Histone H4, the cell cycle and a question of integrity

Proteome Alterations and Nucleosome Activation in Rat Myoblasts Treated with Cerium Oxide Nanoparticles

Oxidative stress is a widespread causative agent of disease. Together with its general relevance for biomedicine, such a dynamic is recognizably detrimental to space exploration. Among other solutions, cerium oxide nanoparticles (or nanoceria, NC) display a long-lasting, self-renewable antioxidant activity. In a previous experiment, we evaluated oxidative imbalance in rat myoblasts in space, aboard the International Space Station, and unveiled possible protective effects from NC through RNA sequencing. Here, we focus on the myoblast response to NC on land by means of proteomics, defining a list of proteins that putatively react to NC and confirming nucleosomes/histones as likely mediators of its molecular action. The proteomics data set we present here and its counterpart from the space study share four factors. These are coherently either up- (Hist1h4b) or down-regulated (Gnl3, Mtdh, Trip12) upon NC exposure.

Roles of four targets in the pathogenesis of graves' orbitopathy

Graves' orbitopathy (GO) is an autoimmune disease that involves complex immune systems. The mainstays of clinical management for this disease are surgery, targeted drugs therapy, and no-targeted drugs drug therapy. targeted drugs can improve therapeutic efficacy and enhance the quality of life for GO patients. However, as a second-line treatment for GO, targeted drugs such as tocilizumab and rituximab have very limited therapeutic effects and may be accompanied by side effects. The introduction of Teprotumumab, which targets IGF-IR, has made significant progress in the clinical management of GO. The pathophysiology of GO still remains uncertain as it involves a variety of immune cells and fibroblast interactions as well as immune responses to relevant disease targets of action. Therfore, learning more about immune response feedback pathways and potential targets of action will assist in the treatment of GO. In this discussion, we explore the pathogenesis of GO and relevant work, and highlight four potential targets for GO: Interleukin-23 receptor (IL-23 R), Leptin receptor (LepR), Orbital fibroblast activating factors, and Plasminogen activator inhibitor-1 (PAI-1). A deeper understanding of the pathogenesis of GO and the role of potential target signaling pathways is crucial for effective treatment of this disease.

Col3.6-HSD2 transgenic mice: a glucocorticoid loss-of-function model spanning early and late osteoblast differentiation

The goal of this study was to characterize the bone phenotype and molecular alterations in Col3.6-HSD2 mice in which a 3.6-kb Col1a1 promoter fragment drives 11beta-HSD2 expression broadly in the osteoblast lineage to reduce glucocorticoid signaling. Serum corticosterone was unchanged in transgenic females excluding a systemic effect of the transgene. Adult transgenic mice showed reduced vertebral trabecular bone volume and reduced femoral and tibial sub-periosteal and sub-endosteal areas as assessed by microCT. In adult female transgenic mice, histomorphometry showed that vertebral bone mass and trabecular number were reduced but that osteoblast and osteoclast numbers and the mineral apposition and bone formation rates were not changed, suggesting a possible developmental defect in the formation of trabeculae. In a small sample of male mice, osteoblast number and percent osteoid surface were increased but the mineral apposition bone formation rates were not changed, indicating subtle sex-specific phenotypic differences in Col3.6-HSD2 bone. Serum from transgenic mice had decreased levels of the C-terminal telopeptide of alpha1(I) collagen but increased levels of osteocalcin. Transgenic calvarial osteoblast and bone marrow stromal cultures showed decreased alkaline phosphatase and mineral staining, reduced levels of Col1a1, bone sialoprotein and osteocalcin mRNA expression, and decreased cell growth and proliferation. Transgenic bone marrow cultures treated with RANKL and M-CSF showed greater osteoclast formation; however, osteoclast activity as assessed by resorption of a calcium phosphate substrate was decreased in transgenic cultures. Gene profiling of cultured calvarial osteoblasts enriched in the Col3.6-HSD2 transgene showed modest but significant changes in gene expression, particularly in cell cycle and integrin genes. In summary, Col3.6-HSD2 mice showed a low bone mass phenotype, with decreased ex vivo osteogenesis. These data further strengthen the concept that endogenous glucocorticoid signaling is required for optimal bone mass acquisition and highlight the complexities of glucocorticoid signaling in bone cell lineages.

Analysis of promoter activity of selected Cotesia plutellae bracovirus genes

In a previous study, we cloned 27 discrete genome segments of Cotesia plutellae bracovirus (CpBV) and provided the complete nucleotide sequences and annotation. Seven putative coding regions were predicted from one of the largest segments, CpBV-S30. The activity of promoters associated with six predicted ORFs from this segment were investigated using both transient and baculovirus expression assays with enhanced green fluorescent protein as a reporter gene. CpBV promoters showed activity earlier than the polyhedrin promoter and the activity of some of these promoters was superior to that of the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ie-1 promoter in the baculovirus expression assays. The promoter of ORF3004 showed the highest level of activity in insect cells, exhibiting 24 % of the activity obtained with the AcMNPV polyhedrin promoter in Sf9 cells. In Spodoptera exigua larvae, the ORF3006 promoter showed the highest activity, with about 35 % of the activity measured with the polyhedrin promoter. In addition, analysis of the ORF3006 promoter revealed that the region between -382 and -422 from the translation start point was critical for activity of this promoter. These results suggest that the CpBV-S30 promoters characterized here could be useful tools in a variety of biotechnological applications, such as gene expression analyses and insecticide development.

Three-dimensional structure of the bacterial multidrug transporter EmrE shows it is an asymmetric homodimer

The small multidrug resistance family of transporters is widespread in bacteria and is responsible for bacterial resistance to toxic aromatic cations by proton-linked efflux. We have determined the three-dimensional (3D) structure of the Escherichia coli multidrug transporter EmrE by electron cryomicroscopy of 2D crystals, including data to 7.0 A resolution. The structure of EmrE consists of a bundle of eight transmembrane alpha-helices with one substrate molecule bound near the centre. The substrate binding chamber is formed from six helices and is accessible both from the aqueous phase and laterally from the lipid bilayer. The most remarkable feature of the structure of EmrE is that it is an asymmetric homodimer. The possible arrangement of the two polypeptides in the EmrE dimer is discussed based on the 3D density map.

Regulation of transcription by H1 phosphorylation in Tetrahymena is position independent and requires clustered sites

In Tetrahymena cells, constitutive phosphorylation of histone H1 phenocopies the loss of H1 from chromatin. Regulation of transcription by H1 phosphorylation is achieved by altering the overall charges of a small domain. Here, we further explore the electrostatic properties of this domain and the mechanism by which it regulates transcription. We demonstrate that the regulatory effect of the clustered charges does not require any long-range interaction and is position independent. However, when the same number of charges was dispersed throughout the H1 molecule, the effect became undetectable. The results are explained by a nucleation-propagation model and provide in vivo evidence that the synergy of the clustered positive charges plays a role in histone function and gene regulation.

Histone H2A.Z acetylation modulates an essential charge patch

Histone H2A.Z is structurally and functionally distinct from the major H2As. To understand the function of H2A.Z acetylation, we performed a mutagenic analysis of the six acetylated lysines in the N-terminal tail of Tetrahymena H2A.Z. Tetrahymena cannot survive with arginines at all six sites. Retention of one acetylatable lysine is sufficient to provide the essential function of H2A.Z acetylation. This essential function can be mimicked by deleting the region encompassing all six sites, or by mutations that reduce the positive charge of the N terminus at the acetylation sites themselves, or at other sites in the tail. These properties argue that the essential function of H2A.Z acetylation is to modify a "charge patch" by reducing the charge of the tail.

High-resolution structural analysis of chromatin at specific loci: Saccharomyces cerevisiae silent mating type locus HMLalpha

Genetic studies have suggested that chromatin structure is involved in repression of the silent mating type loci in Saccharomyces cerevisiae. Chromatin mapping at nucleotide resolution of the transcriptionally silent HMLalpha and the active MATalpha shows that unique organized chromatin structure characterizes the silent state of HMLalpha. Precisely positioned nucleosomes abutting the silencers extend over the alpha1 and alpha2 coding regions. The HO endonuclease recognition site, nuclease hypersensitive at MATalpha, is protected at HMLalpha. Although two precisely positioned nucleosomes incorporate transcription start sites at HMLalpha, the promoter region of the alpha1 and alpha2 genes is nucleosome free and more nuclease sensitive in the repressed than in the transcribed locus. Mutations in genes essential for HML silencing disrupt the nucleosome array near HML-I but not in the vicinity of HML-E, which is closer to the telomere of chromosome III. At the promoter and the HO site, the structure of HMLalpha in Sir protein and histone H4 N-terminal deletion mutants is identical to that of the transcriptionally active MATalpha. The discontinuous chromatin structure of HMLalpha contrasts with the continuous array of nucleosomes found at repressed a-cell-specific genes and the recombination enhancer. Punctuation at HMLalpha may be necessary for higher-order structure or karyoskeleton interactions. The unique chromatin architecture of HMLalpha may relate to the combined requirements of transcriptional repression and recombinational competence.

Essential and redundant functions of histone acetylation revealed by mutation of target lysines and loss of the Gcn5p acetyltransferase

The Gcn5p histone acetyltransferase exhibits a limited substrate specificity in vitro. However, neither the specificity of this enzyme in vivo nor the importance of particular acetylated residues to transcription or cell growth are well defined. To probe these questions, we mutated specific lysines in the N-termini of histones H3 and H4 and examined the effects of these mutations in yeast strains with and without functional GCN5. We found that in vivo, GCN5 is required either directly or indirectly for the acetylation of several sites in H3 and H4 in addition to those recognized by the recombinant enzyme in vitro. Moreover, in the absence of GCN5, cells accumulate in G2/M indicating that Gcn5p functions are important for normal cell-cycle progression. Mutation of K14 in H3, which serves as the major target of recombinant Gcn5p acetylation in vitro, confers a strong, synthetic growth defect in gcn5 cells. Synergistic growth defects were also observed in gcn5 cells carrying mutations in lysine pairs (K8/K16 or K5/K12) in histone H4. Strikingly, simultaneous mutation of K14 in H3 and K8 and K16 in H4 to arginine, or deletion of either the H3 or the H4 N-terminal tail, results in the death of gcn5 cells. Mutation of these same three sites to glutamine is not lethal. Indeed, this combination of mutations largely bypasses the need for GCN5 for transcriptional activation by Gal4-VP16, supporting an important role for histone acetylation in Gcn5p-mediated regulation of transcription. Our data indicate that acetylation of particular lysines in histones H3 and H4 serves both unique and overlapping functions important for normal cell growth, and that a critical overall level of histone acetylation is essential for cell viability.

Chromatin assembly coupled to DNA repair: a new role for chromatin assembly factor I

DNA repair in the eukaryotic cell disrupts local chromatin organization. To investigate whether the resetting of nucleosomal arrays can be linked to the repair process, we developed model systems, with both Xenopus egg extract and human cell extracts, to follow repair and chromatin assembly in parallel on circular DNA templates. Both systems were able to carry out nucleotide excision repair of DNA lesions. We observed that UV-dependent DNA synthesis occurs simultaneously with chromatin assembly, strongly indicating a mechanistic coupling between the two processes. A complementation assay established that chromatin assembly factor I (CAF1) is necessary for this repair associated chromatin formation.