title: Curcumin regulates low-linear energy transfer γ-radiation-induced NFκB-dependent telomerase activity in human neuroblastoma cells.
abstract: OBJECTIVE
  We recently reported that curcumin attenuates ionizing radiation (IR)-induced survival signaling and proliferation in human neuroblastoma cells. Also, in the endothelial system, we have demonstrated that NFκB regulates IR-induced telomerase activity (TA). Accordingly, we investigated the effect of curcumin in inhibiting IR-induced NFκB-dependent hTERT transcription, TA, and cell survival in neuroblastoma cells.
  
  
  METHODS
  SK-N-MC or SH-SY5Y cells exposed to IR and treated with curcumin (10-100 nM) with or without IR were harvested after 1 h through 24 h. NFκB-dependent regulation was investigated either by luciferase reporter assays using pNFκB-, pGL3-354-, pGL3-347-, or pUSE-IκBα-Luc, p50/p65, or RelA siRNA-transfected cells. NFκB activity was analyzed using an electrophoretic mobility shift assay and hTERT expression using the quantitative polymerase chain reaction. TA was determined using the telomerase repeat amplification protocol assay and cell survival using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltertrazolium bromide and clonogenic assay.
  
  
  RESULTS
  Curcumin profoundly inhibited IR-induced NFκB. Consequently, curcumin significantly inhibited IR-induced TA and hTERT mRNA at all points investigated. Furthermore, IR-induced TA is regulated at the transcriptional level by triggering telomerase reverse transcriptase (TERT) promoter activation. Moreover, NFκB becomes functionally activated after IR and mediates TA upregulation by binding to the κB-binding region in the promoter region of the TERT gene. Consistently, elimination of the NFκB-recognition site on the telomerase promoter or inhibition of NFκB by the IκBα mutant compromises IR-induced telomerase promoter activation. Significantly, curcumin inhibited IR-induced TERT transcription. Consequently, curcumin inhibited hTERT mRNA and TA in NFκB overexpressed cells. Furthermore, curcumin enhanced the IR-induced inhibition of cell survival.
  
  
  CONCLUSIONS
  These results strongly suggest that curcumin inhibits IR-induced TA in an NFκB dependent manner in human neuroblastoma cells.
authors.affiliation: Department of Radiation Oncology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA. naravind@ouhsc.edu
authors.forename: Natarajan
authors.initials: N
authors.lastname: Aravindan
authors.forename: Jamunarani
authors.initials: J
authors.lastname: Veeraraghavan
authors.forename: Rakhesh
authors.initials: R
authors.lastname: Madhusoodhanan
authors.forename: Terence S
authors.initials: TS
authors.lastname: Herman
authors.forename: Mohan
authors.initials: M
authors.lastname: Natarajan
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D003474:Curcumin / Q000494:pharmacology*; D005720:Gamma Rays; D006801:Humans; D018499:Linear Energy Transfer / Q000187:drug effects* / Q000502:physiology; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000502:physiology / Q000528:radiation effects; D009447:Neuroblastoma / Q000201:enzymology*; D011401:Promoter Regions, Genetic / Q000528:radiation effects; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D011836:Radiation Tolerance; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*
chemical_list: D016328:NF-kappa B; D012333:RNA, Messenger; D019098:Telomerase; D003474:Curcumin