Search

Chromatin regulators included in this study

Clinical characteristics of the Institut Curie patient cohort

Supplementary Figure from PBRM1 Deficiency Confers Synthetic Lethality to DNA Repair Inhibitors in Cancer

Supplementary Table from PBRM1 Deficiency Confers Synthetic Lethality to DNA Repair Inhibitors in Cancer

Supplementary data from PBRM1 Deficiency Confers Synthetic Lethality to DNA Repair Inhibitors in Cancer

Inactivation of Polybromo 1 (PBRM1), a specific subunit of the PBAF chromatin remodeling complex, occurs frequently in cancer, including 40% of clear cell renal cell carcinomas (ccRCC). To identify novel therapeutic approaches to targeting PBRM1-defective cancers, we used a series of orthogonal functional genomic screens that identified PARP and ATR inhibitors as being synthetic lethal with PBRM1 deficiency. The PBRM1/PARP inhibitor synthetic lethality was recapitulated using several clinical PARP inhibitors in a series of in vitro model systems and in vivo in a xenograft model of ccRCC. In the absence of exogenous DNA damage, PBRM1-defective cells exhibited elevated levels of replication stress, micronuclei, and R-loops. PARP inhibitor exposure exacerbated these phenotypes. Quantitative mass spectrometry revealed that multiple R-loop processing factors were downregulated in PBRM1-defective tumor cells. Exogenous expression of the R-loop resolution enzyme RNase H1 reversed the sensitivity of PBRM1-deficient cells to PARP inhibitors, suggesting that excessive levels of R-loops could be a cause of this synthetic lethality. PARP and ATR inhibitors also induced cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) innate immune signaling in PBRM1-defective tumor cells. Overall, these findings provide the preclinical basis for using PARP inhibitors in PBRM1-defective cancers.Significance:This study demonstrates that PARP and ATR inhibitors are synthetic lethal with the loss of PBRM1, a PBAF-specific subunit, thus providing the rationale for assessing these inhibitors in patients with PBRM1-defective cancer.

6 supplementary figures from Chromatin Assembly Factor-1, a Marker of Clinical Value to Distinguish Quiescent from Proliferating Cells

Histone synthesis and chromatin assembly are mainly associated with DNA replication and are thus intimately involved in cell cycle regulation. The expression of key components involved in these events in human cells was studied in relation to cell-proliferative status. Among several chromatin assembly factors, chromatin assembly factor (CAF)-1 stood out as the most discriminating marker of the proliferative state. We show, using both immunofluorescence and Western blot analysis, that the expression of both CAF-1 large subunits, p150 and p60, is massively down-regulated during quiescence in several cell lines. Upon exit from the quiescent state, the CAF-1 subunits are re-expressed early, before DNA replication. The amounts of either total or chromatin-associated pools of CAF-1 proteins correlate directly with cell proliferation. Regulation of CAF-1 expression is partly controlled at the RNA level, as shown by quantitative reverse transcription-PCR and Northern blot experiments. Biological material from benign and malignant human breast tumors analyzed by immunocytochemistry and immunohistochemistry exhibits a strong positive correlation between CAF-1 p60 expression and the following proliferation markers: S-phase fraction (r = 0.84, P < 0.0001); Ki-67 (r = 0.94, P < 0.0001); and proliferating cell nuclear antigen (r = 0.95, P = 0.0001). We discuss the advantages of using CAF-1 to assess cell proliferation. High CAF-1 p60 levels are also shown to be associated with various prognostic factors. Our data highlight the precise association of CAF-1 expression with the proliferative state and validate the use of this factor as a useful proliferation marker and prognostic indicator in malignant and benign breast lesions.

Legends to supplementary figures from Chromatin Assembly Factor-1, a Marker of Clinical Value to Distinguish Quiescent from Proliferating Cells

SUMMARYIn S phase, duplication and assembly of the whole genome into chromatin requires upregulation of replicative histone gene expression. Here, we explored a potential role of histone chaperones in this process thereby linking chromatin assembly with histone production in human cells. Depletion of the ASF1 chaperone specifically decreased the pool of replicative histones both at the levels of soluble protein and total RNA, while depletion of CAF-1 did not. Most replicative histone genes decreased in their overall expression as revealed by total RNA-seq. In contrast, both their newly synthesized RNAs and nascent RNAs at transcription sites increased as shown by 4sU-labeled RNA-seq and single-molecule RNA FISH, respectively. Further inspection of the sequences corresponding to replicative histone RNAs showed a 3’ processing defect, leading to unprocessed transcripts usually targeted for degradation. We discuss how this regulation of replicative histone RNA metabolism by ASF1 fine-tunes the histone dosage to avoid unbalanced situations deleterious for cell survival.

Centromeres are key architectural components of chromosomes. Here, we examine their construction, maintenance, and functionality. Focusing on the mammalian centromere- specific histone H3 variant, CENP-A, we highlight its coevolution with both centromeric DNA and its chaperone, HJURP. We then consider CENP-A de novo deposition and the importance of centromeric DNA recently uncovered with the added value from new ultra-long-read sequencing. We next review how to ensure the maintenance of CENP-A at the centromere throughout the cell cycle. Finally, we discuss the impact of disrupting CENP-A regulation on cancer and cell fate.

Centromeres are key architectural components of chromosomes. Here, we examine their construction, maintenance, and functionality. Focusing on the mammalian centromerespecific histone H3 variant, CENP-A, we highlight its co-evolution with both centromeric DNA and its chaperone, HJURP. We then consider CENP-A de novo deposition and the importance of centromeric DNA recently uncovered with the added value from new ultra-long-read sequencing. We next review how to ensure the maintenance of CENP-A at the centromere throughout the cell cycle. Finally, we discuss the impact of disrupting CENP-A regulation on cancer and cell fate.

Histone variant H3.3 is incorporated into chromatin throughout the cell cycle and even in non-cycling cells. This histone variant marks actively transcribed chromatin regions with high nucleosome turnover, as well as silent pericentric and telomeric repetitive regions. In the past few years, significant progress has been made in our understanding of mechanisms involved in the transcription-coupled deposition of H3.3. Here we review how, during transcription, new H3.3 deposition intermingles with the fate of the old H3.3 variant and its recycling. First, we describe pathways enabling the incorporation of newly synthesized vs old H3.3 histones in the context of transcription. We then review the current knowledge concerning differences between these two H3.3 populations, focusing on their PTMs composition. Finally, we discuss the implications of H3.3 recycling for the maintenance of the transcriptional state and underline the emerging importance of H3.3 as a potent epigenetic regulator for both maintaining and switching a transcriptional state.

International audience; Histone chaperones are key regulators of chromatin structure and function. Their frequent mis-regulation in various cancers can impact tumor initiation and progression. Here, we focus on H3-H4 histone chaperones to highlight recent studies concerning their roles in several cancers thereby expanding on previous reports illustrating their functions as tumor-promoting and/or as useful biomarkers for clinical applications. In particular, we discuss how imperfect compensation between H3-H4 histone chaperones favors tumor progression by stimulating the Epithelial mesenchymal transition (EMT) or the Alternative lengthening of telomeres (ALT) pathway. Finally, we present initial studies pointing towards therapies that target H3-H4 histone chaperones for cancer treatment.; Les chaperons d'histone sont des régulateurs clés de la structure et de la fonction de la chromatine. Leur mauvaise régulation fréquente dans divers cancers peut avoir un impact sur l'initiation et la progression de la tumeur. Ici, nous nous concentrons sur les chaperons d'histones H3-H4 pour mettre en évidence des études récentes concernant leurs rôles dans plusieurs cancers, développant ainsi des rapports antérieurs illustrant leurs fonctions de promotion de tumeurs et/ou de biomarqueurs utiles pour des applications cliniques. En particulier, nous discutons comment la compensation imparfaite entre les chaperons d'histones H3-H4 favorise la progression tumorale en stimulant la transition mésenchymateuse épithéliale (EMT) ou la voie d'allongement alternatif des télomères (ALT). Enfin, nous présentons des études initiales pointant vers des thérapies qui ciblent les chaperons d'histone H3-H4 pour le traitement du cancer.

Effective biomarkers predictive of the response to treatments are key for precision medicine. This study identifies the staining pattern of the centromeric histone 3 variant, CENP-A, as a predictive biomarker of locoregional disease curability by chemoradiation therapy. We compared by imaging the subnuclear distribution of CENP-A in normal and tumoral tissues, and in a retrospective study in biopsies of 62 locally advanced head and neck squamous cell carcinoma (HNSCC) patients treated by chemoradiation therapy. We looked for predictive factors of locoregional disease control and patient’s survival, including CENP-A patterns, Ki67, HPV status and anisokaryosis. In different normal tissues, we reproducibly found a CENP-A subnuclear pattern characterized by CENP-A clusters both localized at the nuclear periphery and regularly spaced. In corresponding tumors, both features are lost. In locally advanced HNSCC, a specific CENP-A pattern identified in pretreatment biopsies predicts definitive locoregional disease control after chemoradiation treatment in 96% (24/25) of patients (OR = 17.6 CI 95% [2.6, 362.8], p = 0.002), independently of anisokaryosis, Ki67 labeling or HPV status. The characteristics of the subnuclear pattern of CENP-A in cell nuclei revealed by immunohistochemistry could provide an easy to use a reliable marker of disease curability by chemoradiation therapy in locally advanced HNSCC patients.

International audience; While major advances in single cell transcriptomics have occurred, the epigenomics arena has only more recently gained momentum. Indeed, methods to track changes in different molecules present in biological samples have developed both in scale – providing a global view in each case – and in terms of resolution, allowing us today to disentangle heterogeneity within samples and access at the level of a single cell. The application of omics methods, comprising analysis of genomes, epigenomes, transcriptomes, proteomes and metabolomes, among other functional genomics techniques, individually or in combination, provides a wealth of valuable datasets. The treatment of these data with the development of artificial intelligence tools opens unprecedented avenues. The possibility to gain a holistic view of cells functioning within organs and during their formation will allow us to tackle fundamental questions of normal organism development and also to reveal early changes associated with disease onset and progression. In this editorial, we discuss the place of epigenomics research in an era where mapping cellular trajectories and mechanisms offers unique opportunities to address fundamental questions related to cell identity of key importance for medical applications.

Inactivation of Polybromo 1 (PBRM1), a specific subunit of the PBAF chromatin remodeling complex, occurs frequently in cancer, including 40% of clear cell renal cell carcinomas (ccRCC). To identify novel therapeutic approaches to targeting PBRM1-defective cancers, we used a series of orthogonal functional genomic screens that identified PARP and ATR inhibitors as being synthetic lethal with PBRM1 deficiency. The PBRM1/PARP inhibitor synthetic lethality was recapitulated using several clinical PARP inhibitors in a series of in vitro model systems and in vivo in a xenograft model of ccRCC. In the absence of exogenous DNA damage, PBRM1-defective cells exhibited elevated levels of replication stress, micronuclei, and R-loops. PARP inhibitor exposure exacerbated these phenotypes. Quantitative mass spectrometry revealed that multiple R-loop processing factors were downregulated in PBRM1-defective tumor cells. Exogenous expression of the R-loop resolution enzyme RNase H1 reversed the sensitivity of PBRM1-deficient cells to PARP inhibitors, suggesting that excessive levels of R-loops could be a cause of this synthetic lethality. PARP and ATR inhibitors also induced cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) innate immune signaling in PBRM1-defective tumor cells. Overall, these findings provide the preclinical basis for using PARP inhibitors in PBRM1-defective cancers. Significance: This study demonstrates that PARP and ATR inhibitors are synthetic lethal with the loss of PBRM1, a PBAF-specific subunit, thus providing the rationale for assessing these inhibitors in patients with PBRM1-defective cancer.

International audience; The lack of a consensus DNA sequence defining replication origins in mammals has led researchers to consider chromatin as a means to specify these regions. However, to date, there is no mechanistic understanding of how this could be achieved and maintained given that nucleosome disruption occurs with each fork passage and with transcription. Here, by genome-wide mapping of the de novo deposition of the histone variants H3.1 and H3.3 in human cells during S phase, we identified how their dual deposition mode ensures a stable marking with H3.3 flanked on both sides by H3.1. These H3.1/H3.3 boundaries correspond to the initiation zones of early origins. Loss of the H3.3 chaperone HIRA leads to the concomitant disruption of H3.1/H3.3 boundaries and initiation zones. We propose that the HIRA-dependent deposition of H3.3 preserves H3.1/H3.3 boundaries by protecting them from H3.1 invasion linked to fork progression, contributing to a chromatin-based definition of early replication zones.; L'absence d'une séquence d'ADN consensuelle définissant les origines de réplication chez les mammifères a conduit les chercheurs à considérer la chromatine comme un moyen de spécifier ces régions. Cependant, à ce jour, il n'y a pas de compréhension mécaniste de la façon dont cela pourrait être réalisé et maintenu étant donné que la rupture des nucléosomes se produit à chaque passage de fourche et avec la transcription. Ici, en cartographiant à l'échelle du génome le dépôt de novo des variants d'histone H3.1 et H3.3 dans les cellules humaines pendant la phase S, nous avons identifié comment leur mode de dépôt double assure un marquage stable avec H3.3 flanqué des deux côtés par H3.1. Ces frontières H3.1/H3.3 correspondent aux zones d'initiation des origines précoces. La perte du chaperon H3.3 HIRA conduit à la perturbation concomitante des frontières H3.1/H3.3 et des zones d'initiation. Nous proposons que le dépôt de H3.3 dépendant de HIRA préserve les frontières H3.1/H3.3 en les protégeant de l'invasion de H3.1 liée à la progression des fourches, contribuant ainsi à une définition chromatinienne des zones de réplication précoce.

Within the cell nucleus, the organization of the eukaryotic DNA into chromatin uses histones as components of its building block, the nucleosome. This chromatin organization contributes to the regulation of all DNA template-based reactions impacting genome function, stability, and plasticity. Histones and their variants endow chromatin with unique properties and show a distinct distribution into the genome that is regulated by dedicated deposition machineries. The histone variants have important roles during early development, cell differentiation, and chromosome segregation. Recent progress has also shed light on how mutations and transcriptional deregulation of these variants participate in tumorigenesis. In this chapter we introduce the organization of the genome in chromatin with a focus on the basic unit, the nucleosome, which contains histones as the major protein component. Then we review our current knowledge on the histone H3 family and its variants-in particular H3.3 and CenH3

International audience; Nucleosomes represent a challenge in regard to transcription. Histone eviction enables RNA polymerase II (RNAPII) progression through DNA, but compromises chromatin integrity. Here, we used the SNAP-tag system to distinguish new and old histones and monitor chromatin reassembly coupled to transcription in human cells. We uncovered a transcription-dependent loss of old histone variants H3.1 and H3.3. At transcriptionally active domains, H3.3 enrichment reflected both old H3.3 retention and new deposition. Mechanistically, we found that the histone regulator A (HIRA) chaperone is critical to processing both new and old H3.3 via different pathways. De novo H3.3 deposition is totally dependent on HIRA trimerization as well as on its partner ubinuclein 1 (UBN1), while antisilencing function 1 (ASF1) interaction with HIRA can be bypassed. By contrast, recycling of H3.3 requires HIRA but proceeds independently of UBN1 or HIRA trimerization and shows absolute dependency on ASF1–HIRA interaction. We propose a model whereby HIRA coordinates these distinct pathways during transcription to fine-tune chromatin states.; Les nucléosomes représentent un défi en ce qui concerne la transcription. L'éviction des histones permet la progression de l'ARN polymérase II (RNAPII) dans l'ADN, mais compromet l'intégrité de la chromatine. Ici, nous avons utilisé le système SNAP-tag pour distinguer les nouvelles et les anciennes histones et surveiller le réassemblage de la chromatine couplé à la transcription dans les cellules humaines. Nous avons découvert une perte dépendante de la transcription des anciens variants d'histones H3.1 et H3.3. Au niveau des domaines transcriptionnellement actifs, l'enrichissement en H3.3 reflétait à la fois la rétention de l'ancien H3.3 et le nouveau dépôt. Sur le plan mécanique, nous avons constaté que le chaperon du régulateur d'histone A (HIRA) est essentiel pour traiter à la fois le nouveau et l'ancien H3.3 par des voies différentes. Le dépôt de novo de H3.3 dépend totalement de la trimérisation de l'HIRA ainsi que de son partenaire l'ubinucléine 1 (UBN1), tandis que l'interaction de la fonction antisilencing 1 (ASF1) avec l'HIRA peut être contournée. En revanche, le recyclage du H3.3 nécessite l'AERH mais se fait indépendamment de la trimérisation de l'UBN1 ou de l'AERH et montre une dépendance absolue de l'interaction ASF1-AERH. Nous proposons un modèle dans lequel l'ARHI coordonne ces voies distinctes pendant la transcription pour affiner les états de la chromatine.

Tumour evolution is driven by both genetic and epigenetic changes. CENP-A, the centromeric histone H3 variant, is an epigenetic mark that directly perturbs genetic stability and chromatin when overexpressed. Although CENP-A overexpression is a common feature of many cancers, how this impacts cell fate and response to therapy remains unclear. Here, we established a tunable system of inducible and reversible CENP-A overexpression combined with a switch in p53 status in human cell lines. Through clonogenic survival assays, single-cell RNA-sequencing and cell trajectory analysis, we uncover the tumour suppressor p53 as a key determinant of how CENP-A impacts cell state, cell identity and therapeutic response. If p53 is functional, CENP-A overexpression promotes senescence and radiosensitivity. Surprisingly, when we inactivate p53, CENP-A overexpression instead promotes epithelial-mesenchymal transition, an essential process in mammalian development but also a precursor for tumour cell invasion and metastasis. Thus, we uncover an unanticipated function of CENP-A overexpression to promote cell fate reprogramming, with important implications for development and tumour evolution., Jeffery et al. develop a system of inducible and reversible CENP-A overexpression, combined with a switch in p53 status in human cell lines. They find the tumor suppressor p53 as a key determinant of how CENP-A impacts cell state, cell identity and therapeutic response. This study suggests that CENP-A overexpression promotes the reprogramming of cell fates in the context of tumor evolution.

International audience; Epigenetic dysregulation has long been recognized as a key factor contributing to tumorigenesis and tumour maintenance that can influence all of the recognized hallmarks of cancer. Despite regulatory approvals for the treatment of certain haematological malignancies, the efficacy of the first generation of epigenetic drugs (epi-drugs) in patients with solid tumours has been disappointing; however, successes have now been achieved in selected solid tumour subtypes, thanks to the development of novel compounds and a better understanding of cancer biology that have enabled precision medicine approaches. Several lines of evidence support that, beyond their potential as monotherapies, epigenetic drugs could have important roles in synergy with other anticancer therapies or in reversing acquired therapy resistance. Herein, we review the mechanisms by which epi-drugs can modulate the sensitivity of cancer cells to other forms of anticancer therapy, including chemotherapy, radiation therapy, hormone therapy, molecularly targeted therapy and immunotherapy. We provide a critical appraisal of the preclinical rationale, completed clinical studies and ongoing clinical trials relating to combination therapies incorporating epi-drugs. Finally, we propose and discuss rational clinical trial designs and drug development strategies, considering key factors including patient selection, tumour biomarker evaluation, drug scheduling and response assessment and study end points, with the aim of optimizing the development of such combinations.; La dysrégulation épigénétique est depuis longtemps reconnue comme un facteur clé contribuant à la tumorigénèse et à la maintenance des tumeurs qui peut influencer toutes les caractéristiques reconnues du cancer. Malgré les approbations réglementaires pour le traitement de certaines malignités hématologiques, l'efficacité de la première génération de médicaments épigénétiques (épi-drugs) chez les patients atteints de tumeurs solides a été décevante ; cependant, des succès ont maintenant été obtenus dans certains sous-types de tumeurs solides, grâce au développement de nouveaux composés et à une meilleure compréhension de la biologie du cancer qui ont permis des approches médicales de précision. Plusieurs sources de preuves soutiennent que, au-delà de leur potentiel en tant que monothérapies, les médicaments épigénétiques pourraient jouer un rôle important en synergie avec d'autres thérapies anticancéreuses ou pour inverser la résistance acquise à la thérapie. Nous passons ici en revue les mécanismes par lesquels les médicaments épigénétiques peuvent moduler la sensibilité des cellules cancéreuses à d'autres formes de thérapie anticancéreuse, notamment la chimiothérapie, la radiothérapie, l'hormonothérapie, la thérapie moléculaire ciblée et l'immunothérapie. Nous fournissons une évaluation critique du raisonnement préclinique, des études cliniques achevées et des essais cliniques en cours concernant les thérapies combinées incorporant des médicaments d'épinéphrine. Enfin, nous proposons et discutons des plans d'essais cliniques rationnels et des stratégies de développement de médicaments, en tenant compte de facteurs clés tels que la sélection des patients, l'évaluation des biomarqueurs tumoraux, la programmation des médicaments et l'évaluation de la réponse et les résultats des études, dans le but d'optimiser le développement de ces combinaisons.

International audience; The synthesis of poly(ADP-ribose) (PAR) reconfigures the local chromatin environment and recruits DNA-repair complexes to damaged chromatin. PAR degradation by poly(ADP-ribose) glycohydrolase (PARG) is essential for progression and completion of DNA repair. Here, we show that inhibition of PARG disrupts homology-directed repair (HDR) mechanisms that underpin alternative lengthening of telomeres (ALT). Proteomic analyses uncover a new role for poly(ADP-ribosyl)ation (PARylation) in regulating the chromatin-assembly factor HIRA in ALT cancer cells. We show that HIRA is enriched at telomeres during the G2 phase and is required for histone H3.3 deposition and telomere DNA synthesis. Depletion of HIRA elicits systemic death of ALT cancer cells that is mitigated by re-expression of ATRX, a protein that is frequently inactivated in ALT tumors. We propose that PARylation enables HIRA to fulfill its essential role in the adaptive response to ATRX deficiency that pervades ALT cancers.

International audience; Within the cell nucleus, the organization of the eukaryotic DNA into chromatin uses histones as components of its building block, the nucleosome. This chromatin organization contributes to the regulation of all DNA template-based reactions impacting genome function, stability and plasticity. Histones and their variants endow chromatin with unique properties and show a distinct distribution into the genome that is regulated by dedicated deposition machineries. The histone variants have important roles during early development, cell differentiation and chromosome segregation. Recent progress has also shed light on how mutations and transcriptional deregulation of these variants participate in tumorigenesis. In this chapter we introduce the organization of the genome in chromatin with a focus on the basic unit, the nucleosome, which contains histones as the major protein component. Then we review our current knowledge on the histone H3 family and its variants-in particular H3.3 and CenH3 CENP-Afocusing on their deposition pathways and their dedicated histone chaperones that are key players in histone dynamics.; Dans le noyau de la cellule, l'organisation de l'ADN eucaryote en chromatine utilise les histones comme composants de son élément constitutif, le nucléosome. Cette organisation de la chromatine contribue à la régulation de toutes les réactions basées sur les modèles d'ADN qui ont un impact sur la fonction, la stabilité et la plasticité du génome. Les histones et leurs variantes confèrent à la chromatine des propriétés uniques et présentent une distribution distincte dans le génome qui est régulée par des mécanismes de dépôt dédiés. Les variants d'histones jouent un rôle important dans le développement précoce, la différenciation des cellules et la ségrégation des chromosomes. Les progrès récents ont également mis en lumière la manière dont les mutations et la dérégulation transcriptionnelle de ces variants participent à la tumorigenèse. Dans ce chapitre, nous présentons l'organisation du génome dans la chromatine en nous concentrant sur l'unité de base, le nucléosome, qui contient des histones comme principal composant protéique. Ensuite, nous passons en revue nos connaissances actuelles sur la famille des histones H3 et ses variants - en particulier H3.3 et CenH3CENP-A - en nous concentrant sur leurs voies de dépôt et leurs chaperons d'histones dédiés qui sont des acteurs clés dans la dynamique des histones.

DNA replication is a challenge for the faithful transmission of parental information to daughter cells, as both DNA and chromatin organization must be duplicated. Replication stress further complicates the safeguard of epigenome integrity. Here, we investigate the transmission of the histone variants H3.3 and H3.1 during replication. We follow their distribution relative to replication timing, first in the genome and, second, in 3D using super-resolution microscopy. We find that H3.3 and H3.1 mark early- and late-replicating chromatin, respectively. In the nucleus, H3.3 forms domains, which decrease in density throughout replication, while H3.1 domains increase in density. Hydroxyurea impairs local recycling of parental histones at replication sites. Similarly, depleting the histone chaperone ASF1 affects recycling, leading to an impaired histone variant landscape. We discuss how faithful transmission of histone variants involves ASF1 and can be impacted by replication stress, with ensuing consequences for cell fate and tumorigenesis., Epigenetic modifications are a key contributor to cell identity, and their propagation is crucial for proper development. Here the authors use a super-resolution microscopy approach to reveal how histone variants are faithfully transmitted during genome duplication, and reveal an important role for the histone chaperone ASF1 in the redistribution of parental histones.

International audience; During cell division, maintenance of chromatin features from the parental genome requires their proper establishment on its newly synthetized copy. The loss of epigenetic marks within heterochromatin, typically enriched in repetitive elements, endangers genome stability and permits chromosomal rearrangements via recombination. However, how histone modifications associated with heterochromatin are maintained across mitosis remains poorly understood. KAP1 is known to act as a scaffold for a repressor complex that mediates local heterochromatin formation, and was previously demonstrated to play an important role during DNA repair. Accordingly, we investigated a putative role for this protein in the replication of heterochromatic regions. We first found that KAP1 associates with several DNA replication factors including PCNA, MCM3 and MCM6. We then observed that these interactions are promoted by KAP1 phosphorylation on serine 473 during S phase. Finally, we could demonstrate that KAP1 forms a complex with PCNA and the histone-lysine methyltransferase Suv39h1 to reinstate heterochromatin after DNA replication.

International audience; Introduction: A mission-oriented approach to cancer care in Europe was proposed by Julio Celis and Dainius Pavalkis in 2017. The major proposed objective is to achieve long-term survival of 3 out of 4 cancer patients by 2030. Background: The authors are president or president-elect of Organization of European Cancer Institutes (OECI) EU Life or European Cancer Community Organization (ECCO). Results: The goal is laudable and ambitious. However, it can only be successful if it is coordinated with active involvement of all stakeholders and interacts with an already well-organized, recognized, and certified European Accreditation and Designation quality approach to identify and select the potential candidates to participate in such a virtual network. Conclusion: The building of a virtual European Cancer Institute based on coordinated networks should refer to unquestioned criteria using a solid and proven methodology operated by an independent arbitration body. The cancer community must share a fundamental responsibility to act collectively and in today's era of the World Wide Web, it is time to think out of the box and consider the possibility of establishing networks of networks.; Introduction : Une approche de la prise en charge du cancer en Europe axée sur la mission a été proposée par Julio Celis et Dainius Pavalkis en 2017. Le principal objectif proposé est de parvenir à la survie à long terme de 3 patients sur 4 atteints de cancer d'ici 2030. Contexte : Les auteurs sont président ou président élu de l'Organisation des instituts européens du cancer (OECI) EU Life ou de l'Organisation communautaire européenne du cancer (ECCO). Résultats : L'objectif est louable et ambitieux. Toutefois, il ne peut être atteint que s'il est coordonné avec la participation active de toutes les parties prenantes et s'il interagit avec une approche de qualité déjà bien organisée, reconnue et certifiée de l'accréditation et de la désignation européennes pour identifier et sélectionner les candidats potentiels à participer à un tel réseau virtuel. Conclusion : La construction d'un Institut européen du cancer virtuel basé sur des réseaux coordonnés devrait se référer à des critères incontestables en utilisant une méthodologie solide et éprouvée gérée par un organisme d'arbitrage indépendant. La communauté de lutte contre le cancer doit partager la responsabilité fondamentale d'agir collectivement et, à l'ère du World Wide Web, il est temps de sortir des sentiers battus et d'envisager la possibilité d'établir des réseaux de réseaux.

International audience; Treating metastatic cancers is an ongoing challenge in oncology. A recent paper by Gomes and colleagues proposes histone H3 variant dynamics as major regulator of cell fate transition during metastasis and suggests histone chaperones as therapeutic targets for invasive carcinoma.; Le traitement des cancers métastatiques est un défi permanent en oncologie. Un article récent de Gomes et ses collègues propose la dynamique du variant de l'histone H3 comme régulateur majeur de la transition du destin cellulaire pendant la métastase et suggère les chaperons d'histones comme cibles thérapeutiques pour les carcinomes invasifs.

Newly synthesized histones H3 and H4 undergo a cascade of maturation steps to achieve proper folding and to establish post-translational modifications prior to chromatin deposition. Acetylation of H4 on lysines 5 and 12 by the HAT1 acetyltransferase is observed late in the histone maturation cascade. A key question is to understand how to establish and regulate the distinct timing of sequential modifications and their biological significance. Here, we perform proteomic analysis of the newly synthesized histone H4 complex at the earliest time point in the cascade. In addition to known binding partners Hsp90 and Hsp70, we also identify for the first time two subunits of the histone acetyltransferase inhibitor complex (INHAT): PP32 and SET/TAF-Iβ. We show that both proteins function to prevent HAT1-mediated H4 acetylation in vitro. When PP32 and SET/TAF-Iβ protein levels are down-regulated in vivo, we detect hyperacetylation on lysines 5 and 12 and other H4 lysine residues. Notably, aberrantly acetylated H4 is less stable and this reduces the interaction with Hsp90. As a consequence, PP32 and SET/TAF-Iβ depleted cells show an S-phase arrest. Our data demonstrate a novel function of PP32 and SET/TAF-Iβ and provide new insight into the mechanisms regulating acetylation of newly synthesized histone H4.