Temporal position of G1 arrest in normal human fibroblasts after exposure to gamma-rays.
G1 phase cell cycle arrest after exposure to ionizing radiation has been documented in cells with wild-type p53. The temporal location of this arrest within G1 phase, however, has not been determined. We have now used flow cytometric analysis of bromodeoxyuridine (BrdUrd)-labeled cells to obtain further information about the location of the G1 phase radiation checkpoint. Human fibroblasts were irradiated with gamma-rays and treated with colcemid to stop unlabeled G2 cells from entering the G1 phase. Analysis of BrdUrd incorporation revealed that 73% of G1 phase human lung fibroblasts remain in G1 phase after exposure to gamma-rays, thereby placing the G1 radiation checkpoint near the end of G1 phase. The location of the radiation checkpoint correlates with the reported increased expression of cyclin E, increased cyclin E/cdk2 kinase activity, and hyperphosphorylation of pRb in proliferating human fibroblasts.
Gadbois
D M
DM
Life Sciences Division, Los Alamos National Laboratory, New Mexico 87545, USA. gadbois@telomere.lanl.gov
Lehnert
B E
BE
D002453:Cell Cycle / Q000528:radiation effects*; D002478:Cells, Cultured; D004171:Diploidy; D005347:Fibroblasts / Q000166:cytology / Q000528:radiation effects; D016193:G1 Phase / Q000528:radiation effects*; D005720:Gamma Rays; D006801:Humans; D008168:Lung / Q000166:cytology; D013997:Time Factors