4,955 research outputs found

    Human THO‚ÄďSin3A interaction reveals new mechanisms to prevent R-loops that cause genome instability

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    R-loops, formed by co-transcriptional DNA‚ÄďRNA hybrids and a displaced DNA single strand (ssDNA), fulfill certain positive regulatory roles but are also a source of genomic instability. One key cellular mechanism to prevent R-loop accumulation centers on the conserved THO/TREX complex, an RNA-binding factor involved in transcription elongation and RNA export that contributes to messenger ribonucleoprotein (mRNP) assembly, but whose precise function is still unclear. To understand how THO restrains harmful R-loops, we searched for new THO-interacting factors. We found that human THO interacts with the Sin3A histone deacetylase complex to suppress co-transcriptional R-loops, DNA damage, and replication impairment. Functional analyses show that histone hypo-acetylation prevents accumulation of harmful R-loops and RNA-mediated genomic instability. Diminished histone deacetylase activity in THO- and Sin3A-depleted cell lines correlates with increased R-loop formation, genomic instability, and replication fork stalling. Our study thus uncovers physical and functional crosstalk between RNA-binding factors and chromatin modifiers with a major role in preventing R-loop formation and RNA-mediated genome instability.European Research Council ERC2014 AdG669898 TARLOOPMinisterio de Econom√≠a y Competitividad BFU2013-42918-P, BFU2016-75058-PJunta de Andaluc√≠a BIO123

    Resveratrol mediated modulation of Sirt-1/Runx2 promotes osteogenic differentiation of mesenchymal stem cells: potential role of Runx2 deacetylation.

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    Osteogenic repair in response to bone injury is characterized by activation and differentiation of mesenchymal stem cells (MSCs) to osteoblasts. This study determined whether activation of Sirt-1 (a NAD(+)-dependent histone deacetylase) by the phytoestrogen resveratrol affects osteogenic differentiation. Monolayer and high-density cultures of MSCs and pre-osteoblastic cells were treated with an osteogenic induction medium with/without the Sirt-1 inhibitor nicotinamide or/and resveratrol in a concentration dependent manner. MSCs and pre-osteoblastic cells differentiated to osteoblasts when exposed to osteogenic-induction medium. The osteogenic response was blocked by nicotinamide, resulting in adipogenic differentiation and expression of the adipose transcription regulator PPAR-ő≥ (peroxisome proliferator-activated receptor). However, in nicotinamide-treated cultures, pre-treatment with resveratrol significantly enhanced osteogenesis by increasing expression of Runx2 (bone specific transcription factor) and decreasing expression of PPAR-ő≥. Activation of Sirt-1 by resveratrol in MSCs increased its binding to PPAR-ő≥ and repressed PPAR-ő≥ activity by involving its cofactor NCoR (nuclear receptor co-repressor). The modulatory effects of resveratrol on nicotinamide-induced expression of PPAR-ő≥ and its cofactor NCoR were found to be mediated, at least in part, by Sirt-1/Runx2 association and deacetylation of Runx2. Finally, knockdown of Sirt-1 by using antisense oligonucleotides downregulated the expression of Sirt-1 protein and abolished the inhibitory effects of resveratrol, namely nicotinamide-induced Sirt-1 suppression and Runx2 acetylation, suggesting that the acetylated content of Runx2 is related to downregulated Sirt-1 expression. These data support a critical role for Runx2 acetylation/deacetylation during osteogenic differentiation in MSCs in vitro. (242 words in abstract)

    Pharmacological activation of SIRT6 triggers lethal autophagy in human cancer cells

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    Sirtuin 6 (SIRT6) is a member of the NAD+-dependent class III deacetylase sirtuin family, which plays a key role in cancer by controlling transcription, genome stability, telomere integrity, DNA repair, and autophagy. Here we analyzed the molecular and biological effects of UBCS039, the first synthetic SIRT6 activator. Our data demonstrated that UBCS039 induced a time-dependent activation of autophagy in several human tumor cell lines, as evaluated by increased content of the lipidated form of LC3B by western blot and of autophagosomal puncta by microscopy analysis of GFP-LC3. UBCS039-mediated activation of autophagy was strictly dependent on SIRT6 deacetylating activity since the catalytic mutant H133Y failed to activate autophagy. At the molecular level, SIRT6-mediated autophagy was triggered by an increase of ROS levels, which, in turn, resulted in the activation of the AMPK-ULK1-mTOR signaling pathway. Interestingly, antioxidants were able to completely counteract UBCS039-induced autophagy, suggesting that ROS burst had a key role in upstream events leading to autophagy commitment. Finally, sustained activation of SIRT6 resulted in autophagy-related cell death, a process that was markedly attenuated using either a pan caspases inhibitor (zVAD-fmk) or an autophagy inhibitor (CQ). Overall, our results identified UBCS039 as an efficient SIRT6 activator, thereby providing a proof of principle that modulation of the enzyme can influence therapeutic strategy by enhancing autophagy-dependent cell death
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