title: Homologous recombination preferentially repairs heat-induced DNA double-strand breaks in mammalian cells.
abstract: OBJECTIVE
  Heat shock induces DNA double-strand breaks (DSBs), but the precise mechanism of repairing heat-induced damage is unclear. Here, we investigated the DNA repair pathways involved in cell death induced by heat shock.
  
  
  METHODS
  B02, a specific inhibitor of human RAD51 (homologous recombination; HR), and NU7026, a specific inhibitor of DNA-PK (non-homologous end-joining; NHEJ), were used for survival assays of human cancer cell lines with different p53-gene status. Mouse embryonic fibroblasts (MEFs) lacking Lig4 (NHEJ) and/or Rad54 (HR) were used for survival assays and a phosphorylated histone H2AX at Ser139 (γH2AX) assay. MEFs lacking Rad51d (HR) were used for survival assays. SPD8 cells were used to measure HR frequency after heat shock.
  
  
  RESULTS
  Human cancer cells were more sensitive to heat shock in the presence of B02 despite their p53-gene status, and the effect of B02 on heat sensitivity was specific to the G2phase. Rad54-deficient MEFs were sensitive to heat shock and showed prolonged γH2AX signals following heat shock. Rad51d-deficient MEFs were also sensitive to heat shock. Moreover, heat shock-stimulated cells had increased HR.
  
  
  CONCLUSIONS
  The HR pathway plays an important role in the survival of mammalian cells against death induced by heat shock via the repair of heat-induced DNA DSBs.
authors: a Gunma University Heavy Ion Medical Center , Gunma , Japan.
authors: Akihisa
authors: A
authors: Takahashi
authors: b Department of Radiation Oncology , Nara Medical University , Nara, Japan.
authors: Eiichiro
authors: E
authors: Mori
authors: c Department of Oral and Maxillofacial Surgery , Nara Medical University , Nara, Japan.
authors: Yosuke
authors: Y
authors: Nakagawa
authors: c Department of Oral and Maxillofacial Surgery , Nara Medical University , Nara, Japan.
authors: Atsuhisa
authors: A
authors: Kajihara
authors: c Department of Oral and Maxillofacial Surgery , Nara Medical University , Nara, Japan.
authors: Tadaaki
authors: T
authors: Kirita
authors: d Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy , University of South Carolina , Columbia , SC , USA.
authors: Douglas L
authors: DL
authors: Pittman
authors: b Department of Radiation Oncology , Nara Medical University , Nara, Japan.
authors: Masatoshi
authors: M
authors: Hasegawa
authors: b Department of Radiation Oncology , Nara Medical University , Nara, Japan.
authors: Takeo
authors: T
authors: Ohnishi
keywords: DNA double-strand break; heat shock; homologous recombination; non-homologous end-joining; γH2AX