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Chd1 regulates repair of promoter-proximal DNA breaks to sustain hypertranscription in embryonic stem cells

ABSTRACT: Stem and progenitor cells undergo a global elevation of nascent transcription, or hypertranscription, during key developmental transitions involving rapid cell proliferation. The chromatin remodeler Chd1 binds to RNA Pol I and II genes and is required for hypertranscription in embryonic stem (ES) cells in vitro and the early post-implantation epiblast in vivo. Biochemically, Chd1 has been shown to facilitate transcription at least in part by removing nucleosomal barriers to elongation, but its mechanism of action in stem cells remains poorly understood. Here we report a novel role for Chd1 in the repair of promoter-proximal endogenous double-stranded DNA breaks (DSBs) in ES cells. An unbiased proteomics approach revealed that Chd1 interacts with several DNA repair factors including ATM, Parp1, Kap1 and Topoisomerase 2. We show that wild-type ES cells display high levels of phosphorylated H2AX and Kap1 at chromatin, notably at rDNA in the nucleolus, in a Chd1-dependent manner. Loss of Chd1 leads to an extensive accumulation of DSBs at Chd1 target Pol II genes and rDNA. Genes prone to DNA breaks in Chd1-null ES cells tend to be longer genes with GC-rich promoters, a more labile nucleosomal structure and roles in chromatin organization, transcription and signaling. These results reveal a vulnerability of hypertranscribing stem cells to endogenous DNA breaks, with important implications for developmental and cancer biology.

INSTRUMENT(S): LTQ Orbitrap Velos

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Cell Culture, Early Embryonic Cell

SUBMITTER: Andrew Williamson

LAB HEAD: Miguel Ramalho-Santos

PROVIDER: PXD024604 | Pride | 2021-06-14

REPOSITORIES: Pride

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Project description:The glucocorticoid receptor (GR) regulates gene expression throughout the human genome in a cell-type-specific manner, governing various aspects of homeostasis. The influence of this transcriptional regulator is seen in multiple pathologies, including cancer. Pharmacological activation of the GR is frequently used to alleviate side-effects caused by therapy for patients with various non-lymphoid solid (i.e. non-hematologic) cancers; however, prior studies have shown that this treatment might also have anti-proliferative action on cancer cells. Nonetheless, the molecular underpinnings of glucocorticoid action and its direct effectors in non-lymphoid solid cancers remain elusive. Here, we study the molecular mechanisms of glucocorticoid response in non-lymphoid solid cancers models, focusing on lung cancer. Activation of the GR induces reversible cancer cell dormancy in which cells are tolerant to large array of anti-cancer drugs. This state transition is accompanied by induction of growth factor survival signalling (IGF-1R) and acquired vulnerability to inhibitors of this pathway, both in vitro and in vivo. The observed phenotype is dependent on a single GR target gene - CDKN1C, which encodes for a cell cycle inhibitor protein p57. We have discovered an upstream distal enhancer of CDKN1C, which through GR-induced chromatin looping regulates the expression of this key gene, as confirmed in human tumour specimens. Furthermore, we demonstrate that the SWI/SNF complex composition fine-tunes the GR transcriptional activity at the CDKN1C locus, allowing for precise regulation of cell dormancy induction. Collectively, we show that SWI/SNF-facilitated regulation of CDKN1C underlines GR-induced reversible drug-tolerant state in cancer cells. These insights illustrate the importance of GR signalling in non-lymphoid solid cancer biology, particularly in lung cancer, and warrant caution for use of glucocorticoids in treatment of anti-cancer therapy related side-effects.

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Chd1 regulates repair of promoter-proximal DNA breaks to sustain hypertranscription in embryonic stem cells

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