A comprehensive study of p53 transcriptional activity in thymus and spleen of gamma irradiated mouse: high sensitivity of genes involved in the two main apoptotic pathways.
OBJECTIVE
Gamma-irradiation leads to activation of p53 tumour suppressor gene and to p53-dependant stimulation of a large panel of cellular genes including proapoptotic genes involved in intrinsic and extrinsic pathways. Most in vivo published data referred to high (lethal) irradiation doses. The present study was performed to analyse the p53-dependent response to more relevant low irradiation doses.


METHODS
Mice were whole body exposed to irradiation doses decreasing from 5 - 0.05 Gy. Gene expression was estimated by real time reverse transcriptase polymerase chain reaction measurements on RNA extracted from thymus and spleen. Apoptosis was evaluated by the percentage of either annexin V positive or sub-G1 cells.


RESULTS
A 0.1 Gy irradiation dose already gives a significant stimulation of Puma (p53 up-regulated modulator of apoptosis), and 0.2 Gy of Bax (Bcl-2-associated X protein) and Killer/DR5 (Death Receptor 5). The expression of genes involved in the two apoptotic pathways was induced as soon as 1 h post-irradiation and reached a maximum at 3 h, the induction level depending on both the gene and the organ. A significant increase in the number of apoptotic cells is already detectable at 0.5 Gy with a maximum of induction at 6 h.


CONCLUSIONS
Our results reveal the high in vivo sensitivity of p53-dependent transcriptional activation of genes involved in the two main apoptotic pathways, their stimulation preceding the induction of apoptosis.
Alvarez
Sandra
S
Commissariat à l'Energie Atomique (CEA), Centre National de la Recherche Scientifique (CNRS), Laboratoire de Cancérogenèse Moléculaire, 92265 Fontenay-aux-Roses Cedex, France.
Drané
Pascal
P
Meiller
Anne
A
Bras
Marlene
M
Deguin-Chambon
Valerie
V
Bouvard
Veronique
V
May
Evelyne
E
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D051017:Apoptosis Regulatory Proteins; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D005786:Gene Expression Regulation / Q000528:radiation effects*; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics; D013154:Spleen / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D013950:Thymus Gland / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000235:genetics; D014916:Whole-Body Irradiation; D051020:bcl-X Protein / Q000235:genetics
D051017:Apoptosis Regulatory Proteins; D008565:Membrane Proteins; C488588:PUMA protein, mouse; C406964:Perp protein, mouse; D012333:RNA, Messenger; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D051020:bcl-X Protein