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Periodicity of strong nucleosome positioning sites around the chicken adult beta-globin gene may encode regularly spaced chromatin.

Positioned nucleosomes contribute to both the structure and the function of the chromatin fiber and can play a decisive role in controlling gene expression. We have mapped, at high resolution, the translational positions adopted by limiting amounts of core histone octamers reconstituted onto 4.4 kb of DNA comprising the entire chicken adult beta-globin gene, its enhancer, and flanking sequences. The octamer displays extensive variation in its affinity for different positioning sites, the range exhibited being about 2 orders of magnitude greater than that of the initial binding of the octamer. Strong positioning sites are located 5' and 3' of the globin gene and in the second intron but are absent from the coding regions. These sites exhibit a periodicity (approximately 200 bp) similar to the average spacing of nucleosomes on the inactive beta-globin gene in vivo, which could indicate their involvement in packaging the gene into higher-order chromatin structure. Overlapping, alternative octamer positioning sites commonly exhibit spacings of 20 and 40 bp, but not of 10 bp. These short-range periodicities could reflect features of the core particle structure contributing to the pronounced sequence-dependent manner in which the core histone octamer interacts with DNA.

Animals↗

Dual involvement of protein kinase C delta in apoptosis induced by syndecan-2 in osteoblasts.

Syndecans are proteoglycans that act as signaling molecules. Previously, we showed that syndecan-2 (SYND2) is involved in the control of osteoblastic (OB) cell apoptosis. Here, we show a novel functional interaction between SYND2 and protein kinase C delta (PKCdelta). Overexpression of SYND2 in MG63 OB cells resulted in increased PKCdelta protein level without change in PKCdelta mRNA production. In SYND2-transfected cells, the increase in PKCdelta was restricted to the cytosolic compartment, threonine 505-PKCdelta was underphosphorylated and immunoprecipitated PKCdelta showed decreased capacity to phosphorylate histone, indicating that SYND2 decreased PKCdelta activity. Inhibition of PKCdelta by Rottlerin or a dead-kinase dominant negative (DN) construct activated effector caspases and increased the number of apoptotic cells. In addition, rescue of kinase activity with a construct coding, the PKCdelta catalytic domain (CAT) reduced SYND2-induced apoptosis. This indicates that PKCdelta acts as a pro-survival kinase and that SYND2 inhibits the anti-apoptotic action of PKCdelta in OB cells. We also showed that overexpression of PKCdelta wild type (WT) induced osteoblast apoptosis. Moreover, inhibition of PKCdelta by siRNA resulted in increased apoptosis in control cells but reduced apoptosis in SYND2-overexpressing osteoblasts, indicating that SYND2 requires PKCdelta accumulation to induce apoptosis. These results show that SYND2 modulates PKCdelta actions by inhibition of the canonical allosterical activation pathway that plays an anti-apoptotic role in OB cells, and promotion of a pro-apoptotic role that may depend on PKCdelta protein level and that participates to the induction of cell death by SYND2. This establishes a functional interaction between SYND2 and PKCdelta in osteoblasts.

Apoptosis↗

The human SETMAR protein preserves most of the activities of the ancestral Hsmar1 transposase.

Transposons have contributed protein coding sequences to a unexpectedly large number of human genes. Except for the V(D)J recombinase and telomerase, all remain of unknown function. Here we investigate the activity of the human SETMAR protein, a highly expressed fusion between a histone H3 methylase and a mariner family transposase. Although SETMAR has demonstrated methylase activity and a DNA repair phenotype, its mode of action and the role of the transposase domain remain obscure. As a starting point to address this problem, we have dissected the activity of the transposase domain in the context of the full-length protein and the isolated transposase domain. Complete transposition of an engineered Hsmar1 transposon by the transposase domain was detected, although the extent of the reaction was limited by a severe defect for cleavage at the 3' ends of the element. Despite this problem, SETMAR retains robust activity for the other stages of the Hsmar1 transposition reaction, namely, site-specific DNA binding to the transposon ends, assembly of a paired-ends complex, cleavage of the 5' end of the element in Mn(2+), and integration at a TA dinucleotide target site. SETMAR is unlikely to catalyze transposition in the human genome, although the nicking activity may have a role in the DNA repair phenotype. The key activity for the mariner domain is therefore the robust DNA-binding and looping activity which has a high potential for targeting the histone methylase domain to the many thousands of specific binding sites in the human genome provided by copies of the Hsmar1 transposon.

Amino Acid Sequence↗

Glucocorticoid pathways in chronic obstructive pulmonary disease therapy.

Lung function measures in patients with chronic obstructive pulmonary disease remain insensitive to corticosteroid actions, in contrast to the clinical improvements observed in most patients with asthma. By uncovering the reason for this paradox, physicians should be able to implement treatment regimens that restore corticosteroid sensitivity. Corticosteroids exert their effects by binding to a cytoplasmic glucocorticoid receptor, which is subjected to post-translational modification by phosphorylation. Receptor phosphorylation may influence hormone binding and nuclear translocation, as well as alter other glucocorticoid receptor interactions, its protein half-life, and downregulation processes. This suggests that a "phosphorylation code" may exist for glucocorticoid receptor function. Oxidative stress due to cigarette smoke may also be a mechanism for the corticosteroid resistance observed in chronic obstructive pulmonary disease, as it enhances proinflammatory transcription. Reduced glucocorticoid nuclear translocation along with attenuated histone deacetylase activity may be partially responsible for this effect. Therapies targeting these aspects of the glucocorticoid receptor activation pathway may reverse steroid resistance in patients with chronic obstructive pulmonary disease.

Administration, Inhalation↗

The human H2A and H2B histone gene complement.

Sequences and expression patterns of newly isolated human histone H2A and H2B genes and the respective proteins were compared with previously isolated human H2A and H2B genes and proteins. Altogether, 15 human H2A genes and 17 human H2B genes have been identified. 14 of these are organized as H2A/H2B gene pairs, while one H2A gene and three H2B genes are solitary genes. Two H2A genes and two H2B genes turned outto be pseudogenes. The 13 H2A genes code for at least 6 different amino acid sequences, and the 15 H2B genes encode 11 different H2B isoforms. Each H2A/H2B gene pair is controlled by a divergent promoter spanning 300 to 330 nucleotides between the coding regions of the two genes. The highly conserved divergent H2A/H2B promoters can be classified in two groups based on the patterns of consensus sequence elements. Group I promoters contain a TATA box for each gene, two Oct-1 factor binding sites, and three CCAAT boxes. Group II promoters contain the same elements as group I promoters and an additional CCAAT box, a binding motif for E2F and adjacent a highly conserved octanucleotide (CACAGCTT) that has not been described so far. Five of the 6 gene pairs and 4 solitary genes with group I promoters are localized in the large histone gene cluster at 6p21.3-6p22, and one gene pair is located at 1q21. All group II promoter associated genes are contained within the histone gene subcluster at D6S105, which is located at a distance of about 2 Mb from the major subcluster at 6p21.3-6p22 containing histone genes with group I promoters. Almost all group II H2A genes encode identical amino acid sequences, whereas group I H2A gene products vary at several positions. Using human cell lines, we have analyzed the expression patterns of functional human H2A/H2B gene pairs organized within the two histone gene clusters on the short arm of chromosome 6. The genes show varying expression patterns in different tumor cell lines.

Amino Acid Sequence↗

Molecular cloning and characterization of cDNA encoding a ubiquitin-conjugating enzyme from Clonorchis sinensis.

The ubiquitin-proteasome system is an essential mechanism for protein degradation in eukaryotes. Protein ubiquitination is composed of a series of enzymatic reactions. The ubiquitin-conjugating enzyme (E2) is one of the important enzymes involved in the process. A cDNA encoding an E2 enzyme was cloned from a Clonorchis sinensis cDNA library by large-scale sequencing. This new cDNA contains 862 bp with a putative open reading frame of 156 amino acids. The deduced amino acid sequence is 77% identical to the human E2, HHR6A and HHR6B. The coding region of this cDNA was expressed in E. coli as a GST-tagged protein, and was purified to electrophoretic homogeneity. Enzymatic assays showed that this E2 had the capacity to form a thiolester linkage, and could conjugate ubiquitin to histone H2A in an E3-independent manner in vitro, which indicated that the expressed protein was functionally active. The nucleotide sequence reported in this paper has been submitted to the Genbank Database with accession number AY632078.

Amino Acid Sequence↗

Cell-type non-selective transcription of mouse and human genes encoding neural-restrictive silencer factor.

Neural-restrictive silencer (NRS) has been identified in at least twenty neuron-specific genes, and its nuclear DNA-binding factor, NRSF (also known as RE1-silencing transcription factor (REST)), has been cloned from human and rat, and was shown to repress transcription by recruiting corepressors mSin3 and/or CoREST via its N- and C-terminal domains, leading to chromatin reorganization by mSin3-associated histone deacetylase, HDAC. However, it is largely unknown how NRSF gene expression is regulated. To elucidate the mechanisms for gene expression of NRSF, we isolated the transcriptional unit of the NRSF gene from mouse and human, identified three 5'-non-coding exons in addition to three coding exons, determined transcription start sites, and identified two basal promoter activities in the upstream of the first two non-coding exons. Both promoters functioned equally in neuronal and non-neuronal cells, suggesting that levels of initial transcripts of NRSF gene are similar in neuronal and non-neuronal cells. These results suggest that the level of NRSF gene expression is not determined by transcription per se, and rather is modulated at the post-transcriptional level, e.g. splicing, mRNA stability, and/or post-translational modifications, in a cell-specific manner. Consistent with this idea, NRSF protein was apparently present even in neuronal cells and tissues, but was unable to bind to the NRS element, suggesting that NRSF is regulated at least in part post-translationally.

3T3 Cells↗

Epigenotypes of latent herpesvirus genomes.

Epigenotypes are modified cellular or viral genotypes which differ in transcriptional activity in spite of having an identical (or nearly identical) DNA sequence. Restricted expression of latent, episomal herpesvirus genomes is also due to epigenetic modifications. There is no virus production (lytic viral replication, associated with the expression of all viral genes) in tight latency. In vitro experiments demonstrated that DNA methylation could influence the activity of latent (and/or crucial lytic) promoters of prototype strains belonging to the three herpesvirus subfamilies (alpha-, beta-, and gamma-herpesviruses). In vivo, however, DNA methylation is not a major regulator of herpes simplex virus type 1 (HSV-1, a human alpha-herpesvirus) latent gene expression in neurons of infected mice. In these cells, the promoter/enhancer region of latency-associated transcripts (LATs) is enriched with acetyl histone H3, suggesting that histone modifications may control HSV-1 latency in terminally differentiated, quiescent neurons. Epstein-Barr virus (EBV, a human gamma-herpesvirus) is associated with a series of neoplasms. Latent, episomal EBV genomes are subject to host cell-dependent epigenetic modifications (DNA methylation, binding of proteins and protein complexes, histone modifications). The distinct viral epigenotypes are associated with distinct EBV latency types, i.e., cell type-specific usage of latent EBV promoters controlling the expression of latent, growth transformation-associated EBV genes. The contribution of major epigenetic mechanisms to the regulation of latent EBV promoters is variable. DNA methylation contributes to silencing of Wp and Cp (alternative promoters for transcripts coding for the nuclear antigens EBNA 1-6) and LMP1p, LMP2Ap, and LMP2Bp (promoters for transcripts encoding transmembrane proteins). DNA methylation does not control, however, Qp (a promoter for EBNA1 transcripts only) in lymphoblastoid cell lines (LCLs), although in vitro methylated Qp-reporter gene constructs are silenced. The invariably unmethylated Qp is probably switched off by binding of a repressor protein in LCLs.

DNA Methylation↗

Distribution of histone H3.3 in hematopoietic cell lineages.

We have introduced the histone variant H3.3 into chicken erythroid cell lines and examined its distribution in the neighborhood of the folate receptor (FR) and beta-globin genes by using high-resolution chromatin immunoprecipitation (ChIP). Marked incorporation of tagged H3.3 into the FR gene is confined to its upstream regulatory region and is observed whether or not the gene is transcriptionally active. Incorporation is also observed over locus control regulatory elements in the absence of transcription of genes regulated by these elements, suggesting that gene activity per se is not necessarily required to replace H3 with H3.3. Other active genes display various behaviors, either incorporating H3.3 over both the coding region and upstream regulatory region or over upstream sequences only. There is, however, no straightforward correlation between sites of H3.3 incorporation and regions of enrichment in H3 acetylation and lysine-4 methylation. In the case of FR and VEGF-D, in which incorporation is confined to upstream regions, the presence of exogenous H3 results in reduced expression, whereas H3.3 stimulates expression. This finding suggests that these histone variants can be active rather than passive participants in regulation of expression.

Animals↗

Effects of estrogen and progesterone on transcription, chromatin and ovalbumin gene expression in the chick oviduct.

The effects of estrogen, progesterone and estrogen + progesterone combined on nuclear transcriptional processes in oviducts of immature chicks, previously withdrawn from estrogen, are reported. The responses to the steroids of the endogenous nuclear RNA polymerase activities, both nucleolar (I) and nucleoplasmic (II), the chromatin compositions and template capacities, and the appearance of ovalbumin messenger RNA (mRNA) are compared. When immature chicks (previously treated at 14 days with estrogen) are withdrawn from estrogen treatment, there is a gradual reduction in both polymerase activities. Diurnal variations in polymerase II activties in the oviduct of withdrawn chicks required that subsequent experiments include time-matched controls. The hormones alter RNA polymerase II and II activities in vivo as assayed in isolated nuclei. Progesterone represses the polymerase I and II activities, while estrogen alone and estrogen + progesterone enhance both polymerase activities immediately after injection. Diethylstillbestrol, a synthetic estrogen, causes changes similar to those of estrogen. The effects of these steroids on the polymerases are detected within 15 min of hormone injection. Changes in the capacities of chromatins to serve as template for RNA synthesis in general correlated with changes in polymerase II activities. Interestingly, in the case of estrogen treatment, the acidic chromatin protein (but not histone) levels fluctuate positively with the template capacities of the chromatin. An antagonism between estrogen and progesterone is observed in the responses of both RNA polymerases I and II activities as well as in the chromatin template capacity. Levels of messenger RNA coding for ovalbumin, as detected by hybridization with labeled complementary DNA, increase in oviducts of withdrawn chicks within 2--3 of the injection of estrogen, progesterone or estrogen + progesterone. This rapid accumulation of ovalbumin mRNA is not accompanied in each case by a similar increase in polymerase II activity or chromatin template capacity.

Animals↗

The genome of Entamoeba histolytica.

Estimation of genome size of Entamoeba histolytica by different methods has failed to give comparable values due to the inherent complexities of the organism, such as the uncertain level of ploidy, presence of multinucleated cells and a poorly demarcated cell division cycle. The genome of E. histolytica has a low G+C content (22.4%), and is composed of both linear chromosomes and a number of circular plasmid-like molecules. The rRNA genes are located exclusively on some of the circular DNAs. Karyotype analysis by pulsed field gel electrophoresis suggests the presence of 14 conserved linkage groups and an extensive size variation between homologous chromosomes from different isolates. Several repeat families have been identified, some of which have been shown to be present in all the electrophoretically separated chromosomes. The typical nucleosomal structure has not been demonstrated, though most of the histone genes have been identified. Most Entamoeba genes lack introns, have short 3' and 5' untranslated regions, and are tightly packed. Promoter analysis revealed the presence of three conserved motifs and several upstream regulatory elements. Unlike typical eukaryotes, the transcription of protein coding genes is alpha-amanitin resistant. Expressed Sequence Tag analysis has identified a group of highly abundant polyadenylated RNAs which are unlikely to be translated. The Expressed Sequence Tag approach has also helped identify several important genes which encode proteins that may be involved in different biochemical pathways, signal transduction mechanisms and organellar functions.

Animals↗

Synonymous codon usage in Zea mays L. nuclear genes is varied by levels of C and G-ending codons.

A multivariate statistical method called correspondence analysis was used to examine the codon usage of one-hundred-and-one nuclear genes of maize (Zea mays L.). Forty percent of the variation in codon usage was due to bias toward G or C-ending versus A or U-ending codons. Differences in levels of G-ending codons showed the weakest correlation with the major codon usage bias. The bias toward C or U versus A or G in the silent third nucleotide position of synonymous codons accounted for approximately 10% of the variation in codon usage. The G+C content of the silent third nucleotide position of coding regions was not strongly correlated with G+C content of introns. Codon usage was strongly biased toward codons ending in G or C for a number of highly expressed genes including most light-regulated chloroplast proteins, ABA-induced proteins, histones, and anthocyanin biosynthetic enzymes. Codon usage of genes encoding storage proteins and regulatory proteins, such as transposases, kinases, phosphatases and transcription factors, was more random than that of genes encoding cytosolic enzymes with similar bias toward G or C-ending codons. Codon usage in maize may reflect both regional bias on nucleotide composition and selection on the silent third nucleotide position.

Base Composition↗

The HIV-1 Tat protein enhances megakaryocytic commitment of K562 cells by facilitating CREB transcription factor coactivation by CBP.

The human immunodeficiency virus type 1 (HIV-1) Tat protein regulates transcription factor functions and alters cellular gene expression. Because hematopoietic progenitor cell (HPC) differentiation requires activation of lineage-specific transcription factors, Tat may affect hematopoiesis in HIV-1-infected micro-environments. We have monitored the molecular effects of Tat on megakaryocytic differentiation in the HPC line, K562. Flow cytometry analysis of CD61 indicated that phorbol myristate acetate (PMA) (16 nM) stimulated megakaryocytic commitment of K562 cells was increased (3- to 4-fold) following exposure to Tat (1-100 ng/ml). Activation of the megakaryocytic transcription factor cAMP regulatory element binding protein (CREB) and its coactivation by the CREB binding protein (CBP) was subsequently monitored. CREB phosphorylation and DNA binding were measured by Western immunodetection and electrophoretic mobility shift assays (EMSA), respectively. Within 2 hrs after stimulation, Tat increased both CREB phosphorylation and DNA binding by 7- to 10-fold. Transient cotransfection with CREB reporter and CBP expression plasmids demonstrated that Tat treatment increases (3- to 4-fold) both PMA-stimulated and CBP-mediated transcription via the cAMP regulatory element. Histone acetyl transferase (HAT) activity was increased (8- to 10-fold) in Tat-stimulated cells, which suggested increased chromosomal accessibility of transcription factors. Two-hybrid cotransfection assays using reporter plasmid containing the GAL4 DNA-binding domain and expression plasmid coding for the GAL4-CBP fusion protein, showed that Tat increases (2-fold) CBP-mediated coactivation of CREB. Both reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis showed that Tat treatment increases CBP gene expression (7- to 9-fold) and protein levels (5- to 7-fold) within 6-12 hrs after stimulation. Our findings indicated that Tat treatment increases both CREB function and CREB coactivation by CBP, which may facilitate megakaryocytic commitment of K562 cells. Induction of this molecular signaling by HIV-1 Tat protein may have relevance in understanding the HIV-induced hematologic manifestations and possibly in regulation of viral infectivity parameters in progenitor cell reservoirs.

CREB-Binding Protein↗

The chlamydial EUO gene encodes a histone H1-specific protease.

Chlamydia trachomatis is an obligate intracellular pathogen, long recognized as an agent of blinding eye disease and more recently as a common sexually transmitted infection. Recently, two eukaryotic histone H1-like proteins, designated Hc1 and Hc2, have been identified in Chlamydia. Expression of Hc1 in recombinant Escherichia coli produces chromatin condensation similar to nucleoid condensation observed late in the parasite's own life cycle. In contrast, chromatin decondensation, observed during the early life cycle, accompanies down-regulation and nondetection of Hc1 and Hc2 among internalized organisms. We reasoned that the early upstream open reading frame (EUO) gene product might play a role in Hc1 degradation and nucleoid decondensation since it is expressed very early in the chlamydial life cycle. To explore this possibility, we fused the EUO coding region between amino acids 4 and 177 from C. trachomatis serovar Lz with glutathione S-transferase (GST) and examined the effects of fusion protein on Hc1 in vitro. The purified fusion protein was able to digest Hc1 completely within 1 h at 37 degrees C. However, GST alone exhibited no Hc1-specific proteolytic activity. The chlamydial EUO-GST gene product also cleaves very-lysine-rich calf thymus histone H1 and chicken erythrocyte histone H5 but displays no measurable activity towards core histones H2A, H2B, H3, and H4 or chlamydial RNA polymerase alpha-subunit. This proteolytic activity appears sensitive to the serine protease inhibitor 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride (AEBSF) and aspartic protease inhibitor pepstatin but resistant to high temperature and other broad-spectrum protease inhibitors. The proteolytic activity specified by the EUO-GST fusion product selectively digested the C-terminal portion of chlamydial Hc1, the domain involved in DNA binding, while leaving the N terminus intact. At a molar equivalent ratio of 1:1 between Hc1 and DNA, the EUO gene product cleaves Hc1 complexed to DNA and this cleavage appears sufficient to initiate dissociation of DNA-Hc1 complexes. However, at a higher molar equivalent ratio of Hc1/DNA (10:1), there is partial protection conferred upon Hc1 to an extent that prevents dissociation of DNA-Hc1 complexes.

Amino Acid Sequence↗

hns, rpoS and lrp mutations affect stationary-phase survival at high osmolarity.

The survival of enteric bacteria during stationary phase requires the expressions of different genes than those required for growth during log phase. Genes coding for functions protecting cells from environmental stress are expressed during the onset of stationary phase. Many promoters of these genes require sigma s, the product of the rpoS gene, for transcription. During stationary phase, we found that strains lacking the neutral, histone-like, DNA-binding protein H-NS (hns- rpoS- double mutants) are more viable at high osmolarity at 37 degrees C than hns+ rpoS- cells. We did not observe differential viability at high osmolarity at 30 degrees C or at normal osmolarity at 37 degrees C. We showed that this effect is due to the absence of H-NS. The leucine-responsive regulatory protein acts without H-NS to protect a strain containing an rpoS mutation from death in stationary phase at high osmolarity. We present evidence that hns- rpoS double mutants can synthesize the log phase osmotic shock protective system.

Bacterial Proteins↗

Epigenetic regulation of mammalian genomic imprinting.

Imprinted genes play important roles in development, and most are clustered in large domains. Their allelic repression is regulated by 'imprinting control regions' (ICRs), which are methylated on one of the two parental alleles. Non-histone proteins and nearby sequence elements influence the establishment of this differential methylation during gametogenesis. DNA methylation, histone modifications, and also polycomb group proteins are important for the somatic maintenance of imprinting. The way ICRs regulate imprinting differs between domains. At some, the ICR constitutes an insulator that prevents promoter-enhancer interactions, when unmethylated. At other domains, non-coding RNAs could be involved, possibly by attracting chromatin-modifying complexes. The latter silencing mechanism has similarities with X-chromosome inactivation.

Animals↗

Analysis of the Leishmania donovani transcriptome reveals an ordered progression of transient and permanent changes in gene expression during differentiation.

Leishmania donovani is an intracellular protozoan parasite that causes kala-azar in humans. During infection the extracellular insect forms (promastigotes) undergo rapid differentiation to intracellular amastigotes that proliferates in phagolysosomes of mammalian macrophages. We used microarray-based expression profiling to investigate the time-course of changes in RNA abundance during promastigote-to-amastigote differentiation in a host-free system that mimics this process. These studies revealed that several hundred genes underwent an ordered progression of transient or permanent up- and down-regulation during differentiation. Genes that were permanently up-regulated in amastigotes were enriched for transporters and surface proteins, but under-represented in genes involved in protein and other metabolism. Most of these changes occurred late in the differentiation process, when morphological differentiation was essentially complete. Down-regulated genes were over-represented in those involved in cell motility, growth and/or maintenance, and these changes generally occurred earlier in the process. Genes that were transiently up- or down-regulated during differentiation included those encoding heat shock proteins, ubiquitin hydrolases, RNA binding proteins, protein kinases, a protein phosphatase, and a histone deacetylase. These results suggest that changes in mRNA abundance may be important in signal transduction, as well as protein and mRNA turnover, during differentiation. In addition to these mRNA changes, other transcripts including one or more rRNAs and snoRNAs, and non-coding RNAs from several telomeres, also showed substantial changes in abundance during the differentiation process. This paper provides the first genome-scale quantitative analysis of gene expression during the transition from promastigotes to amastigotes and demonstrates the utility of the host-free differentiation system.

Animals↗