ATRX-mediated chromatin association of histone variant macroH2A1 regulates α-globin expression.

The histone variant macroH2A generally associates with transcriptionally inert chromatin; however, the factors that regulate its chromatin incorporation remain elusive. Here, we identify the SWI/SNF helicase ATRX (α-thalassemia/MR, X-linked) as a novel macroH2A-interacting protein. Unlike its role in assisting H3.3 chromatin deposition, ATRX acts as a negative regulator of macroH2A's chromatin association. In human erythroleukemic cells deficient for ATRX, macroH2A accumulates at the HBA gene cluster on the subtelomere of chromosome 16, coinciding with the loss of α-globin expression. Collectively, our results implicate deregulation of macroH2A's distribution as a contributing factor to the α-thalassemia phenotype of ATRX syndrome.

Technique for suppressing the electronic offset drift of interferometric open-loop fiber optic gyroscopes.

A technique to eliminate the offset drift in the demodulator circuitry of open-loop interferometric fiber optic gyroscopes is presented. This technique employs a demodulation scheme that uses the area of the negative half-cycles of the output signal of a sinusoidally modulated gyroscope to obtain the angular velocity. We propose an electronic circuitry that periodically reverses the demodulator input, allowing for the acquisition of two samples of the gyroscope signal with the same magnitude and opposite polarities. The angular velocity is obtained from the subtraction of these two samples, suppressing the electronic offset. Experiments showed that the proposed method reduces the demodulator offset drift from 4.4 µV/°C to about 14 nV/°C, which is equivalent to a reduction, from 0.2 deg/h/°C to about 0.0006 deg/h/°C in the tested gyroscope. The proposed technique improved the bias stability of the tested gyroscope from 0.0162 to 0.0071 deg/h.

Histone variants: emerging players in cancer biology.

Histone variants are key players in shaping chromatin structure, and, thus, in regulating fundamental cellular processes such as chromosome segregation and gene expression. Emerging evidence points towards a role for histone variants in contributing to tumor progression, and, recently, the first cancer-associated mutation in a histone variant-encoding gene was reported. In addition, genetic alterations of the histone chaperones that specifically regulate chromatin incorporation of histone variants are rapidly being uncovered in numerous cancers. Collectively, these findings implicate histone variants as potential drivers of cancer initiation and/or progression, and, therefore, targeting histone deposition or the chromatin remodeling machinery may be of therapeutic value. Here, we review the mammalian histone variants of the H2A and H3 families in their respective cellular functions, and their involvement in tumor biology.

MacroH2A histone variants modulate enhancer activity to repress oncogenic programs and cellular reprogramming.

Considerable efforts have been made to characterize active enhancer elements, which can be annotated by accessible chromatin and H3 lysine 27 acetylation (H3K27ac). However, apart from poised enhancers that are observed in early stages of development and putative silencers, the functional significance of cis-regulatory elements lacking H3K27ac is poorly understood. Here we show that macroH2A histone variants mark a subset of enhancers in normal and cancer cells, which we coined 'macro-Bound Enhancers', that modulate enhancer activity. We find macroH2A variants localized at enhancer elements that are devoid of H3K27ac in a cell type-specific manner, indicating a role for macroH2A at inactive enhancers to maintain cell identity. In following, reactivation of macro-bound enhancers is associated with oncogenic programs in breast cancer and their repressive role is correlated with the activity of macroH2A2 as a negative regulator of BRD4 chromatin occupancy. Finally, through single cell epigenomic profiling of normal mammary stem cells derived from mice, we show that macroH2A deficiency facilitates increased activity of transcription factors associated with stem cell activity.

Therapeutic and technological potential of 7-chloro-4-phenylselanyl quinoline for the treatment of atopic dermatitis-like skin lesions in mice.

This study investigated the main effects of the oral treatment with 7-chloro-4-phenylselanyl quinoline (4-PSQ) on symptoms, inflammatory and oxidative parameters in an atopic dermatitis (AD) model in BALB/c mice. In addition, the possibility of antioxidant property of 4-PSQ improves the potential of a biofilm (based on chitosan/poly(vinyl alcohol) (PVA)/ bovine bone powder (BBP)) for the treatment of AD-like skin lesions was evaluated. 2,4-Dinitrochlorobenzene (DNCB) was applied to the dorsal skin on days 1-3 for sensitization. Mice were challenged with DNCB on the ear (on days 14-29) and dorsal skin (on days 14, 17, 20, 23, 26, and 29) and treated with 4-PSQ, dexamethasone, biofilm (biofilm sample without 4-PSQ) or 4-PSQ-loaded biofilms. On the day 30, skin severity scores and scratching behavior were determined. After that, animals were sacrificed, and ears and dorsal skin were removed for determination of inflammatory and oxidative parameters. DNCB induced the skin lesions, scratching behavior and ear swelling, increased myeloperoxidase (MPO) activity (ear and back) and reactive species (RS) levels (back). 4-PSQ, 4-PSQ-loaded biofilms and biofilm treatments ameliorated skin severity scores, scratching behavior and inflammatory response induced by DNCB. 4-PSQ and 4-PSQ-loaded biofilm treatments partially protected against the increase in the RS levels induced by DNCB. Our results revealed that the incorporation of 4-PSQ improved the therapeutic effect of the biofilm. The efficacy of 4-PSQ in treating AD-like lesions was similar or better than dexamethasone. In summary, 4-PSQ has a potential therapeutic advantage in the treatment and management of AD.

Organoselenium group is critical for antioxidant activity of 7-chloro-4-phenylselenyl-quinoline.

The quinolone compounds have been reported for many biological properties, especially as potent antioxidants. This study investigated the antioxidant effect of 7-chloro-4-phenylselenyl-quinoline (PSQ), a quinolone derivative with organoselenium group, against oxidative stress induced by sodium nitroprusside (SNP) in brains of mice. A second objective was to verify the importance of phenylselenyl group presents at position 4 of the quinoline structure to antioxidant effect of compound. So, it was compared the antioxidant effect of PSQ with a quinoline without organoseleniun group (7-chloroquinoline [QN]). Swiss mice were used and received SNP (0.335 µmol/site, intracerebroventricular) 30 min after treatment with PSQ or QN, at the doses of 50 mg/kg (intragastrically). After 1 h, animals were sacrificed and the brains were removed to biochemistry analysis. Thiobarbituric acid reactive species (TBARS), protein carbonyl (PC) and non-protein thiol (NPSH) levels, as well as catalase (CAT), glutathione S transferase (GST) and δ -aminolevulinic acid (δ-ALA-D) activities were determined. SNP increased TBARS and PC levels, and reduced the enzymatic (CAT and GST activity) and non-enzymatic (NPSH levels) antioxidant defenses and inhibited the δ-ALA-D activity. PSQ avoided the increase in the lipid peroxidation and PC levels, as well as the decrease in the NPSH levels, CAT, GST and δ-ALA-D activities QN partially avoided the increase in lipid peroxidation, but it not protected against alterations induced by SNP. In conclusion, phenylselenyl group present in quinoline structure is critical for antioxidant activity of PSQ.

Histone H3.3 and its proteolytically processed form drive a cellular senescence programme.

The process of cellular senescence generates a repressive chromatin environment, however, the role of histone variants and histone proteolytic cleavage in senescence remains unclear. Here, using models of oncogene-induced and replicative senescence, we report novel histone H3 tail cleavage events mediated by the protease Cathepsin L. We find that cleaved forms of H3 are nucleosomal and the histone variant H3.3 is the preferred cleaved form of H3. Ectopic expression of H3.3 and its cleavage product (H3.3cs1), which lacks the first 21 amino acids of the H3 tail, is sufficient to induce senescence. Further, H3.3cs1 chromatin incorporation is mediated by the HUCA histone chaperone complex. Genome-wide transcriptional profiling revealed that H3.3cs1 facilitates transcriptional silencing of cell cycle regulators including RB/E2F target genes, likely via the permanent removal of H3K4me3. Collectively, our study identifies histone H3.3 and its proteolytically processed forms as key regulators of cellular senescence.

Preparation of group I introns for biochemical studies and crystallization assays by native affinity purification.

The study of functional RNAs of various sizes and structures requires efficient methods for their synthesis and purification. Here, 23 group I intron variants ranging in length from 246 to 341 nucleotides -- some containing exons -- were subjected to a native purification technique previously applied only to shorter RNAs (<160 nucleotides). For the RNAs containing both exons, we adjusted the original purification protocol to allow for purification of radiolabeled molecules. The resulting RNAs were used in folding assays on native gel electrophoresis and in self-splicing assays. The intron-only RNAs were subjected to the regular native purification scheme, assayed for folding and employed in crystallization screens. All RNAs that contained a 3' overhang of one nucleotide were efficiently cleaved off from the support and were at least 90% pure after the non-denaturing purification. A representative subset of these RNAs was shown to be folded and self-splicing after purification. Additionally, crystals were grown for a 286 nucleotide long variant of the Clostridium botulinum intron. These results demonstrate the suitability of the native affinity purification method for the preparation of group I introns. We hope these findings will stimulate a broader application of this strategy to the preparation of other large RNA molecules.

Induction of parallel human telomeric G-quadruplex structures by Sr(2+).

Human telomeric DNA forms G-quadruplex secondary structures, which can inhibit telomerase activity and are targets for anti-cancer drugs. Here we show that Sr(2+) can induce human telomeric DNA to form both inter- and intramolecular structures having characteristics consistent with G-quadruplexes. Unlike Na(+) or K(+), Sr(2+) facilitated intermolecular structure formation for oligonucleotides with 2 to 5 5'-d(TTAGGG)-3' repeats. Longer 5'-d(TTAGGG)-3' oligonucleotides formed exclusively intramolecular structures. Altering the 5'-d(TTAGGG)-3' to 5'-d(TTAGAG)-3' in the 1st, 3rd, or 4th repeats of 5'-d(TTAGGG)(4)-3' stabilized the formation of intermolecular structures. However, a more compact, intramolecular structure was still observed when the 2nd repeat was altered. Circular dichroism spectroscopy results suggest that the structures were parallel-stranded, distinguishing them from similar DNA sequences in Na(+) and K(+). This study shows that Sr(2+), promotes parallel-stranded, inter- and intramolecular G-quadruplexes that can serve as models to study DNA substrate recognition by telomerase.

Sequence specificity of inter- and intramolecular G-quadruplex formation by human telomeric DNA.

Human telomeric DNA consists of tandem repeats of the sequence 5'-d(TTAGGG)-3'. Guanine-rich DNA, such as that seen at telomeres, forms G-quadruplex secondary structures. Alternative forms of G-quadruplex structures can have differential effects on activities involved in telomere maintenance. With this in mind, we analyzed the effect of sequence and length of human telomeric DNA on G-quadruplex structures by native polyacrylamide gel electrophoresis and circular dichroism. Telomeric oligonucleotides shorter than four, 5'-d(TTAGGG)-3' repeats formed intermolecular G-quadruplexes. However, longer telomeric repeats formed intramolecular structures. Altering the 5'-d(TTAGGG)-3' to 5'-d(TTAGAG)-3' in any one of the repeats of 5'-d(TTAGGG)(4)-3' converted an intramolecular structure to intermolecular G-quadruplexes with varying degrees of parallel or anti-parallel-stranded character, depending on the length of incubation time and DNA sequence. These structures were most abundant in K(+)-containing buffers. Higher-order structures that exhibited ladders on polyacrylamide gels were observed only for oligonucleotides with the first telomeric repeat altered. Altering the sequence of 5'-d(TTAGGG)(8)-3' did not result in the substantial formation of intermolecular structures even when the oligonucleotide lacked four consecutive telomeric repeats. However, many of these intramolecular structures shared common features with intermolecular structures formed by the shorter oligonucleotides. The wide variability in structure formed by human telomeric sequence suggests that telomeric DNA structure can be easily modulated by proteins, oxidative damage, or point mutations resulting in conversion from one form of G-quadruplex to another.