ATM-dependent activation of p53 involves dephosphorylation and association with 14-3-3 proteins

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The p53 tumour-suppressor protein is a sequence-specific DNA-binding transcription factor that induces cell cycle arrest or apoptosis in response to genotoxic stress1,2,3,4,5,6. Activation of p53 by DNA-damaging agents is critical for eliminating cells with damaged genomic DNA and underlies the apoptotic response of human cancers treated with ionizing radiation (IR) and radiomimetic drugs7,8. The molecular mechanisms by which DNA damage activates p53 have not been elucidated. Both the levels of p53 protein and its affinity for specific DNA sequences increase in response to genotoxic stress6,9,10. In vitro, the affinity of p53 for DNA is regulated by its carboxy-terminus11,12,13. We therefore examined whether this region of p53 is targeted by DNA-damage signalling pathways in vivo. In non-irradiated cells, serines 376 and 378 of p53 were phosphorylated. IR led to dephosphorylation of Ser376, creating a consensus binding site for 14-3-3 proteins and leading to association of p53 with 14-3-3. In turn, this increased the affinity of p53 for sequence-specific DNA. Consistent with the lack of p53 activation by IR in ataxia telangiectasia (AT; Refs 14,15), neither Ser376 dephosphorylation, nor the interaction of p53 with 14-3-3 proteins occurred in AT cells.

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Figure 1: Dephosphorylation of Ser376 of p53 by IR.
Figure 2: IR induces association of p53 with 14-3-3 proteins.
Figure 3: Interaction of p53 with 14-3-3 proteins in vitro.
Figure 4: Activation of p53 DNA binding by 14-3-3.
Figure 5: ATM-dependence of the dephosphorylation of Ser376 of p53 and association of p53 with 14-3-3 by IR.
Figure 6: Model for the ATM-dependent activation of p53 in response to IR.


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We thank G. Rovera, C. Prives, P. Leder, J. Shafer, F. Rauscher III, D. George, T. Roberts, L. Chodosh, R. Muschel, N. Chehab, D. Scolnick and M. Lien for helpful discussions and reagents. Financial support was provided by the American Cancer Society and the W. W. Smith Charitable Trust (T.D.H.), an NIH Program Project for Breast Cancer Pilot Studies to the University of Pennsylvania, the Wistar Institute NIH training grant (M.J.F.W.) and the National Cancer Center (E.S.S.).

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Correspondence to Thanos D. Halazonetis.

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