and protein levels in neuronal cells. This increase in MOR expression was reversed by inhibition of the p38 mitogen-activated protein kinase (MAPK) pathway, but not by inhibition of the mitogen-activated protein/extracellular signal-regulated kinase (MEK) pathway. Further experiments using cell signaling inhibitors showed that MOR upregulation by JNK inhibition involved nuclear factor-kappa B (NF-κB). The p38 MAPK dependent phosphorylation of p65 NF-κB subunit in the nucleus was increased by SP600125 treatment. We also observed by chromatin immunoprecipitation (ChIP) analysis that JNK inhibition led to increased bindings of CBP and histone-3 dimethyl K4, and decreased bindings of HDAC-2, MeCP2, and histone-3 trimethyl K9 to the MOR promoter indicating a transcriptional regulation of MOR by JNK inhibition. All these results suggest a regulatory role of the p38 MAPK and NF-κB pathways in MOR gene expression and aid to our better understanding of the MOR gene regulation.

MicroRNA 339 down-regulates μ-opioid receptor at the post-transcriptional level in response to opioid treatment

μ-Opioid receptor (MOR) level is directly related to the function of opioid drugs, such as morphine and fentanyl. Although agonist treatment generally does not affect transcription of mor, previous studies suggest that morphine can affect the translation efficiency of MOR transcript via microRNAs (miRNAs). On the basis of miRNA microarray analyses of the hippocampal total RNA isolated from mice chronically treated with μ-opioid agonists, we found a miRNA (miR-339-3p) that was consistently and specifically increased by morphine (2-fold) and by fentanyl (3.8-fold). miR-339-3p bound to the MOR 3'-UTR and specifically suppressed reporter activity. Suppression was blunted by adding miR-339-3p inhibitor or mutating the miR-339-3p target site. In cells endogenously expressing MOR, miR-339-3p inhibited the production of MOR protein by destabilizing MOR mRNA. Up-regulation of miR-339-3p by fentanyl (EC(50)=0.75 nM) resulted from an increase in primary miRNA transcript. Mapping of the miR-339-3p primary RNA and its promoter revealed that the primary miR-339-3p was embedded in a noncoding 3'-UTR region of an unknown host gene and was coregulated by the host promoter. The identified promoter was activated by opioid agonist treatment (10 nM fentanyl or 10 μM morphine), a specific effect blocked by the opioid antagonist naloxone (10 μM). Taken together, these results suggest that miR-339-3p may serve as a negative feedback modulator of MOR signals by regulating intracellular MOR biosynthesis.

The transcription factor SOX18 regulates the expression of matrix metalloproteinase 7 and guidance molecules in human endothelial cells

Background

Mutations in the transcription factor SOX18 are responsible for specific cardiovascular defects in humans and mice. In order to gain insight into the molecular basis of its action, we identified target genes of SOX18 and analyzed one, MMP7, in detail.

Methodology/Principal Findings

SOX18 was expressed in HUVEC using a recombinant adenoviral vector and the altered gene expression profile was analyzed using microarrays. Expression of several regulated candidate SOX18 target genes was verified by real-time PCR. Knock-down of SOX18 using RNA interference was then used to confirm the effect of the transcription factor on selected genes that included the guidance molecules ephrin B2 and semaphorin 3G. One gene, MMP7, was chosen for further analysis, including detailed promoter studies using reporter gene assays, electrophoretic mobility shift analysis and chromatin-immunoprecipitation, revealing that it responds directly to SOX18. Immunohistochemical analysis demonstrated the co-expression of SOX18 and MMP7 in blood vessels of human skin.

Conclusions/Significance

The identification of MMP7 as a direct SOX18 target gene as well as other potential candidates including guidance molecules provides a molecular basis for the proposed function of this transcription factor in the regulation of vessel formation.

Transcriptional and epigenetic regulation of opioid receptor genes: present and future

Three opioid receptors (ORs) are known: μ opioid receptors (MORs), δ opioid receptors (DORs), and κ opioid receptors (KORs). Each is encoded by a distinct gene, and the three OR genes share a highly conserved genomic structure and promoter features, including an absence of TATA boxes and sensitivity to extracellular stimuli and epigenetic regulation. However, each of the genes is differentially expressed. Transcriptional regulation engages both basal and regulated transcriptional machineries and employs activating and silencing mechanisms. In retinoic acid-induced neuronal differentiation, the opioid receptor genes undergo drastically different chromatin remodeling processes and display varied patterns of epigenetic marks. Regulation of KOR expression is distinctly complex, and KOR exerts a unique function in neurite extension, indicating that KOR is not simply a pharmacological cousin of MOR and DOR. As the expression of OR proteins is ultimately controlled by extensive posttranscriptional processing, the pharmacological implication of OR gene regulation at the transcriptional level remains to be determined.

Early growth response protein 1 acts as an activator of SOX18 promoter

Sex-determining region Y box 18 (Sox18/SOX18) gene is an important regulator of vascular development playing a role in endothelial cell specification or differentiation, angiogenesis and atherogenesis. The aim of this study was to perform comprehensive functional characterization of the human SOX18 promoter, including determination of transcription start point (tsp) and identification of control elements involved in the regulation of SOX18 gene expression, with an emphasis on angiogenesis-related transcription factors. Analyses were performed in HeLa cells, representing a tumor cell line, and in EA.hy926 cells used as an endothelial model system. We have determined unique tsp of SOX18 gene, located 172 nucleotides upstream from ATG codon. Further, we have shown that SOX18 promoter region, -726 to -89 bp relative to tsp, contains positive cis-regulatory element(s) that stimulates SOX18 promoter activity, while region -89 to+166 represents the minimal promoter. Within this region we have recognized the presence of essential element(s), positioned from -89 to +29, which harbors cluster of three putative early growth response 1 (EGR1) binding sites. By in vitro binding assays and functional analyses we have shown that these three putative binding sites are functionally relevant and sufficient for EGR1-induced SOX18 transcription. Mutations of these binding sites significantly impaired activity of the SOX18 promoter, particularly in EA.hy926 cells, indicating the importance of these regulatory elements for SOX18 promoter activity in endothelial setting. By data presented in this study, we have established SOX18 as a novel target gene regulated by EGR1 transcription factor, thus providing the first functional link between two transcription factors previously shown to be involved in the control of angiogenesis.

Long-term morphine treatment decreases the association of mu-opioid receptor (MOR1) mRNA with polysomes through miRNA23b

Mu-opioid receptor (MOR) mediates most of the pharmacological effects of opioid drugs. The expression of MOR is temporarily and spatially regulated at both the transcriptional and post-transcriptional levels. Long-term morphine treatment that induces tolerance does not alter MOR mRNA expression, suggesting no direct link between agonist treatment and MOR gene transcription. We previously identified the 3'-untranslated region (3'-UTR) of the major transcript of mu-opioid receptor (MOR1) and revealed a novel trans-acting factor, miRNA23b, that binds to the K box motif in the 3'-UTR. The interaction between miRNA23b with the MOR1 3'-UTR suppressed receptor translation by inhibiting polysome-mRNA association. In this report, we demonstrate that long-term morphine treatment increases miRNA23b expression in a dose- and time-dependent manner and represses the association of MOR1 mRNA with polysomes through the MOR1 3'-UTR. The translational luciferase reporter assay shows a suppression effect of morphine on reporter activity that requires the MOR1 3'-UTR. This suggests a potential link between MOR expression and morphine treatment at the post-transcriptional level in which a specific miRNA, miRNA23b, is involved.

Evidence of the neuron-restrictive silencer factor (NRSF) interaction with Sp3 and its synergic repression to the mu opioid receptor (MOR) gene

Previously, we reported that the neuron-restrictive silencer element (NRSE) of mu opioid receptor (MOR) functions as a critical regulator to repress the MOR transcription in specific neuronal cells, depending on neuron-restriction silence factor (NRSF) expression levels [C.S.Kim, C.K.Hwang, H.S.Choi, K.Y.Song, P.Y.Law, L.N.Wei and H.H.Loh (2004) J. Biol. Chem., 279, 46464–46473]. Herein, we identify a conserved GC sequence next to NRSE region in the mouse MOR gene. The inhibition of Sp family factors binding to this GC box by mithramycin A led to a significant increase in the endogenous MOR transcription. In the co-immunoprecipitation experiment, NRSF interacted with the full-length Sp3 factor, but not with Sp1 or two short Sp3 isoforms. The sequence specific and functional binding by Sp3 at this GC box was confirmed by in vitro gel-shift assays using either in vitro translated proteins or nuclear extract, and by in vivo chromatin immunoprecipitation assays. Transient transfection assays showed that Sp3-binding site of the MOR gene is a functionally synergic repressor element with NRSE in NS20Y cells, but not in the NRSF negative PC12 cells. The results suggest that the synergic interaction between NRSF and Sp3 is required to negatively regulate MOR gene transcription and that transcription of MOR gene would be governed by the context of available transcription factors rather than by a master regulator.

Transcriptional regulation of mouse mu opioid receptor gene: Sp3 isoforms (M1, M2) function as repressors in neuronal cells to regulate the mu opioid receptor gene

The 5'-flanking region of the mouse mu opioid receptor (MOR) gene has two promoters, referred to as distal and proximal. MOR mRNA is predominantly initiated by the proximal promoter. Previously, several important cis-elements and trans-factors have been shown to play a functional role in the proximal promoter of the MOR gene. In this study, we defined another functional, negative regulatory element located in the -219- to -189-base pair (translational start site designed as +1) region of the proximal promoter. It is designated as the Sp binding sequence for its sequence homology to the consensus Sp binding element. Mutation of the Sp binding element led to a 100% increase of MOR promoter activity in MOR-positive cells (NMB cells), confirming the negative role of the Sp binding sequence. Surprisingly, electrophoretic mobility shift analysis and chromatin immunoprecipitation assays revealed that Sp3 and its isoforms (M1 and M2) were specifically bound to the Sp binding sequence. In cotransfection assays of Drosophila melanogaster SL2 cells using cDNA encoding Sp1, Sp3, and the M1 and M2 isoforms of Sp3, the M1 and M2 isoforms trans-repressed the MOR promoter, whereas Sp1 and Sp3 trans-activated the MOR promoter. Significantly, ectopic expression of the M1 and M2 isoforms of Sp3 led to repression of the endogenous MOR gene transcripts in NMB cells. These results suggest that the binding of the M1 and M2 isoforms of the Sp3 transcription factor to the Sp binding sequence may play a role in mouse MOR gene expression.

Insights into the receptor transcription and signaling: implications in opioid tolerance and dependence

Drug addiction has great social and economical implications. In order to resolve this problem, the molecular and cellular basis for drug addiction must be elucidated. For the past three decades, our research has focused on elucidating the molecular mechanisms behind morphine tolerance and dependence. Although there are many working hypotheses, it is our premise that cellular modulation of the receptor signaling, either via transcriptional or post-translational control of the receptor, is the basis for morphine tolerance and dependence. Thus, in the current review, we will summarize our recent work on the transcriptional and post-translational control of the opioid receptor, with special emphasis on the mu-opioid receptor, which is demonstrated to mediate the in vivo functions of morphine.

Differential promoter usage of mouse mu-opioid receptor gene during development

Previously, we demonstrated that mouse mu-opioid receptor (MOR) gene expression is regulated by both distal and proximal promoters, with the latter playing a major role in controlling MOR transcription in the adult mouse brain. Here, we report studies of the relative usages of the mouse MOR dual promoters during murine development. We used the reverse transcription-polymerase chain reaction (RT-PCR) method, which gave results similar to those using binding assays or in situ hybridization. However, due to the greater sensitivity of RT-PCR method, we were able to detect the emergence of MOR as early as at embryonic day 8.5 (E8.5). We found that both proximal and distal promoters were active at E8.5. The proximal promoter initiated approximately two-thirds of total MOR transcripts at E8.5, with the distal promoter directing transcription of the remaining one-third. This is the greatest relative contribution of the distal promoter to MOR transcription we have observed during any time in development. Thereafter, the percentage of transcripts directed by the distal promoter gradually declined, and remained at a low but detectable level (approximately 5% of total MOR transcripts) throughout development and adulthood. Conversely, a progressive increase of the contribution of the proximal promoter to MOR transcription was observed during development, reaching its maximum in the adult. In summary, our results demonstrated the pivotal role of the proximal promoter in directing MOR transcription during murine development.

Divergent regulation of the growth-promoting gene IEX-1 by the p53 tumor suppressor and Sp1

IEX-1, a recently discovered early response gene, regulates cell growth and apoptosis. IEX-1 gene expression is regulated by a variety of factors such as x-irradiation, ultraviolet radiation, steroids, growth factors, and inflammatory stimuli. By systematic examination of the IEX-1 promoter, we show that IEX-1 gene expression is controlled by multiple conserved gene regulatory elements and that IEX-1 is a downstream target of the p53 tumor suppressor and Sp1. In addition, p300, Sox, nuclear factor-kappaB, and AP4 appear to be modulators of IEX-1 gene expression to a lesser degree. We found that there is at least one Sp1 element that functions as an activator and contributes to high basal transcriptional levels of the IEX-1 gene. We demonstrate the presence of a p53 response element that represses IEX-1 promoter activity in HaCaT keratinocytes, indicating that Sp1 and p53 have opposite effects on IEX-1 gene expression. We conclude that IEX-1 expression in cells is regulated by the p53 tumor suppressor and Sp1, thus providing a direct mechanism for control of cell proliferation.