Abstract 1203: Coordinated regulation of intestinal radio-sensitivity by PUMA and p21

Abstract

Abstract p53-upregulated modulator of apoptosis (PUMA) has been shown to be vital for radio-sensitivity in the small intestine. PUMA ablation results in drastic radio-resistance, lengthening the survival of mice exposed to 15 Gy whole body irradiation and blocking apoptosis in the crypts. In contrast, we and others have found that p21 ablation leads to slightly increased radio-sensitivity. To better elucidate the relative and perhaps linked roles of PUMA and p21 in the intestinal responses to irradiation, we produced PUMA/p21 double knockout (DKO) mice. Initial experiments revealed that DKO mice responded similarly to PUMA KO mice within the first 24 hours after 15 Gy ionizing radiation as measured by the DNA damage response and apoptosis in the crypts. Both groups showed more rapid, though less sustained, phosphorylation of H2AX than wild-type (WT) mice, while displaying significantly less apoptosis in the crypts. However, DKO mice were found to have similarly enhanced overall radio-sensitivity as p21 KO mice. Further studies revealed that DKO and PUMA KO mice may not be equally effective at repair despite their similar kinetics in the initial DNA damage response. At 48 and 72 hours post-irradiation, the crypts in DKO mice had a substantial number of TUNEL+ cells, while those in PUMA KO or WT mice had almost none. At 48 hours after irradiation, the crypts in p21 KO mice also had a large number of TUNEL+ cells, which declined by 72 hours. Additionally, the crypt cells in DKO and p21 KO mice, but not in WT or PUMA KO mice, were found to be positive for both γ-H2AX and the mitosis marker phospo-H3, indicating abrogated cell cycle control likely due to a futile attempt at proliferation. These data further suggest that the protection of intestinal epithelium against radiation injury through ablation of PUMA requires a functional p21 checkpoint in addition to inhibition of crypt apoptosis. Additional studies are underway in our laboratory to further elucidate how these two proteins might coordinately regulate intestinal injury and regeneration by modulating the survival and proliferation of intestinal stem cells and progenitors following irradiation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1203.