title: Inhibition of c-Jun N-terminal kinase activity enhances vestibular schwannoma cell sensitivity to gamma irradiation.
abstract: BACKGROUND
  Radiosurgery is increasingly used to treat vestibular schwannomas (VSs). Increasing the sensitivity of VS cells to irradiation (IR) could allow for lower and/or more effective doses of IR, improving safety and efficacy. Persistent c-Jun N-terminal kinase (JNK) activity in VS cells reduces cell death by suppressing the accumulation of reactive oxygen species (ROS), raising the possibility that JNK activity protects against IR-induced VS cell death, which is mediated by ROS.
  
  
  OBJECTIVE
  To determine the extent to which JNK signaling contributes to VS cell radiosensitivity.
  
  
  METHODS
  Primary human VS cultures, derived from acutely resected tumors, received single doses (5-40 Gy) of gamma irradiation. Histone 2AX phosphorylation, a marker of IR-induced DNA damage, was assayed by Western blot and immunostaining. ROS levels were quantified by measuring 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) fluorescence. Cell apoptosis was determined by terminal deoxynucleotidyl transferase 2'-deoxyuridine, 5'-triphosphate nick end labeling.
  
  
  RESULTS
  The JNK inhibitors SP6000125 and I-JIP reduced histone 2AX phosphorylation after IR. They also increased H2DCFDA fluorescence in nonirradiated cultures and significantly increased IR-induced (5-10 Gy) H2DCFDA fluorescence 72 hours, but not 2 hours, after IR. Finally, I-JIP (50 μmol/L) significantly increased VS cell apoptosis in cultures treated with 20 to 40 Gy. I-JIP (20 μmol/L), SP600125 (20 μmol/L), and JNK1/2 short interfering RNA knockdown each increased VS cell apoptosis in cultures treated with 30 to 40 Gy, but not lower doses, of IR.
  
  
  CONCLUSIONS
  Inhibition of JNK signaling decreases histone 2AX phosphorylation and increases ROS and apoptosis in VS cells after gamma irradiation. These results raise the possibility of using JNK inhibitors to increase the effectiveness of radiosurgery for treatment of VSs.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Wei Ying
authors.initials: WY
authors.lastname: Yue
authors.forename: J Jason
authors.initials: JJ
authors.lastname: Clark
authors.forename: Michael
authors.initials: M
authors.lastname: Telisak
authors.forename: Marlan R
authors.initials: MR
authors.lastname: Hansen
mesh_terms: D017209:Apoptosis / Q000528:radiation effects; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects*; D006657:Histones / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000528:radiation effects*; D009464:Neuroma, Acoustic / Q000473:pathology*; D010766:Phosphorylation / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000528:radiation effects
chemical_list: D006657:Histones; D017382:Reactive Oxygen Species; D048031:JNK Mitogen-Activated Protein Kinases