title: Targeting BRG1 chromatin remodeler via its bromodomain for enhanced tumor cell radiosensitivity in vitro and in vivo.
abstract: Radiotherapy treats cancer by inducing DNA double-strand breaks (DSB) in tumor cells using ionizing radiation. However, DNA repair in tumor cells often leads to radioresistance and unsuccessful outcome. Inhibition of DNA repair by targeting repair proteins can increase radiosensitivity of tumor cells. The BRG1 chromatin remodeling enzyme assists DSB repair by stimulating γ-H2AX formation and BRG1 binding to acetylated histones at DSBs via bromodomain (BRD) is critical for this activity. Here, we show that ectopic expression of BRG1-BRD inhibited γ-H2AX and DSB repair after irradiation and increased the radiosensitivity in various human cancer cells, including HT29 colon cancer. Dimerization of BRG1-BRD, increasing its chromatin binding affinity, aggravated the defects in γ-H2AX and DSB repair and further enhanced the radiosensitivity. While little affecting the upstream ATM activation, BRG1-BRD in irradiated HT29 cells inhibited the recruitment of 53BP1 to damaged chromatin, the downstream event of γ-H2AX, and compromised the G2-M checkpoint and increased apoptosis. Importantly, in a xenograft mouse model, BRG1-BRD increased the radiosensitivity of HT29 tumors, which was further enhanced by dimerization. These data suggest that BRG1-BRD radiosensitizes tumor cells by a dominant negative activity against BRG1, which disrupts γ-H2AX and its downstream 53BP1 pathways, leading to inefficient DNA repair, G2-M checkpoint defect, and increased apoptosis. This work therefore identifies BRG1-BRD as a novel tumor radiosensitizer and its action mechanism, providing the first example of chromatin remodeler as a target for improving cancer radiotherapy.
authors.affiliation: Department of Life Science, The Research Center for Cellular Homeostasis, Ewha Womans University, Seoul, Korea.
authors.forename: Su-Jung
authors.initials: SJ
authors.lastname: Kwon
authors.affiliation: Department of Life Science, The Research Center for Cellular Homeostasis, Ewha Womans University, Seoul, Korea.
authors.forename: Seul-Ki
authors.initials: SK
authors.lastname: Lee
authors.affiliation: Department of Nuclear Medicine and Biomedical Sciences, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Juri
authors.initials: J
authors.lastname: Na
authors.affiliation: Department of Life Science, The Research Center for Cellular Homeostasis, Ewha Womans University, Seoul, Korea.
authors.forename: Shin-Ai
authors.initials: SA
authors.lastname: Lee
authors.affiliation: Department of Life Science, The Research Center for Cellular Homeostasis, Ewha Womans University, Seoul, Korea.
authors.forename: Han-Sae
authors.initials: HS
authors.lastname: Lee
authors.affiliation: Department of Life Science, The Research Center for Cellular Homeostasis, Ewha Womans University, Seoul, Korea.
authors.forename: Ji-Hye
authors.initials: JH
authors.lastname: Park
authors.affiliation: Department of Nuclear Medicine and Biomedical Sciences, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea. Tumor Microenvironment Global Core Research Center, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: June-Key
authors.initials: JK
authors.lastname: Chung
authors.affiliation: Department of Nuclear Medicine and Biomedical Sciences, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea. Tumor Microenvironment Global Core Research Center, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Korea. Cancer Imaging Center, Seoul National University Hospital, Jongno-Gu, Seoul, Korea. jongkwon@ewha.ac.kr hwyoun@snu.ac.kr.
authors.forename: Hyewon
authors.initials: H
authors.lastname: Youn
authors.affiliation: Department of Life Science, The Research Center for Cellular Homeostasis, Ewha Womans University, Seoul, Korea. jongkwon@ewha.ac.kr hwyoun@snu.ac.kr.
authors.forename: Jongbum
authors.initials: J
authors.lastname: Kwon
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism; D042002:Chromatin Assembly and Disassembly / Q000187:drug effects / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects / Q000528:radiation effects; D004265:DNA Helicases / Q000737:chemistry* / Q000378:metabolism*; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects / Q000528:radiation effects; D006657:Histones / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000378:metabolism; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011836:Radiation Tolerance / Q000187:drug effects / Q000528:radiation effects; D011839:Radiation, Ionizing; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D000071857:Tumor Suppressor p53-Binding Protein 1
chemical_list: D000970:Antineoplastic Agents; D002843:Chromatin; C468783:H2AX protein, human; D006657:Histones; D047908:Intracellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C498301:TP53BP1 protein, human; D014157:Transcription Factors; D000071857:Tumor Suppressor p53-Binding Protein 1; C084108:SMARCA4 protein, human; D004265:DNA Helicases