title: Mechanisms of increased risk of tumorigenesis in Atm and Brca1 double heterozygosity.
abstract: BACKGROUND
  Both epidemiological and experimental studies suggest that heterozygosity for a single gene is linked with tumorigenesis and heterozygosity for two genes increases the risk of tumor incidence. Our previous work has demonstrated that Atm/Brca1 double heterozygosity leads to higher cell transformation rate than single heterozygosity. However, the underlying mechanisms have not been fully understood yet. In the present study, a series of pathways were investigated to clarify the possible mechanisms of increased risk of tumorigenesis in Atm and Brca1 heterozygosity.
  
  
  METHODS
  Wild type cells, Atm or Brca1 single heterozygous cells, and Atm/Brca1 double heterozygous cells were used to investigate DNA damage and repair, cell cycle, micronuclei, and cell transformation after photon irradiation.
  
  
  RESULTS
  Remarkable high transformation frequency was confirmed in Atm/Brca1 double heterozygous cells compared to wild type cells. It was observed that delayed DNA damage recognition, disturbed cell cycle checkpoint, incomplete DNA repair, and increased genomic instability were involved in the biological networks. Haploinsufficiency of either ATM or BRCA1 negatively impacts these pathways.
  
  
  CONCLUSIONS
  The quantity of critical proteins such as ATM and BRCA1 plays an important role in determination of the fate of cells exposed to ionizing radiation and double heterozygosity increases the risk of tumorigenesis. These findings also benefit understanding of the individual susceptibility to tumor initiation.
authors.affiliation: Key Laboratory of Heavy Ion Radiation Biology and Medicine, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, P R China.
authors.forename: Jufang
authors.initials: J
authors.lastname: Wang
authors.forename: Fengtao
authors.initials: F
authors.lastname: Su
authors.forename: Lubomir B
authors.initials: LB
authors.lastname: Smilenov
authors.forename: Libin
authors.initials: L
authors.lastname: Zhou
authors.forename: Wentao
authors.initials: W
authors.lastname: Hu
authors.forename: Nan
authors.initials: N
authors.lastname: Ding
authors.forename: Guangming
authors.initials: G
authors.lastname: Zhou
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D019313:BRCA1 Protein / Q000235:genetics*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics*; D002470:Cell Survival; D002471:Cell Transformation, Neoplastic; D020552:Comet Assay; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006579:Heterozygote; D006657:Histones / Q000378:metabolism; D006801:Humans; D015162:Micronucleus Tests; D009369:Neoplasms / Q000235:genetics* / Q000532:radiotherapy; D017785:Photons; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D012306:Risk; D025521:Tumor Suppressor Proteins / Q000235:genetics*
chemical_list: D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases