Figure 2
From: Endogenous c-Myc is essential for p53-induced apoptosis in response to DNA damage in vivo
Myc deletion prevents P53 accumulation after DNA damage. (a) IHC for P53 or P21 in wildtype (AhCre Myc+/+) or MYC-deficient (AhCre Mycfl/f) mice 6 h after 14 Gy γ-irradiation. Note the induction of nuclear P53 following irradiation in wild-type mice that is attenuated in MYC-deficient enterocytes, and the upregulation of P21 following irradiation in both wild type and MYC-deficient enterocytes. Scale bars=50 μm. (b) Immunoblotting shows a marked increase in P53 levels following irradiation that is not seen in MYC-deficient intestinal extracts (top panels). Immunoblotting shows a marked increase in P21 levels following irradiation in both wild type and MYC-deficient intestinal extracts (bottom panels). (c) Scoring of apoptotic cells per crypt on the genotypes indicated 6 h after exposure to 14 Gy. AhCre+ Mycfl/fl P21−/− mice display the same lack of apoptotic response to 14 Gy irradiation as the MYC-deficient mice, illustrating that the induction of P21 in AhCre Mycfl/f mice is not responsible for the failure to upregulate P53 and induce apoptosis (AhCre Mycfl/fl versus AhCre+ Mycfl/fl P21−/−, P=0.7656, Mann Whitney n=5 versus 3). (d) Immunohistochemistry for γ-H2AX in wild-type (AhCre Myc+/+) or MYC-deficient (AhCre Mycfl/f) mice following 14 Gy γ-irradiation or cisplatin treatment. The large upregulation of γ-H2AX 30 min after irradiation is beginning to clear by 6 h after irradiation as DNA damage is repaired. This expression pattern is observed in both wild type and MYC-deficient crypts (and cisplatin treated), illustrating that MYC-deficient enterocytes are able to sense DNA damage stimuli. Scale bars=50 μm
