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Lymphocyte-specific chromatin accessibility pre-determines glucocorticoid resistance in acute lymphoblastic leukemia [WGBS]

ABSTRACT: Semi-synthetic glucocorticoids are used to treat a broad range of medical conditions including inflammation, autoimmunity, and lymphoid malignancies. While a large component of these effects can be attributed to glucocorticoid-induced apoptosis of normal and malignant lymphocyte, the molecular basis for the lymphocyte-specific apoptosis remains unclear. Moreover, the mechanisms of glucocorticoid resistance in lymphoid malignancy are poorly defined, and remain a significant barrier to cure. To address these issues, we first performed a global analysis of chromatin accessibility in lymphoid and non-lymphoid cells to map lymphocyte-specific open chromatin domains (LSOs). We then integrated these domains with glucocorticoid receptor (GR) binding-induced RNA transcription and chromatin modulation in an in vivo patient-derived xenograft (PDX) model of acute lymphoblastic leukemia (ALL). This led to the identification of LSOs associated with glucocorticoid resistance in ALL. One such LSO was at the pro-apoptotic BIM gene locus, where a chromatin architectural protein CTCF binding was found only in lymphocytes but not in other cell types. The GR cooperated with CTCF to mediate interactions between the BIM promoter and the LSO to direct DNA looping, thus triggering BIM transcription. Importantly, this LSO was heavily DNA methylated in glucocorticoid resistant PDXs and non-lymphoid cells. This study demonstrates for the first time that lymphocyte-specific chromatin accessibility pre-determines glucocorticoid resistance in ALL and proposes a model for the lack of glucocorticoid sensitivity in non-lymphoid cell types. This submission represents the WGBS component of the study.

ORGANISM(S): Homo sapiens

PROVIDER: GSE109948 | GEO | 2019/11/08

REPOSITORIES: GEO

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Project description:LC-MS data and DIA-NN search files relating to: PU.1 Eviction at Lymphocyte-Specific Chromatin Domains Mediates Glucocorticoid Response in Acute Lymphoblastic Leukemia. Abstract: The epigenetic landscape plays a critical role in the onset and evolution of various malignancies, but its therapeutic utility remains underutilized. Glucocorticoids are an essential part of many multi-agent treatment regimens for lymphoid malignancies. However, the emergence of glucocorticoid resistance is a significant barrier to cure, which is in part due to epigenetic alterations, including aberrant chromatin accessibility and hypermethylation at lymphocyte-specific glucocorticoid-response elements (GREs). To gain a deeper understanding of regulatory mechanisms leading to these epigenetic alterations, we conducted a multi-omics study, including chromosome conformation capture sequencing (HiC), to examine changes in the 3D genome structure following the in vivo treatment of acute lymphoblastic leukemia (ALL) patient-derived xenografts (PDXs) with glucocorticoid. We found that glucocorticoid treatment led to distinct patterns of topologically associated domains (TADs) in glucocorticoid sensitive compared to resistant PDXs. Furthermore, we show that these TADs were primed by the development-related pioneer transcription factor PU.1, which extensively interacts with the glucocorticoid receptor (GR) exclusively in glucocorticoid-sensitive ALL PDXs. An integrative analysis of rapid immunoprecipitation mass spectrometry of endogenous protein (RIME) and ChIP-seq revealed that PU.1 binding was associated with lymphocyte-specific activation of GREs and GRE-interacting super-enhancers. The PU.1-associated TADs modulated epigenetic marks, and particularly the eviction of PU.1 promoted GR binding and the expression of signature genes, including BIM, ZBTB16 and RASA1, mediating glucocorticoid-induced apoptosis in ALL. These findings were phenocopied using a PU.1 inhibitor DB2313 to restore glucocorticoid sensitivity in ALL. Taken together, this study identified a new epigenetic pathway integrating PU.1 priming and PU.1-GR interaction which ultimately leads to PU.1 eviction in ALL. This pathway provides the first link between the activity of a lineage-specific transcription factor and epigenetic modulators mediating the response to glucocorticoids and thus offers a new avenue to translate fundamental epigenetic research into the clinic.

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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Lymphocyte-specific chromatin accessibility pre-determines glucocorticoid resistance in acute lymphoblastic leukemia [WGBS]

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