p21 protects "Super p53" mice from the radiation-induced gastrointestinal syndrome.
ABSTRACT Exposure of the gastrointestinal (GI) tract to high doses of radiation can lead to lethality from the GI syndrome. Although the molecular mechanism regulating the GI syndrome remains to be fully defined, we have recently demonstrated that p53 within the GI epithelial cells controls the radiation-induced GI syndrome. Mice lacking p53 in the GI epithelium were sensitized to the GI syndrome, while transgenic mice with one additional copy of p53 called "Super p53" mice were protected from the GI syndrome. Here, we crossed Super p53 mice to p21⁻/⁻ mice that lack the cyclin-dependent kinase inhibitor p21. Super p53; p21⁻/⁻ mice were sensitized to the GI syndrome compared to Super p53 mice that retain one p21 allele. In addition, mice lacking p21 were not protected from the GI syndrome with one extra copy of p53. These results suggest that p21 protects Super p53 mice from the GI syndrome.
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ABSTRACT: Radiation is one of the most effective cancer treatments. However, gastrointestinal (GI) syndrome is a major limiting factor in abdominal and pelvic radiotherapy. The loss of crypt stem cells or villus endothelial cells has been suggested to be responsible for radiation-induced intestinal damage. We report here a critical role of the BH3-only protein p53 upregulated modulator of apoptosis (PUMA) in the radiosensitivity of intestinal epithelium and pathogenesis of GI syndrome. PUMA was induced in a p53-dependent manner and mediated radiation-induced apoptosis via the mitochondrial pathway in the intestinal mucosa. PUMA-deficient mice exhibited blocked apoptosis in the intestinal progenitor and stem cells, enhanced crypt proliferation and regeneration, and prolonged survival following lethal doses of radiation. Unexpectedly, PUMA deficiency had little effect on radiation-induced intestinal endothelial apoptosis. Suppressing PUMA expression by antisense oligonucleotides provided significant intestinal radioprotection. Therefore, PUMA-mediated apoptosis in the progenitor and stem cell compartments is crucial for radiation-induced intestinal damage.Cell stem cell 06/2008; 2(6):576-83. · 23.56 Impact Factor
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ABSTRACT: 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.Oncogene 07/1997; 14(23):2759-66. · 7.36 Impact Factor
- New England Journal of Medicine 06/2002; 346(20):1554-61. · 51.66 Impact Factor