Endoplasmic reticulum calcium release through ITPR2 channels leads to mitochondrial calcium accumulation and senescence

International audienceSenescence is involved in various pathophysiological conditions. Besides loss of retinoblastoma and p53 pathways, little is known about other pathways involved in senescence. Here we identify two calcium channels; inositol 1,4,5-trisphosphate receptor, type 2 (ITPR2) (also known as inositol 1,4,5-triphosphate receptor 2 (IP3R2)) and mitochondrial calcium uniporter (MCU) as new senescence regulators in a loss-of-function genetic screen. We show that loss of ITPR2, known to mediate endoplasmic reticulum (ER) calcium release, as well as loss of MCU, necessary for mitochondrial calcium uptake, enable escape from oncogene-induced senescence (OIS). During OIS, ITPR2 triggers calcium release from the ER, followed by mitochondrial calcium accumulation through MCU channels. Mitochondrial calcium accumulation leads to a subsequent decrease in mitochondrial membrane potential, reactive oxygen species accumulation and senescence. This ER-mitochondria calcium transport is not restricted to OIS, but is also involved in replicative senescence. Our results show a functional role of calcium release by the ITPR2 channel and its subsequent accumulation in the mitochondria

Regulation of ploidy and senescence by the AMPK-related kinase NUAK1.

Senescence is an irreversible cell-cycle arrest that is elicited by a wide range of factors, including replicative exhaustion. Emerging evidences suggest that cellular senescence contributes to ageing and acts as a tumour suppressor mechanism. To identify novel genes regulating senescence, we performed a loss-of-function screen on normal human diploid fibroblasts. We show that downregulation of the AMPK-related protein kinase 5 (ARK5 or NUAK1) results in extension of the cellular replicative lifespan. Interestingly, the levels of NUAK1 are upregulated during senescence whereas its ectopic expression triggers a premature senescence. Cells that constitutively express NUAK1 suffer gross aneuploidies and show diminished expression of the genomic stability regulator LATS1, whereas depletion of NUAK1 with shRNA exerts opposite effects. Interestingly, a dominant-negative form of LATS1 phenocopies NUAK1 effects. Moreover, we show that NUAK1 phosphorylates LATS1 at S464 and this has a role in controlling its stability. In summary, our work highlights a novel role for NUAK1 in the control of cellular senescence and cellular ploidy.We thank the members of the Laboratory for helpful discussions. We also thank Virginie Glippa and Julie Bertout for technical assistance. We thank H Esumi for the NUAK1 cDNA, E Hara and H Saya for the LATS1‐encoding vector. This work was carried out with the support of the ‘Association pour la Recherche sur le Cancer’, the ‘Fondation pour la Recherche Médicale Nord Pas de Calais’, the ‘Comité du Pas de Calais de la Ligue Nationale contre le Cancer’, the RTRS Fondation Synergie Lyon Cancer, and the Medical Research Council, UK.S

Repression of PLA2R1 by c-MYC and HIF-2alpha promotes cancer growth

Loss of secreted phospholipase A2 receptor (PLA2R1) has recently been found to render human primary cells more resistant to senescence whereas increased PLA2R1 expression is able to induce cell cycle arrest, cancer cell death or blockage of cancer cell transformation in vitro, suggesting that PLA2R1 displays tumor suppressive activities. Here we report that PLA2R1 expression strongly decreases in samples of human renal cell carcinoma (RCC). Knockdown of PLA2R1 increases renal cancer cell tumorigenicity supporting a role of PLA2R1 loss to promote in vivo RCC growth. Most RCC result from Von Hippel-Lindau (VHL) tumor suppressor loss-of-function and subsequent gain-of-function of the oncogenic HIF-2alpha/c-MYC pathway. Here, by genetically manipulating VHL, HIF-2alpha and c-MYC, we demonstrate that loss of VHL, stabilization of HIF-2alpha and subsequent increased c-MYC activity, binding and transcriptional repression, through induction of PLA2R1 DNA methylation closed to PLA2R1 transcriptional start site, results in decreased PLA2R1 transcription. Our results describe for the first time an oncogenic pathway leading to PLA2R1 transcriptional repression and the importance of this repression for tumor growth

Bone morphogenetic protein 7 in dormancy and metastasis of prostate cancer stem-like cells in bone

BMP7 released by bone marrow stromal cells induces reversible senescence of prostate cancer stem-like cells, and BMPR2 expression inversely correlates with bone metastasis and recurrence in prostate cancer patients

Modulation au niveau musculaire des effets de l'insuline pour l'exercice ou l'immobilisation

SIGLECNRS T 58014 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Le récepteur aux phospholipases A2 (PLA2R1) est un nouveau régulateur inattendu de la sénescence cellulaire et un gène suppresseur de tumeurs

Activée dans les stades précoces du développement tumoral, la sénescence empêche la progression tumorale en induisant un arrêt de prolifération cellulaire. Ainsi, tout comme l’apoptose, ce mécanisme doit être altéré pour qu’une cellule devienne tumorale. Malgré ce rôle crucial de protection contre la progression tumorale, nous connaissons peu les mécanismes moléculaires qui régulent l’échappement à la sénescence. A l’aide d’une banque de shRNA ciblant 8000 gènes, nous avons réalisé un criblage génétique dans le but d’isoler de nouveaux régulateurs, qui lors qu’ils sont inhibés, favorisent un échappement à la sénescence. Ce criblage nous a ainsi permis d’isoler PLA2R1 comme un nouveau régulateur de la sénescence. Nous avons montré que ce gène régulait la sénescence par l’activation du gène suppresseur de tumeurs p53. Un deuxième travail nous a ensuite permis d’identifier PLA2R1 comme un nouveau gène suppresseur de tumeurs. Dans un futur proche PLA2R1 pourra, peut-être, être utilisé comme bio-marqueur. De plus nous avons récemment démontré que cette protéine pourrait avoir un potentiel à visée thérapeutique étant donné son potentiel d’action sur les cellules tumorales. L’ensemble de ces travaux nous ont donc permis d’isoler PLA2R1 comme un nouveau régulateur de la sénescence et gène suppresseur de tumeurs.Activated in early stages of tumorigenesis, senescence, by blocking proliferation, inhibits tumour growth. Therefore, just like other fails safe mechanisms such as apoptosis, its escape is a property that cancer cell acquire. Although senescence plays a crucial role in tumour suppression and blockade, there is still much to learn about the mechanisms regulating this phenomenon. Using a shRNA library targeting 8000 human genes, we performed a loss of function genetic screen in order to identify genes that when down-regulated, would allow a senescence escape. Using this strategy, we were able to identify PLA2R1 as a novel regulator of cellular senescence by modulating the activation of the p53 tumour suppressor gene. In a second work, we demonstrated that PLA2R1 is a candidate tumour suppressor gene. In the future, PLA2R1 might be used as a biomarker. Finally, we have demonstrated that PLA2R1 could have therapeutic potential as it induces apoptosis in a myriad of cancer cell lines. Altogether, the work performed during my thesis as enabled us to identify PLA2R1 as a novel cellular senescence regulator and a putative new tumour suppressor gene with therapeutic potential

Tissus durs et âge individuel des vertébrés

Chez la grenouille rousse (#Rana temporaria$ L.), la squelettochronologie appliquée sur les phalanges est une méthode efficace de détermination de l'âge individuel. Cette méthode permet d'établir certains paramètres démographiques (longévité, survie) lorsque d'autres méthodes sont rendues inefficaces à cause d'effectifs elevés. Les problèmes d'interprétation des coupes histologiques sont rares. Leur lecture apporte des informations non seulement sur la structure d'âge, mais aussi sur la croissance et la maturation. L'estimation de ce dernier paramètre est problématique chez certains individus à la seule lecture de leurs squelettogrammes. En effet, le rapprochement des Lignes d'Arrêt de Croissance (LAC) ne signifie sans doute pas toujours que la maturité sexuelle a été atteinte l'année précédente. (Résumé d'auteur