Gamma-radiation-induced cell death in the fetal rat brain possesses molecular characteristics of apoptosis and is associated with specific messenger RNA elevations.
Low-dose ionizing irradiation of 16-18-day pregnant rats rapidly kills stem cells in the fetal forebrain. We have examined gamma-irradiated 17-day fetal rat brain tissue for molecular characteristics of apoptosis and changes in levels of mRNAs relevant to apoptosis. In many forebrain cells radiation elicits within 5 h nuclear condensation and fragmentation consistent with apoptosis. An electrophoretic DNA ladder indicative of internucleosomal chromatin cleavage was prominent within 3 h after irradiation. Pretreatment of pregnant rats with cycloheximide, or pretreatment of dissociated fetal brain cells in culture with actinomycin D, abolished the radiation-induced internucleosomal DNA fragmentation, demonstrating requirements for protein and RNA synthesis. Irradiation dramatically increased the level of the p53 transcription factor and the abundances of mRNAs coding for the cell-cycle inhibitor p21/Waf-1/Cip-1 and the AP-1-associated transcription factors Fos and JunB. Irradiation moderately increased the level of mRNA for the positive apoptosis regulator Bax. In contrast, irradiation reduced by 50-70% the abundances of most other mRNAs tested, including those for housekeeping proteins, p53, Jun, Myc, interleukin-1-beta-converting enzyme, and the negative apoptosis regulators Bcl-2 and Bcl-xL. These results indicate that radiation-elicited apoptosis of fetal brain cells is associated with activation of the p53 system, probable increases in AP-1 Fos/JunB heterodimers, and an increased ratio of Bax to Bcl-2 + Bcl-xL.
Borovitskaya
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Laboratory of Biochemical Genetics, National Heart, Lung, and Blood Institute, Bethesda, MD 20892, USA.
Evtushenko
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Sabol
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D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D015152:Blotting, Northern; D001921:Brain / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D016923:Cell Death; D002478:Cells, Cultured; D004247:DNA / Q000032:analysis; D017931:DNA Primers; D015342:DNA Probes; D005260:Female; D005333:Fetus; D005720:Gamma Rays; D016762:Genes, fos; D016758:Genes, jun; D016259:Genes, myc; D016158:Genes, p53; D008969:Molecular Sequence Data; D011247:Pregnancy; D016548:Prosencephalon / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2; D011519:Proto-Oncogenes; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000528:radiation effects*; D051028:bcl-2-Associated X Protein
C494828:Bax protein, rat; D017931:DNA Primers; D015342:DNA Probes; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; D004247:DNA