G2-phase chromosomal radiosensitivity of primary fibroblasts from hereditary retinoblastoma family members and some apparently normal controls

Abstract

We previously described an enhanced sensitivity for cell killing and gamma-H2AX focus induction after both high-dose-rate and continuous low-dose-rate gamma irradiation in 14 primary fibroblast strains derived from hereditary-type retinoblastoma family members (both affected RB1(+/-) probands and unaffected RB1(+/+) parents). Here we present G(2)-phase chromosomal radiosensitivity assay data for primary fibroblasts derived from these RB family members and five Coriell cell bank controls (four apparently normal individuals and one bilateral RB patient). The RB family members and two normal Coriell strains had significantly higher ( approximately 1.5-fold, P < 0.05) chromatid-type aberration frequencies in the first postirradiation mitosis after doses of 50 cGy and 1 Gy of (137)Cs gamma radiation compared to the remaining Coriell strains. The induction of chromatid-type aberrations by high-dose-rate G(2)-phase gamma irradiation is significantly correlated to the proliferative ability of these cells exposed to continuous low-dose-rate gamma irradiation (reported in Wilson et al., Radiat. Res. 169, 483-494, 2008). Our results suggest that these moderately radiosensitive individuals may harbor hypomorphic genetic variants in genomic maintenance and/or DNA repair genes or may carry epigenetic changes involving genes that more broadly modulate such systems, including G(2)-phase-specific DNA damage responses.

FIG. 1

Histogram of mean radiation-induced chromatid-type aberrations/cell/Gy (averaged for 50 cGy and 1 Gy) for the 19 primary fibroblast strains examined in this study using the G₂ chromosomal radiosensitivity assay.

FIG. 2

Panel A: Plot of the dose rates (in cGy/h) required to reduce relative survival to 10% (filled symbols, heavier dashed line) and 1% (open symbols, lighter dashed line) in the continuous low-dose-rate irradiation colony formation assay (1) compared to the total chromatid-type aberration frequencies (spontaneous plus radiation-induced) measured after 0, 50 cGy and 1 Gy high-dose-rate irradiation in G₂ phase in this study. The low-dose-rate colony formation assay described in ref. (1) measures the proliferative capacity of cells continuously exposed to low-dose-rate (0.5–8.4 cGy/h) ¹³⁷Cs γ radiation for 2 weeks. Panel B: Identification of the individual fibroblast strains from panel A using the 50 cGy/1% low-dose-rate survival data set and the same legend symbols from Fig. 1; this arrangement of strains is repeated for each of the G₂ assay data sets for 50 cGy and 1 Gy.