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Dynamic interplay of BRD4 isoforms in embryonal rhabdomyosarcoma

ABSTRACT: In this study, we show that long and short isoform of the epigenetic regulator BRD4 is overexpressed in ERMS patient-derived cell lines and patient tumour specimens. Functionally, knockdown of long isoform of BRD4 reduced proliferation and promotes differentiation. Knockdown of the short isoform on the other hand promotes migration and invasion. The functional observations were confirmed in vitro and in vivo. Through RNA Sequencing analysis, we identified Myostatin (MSTN) and Integrins (ITGs) as important downstream target of long and short isoform of BRD4 respectively. We thus conclude from this study that long isoform functions as an oncogenic driver and can only promote metastasis only when the short isoform that functions as a blocker of tumor spread is removed. The interplay of the isoform identifies the long form as a therapeutic target and the short form as a predictive biomarker for metastasis in ERMS.

ORGANISM(S): Homo sapiens

PROVIDER: GSE215393 | GEO | 2023/12/01

REPOSITORIES: GEO

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Project description:DNA damage activates a complex signaling network in cells that blocks cell cycle progression, recruits factors involved in DNA repair, and/or triggers programs that control senescence or programmed cell death. Alterations in chromatin structure are known to be important for the initiation and propagation of the DNA damage response, although the molecular details are unclear. We investigated the role of chromatin structure in the DNA damage response by monitoring multiple timedependent checkpoint signaling and response events with a high-content multiplex image-based RNAi screen of chromatin modifying and interacting genes. We discovered that Brd4, a double bromodomain-containing protein, functions as an endogenous inhibitor of DNA damage signaling by binding to acetylated histones at sites of open chromatin and altering chromatin accessibility. Loss of Brd4 or disruption of acetyl-lysine binding results in an increase in both the number and size of radiation-induced !H2AX nuclear foci while overexpression of a Brd4 splice isoform completely suppresses !H2AX formation, despite equivalent double strand break formation. Brd4 knock-down cells displayed altered chromatin structure, prolonged cell cycle checkpoint arrest and enhanced survival after irradiation, while overexpression of Brd4 isoform B results in enhanced radiationinduced lethality. Brd4 is the target of the t(15;19) chromosomal translocation in a rare form of cancer, NUT Midline Carcinoma. Acetyl lysine-bromodomain interactions of the Brd4-NUT fusion protein suppresses !H2AX foci in discrete nuclear compartments, rendering cells more radiosensitive, mimicking overexpression of Brd4 isoform B. NUT Midline Carcinoma is sensitive to radiotherapy, however tumor material from this rare cancer is scarce. We therefore investigated Brd4 expression in another human cancer commonly treated with radiotherapy, glioblastoma multiforme, and found that expression of Brd4 isoform B correlated specifically with treatment response to radiotherapy. These data implicate Brd4 as an endogenous insulator of DNA damage signaling through recognition of epigenetic modifications in chromatin and suggest that expression of the Brd4 in human cancer can modulate the clinical response to DNA-damaging cancer therapy. Two replicates each of U2OS cells expressing either Brd4 shRNA or a control shRNA

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Dynamic interplay of BRD4 isoforms in embryonal rhabdomyosarcoma

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