title: RAD9 deficiency enhances radiation induced bystander DNA damage and transcriptomal response.
abstract: BACKGROUND
  Radiation induced bystander effects are an important component of the overall response of cells to irradiation and are associated with human health risks. The mechanism responsible includes intra-cellular and inter-cellular signaling by which the bystander response is propagated. However, details of the signaling mechanism are not well defined.
  
  
  METHODS
  We measured the bystander response of Mrad9+/+ and Mrad9-/- mouse embryonic stem cells, as well as human H1299 cells with inherent or RNA interference-mediated reduced RAD9 levels after exposure to 1 Gy α particles, by scoring chromosomal aberrations and micronuclei formation, respectively. In addition, we used microarray gene expression analyses to profile the transcriptome of directly irradiated and bystander H1299 cells.
  
  
  RESULTS
  We demonstrated that Mrad9 null enhances chromatid aberration frequency induced by radiation in bystander mouse embryonic stem cells. In addition, we found that H1299 cells with reduced RAD9 protein levels showed a higher frequency of radiation induced bystander micronuclei formation, compared with parental cells containing inherent levels of RAD9. The enhanced bystander response in human cells was associated with a unique transcriptomic profile. In unirradiated cells, RAD9 reduction broadly affected stress response pathways at the mRNA level; there was reduction in transcript levels corresponding to genes encoding multiple members of the UVA-MAPK and p38MAPK families, such as STAT1 and PARP1, suggesting that these signaling mechanisms may not function optimally when RAD9 is reduced. Using network analysis, we found that differential activation of the SP1 and NUPR1 transcriptional regulators was predicted in directly irradiated and bystander H1299 cells. Transcription factor prediction analysis also implied that HIF1α (Hypoxia induced factor 1 alpha) activation by protein stabilization in irradiated cells could be a negative predictor of the bystander response, suggesting that local hypoxic stress experienced by cells directly exposed to radiation may influence whether or not they will elicit a bystander response in neighboring cells.
authors.forename: Shanaz A
authors.initials: SA
authors.lastname: Ghandhi
authors.forename: Brian
authors.initials: B
authors.lastname: Ponnaiya
authors.forename: Sunil K
authors.initials: SK
authors.lastname: Panigrahi
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Hopkins
authors.forename: Qingping
authors.initials: Q
authors.lastname: Cui
authors.forename: Tom K
authors.initials: TK
authors.lastname: Hei
authors.forename: Sally A
authors.initials: SA
authors.lastname: Amundson
authors.affiliation: Center for Radiological Research, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA. HBL1@columbia.edu.
authors.forename: Howard B
authors.initials: HB
authors.lastname: Lieberman
mesh_terms: D000818:Animals; D024201:Bystander Effect / Q000235:genetics* / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000172:deficiency* / Q000235:genetics; D002460:Cell Line; D002869:Chromosome Aberrations; D004249:DNA Damage / Q000235:genetics* / Q000528:radiation effects; D053595:Embryonic Stem Cells / Q000528:radiation effects; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D020411:Oligonucleotide Array Sequence Analysis; D011833:Radiation Injuries, Experimental / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D059467:Transcriptome / Q000528:radiation effects*
chemical_list: D018797:Cell Cycle Proteins; C069930:rad9 protein