Department of Molecular Biology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Proc Natl Acad Sci U S A. 2010 Nov 9;107(45):19290-5. doi: 10.1073/pnas.1013078107. Epub 2010 Oct 20.
The transcriptional activity of p53 is regulated by a cascade of posttranslational modifications. Although acetylation of p53 by CREB-binding protein (CBP)/p300 is known to be indispensable for p53 activation, the role of phosphorylation, and in particular multisite phosphorylation, in activation of CBP/p300-dependent p53 transcriptional pathways remains unclear. We investigated the role of single site and multiple site phosphorylation of the p53 transactivation domain in mediating its interaction with CBP and with the ubiquitin ligase HDM2. Phosphorylation at Thr18 functions as an on/off switch to regulate binding to the N-terminal domain of HDM2. In contrast, binding to CBP is modulated by the extent of p53 phosphorylation; addition of successive phosphoryl groups enhances the affinity for the TAZ1, TAZ2, and KIX domains of CBP in an additive manner. Activation of p53-dependent transcriptional pathways requires that p53 compete with numerous cellular transcription factors for binding to limiting amounts of CBP/p300. Multisite phosphorylation represents a mechanism for a graded p53 response, with each successive phosphorylation event resulting in increasingly efficient recruitment of CBP/p300 to p53-regulated transcriptional programs, in the face of competition from cellular transcription factors. Multisite phosphorylation thus acts as a rheostat to enhance binding to CBP/p300 and provides a plausible mechanistic explanation for the gradually increasing p53 response observed following prolonged or severe genotoxic stress.
p53 的转录活性受一系列翻译后修饰的调节。虽然 CREB 结合蛋白 (CBP)/p300 对 p53 的乙酰化作用对于 p53 的激活是必不可少的，但磷酸化的作用，尤其是多位点磷酸化，在激活 CBP/p300 依赖性 p53 转录途径中的作用尚不清楚。我们研究了 p53 转录激活结构域的单点和多点磷酸化在介导其与 CBP 以及与泛素连接酶 HDM2 的相互作用中的作用。Thr18 位点的磷酸化作为一个开/关开关来调节与 HDM2 的 N 端结构域的结合。相比之下，与 CBP 的结合受 p53 磷酸化程度的调节；连续添加磷酸基团以累加的方式增强与 CBP 的 TAZ1、TAZ2 和 KIX 结构域的亲和力。激活 p53 依赖性转录途径需要 p53 与许多细胞转录因子竞争，以结合有限量的 CBP/p300。多位点磷酸化是一种 p53 反应的分级机制，每个连续的磷酸化事件导致 CBP/p300 越来越有效地募集到 p53 调节的转录程序，而不受细胞转录因子的竞争。因此，多位点磷酸化作为一种变阻器，增强了与 CBP/p300 的结合，并为长时间或严重的遗传毒性应激后观察到的 p53 反应逐渐增加提供了一个合理的机制解释。
