title: Constitutive hyperactivity of histone deacetylases enhances radioresistance in Lepidopteran Sf9 insect cells.
abstract: BACKGROUND
  Lepidopteran insect cells withstand multifold higher radiation doses and suffer far less DNA damage despite carrying numerous structural/functional homologies with mammalian cells. Since DNA-histone interactions significantly influence radiation-induced DNA damage, we investigated the role of histones in insect cell radioresistance.
  
  
  METHODS
  Modified comet assay was used to assess the γ-radiation-induced DNA damage following serial histone depletion by varied salt concentrations. Acid-Urea-Triton (AUT) gel analysis combined with in silico predictions was used to compare mammalian and insect histones and acetylation status while HDAC activity was assessed/modified for studying the latter's role in radioresistance. Cell death was measured by morphological analysis and flow cytometry.
  
  
  RESULTS
  High-salt extraction pattern from Sf9 nuclei suggested stronger DNA-histone affinity as the two core histones H2A/H2B could be extracted at much higher (2M) concentration as compared to 1.2M NaCl in mammalian (AA8) cells. Electrophoretic mobility of unirradiated Sf9 cells remained unaltered at all salt concentrations (0.14M-2M NaCl), and radiation-induced DNA damage increased only by 2M-NaCl pre-treatment. In silico analysis confirmed excellent conservation of Lepidopteran H2A/H2B sequence with human histones including comparable N-terminal lysine residues, yet these had ~60% lower acetylation. Importantly, insect cells showed ~70% higher histone deacetylase activity whose inhibition by Trichostatin-A reversed hypo-acetylation state and caused significant radiosensitization, thereby confirming the protective contribution of reduced acetylation.
  
  
  CONCLUSIONS
  Our study reveals that the hypo-acetylated state of well-conserved core histones, maintained by considerable HDAC activity, contributes significantly in Lepidopteran radioresistance.
  
  
  CONCLUSIONS
  This investigation shows constitutively high activity of HDACs as a potential radioprotective mechanism existing in insect cells.
authors.affiliation: Division of Natural Radiation Response Mechanisms, Institute of Nuclear Medicine and Allied Sciences, Brig. SK Mazumdar Road, Delhi 110054, India.
authors.forename: Kanupriya
authors.initials: K
authors.lastname: Sharma
authors.affiliation: Division of Natural Radiation Response Mechanisms, Institute of Nuclear Medicine and Allied Sciences, Brig. SK Mazumdar Road, Delhi 110054, India.
authors.forename: Ashish
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Division of Natural Radiation Response Mechanisms, Institute of Nuclear Medicine and Allied Sciences, Brig. SK Mazumdar Road, Delhi 110054, India. Electronic address: sudhirchandna@yahoo.com.
authors.forename: Sudhir
authors.initials: S
authors.lastname: Chandna
mesh_terms: D000107:Acetylation; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004249:DNA Damage; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006655:Histone Deacetylases / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D007915:Lepidoptera; D008969:Molecular Sequence Data; D011836:Radiation Tolerance
chemical_list: D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; C012589:trichostatin A; D006655:Histone Deacetylases
keywords: DNA damage; Histone deacetylase; Histone post-translational modifications; Radioresistance; Sf9 cells