title: Primary fibroblasts from BRCA1 heterozygotes display an abnormal G1/S cell cycle checkpoint following UVA irradiation but show normal levels of micronuclei following oxidative stress or mitomycin C treatment.
abstract: OBJECTIVE
  There is evidence to suggest that the breast cancer predisposing gene, BRCA1, is involved in cell cycle control and the response to damage but mouse brca1+/- heterozygotes have no distinctive phenotype. Here the response to the three forms of cellular stress was examined in primary human fibroblasts from individuals with a +/+ or +/- genotype for BRCA1.
  
  
  METHODS
  Fibroblasts from individuals carrying mutations in the BRCA1 gene were compared with those from those wild-type for BRCA1 in their response to long wavelength uv (UVA), hydrogen peroxide, and mitomycin C (MMC). Cell cycle progression and micronucleus formation (MN) were used as end points.
  
  
  RESULTS
  After UVA treatment there was no difference between +/- and +/+ cells in the initial fall in DNA synthetic activity (G(1) arrest) but the reentry into S-phase was restored at a faster rate in the BRCA1+/- cells after UVA exposure. Thus, for three normal (+/+) cell lines irradiated in monolayer, S-phase values averaged 15 +/- 3.7% 14 h post-UVA (1 x 10(5) J/m(2)), as compared with 35.7 +/- 1.9 (range) for two BRCA1(+/-) strains. Because a defective G(1)/S checkpoint in BRCA1 heterozygotes could lead to a greater proportion of S-phase cells with unrepaired DNA damage (strand breaks) and a resultant increase in chromosomal instability, the frequency of micronuclei induced by UVA was examined. Three normal (+/+) and three mutant (+/-) strains (two of which were used in the cell cycle experiments) produced mean micronuclei frequencies of 0.077 +/- 0.016 and 0.094 +/- 0.04/binucleate cell respectively (not statistically significant), 48 h after UVA exposure. No differences were found between BRCA1+/+ and +/- cells in MN formation after treatment with MMC or hydrogen peroxide.
  
  
  CONCLUSIONS
  Our data suggest a defective G(1)/S checkpoint in cells from BRCA1 heterozygotes in response to UVA although this is not reflected in genomic instability as measured by micronuclei induction after oxidative stress or MMC treatment.
authors.affiliation: Department of Biological Sciences, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster LA1 4YQ, UK.
authors.forename: Julie
authors.initials: J
authors.lastname: Shorrocks
authors.forename: Simon E
authors.initials: SE
authors.lastname: Tobi
authors.forename: Harry
authors.initials: H
authors.lastname: Latham
authors.forename: John H
authors.initials: JH
authors.lastname: Peacock
authors.forename: Ros
authors.initials: R
authors.lastname: Eeles
authors.forename: Diana
authors.initials: D
authors.lastname: Eccles
authors.forename: Trevor J
authors.initials: TJ
authors.lastname: McMillan
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology; D001943:Breast Neoplasms / Q000235:genetics; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D004249:DNA Damage; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects*; D016193:G1 Phase / Q000235:genetics*; D019398:Genes, BRCA1 / Q000502:physiology*; D020022:Genetic Predisposition to Disease; D006579:Heterozygote; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D048629:Micronuclei, Chromosome-Defective; D015162:Micronucleus Tests; D016685:Mitomycin / Q000494:pharmacology; D009154:Mutation; D018384:Oxidative Stress; D016196:S Phase / Q000235:genetics*; D014466:Ultraviolet Rays
chemical_list: D000477:Alkylating Agents; D016685:Mitomycin; D006861:Hydrogen Peroxide