Reduced RNA turnover as a driver of cellular senescence

Accumulation of senescent cells is an important contributor to chronic inflammation upon aging.Whilecytoplasmic DNA was shown to drivethe inflammatory phenotype of senescent cells, an equivalent role for RNA has never been explored.Here, we show that cellular senescence correlates with reduced expression ofRNA exosomesubunitsand coincident accumulation of promoter RNAs and immature RNA transcripts.Forced accumulation of these RNAs by inactivation of the Exosc3exosome subunit induces expression of senescence markersand reduced mitochondrial gene expression. Reciprocally, mitochondrial suffering and oxidative stress results in reduced RNA decay, suggestive of a feedback loop betweenRNA decay and mitochondrial activity. As severalof the accumulating RNAsare also produced during normal activation of immune cells and contain Alu sequences known to trigger an innate immune response, we propose that stabilizing immature and unstable RNAs participate in driving andmaintaining the permanent inflammatory state characteristic of cellular senescence

Reduced RNA turnover as a driver of cellular senescence

Accumulation of senescent cells is an important contributor to chronic inflammation upon aging. The inflammatory phenotype of senescent cells was previously shown to be driven by cytoplasmic DNA. Here, we propose that cytoplasmic double-stranded RNA has a similar effect. We find that several cell types driven into senescence by different routes share an accumulation of long promoter RNAs and 3' gene extensions rich in retrotransposon sequences. Accordingly, these cells display increased expression of genes involved in response to double stranded RNA of viral origin downstream of the interferon pathway. The RNA accumulation is associated with evidence of reduced RNA turnover, including in some cases, reduced expression of RNA exosome subunits. Reciprocally, depletion of RNA exosome subunit EXOSC3 accelerated expression of multiple senescence markers. A senescence-like RNA accumulation was also observed in cells exposed to oxidative stress, an important trigger of cellular senescence. Altogether, we propose that in a subset of senescent cells, repeat-containing transcripts stabilized by oxidative stress or reduced RNA exosome activity participate in driving and maintaining the permanent inflammatory state characterizing cellular senescence

Impact of Gephyrin alternative splicing on inhibitory synapses function

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Interaction of HP1 and Brg1/Brm with the Globular Domain of Histone H3 Is Required for HP1-Mediated Repression

The heterochromatin-enriched HP1 proteins play a critical role in regulation of transcription. These proteins contain two related domains known as the chromo- and the chromoshadow-domain. The chromo-domain binds histone H3 tails methylated on lysine 9. However, in vivo and in vitro experiments have shown that the affinity of HP1 proteins to native methylated chromatin is relatively poor and that the opening of chromatin occurring during DNA replication facilitates their binding to nucleosomes. These observations prompted us to investigate whether HP1 proteins have additional histone binding activities, envisioning also affinity for regions potentially occluded by the nucleosome structure. We find that the chromoshadow-domain interacts with histone H3 in a region located partially inside the nucleosomal barrel at the entry/exit point of the nucleosome. Interestingly, this region is also contacted by the catalytic subunits of the human SWI/SNF complex. In vitro, efficient SWI/SNF remodeling requires this contact and is inhibited in the presence of HP1 proteins. The antagonism between SWI/SNF and HP1 proteins is also observed in vivo on a series of interferon-regulated genes. Finally, we show that SWI/SNF activity favors loading of HP1 proteins to chromatin both in vivo and in vitro. Altogether, our data suggest that HP1 chromoshadow-domains can benefit from the opening of nucleosomal structures to bind chromatin and that HP1 proteins use this property to detect and arrest unwanted chromatin remodeling

The SWI/SNF ATPase Brm Is a Gatekeeper of Proliferative Control in Prostate Cancer

Factors that drive prostate cancer progression remain poorly defined, thus hindering the development of new therapeutic strategies. Disseminated tumors are treated through regimens that ablate androgen signaling, as prostate cancer cells require androgen for growth and survival. However, recurrent, incurable tumors that have bypassed the androgen requirement ultimately arise. This study reveals that the Brm ATPase, a component of selected SWI/SNF complexes, has significant antiproliferative functions in the prostate that protect against these transitions. First, we show that targeted ablation of Brm is causative for the development of prostatic hyperplasia in mice. Second, in vivo challenge revealed that Brm−/− epithelia acquire the capacity for lobe-specific, castration-resistant cellular proliferation. Third, investigation of human specimens revealed that Brm mRNA and protein levels are attenuated in prostate cancer. Fourth, Brm down-regulation was associated with an increased proliferative index, consistent with the mouse model. Lastly, gene expression profiling showed that Brm loss alters factors upstream of E2F1; this was confirmed in murine models, wherein Brm loss induced E2F1 deregulation in a tissue-specific manner. Combined, these data identify Brm as a major effector of serum androgen–induced proliferation in the prostate that is disrupted in human disease, and indicate that loss of Brm confers a proliferative advantage in prostate cancer

An RNA-Binding Protein Secreted by a Bacterial Pathogen Modulates RIG-I Signaling.

RNA-binding proteins (RBPs) perform key cellular activities by controlling the function of bound RNAs. The widely held assumption that RBPs are strictly intracellular has been challenged by the discovery of secreted RBPs. However, extracellular RBPs have been described in eukaryotes, while secreted bacterial RBPs have not been reported. Here, we show that the bacterial pathogen Listeria monocytogenes secretes a small RBP that we named Zea. We show that Zea binds a subset of L. monocytogenes RNAs, causing their accumulation in the extracellular medium. Furthermore, during L. monocytogenes infection, Zea binds RIG-I, the non-self-RNA innate immunity sensor, potentiating interferon-β production. Mouse infection studies reveal that Zea affects L. monocytogenes virulence. Together, our results unveil that bacterial RNAs can be present extracellularly in association with RBPs, acting as "social RNAs" to trigger a host response during infection

Ciblage et régulation du facteur HP1 sur la chromatine

Chez les mammifères, le facteur HP1 (heterochromatin protein 1) est un acteur majeur dans les processus de formation et de régulation de la chromatine condensée. Le ciblage de HP1 sur la chromatine nécessite sa fixation sur la lysine 9 méthylée de l histone H3 mais également la reconnaissance d un ARN dont la nature reste à ce jour inconnue. Dans un premier temps, nous avons démontré que les modifications post-traductionnelles adjacentes à la lysine 9 de l histone H3 (phosphorylation et acétylation) module la fixation de HP1 sur la chromatine. Par la suite nous avons montré que HP1 est impliqué dans le contrôle de la latence transcriptionnelle du virus VIH-1. Enfin, nous présentons des données suggérant que la machinerie d ARN interférence et en particulier l ARN viral TAR, sont impliqués dans le contrôle de la transcription du VIH-1. L interaction potentielle entre HP1, machinerie d ARN interférence et ARN TAR dans le control de la transcription du virus VIH-1 est discutée.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

DYRK1A est un activateur de la transcription régulant l'activité répressive des protéines HP1

Les protéines HP1 (Heterochromatin Protein 1) jouent un rôle crucial dans l établissement et le maintien de la répression transcriptionnelle des gènes hétérochromatiniens mais également des gènes euchromatiniens. Ces protéines reconnaissent et se fixent sur la lysine 9 de l histone H3 méthylée via son chromodomaine. Récemment, notre laboratoire, ainsi que d autres équipes avons montré que les protéines HP1 peuvent également se fixer sur le domaine globulaire de l histone H3 comme la protéine Brg1 (une des sous-unités catalytiques du complexe Swi/Snf). Cette interaction implique le Chromoshadow domaine (CSD) dans la région C-terminale de HP1 et le motif HP1 box like de l histone H3. Au cours ma thèse, j ai exploré l impact des modifications post-traductionnelles dans le domaine globulaire de l histone H3 sur l interaction avec les protéines HP1. Mes travaux montrés que la kinase DYRK1A peut induire la phosphorylation de la thréonine 45 et de la sérine 57 de l histone H3. Comme la phosphorylation de la tyrosine 41 dans le domaine globulaire de l histone H3, ces phosphorylations induites par DYRK1A interfèrent avec la fixation des protéines HP1 sur leurs gènes cibles. Nous avons également montré que DYRK1A agit comme un activateur de la transcription de gènes proinflammatoires en inhibant l activité répressive des protéines HP1. L ensemble de ces données suggère que DYRK1A est un antagoniste de HP1 et également un activateur transcriptionnel des gènes proinflammatoiresThe heterochromatin proteins HP1 play a critical role in establishing and maintaining gene silencing. These proteins bind methylated histone H3 on lysine 9 through their N-terminal chromodomain. Recently, we and others have shown that HP1 also binds histone H3 within its globular domain like Brg1 one of subunit of hSwi/Snf complexes. This interaction involves the C-terminal chromoshadow domain of HP1 protein and HP1 box motif like of histone 3. Here, we have explored the impact of post-translational histone modifications inside the globular domain of histone H3 and we found that threonine 45 and serine 57 can be phosphorylated by DYRK1A kinase. As the phosphorylation of tyrosine 41 of histone H3, the phosphorylation of the threonine 45 modulates HP1 binding to the globular domain of histone H3. Moreover, we show that DYRK1A functions as positive regulator of the transcription of specific genes repressed by HP1. All together these results suggest that DYRK1A is a novel transcriptional activator and a novel regulator of HP1 repressive activity on inflammatory genesPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF