An intronic Ikaros-binding element mediates retinoic acid suppression of the kappa opioid receptor gene, accompanied by histone deacetylation on the promoters

Differential methylation of OPRK1 in borderline personality disorder is associated with childhood trauma

According to a growing body of neurobiological evidence, the core symptoms of borderline personality disorder (BPD) may be linked to an opioidergic imbalance between the hedonic and stimulatory activity of mu opioid receptors (MOR) and the reward system inhibiting effects of kappa opioid receptors (KOR). Childhood trauma (CT), which is etiologically relevant to BPD, is also likely to lead to epigenetic and neurobiological adaptations by extensive activation of the stress and endogenous opioid systems. In this study, we investigated the methylation differences in the promoter of the KOR gene (OPRK1) in subjects with BPD (N = 47) and healthy controls (N = 48). Comparing the average methylation rates of regulatorily relevant subregions (specified regions CGI-1, CGI-2, EH1), we found no differences between BPD and HC. Analyzing individual CG nucleotides (N = 175), we found eight differentially methylated CG sites, all of which were less methylated in BPD, with five showing highly interrelated methylation rates. This differentially methylated region (DMR) was found on the falling slope (5') of the promoter methylation gap, whose effect is enhanced by the DMR hypomethylation in BPD. A dimensional assessment of the correlation between disease severity and DMR methylation rate revealed DMR hypomethylation to be negatively associated with BPD symptom severity (measured by BSL-23). Finally, analyzing the influence of CT on DMR methylation, we found DMR hypomethylation to correlate with physical and emotional neglect in childhood (quantified by CTQ). Thus, the newly identified DMR may be a biomarker of the risks caused by CT, which likely epigenetically contribute to the development of BPD.

Regulation and Functional Implications of Opioid Receptor Splicing in Opioid Pharmacology and HIV Pathogenesis

Despite the identification and characterization of four opioid receptor subtypes and the genes from which they are encoded, pharmacological data does not conform to the predications of a four opioid receptor model. Instead, current studies of opioid pharmacology suggest the existence of additional receptor subtypes; however, no additional opioid receptor subtype has been identified to date. It is now understood that this discrepancy is due to the generation of multiple isoforms of opioid receptor subtypes. While several mechanisms are utilized to generate these isoforms, the primary mechanism involves alternative splicing of the pre-mRNA transcript. Extensive alternative splicing patterns for opioid receptors have since been identified and discrepancies in opioid pharmacology are now partially attributed to variable expression of these isoforms. Recent studies have been successful in characterizing the localization of these isoforms as well as their specificity in ligand binding; however, the regulation of opioid receptor splicing specificity is poorly characterized. Furthermore, the functional significance of individual receptor isoforms and the extent to which opioid- and/or HIV-mediated changes in the opioid receptor isoform profile contributes to altered opioid pharmacology or the well-known physiological role of opioids in the exacerbation of HIV neurocognitive dysfunction is unknown. As such, the current review details constitutive splicing mechanisms as well as the specific architecture of opioid receptor genes, transcripts, and receptors in order to highlight the current understanding of opioid receptor isoforms, potential mechanisms of their regulation and signaling, and their functional significance in both opioid pharmacology and HIV-associated neuropathology.

Transcription factor Ikaros represses protein phosphatase 2A (PP2A) expression through an intronic binding site

Protein phosphatase 2A (PP2A) is a highly conserved and ubiquitous serine/threonine phosphatase. We have shown previously that PP2A expression is increased in T cells of systemic lupus erythematosus patients and that this increased expression and activity of PP2A plays a central role in the molecular pathogenesis of systemic lupus erythematosus. Although the control of PP2A expression has been the focus of many studies, many aspects of its regulation still remain poorly understood. In this study, we describe a novel mechanism of PP2A regulation. We propose that the transcription factor Ikaros binds to a variant site in the first intron of PP2A and modulates its expression. Exogenous expression of Ikaros leads to reduced levels of PP2Ac message as well as protein. Conversely, siRNA-enabled silencing of Ikaros enhances the expression of PP2A, suggesting that Ikaros acts as a suppressor of PP2A expression. A ChIP analysis further proved that Ikaros is recruited to this site in T cells. We also attempted to delineate the mechanism of Ikaros-mediated PP2Ac gene suppression. We show that Ikaros-mediated suppression of PP2A expression is at least partially dependent on the recruitment of the histone deacetylase HDAC1 to this intronic site. We conclude that the transcription factor Ikaros can regulate the expression of PP2A by binding to a site in the first intron and modulating chromatin modifications at this site via recruitment of HDAC1.

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.

Polypyrimidine tract-binding protein is required for the repression of gene expression by all-trans retinoic acid

All-trans retinoic acid is a key regulator of early development. High concentrations of retinoic acid interfere with differentiation and migration of neural crest cells. Here we report that a dinucleotide repeat in the cis-element of Snail2 (previously known as Slug) gene plays a role in repression by all-trans retinoic acid. We analyzed the cis-acting regulatory regions of the Xenopus Snail2 gene, whose expression is repressed by all-trans retinoic acid. The analysis identified a TG/CA repeat as a necessary element for the repression. By performing a yeast one-hybrid screen, we found that a polypyrimidine tract-binding protein (PTB), which is known to be a regulator of the alternative splicing of pre-messenger RNA, binds to the TG/CA repeat. Overexpression and knockdown experiments for PTB in HEK293 cells and Xenopus embryos indicated that PTB is required for repression by retinoic acid. The green fluorescent protein-PTB fusion protein was localized in the nucleus of 293T cells. In situ hybridization for PTB in Xenopus embryos showed that PTB is expressed at the regions including neural crest at the early stages. Our results indicate that PTB plays a role in the repression of gene expression by retinoic acid through binding to the TG/CA repeats.

Epigenetic regulation of kappa opioid receptor gene in neuronal differentiation

The gene of mouse kappa opioid receptor (KOR) utilizes two promoters, P1 and P2. P1 is active in various brain areas and constitutively in P19 mouse embryonal carcinoma cells. P2 is active in limited brain stem areas of adult animals and only in late differentiated cells of P19 induced for neuronal differentiation in the presence of nerve growth factor (NGF). NGF response of P2 was found to be mediated by a specific binding site for transcription factor activation protein 2 (AP2) located in P2. Electrophoretic gel shift assay showed specific binding of this AP2 site by AP2beta, but not AP2alpha. Knockdown of endogenous AP2beta with siRNA abolished the stimulating effect of NGF on the expression of transcripts driven by P2. Binding of endogenous AP2beta on the endogenous KOR P2 chromatin region was also confirmed by chromatin immunoprecipitation. The effect of NGF was inhibited by LY2942002 (phosphatidylinositol 3-kinase, PI3K inhibitor), suggesting that PI3K was involved in signaling pathway mediating the effect of NGF stimulation on KOR P2. The chromatin of P2 in P19 was found to be specifically modified following NGF stimulation, which included demethylation at Lys9 and dimethylation at Lys4 of histone H3 and was consistent with the increased recruitment of RNA polymerase II to this promoter. This study presents the first evidence for epigenetic changes occurred on a specific KOR promoter triggered by NGF in cells undergoing neuronal differentiation. This epigenetic change is mediated by recruited AP2beta to this promoter and involves the PI3K system.

Evidence of endogenous mu opioid receptor regulation by epigenetic control of the promoters

The pharmacological effect of morphine as a painkiller is mediated mainly via the mu opioid receptor (MOR) and is dependent on the number of MORs in the cell surface membrane. While several studies have reported that the MOR gene is regulated by various cis- and trans-acting factors, many questions remain unanswered regarding in vivo regulation. The present study shows that epigenetic silencing and activation of the MOR gene are achieved through coordinated regulation at both the histone and DNA levels. In P19 mouse embryonal carcinoma cells, expression of the MOR was greatly increased after neuronal differentiation. MOR expression could also be induced by a demethylating agent (5'-aza-2'-deoxycytidine) or histone deacetylase inhibitors in the P19 cells, suggesting involvement of DNA methylation and histone deacetylation for MOR gene silencing. Analysis of CpG DNA methylation revealed that the proximal promoter region was unmethylated in differentiated cells compared to its hypermethylation in undifferentiated cells. In contrast, the methylation of other regions was not changed in either cell type. Similar methylation patterns were observed in the mouse brain. In vitro methylation of the MOR promoters suppressed promoter activity in the reporter assay. Upon differentiation, the in vivo interaction of MeCP2 was reduced in the MOR promoter region, coincident with histone modifications that are relevant to active transcription. When MeCP2 was disrupted using MeCP2 small interfering RNA, the endogenous MOR gene was increased. These data suggest that DNA methylation is closely linked to the MeCP2-mediated chromatin structure of the MOR gene. Here, we propose that an epigenetic mechanism consisting of DNA methylation and chromatin modification underlies the cell stage-specific mechanism of MOR gene expression.

Expression of the 1B isoforms of divalent metal transporter (DMT1) is regulated by interaction of NF-Y with a CCAAT-box element near the transcription start site

The 1B isoforms of the divalent metal transporter (DMT1) have recently been shown to be regulated transcriptionally via NF-kappaB but whether other regulatory elements are present on this promoter, however, have not been determined. Accordingly, studies were performed to delineate a minimal promoter region responsible for basal expression of these isoforms of DMT1. Promoter analysis has established that the 1B promoter is a TATA-less promoter containing a common CCAAT-box element conserved in mouse, rat, and human. Using luciferase reporter assays, it was found that mutation of this sequence leads to more than 95% reduction in the basal activity in mouse P19 cells. Using EMSA and ChIP assay, it was confirmed that NF-YA protein subunit can bind specifically to this site. Transfecting these cells with a dominant negative (DN) form of NF-YA leads to approximately 60% decrease in luciferase activity and approximately 65% decrease in 1B form of mRNA. To determine the location of the CCAAT-box in relation to the transcription start site, 5' RACE was performed. Results of these studies reveal that the CCAAT-box resides at position -6 to -2 upstream from the transcriptional start site. These data demonstrate that binding of NF-Y to this CCAAT-box domain is responsible for the basal regulation of 1B isoforms of DMT1 mRNA.

Axonal mRNA transport and localized translational regulation of kappa-opioid receptor in primary neurons of dorsal root ganglia

kappa-opioid receptor (KOR) is detected pre- and postsynaptically, but the subcellular localization, translation, and regulation of kor mRNA in presynaptic compartments of sensory neurons remain elusive. In situ hybridization detected axonal distribution of kor mRNA in primary neurons of dorsal root ganglia (DRG). The MS2-fused GFP tracked kor mRNA transport from DRG neuronal soma to axons, requiring its 5' and 3' UTRs. In Campenot chambers, axonal translation of kor mRNA was demonstrated for DRG neurons, which depended on its 5' UTR and was stimulated by KCl depolarization. KCl depolarization of DRG neurons rendered redistribution of kor mRNA from the postpolysomal fraction to the translationally active polysomal fraction. This study provided evidence for mRNA transport and regulation of presynaptic protein synthesis of nonstructural proteins like KOR in primary sensory neurons and demonstrated a mechanism of KCl depolarization-stimulated axonal mRNA redistribution for localized translational regulation.

Retinoic acid-induced chromatin remodeling of mouse kappa opioid receptor gene

The mouse kappa opioid receptor (KOR) gene is constitutively expressed in P19 embryonic stem cells but is first suppressed and reactivated during retinoic acid (RA)-induced neuronal differentiation. However, no RA response element (RARE) can be found in this gene regulatory region. The suppression and reactivation of the KOR gene in this neuronal differentiation model suggested chromatin remodeling occurred on this gene promoter triggered by RA induction. This study asks whether RA induces alteration in the nucleosomal structure of this gene promoter that has no apparent RARE and, if so, how RA remodels chromatin of this promoter. The results revealed two loose nucleosomes, N1 at -44 (3' boundary) from the transcription initiation site and N2 spanning the transcription initiation site, that are relevant to active transcription. RA formed a repressive chromatin configuration of this promoter by compacting nucleosome N1, followed by nucleosome N2 condensation. Chromatin immunoprecipitation assay demonstrated RA induced replacement of the c-Myc/Max complex with the Max/Mad1 complex on the E box located within nucleosome N1, coinciding with reduced Sp1 binding to GC boxes located within nucleosome N2 and recruitment of chromatin remodeling factor Brahma-related gene 1 (BRG-1) to this promoter. Consistently, histone deacetylation, Lys9 methylation, and hypophosphorylation of RNA polymerase II C-terminal domain were detected on this promoter after RA treatment. It is concluded that RA induces KOR gene suppression, as early neuronal differentiation marker, by inducing substitution of c-Myc/Max with Max/Mad on the E box and by BRG-1 involved nucleosome recruitment and chromatin condensation, thereby abolishing Sp1 binding.

Nitric oxide transcriptionally down-regulates specific isoforms of divalent metal transporter (DMT1) via NF-?B

Studies were performed to examine the affect of nitric oxide (NO) on expression of the divalent metal transporter (DMT1) in undifferentiated P19 embryonic carcinoma cells. DMT1 has four known isoforms which differ in both the N- and C-terminals. Results demonstrate that exposure of P19 cells to the NO precursor, sodium nitro-prusside (SNP), resulted in a decrease in expression of both positive (+) and negative (-) IRE isoforms of DMT1 with no change in the 1A species. Regulation was not as a result of decreased stability of message but was caused by reduction in transcription of the DMT1 1B isoforms. Similar results were observed in other cell lines, including PC12 and SH-SY5Y cells and rat primary sympathetic neurons. Nuclear NF-kappaB was decreased after SNP treatment, suggesting that NF-kappaB may mediate this response. Luciferase reporter assays with normal and NF-kappaB mutated constructs of the 1B promoter confirm that the NF-kappaB site between -23 to -19 upstream from the transcription start site was responsible for regulating expression. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assays further demonstrate that the p65 subunit of NF-kappaB and not p50 binding is specifically decreased by NO treatment. Results of these studies provide a general mechanism responsible for regulating DMT1 expression induced by stress-related signaling processes in vivo.

Post-translational and transcriptional regulation of DMT1 during P19 embryonic carcinoma cell differentiation by retinoic acid

Studies were performed to determine the regulation of DMT1 (divalent metal transporter 1) during RA (retinoic acid)-induced differentiation of P19 embryonic carcinoma cells. Protein and mRNA expression for the +/-IRE (iron response element) forms of DMT1, but not the 1A isoform, were down-regulated within the first few hours upon removal of RA, at which time the cells began to differentiate. The turnover of the +/-IRE isoforms of DMT1 protein during this period was found to be dependent on both the proteasomal and lysosomal pathways. Changes in mRNA levels were shown to be regulated by nitric oxide produced by the induction of neuronal nitric oxide synthase after removal of RA. Nitric oxide functions by inhibiting NF-kappaB (nuclear factor kappaB) nuclear translocation and the subsequent binding to the putative NF-kappaB response element (at -19 to -23) within the 1B promoter. Gel-shift analysis and chromatin immunoprecipitation assay indicated that nuclear NF-kappaB is capable of binding to this response element and that binding decreases during early stages of differentiation. Luciferase reporter gene assay demonstrated that a mutation in this binding domain leads to decreased activity. These results demonstrate that during neuronal differentiation of P19 cells, there is a decrease in specific isoforms of DMT1 via both post-translational and transcriptional mechanisms.

Retinoid-induced mu opioid receptor expression by phytohemagglutinin-stimulated U937 cells

Opioid use may be associated with an increased risk of neurological disease in human immunodeficiency virus (HIV) infection through effects on immune cell function. Studies were performed to examine the effects of specific retinoid receptor activation on mu opioid receptor (MOR) production by phytohemagglutinin (PHA)-stimulated U937 cells, a mononuclear cell line. PHA stimulation increased activation of the MOR promoter as well as levels of MOR mRNA, total receptor protein in cell lysates, and surface and cytoplasmic receptor expression. Retinoid X receptor (RXR) agonist and retinoic acid receptor (RAR) antagonist further increased MOR expression by the PHA-stimulated cells. In contrast, MOR expression was suppressed by RAR agonist and by RXR antagonist. Finally, opioid receptor binding was also increased by RXR agonist and RXR antagonist; no increase in binding occurred in the presence of RAR agonists and RXR antagonist. All together, these studies suggest that MOR expression in U937 cells can be differentially regulated by specific retinoid receptor activation. Such effects may have important clinical relevance for opioid users with HIV infection, including individuals with neurological disease.

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.

Redefinition of the human kappa opioid receptor gene (OPRK1) structure and association of haplotypes with opiate addiction

The kappa opioid receptor (KOR) plays a role in stress responsivity, opiate withdrawal and responses to cocaine. KOR activation by its endogenous ligand dynorphin A(1-17) decreases basal and drug-induced striatal levels of dopamine. The complete structure of the human KOR gene (hOPRK1) has not been previously determined. This study: (i) characterized the genomic structure of the hOPRK1 gene; (ii) identified single nucleotide polymorphisms (SNPs) in the hOPRK1 gene; and (iii) investigated possible associations of these variants with vulnerability to develop heroin addiction. Analysis of 5'-RACE cDNA clones revealed the presence of a novel exon 1 ranging in length from 167 to 251 nucleotides in the 5' 5'-untranslated region of the hOPRK1 mRNA. We found that the hOPRK1 gene has four major exons and three introns, similar to rodent OPRK1 genes. Direct sequencing of amplified DNA containing all four exons and intron 1 of the hOPRK1 gene were evaluated for polymorphisms in 291 subjects (145 former heroin addicts and 146 controls). Twelve SNPs were identified, nine novel variants and three previously reported SNPs. Using logistic regression with opioid dependence as the dependent variable, the 36G>T SNP exhibited a point-wise significant association (P = 0.016) with disease status. The number of haplotypes seen in the three ethnic groups were nine, six and five for African-Americans, Caucasians, and Hispanics, respectively, with corresponding significance levels for differences in haplotype frequencies between cases and controls of P = 0.0742, 0.1015 and 0.0041. Combining ethnicities by Fisher's method yields an empirical significance level of P = 0.0020.

Mouse kappa-opioid receptor mRNA differential transport in neurons

Three kappa-opioid receptor (KOR) mRNA isoforms have been detected in different parts of the central nervous system. At the cellular level, three KOR mRNA isoforms are also differentially distributed in the axons and cell bodies of adult mouse trigeminal neurons, as well as in the processes and cell bodies of differentiated P19 neurons. To determine the molecular basis underlying differential distribution of KOR mRNA isoforms, a GFP-fused RNA binding domain, MS2, was generated and used to trace movement of KOR mRNA tagged with the MS2-binding sequence in living neurons of dorsal root ganglia and in differentiated P19 neurons. The 5'- and 3'-untranslated regions (UTRs) of KOR, either alone or in combination, are able to mediate transport of mRNAs to processes of P19 neurons and axons of dorsal root ganglia. The efficiency of mRNA transport mediated by each 5'-UTR of KOR varies among the three isoforms; isoform A is most efficient. This study demonstrates the biological activity of the UTRs of KOR mRNA isoforms in directing differential transport of mRNA in mammalian neurons.

Regulation of c-myc gene by nitric oxide via inactivating NF-kappa B complex in P19 mouse embryonal carcinoma cells

Nitric oxide (NO) may regulate gene expression by directly modifying redox state-sensitive residues of transcription factors. Here we show that the NO donor, sodium nitroprusside (SNP), rapidly represses c-myc gene transcription in a protein synthesis-independent manner in P19 embryonal carcinoma cells by inactivation of NF-kappa B. SNP treatment reduces the DNA binding ability of the constitutively active NF-kappa B heterodimer, p65/p50, and its consequent transactivation of the c-myc promoter. Repression can be blocked by the peroxynitrite scavenger, deferoxamine, but not by dithiothreitol, which triggers reduction of S-nitrosylated residues. In HEK293 cells, where tumor necrosis factor-alpha can activate NF-kappa B, SNP likewise suppresses the binding of the active NF-kappa B complex, restoring the binding of the repressive p50/p50 homodimer complex. This effect of SNP in HEK293 cells is also blocked by deferoxamine. Chromatin immunoprecipitation analysis of SNP-treated P19 cells reveals reduced association of p65, but not of p50, with the promoter region of the endogenous c-myc gene. SNP-induced p65 dissociation was associated with the recruitment of histone deacetylase 1 and 2 to the endogenous c-myc gene promoter and the subsequent deacetylation of its chromatin histone. This study is the first to demonstrate that NO modulates the transcriptional activity of the c-myc gene promoter by dissociating the active form of NF-kappa B and replacing it with a repressive NF-kappa B complex, correlated with the recruitment of gene-silencing histone deacetylases. In light of findings that NF-kappa B stimulates Myc oncoprotein expression in cancers, our findings suggest that NO should be investigated as a prospective therapeutic cancer agent.

Characterization of the human gamma-glutamyl hydrolase promoter and its gene expression in human tissues and cancer cell lines

Human gamma-glutamyl hydrolase (hGH) plays an important role in the metabolism of folic acid and the pharmacology of antifolates such as methotrexate. We have previously cloned and characterized hGH cDNA and its gene. We report here that the levels of hGH gene expression are high in tissues such as liver, kidney, and placenta as determined by Northern blot and RT-PCR analyses. In contrast, hGH expression is relatively low in spleen, lung, small intestine, and peripheral blood leukocytes. In addition, high levels of hGH mRNA were detected in most cancer cell lines examined. There was no significant difference in hGH mRNA levels between breast cancer tissues and their normal counterparts, although breast cancer tissues generally appeared to have heterogeneous expression of hGH mRNA. Deletion analysis and transient transfection assays were performed. A positive regulatory element located from -52 to +4 relative to the transcriptional start site was found to be required for basal promoter activity in both HepG2 and MCF-7 cells. Also, transcriptional inhibitory elements were found at -96 to-52 and +88 to+104 in MCF-7 cells, but not in HepG2 cells. These data provide novel insights into the regulation of hGH gene transcription in HepG2 and MCF-7 cells.

Perturbation of Ikaros isoform selection by MLV integration is a cooperative event in Notch(IC)-induced T cell leukemogenesis

The chromosomal translocation t(7;9)(q34;q34.3) in human T cell acute lymphoblastic leukemia (T-ALL) results in the aberrant expression of the intracellular domain of Notch (N(ic)). Consistent with the current multistep model for tumorigenesis, mice that express N(ic) in T cell progenitors develop a T-ALL-like disease with a lengthened latency. Proviral insertional mutagenesis greatly accelerated the onset of leukemia in N(ic) transgenic mice. We demonstrate that the Ikaros (Ik) locus is a common target of proviral integration in N(ic) transgenic mice, which results in the loss of Ik DNA binding activity through altered isoform expression. We propose that cooperative leukemogenesis occurs in cells that have constitutive N(ic) and altered Ik isoform expression because genes normally repressed by Ik become activated by N(ic)/CSL.

Role of an AP-2-like element in transcriptional regulation of mouse mu-opioid receptor gene

Previously, several important cis-elements and trans-factors have been shown to play a functional role in the proximal promoter of mouse mu-opioid receptor (MOR) gene. In this study, we defined another functional element located the in -450 to -400 bp (translational start site designated as +1) region of the proximal promoter, which is also essential for the full promoter activity. It is designated as the morAP-2-like element for its sequence homologous to the consensus AP-2 element. Surprisingly, electrophoretic mobility shift analysis (EMSA) revealed that Sp1 and Sp3, but not AP-2 proteins, were specifically bound to the morAP-2-like element. Mutation of the morAP-2-like element, resulting in a loss of Sp binding, led to an approximately 35% decrease in activity, further confirming the positive role of the morAP-2-like element in MOR gene expression. Dephosphorylation of Sp proteins with alkaline phosphatase also decreased Sp binding to the morAP-2-like element in EMSA, suggesting phosphorylation of Sp is essential for its binding to this element. However, direct or indirect activation of PKA, a classical G-protein coupled signaling pathway, resulted in no significant change of Sp binding to the morAP-2-like element, nor of the promoter activity the SH-SY5Y cells, MOR expressing cells, suggesting that phosphorylation of Sp does not involve PKA. These results suggest that the binding of different phosphorylated forms of Sp proteins to the morAP-2-like element may contribute to the fine tuning of MOR expression in different cells.

Variants of kappa-opioid receptor gene and mRNA in alcohol-preferring and alcohol-avoiding mice

Results of recent studies have indicated an association between voluntary alcohol intake and activities of kappa-opioid receptor systems in animal models. We assessed the possibility that genetic differences observed in alcohol preference among mouse strains are related to possible polymorphisms of the kappa-opioid receptor gene (Oprk1). We compared DNA sequences of the coding region and the promoter/regulatory region of Oprk1 among C57BL/6ByJ (B6, alcohol-preferring), BALB/cJ (alcohol-avoiding), CXBI (alcohol-avoiding), and six B6.C and B6.I Recombinant QTL Introgression (RQI) strains, which carry approximately 3% of the donor BALB/cJ genome in the background B6 genome and showed various alcohol preferences. Although there were no sequence differences in the coding region, BALB/cJ had a single nucleotide polymorphism (SNP) in the promoter region, which was not detected in other strains. The results indicate that the difference in alcohol preference between B6 and BALB/cJ is not correlated with polymorphisms of Oprk1. However, results of further studies comparing Oprk1 mRNA expression between B6 and BALB/cJ showed that Oprk1 expression is regulated differently in these strains. Also, DBA/2J mice (alcohol-avoiding) showed expression of Oprk1 mRNA subtypes (alternatively spliced) different from B6 and BALB/cJ mice. Search of the Celera Genomics database indicated that DBA/2J had several SNP sites in the promoter/regulatory regions, which might explain the different expression of Oprk1 mRNA subtypes in this strain. The strain-dependent variation in the expression of alternatively spliced genes can be a significant source of phenotypic variation of complex traits such as alcohol preference.

Induction of the mouse kappa-opioid receptor gene by retinoic acid in P19 cells

The mouse kappa-opioid receptor (KOR) gene is expressed in mouse embryonal carcinoma P19 cells and induced by retinoic acid (RA) within 24 h. An RA-responsive cis-acting element is identified within promoter I of the KOR gene. This element contains a GC box, a putative binding site for transcription factor Sp1. Enhanced binding of Sp1 to this GC box correlates with RA induction of KOR gene. Phosphatase inhibitor (sodium pyrophosphate) decreases RA induction of this promoter, whereas hypophosphorylation of Sp1 results in an increase in its DNA binding affinity to this promoter as demonstrated by in vitro gel retardation and in vivo chromatin immunoprecipitation assays. Consistently, the inhibitor of MEK, PD98058, dose-dependently enhances RA induction of this promoter, suggesting that the ERK signaling pathway is negatively involved in the RA induction of mouse KOR gene activities. Collectively, enhanced binding of Sp1 to promoter I of the KOR gene as a result of inhibiting the ERK pathway contributes to RA induction of this gene in P19.

A novel signaling pathway of nitric oxide on transcriptional regulation of mouse kappa opioid receptor gene

Nitric oxide (NO) suppressed the transcription of the mouse kappa opioid receptor (KOR) gene, mediated by a rapid downregulation of c-myc gene expression. KOR was constitutively expressed in postnatal day 19 (P19) embryonal carcinoma stem cells and is suppressed by NO donors [sodium nitroprusside (SNP), 3-morpholinosydnonimine-1, and S-nitrosoglutathione] in P19 stem cells within 4 hr. The suppression was reversed by 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, an NO scavenger, but could not be blocked by dithiothreitol, ruling out S-nitrosylation as the underlying mechanism. The suppressive effect of NO on KOR occurred at the level of gene transcription, mediated by E boxes located in promoters I and II of this gene. Protein-DNA complexes that formed on these E boxes contained c-myc; c-myc expression was suppressed by NO in P19 stem cells within 2 hr of treatment. Furthermore, chromatin immunoprecipitation demonstrated reduced c-myc binding to the E boxes and hypoacetylation of histone H3 on the chromatin of endogenous KOR promoters in P19 stem cells treated with SNP. It is proposed that NO regulates KOR at the level of gene transcription, mediated by a rapid suppression of c-myc gene expression and its binding to KOR promoters, and followed by chromatin hypoacetylation of and reduced transcription from KOR promoters in P19 stem cells. A novel pathway mediating the potential interplay between NO and opioid systems is discussed.

Regulation of mouse kappa opioid receptor gene expression by different 3'-untranslated regions and the effect of retinoic acid

The mouse kappa opioid receptor (KOR) gene uses two functional polyadenylation signals, separated by a distance of approximately 2.2 kilobases (kb) in the 3'-end of the gene. As a result, two major groups of KOR transcripts, with sizes of approximately 1.6 and 3.8 kb, respectively, are detected in mouse tissues and P19 cells. Utilization of different poly(A) of the KOR gene produces KOR transcripts of different mRNA stability, transcription efficiency, and regulatability. Retinoic acid specifically suppresses the expression of KOR transcripts using the second poly(A) in P19 cells. A putative transcriptional enhancer region is present within the second 3'-untranslated region (3'-UTR). It is concluded that alternative polyadenylation of the mouse KOR transcripts results in differential regulation of KOR expression at both transcriptional and post-transcriptional levels. A negative regulatory pathway for KOR transcription involves a putative enhancer region in its 3'-UTR. KOR mRNAs using the second poly(A) is more stable than that using the first poly(A).

Ikaros: a key regulator of haematopoiesis

Ikaros is an essential transcription factor for normal lymphocyte development. Because of its interaction with a number of closely related factors, Ikaros is required for correct regulation of differentiation and cell proliferation in T- and B-cell lineages. Interestingly, Ikaros appears to function both as a transcriptional repressor and as an activator through its ability to bind a large number of nuclear factors, including components of both histone deacetylase and ATP-dependent chromatin remodelling complexes. In addition, nuclear localisation is important for Ikaros function--unlike most transcription factors, Ikaros is localised to discrete nuclear foci in lymphoid cells, suggesting it employs novel mechanisms to regulate transcription.