title: SWI/SNF complexes are required for full activation of the DNA-damage response.
abstract: SWI/SNF complexes utilize BRG1 (also known as SMARCA4) or BRM (also known as SMARCA2) as alternative catalytic subunits with ATPase activity to remodel chromatin. These chromatin-remodeling complexes are required for mammalian development and are mutated in ~20% of all human primary tumors. Yet our knowledge of their tumor-suppressor mechanism is limited. To investigate the role of SWI/SNF complexes in the DNA-damage response (DDR), we used shRNAs to deplete BRG1 and BRM and then exposed these cells to a panel of 6 genotoxic agents. Compared to controls, the shRNA knockdown cells were hypersensitive to certain genotoxic agents that cause double-strand breaks (DSBs) associated with stalled/collapsed replication forks but not to ionizing radiation-induced DSBs that arise independently of DNA replication. These findings were supported by our analysis of DDR kinases, which demonstrated a more prominent role for SWI/SNF in the activation of the ATR-Chk1 pathway than the ATM-Chk2 pathway. Surprisingly, γH2AX induction was attenuated in shRNA knockdown cells exposed to a topoisomerase II inhibitor (etoposide) but not to other genotoxic agents including IR. However, this finding is compatible with recent studies linking SWI/SNF with TOP2A and TOP2BP1. Depletion of BRG1 and BRM did not result in genomic instability in a tumor-derived cell line but did result in nucleoplasmic bridges in normal human fibroblasts. Taken together, these results suggest that SWI/SNF tumor-suppressor activity involves a role in the DDR to attenuate replicative stress and genomic instability. These results may also help to inform the selection of chemotherapeutics for tumors deficient for SWI/SNF function.
authors.affiliation: Department of Genetics and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, USA.|Current address: Division of the National Toxicology Program, NIEHS, Research Triangle Park, NC, USA.
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Smith-Roe
authors.affiliation: Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Nakamura
authors.affiliation: Department of Genetics and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Darcy
authors.initials: D
authors.lastname: Holley
authors.affiliation: Department of Biomedical Sciences, William Carey University, Hattiesburg, MS, USA.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Chastain
authors.affiliation: Department of Genetics and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Gary B
authors.initials: GB
authors.lastname: Rosson
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Dennis A
authors.initials: DA
authors.lastname: Simpson
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Ridpath
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Kaufman
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: William K
authors.initials: WK
authors.lastname: Kaufmann
authors.affiliation: Department of Genetics and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Bultman
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D004249:DNA Damage; D004265:DNA Helicases / Q000172:deficiency / Q000235:genetics*; D005260:Female; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000172:deficiency / Q000235:genetics*; D034741:RNA, Small Interfering / Q000235:genetics; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics*; D002583:Uterine Cervical Neoplasms / Q000235:genetics*
chemical_list: D009687:Nuclear Proteins; D034741:RNA, Small Interfering; C084011:SMARCA2 protein, human; D014157:Transcription Factors; C084108:SMARCA4 protein, human; D004265:DNA Helicases