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

Shorrocks, Julie, Tobi, Simon E., Latham, Harry, Peacock, John H., Eeles, Ros, Eccles, Diana and McMillan, Trevor J. (2004) 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. International Journal of Radiation Oncology, Biology, Physics, 58 (2), 470-478. (doi:10.1016/j.ijrobp.2003.09.042).

Abstract

Purpose: 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 and materials: 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 (G1 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 × 105 J/m2), as compared with 35.7 ± 1.9 (range) for two BRCA1(+/?) strains. Because a defective G1/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.
Conclusion: Our data suggest a defective G1/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.

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Contributors

Author: Diana Eccles

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