L'axe RAS/PI3K renforce la sénescence cellulaire par la déstabilisation de ZNF768

RAS est une petite protéine Rho-GTPase à la tête d'un réseau de signalisation prolifératif important. Les sentiers activés par RAS incluent les Mitogen-Activated proteins Kinases (MAPK) et la voie Phosphoinositide-3-kinase (PI3K) /Mechanistic Target of Rapamycin (mTOR). Bien que de nombreuses évidences soutiennent une forte implication de RAS dans la carcinogenèse, les mécanismes moléculaires précis liant RAS et prolifération cellulaire ne sont pas tous élucidés. En utilisant des données publiques de phosphoprotéomique, notre équipe a identifié Zinc Finger Protein 768 (ZNF768) comme une nouvelle cible de RAS essentielle à la croissance et à la prolifération. ZNF768 est un facteur de transcription qui est déstabilisé au niveau post-traductionnel par les voies MAPK et mTOR/AKT. La déplétion aigue de ZNF768 induit prématurément une entrée en sénescence, un état caractérisé par un arrêt irréversible du cycle cellulaire, et souvent mis en place en réponse au stress. Nos études montrent que ZNF768 est dégradée durant ce phénomène ainsi que durant la sénescence réplicative. De plus, la surexpression de ZNF768 réduit l'entrée en sénescence, via un mécanisme majoritairement dépendant du facteur de transcription p53, qui joue un rôle important dans la sénescence. ZNF768 affecte négativement la phosphorylation de certains résidus clés pour l'activation de p53 et inhibe son activité transcriptionnelle. Nous avons par ailleurs démontré une interaction physique entre ces deux protéines. L'ensemble de ces résultats suggère que les voies MAPK et mTOR, toutes deux activées par RAS, déstabilisent ZNF768 afin de renforcer la sénescence prématurée. De manière intéressante, les niveaux de ZNF768 sont élevés dans certaines tumeurs humaines. Ainsi, nous proposons un modèle dans lequel ZNF768 puisse favoriser la carcinogenèse en réduisant la sénescence et en favorisant la prolifération.RAS is a small Rho-GTPase protein that integrates growth factors signaling and activates several proliferating pathways including Mitogen-Activated Proteins Kinases (MAPK) and Phosphoinositide-3-kinase (PI3K)/Mechanistic Target of Rapamycin (mTOR). Although many evidence indicate that RAS is involve in carcinogenesis, the molecular mechanisms that link RAS to cellular proliferation are not well understood. By using phosphoproteomics data, our team identified Zinc Finger Protein 768 (ZNF768) as a new target of RAS signaling essential to growth and proliferation. ZNF768 is a transcription factor destabilized at the post-translational level by MAPK and mTOR/AKT. The acute depletion of ZNF768 induces senescence, a stable arrest of the cell cycle triggered by cellular stress. Our results show that ZNF768 is depleted during replicative and premature senescence. In addition, overexpression of ZNF768 bypasses senescence by a mechanism that is mainly dependent on the activity of p53, a transcription factor involved in senescence. Interestingly, ZNF768 interacts with p53 and inhibits its transcriptional activity by modulating its phosphorylation. Thus, MAPK and mTOR/AKT pathways destabilise ZNF768 to reinforce senescence. Moreover, ZNF768 levels are high in various human tumors. Altogether, these results suggest that ZNF768 promotes carcinogenesis by blocking senescence and by stimulating proliferation

Loss of hepatic DEPTOR alters the metabolic transition to fasting

Objective The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that functions into distinct protein complexes (mTORC1 and mTORC2) that regulates growth and metabolism. DEP-domain containing mTOR-interacting protein (DEPTOR) is part of these complexes and is known to reduce their activity. Whether DEPTOR loss affects metabolism and organismal growth in vivo has never been tested. Methods We have generated a conditional transgenic mouse allowing the tissue-specific deletion of DEPTOR. This model was crossed with CMV-cre mice or Albumin-cre mice to generate either whole-body or liver-specific DEPTOR knockout (KO) mice. Results Whole-body DEPTOR KO mice are viable, fertile, normal in size, and do not display any gross physical and metabolic abnormalities. To circumvent possible compensatory mechanisms linked to the early and systemic loss of DEPTOR, we have deleted DEPTOR specifically in the liver, a tissue in which DEPTOR protein is expressed and affected in response to mTOR activation. Liver-specific DEPTOR null mice showed a reduction in circulating glucose upon fasting versus control mice. This effect was not associated with change in hepatic gluconeogenesis potential but was linked to a sustained reduction in circulating glucose during insulin tolerance tests. In addition to the reduction in glycemia, liver-specific DEPTOR KO mice had reduced hepatic glycogen content when fasted. We showed that loss of DEPTOR cell-autonomously increased oxidative metabolism in hepatocytes, an effect associated with increased cytochrome c expression but independent of changes in mitochondrial content or in the expression of genes controlling oxidative metabolism. We found that liver-specific DEPTOR KO mice showed sustained mTORC1 activation upon fasting, and that acute treatment with rapamycin was sufficient to normalize glycemia in these mice. Conclusion We propose a model in which hepatic DEPTOR accelerates the inhibition of mTORC1 during the transition to fasting to adjust metabolism to the nutritional status. Keywords: DEPTOR; mTOR; Liver; Glucose; Fastin

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Feasibility study of small anaerobic co-digestion at urban district level

International audienc

Modulation of Chromatin Remodelling Induced by the Freshwater Cyanotoxin Cylindrospermopsin in Human Intestinal Caco-2 Cells

International audienceCylindrospermopsin (CYN) is a cyanotoxin that has been recognised as an emerging potential public health risk. Although CYN toxicity has been demonstrated, the mechanisms involved have not been fully characterised. To identify some key pathways related to this toxicity, we studied the transcriptomic profile of human intestinal Caco-2 cells exposed to a sub-toxic concentration of CYN (1.6 mM for 24hrs) using a non-targeted approach. CYN was shown to modulate different biological functions which were related to growth arrest (with down-regulation of cdkn1a and uhrf1 genes), and DNA recombination and repair (with up-regulation of aptx and pms2 genes). Our main results reported an increased expression of some histone-modifying enzymes (histone acetyl and methyltransferases MYST1, KAT5 and EHMT2) involved in chromatin remodelling, which is essential for initiating transcription. We also detected greater levels of acetylated histone H2A (Lys5) and dimethylated histone H3 (Lys4), two products of these enzymes. In conclusion, CYN overexpressed proteins involved in DNA damage repair and transcription, including modifications of nucleosomal histones. Our results highlighted some new cell processes induced by CYN

ZNF768: controlling cellular senescence and proliferation with ten fingers

We recently identified Zinc-finger protein 768 (ZNF768) as a novel transcription factor controlling cell fate decision downstream of Rat sarcoma virus (RAS). We showed that ZNF768 depletion impairs cell cycle progression and triggers cellular senescence, while its overexpression allows cells to bypass oncogene-induced senescence. Elevated ZNF768 levels is common in tumors, suggesting that ZNF768 may help to escape cellular senescence, sustain proliferation and promote malignant transformation. Here, we discuss these recent findings and highlight key questions emerging from our work

Relative gene expression of <i>polr2d</i>, <i>polr2l</i>, <i>med6</i>, <i>ddx20</i>, <i>kat5</i>, <i>myst1</i> and <i>ehmt2</i> in differentiated Caco-2 cells after 24 hrs exposure to 1.6 µM CYN.

<p>Values are presented as means ± SE, and normalised to the reference gene <i>RPLP0</i>. Six independent experiments were performed.</p><p>^{*, **}: significantly different from the control group (respectively <i>P</i><0.005 and <i>P</i><0.001).</p

Tree of the biological processes up-regulated in differentiated Caco-2 cells after CYN exposure.

<p>The 522 genes showing up-regulation after 24 hrs exposure to 1.6 µM CYN were annotated within 22 biological processes (GO terms) with an enrichment score greater than 1.5. GO terms had a false discovery rate score of between 0.05 and 0.01 (in orange) or less than 0.01 (in red); white GO terms were ancestors.</p

Associated network functions in differentiated Caco-2 cells after 24 hrs exposure to 1.6 µM CYN.

<p>The 2911 genes showing differential regulation were associated within networks using Ingenuity Pathway Analysis. In this figure the two networks with the highest score are presented. They are respectively associated with gene expression and RNA Post-Transcriptional Modification (A), or with gene expression (B) biological functions. Lines between gene products represent known interactions, with solid lines representing direct interactions and dashed lines representing indirect interactions. Genes showing up-regulation of expression levels in response to CYN exposure are in red, while down-regulated genes are in green.</p

Cytotoxic effects of CYN in differentiated Caco-2 cells treated for 24 hrs.

<p>Cytotoxicity effect was measured by neutral red uptake assay. Values are presented as means ± SE, and expressed as percentages of the vehicle control. Three independent experiments were performed. *, $: values are (*, <i>P</i><0.05) or tended ($, <i>P</i><0.1) to be different from 100.</p