Waterman M J, Stavridi E S, Waterman J L, Halazonetis T D
Department of Molecular Genetics, The Wistar Institute, Philadelphia, Pennsylvania 19104-4268, USA.
Nat Genet. 1998 Jun;19(2):175-8. doi: 10.1038/542.
The p53 tumour-suppressor protein is a sequence-specific DNA-binding transcription factor that induces cell cycle arrest or apoptosis in response to genotoxic stress. 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 drugs. 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 stress. In vitro, the affinity of p53 for DNA is regulated by its carboxy-terminus. We therefore examined whether this region of p53 is targeted by DNA-damage signalling pathways in vivo. In nonirradiated 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.
p53肿瘤抑制蛋白是一种序列特异性DNA结合转录因子，可响应基因毒性应激诱导细胞周期停滞或凋亡。DNA损伤剂对p53的激活对于清除基因组DNA受损的细胞至关重要，并且是电离辐射（IR）和放射模拟药物治疗的人类癌症凋亡反应的基础。DNA损伤激活p53的分子机制尚未阐明。响应基因毒性应激，p53蛋白水平及其对特定DNA序列的亲和力均会增加。在体外，p53对DNA的亲和力受其羧基末端调控。因此，我们研究了p53的这一区域在体内是否是DNA损伤信号通路的作用靶点。在未受辐射的细胞中，p53的丝氨酸376和378被磷酸化。IR导致Ser376去磷酸化，产生14-3-3蛋白的共有结合位点，并导致p53与14-3-3结合。反过来，这增加了p53对序列特异性DNA的亲和力。与共济失调毛细血管扩张症（AT；参考文献14,15）中IR无法激活p5３一致，在AT细胞中既未发生Ser376去磷酸化，也未发生p53与14-3-3蛋白的相互作用。
