Apoptosis in small intestinal epithelial from p53-null mice: evidence for a delayed, p53-independent G2/M-associated cell death after gamma-irradiation.
The death of small intestinal epithelial cells has been characterized and quantitated after irradiation of mice rendered homozygously null for the p53 gene. In wild-type animals homozygous for p53 a rapid (4.5 h) elevation of p53 protein was observed in the proliferative compartment of the crypts after 8 Gy of irradiation. Cells underwent cell death by apoptosis in this region. We had reported previously a total repression of apoptosis in small intestinal crypt epithelia 4.5 h after the gamma-irradiation (8 Gy) of p53 homozygously null animals. Thus, while 400 apoptotic cells were observed in 200 half crypts taken from wild-type animals at 4.5 h, this fell to background levels (10-30) in the p53 null animals (Merritt et al., 1994) and did not increase by 12 h. However, we have now found a delayed initiation of a p53-independent apoptosis after 8 Gy of gamma-radiation: at 24 h, approximately 100 apoptotic cells were observed in 200 half crypts. This late wave of apoptosis was not observed after 1 Gy of gamma-radiation. The morphological appearance of this p53-independent apoptosis suggested that death may have arisen as the result of aberrant mitosis. Analysis of the regeneration of crypts 3 days after irradiation of mice with between 11 and 17 Gy showed that there was no significant increase (P=0.135) in the potential of clonogenic cells from the p53 null animals to repopulate the crypts. The data support the idea that a p53-independent apoptotic mechanism permits the engagement of apoptosis, probably by a mitotic catastrophe, after 8 Gy of gamma-irradiation in vivo and that a loss of p53 does not make these epithelial cells radioresistant in vivo to doses of 8 Gy and above. In contrast, irradiation with 1 Gy failed to induce a p53-independent apoptosis in vivo, suggesting that the p53 'sensor' of damage was more sensitive than that engaging the p53-independent mechanism of cell death.
Merritt
A J
AJ
Cancer Research Campaign Department of Epithelial Biology, Christie Hospital Trust, School of Biological Sciences, The University of Manchester, UK.
Allen
T D
TD
Potten
C S
CS
Hickman
J A
JA
D000818:Animals; D017209:Apoptosis / Q000502:physiology* / Q000528:radiation effects; D002999:Clone Cells; D004261:DNA Replication; D016195:G2 Phase; D005720:Gamma Rays; D007413:Intestinal Mucosa / Q000166:cytology* / Q000648:ultrastructure; D007421:Intestine, Small; D051379:Mice; D008854:Microscopy, Electron; D008938:Mitosis; D008940:Mitotic Index; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
D016159:Tumor Suppressor Protein p53