Molecular Carcinogenesis Group, International Agency for Research on Cancer, Lyon, Cedex, France.
Oncogene. 2010 May 6;29(18):2691-700. doi: 10.1038/onc.2010.26. Epub 2010 Mar 1.
The tumor suppressor p53 protein is activated by genotoxic stress and regulates genes involved in senescence, apoptosis and cell-cycle arrest. Nine p53 isoforms have been described that may modulate suppressive functions of the canonical p53 protein. Among them, Delta133p53 lacks the 132 proximal residues and has been shown to modulate p53-induced apoptosis and cell-cycle arrest. Delta133p53 is expressed from a specific mRNA, p53I4, driven by an alternative promoter P2 located between intron 1 and exon 5 of TP53 gene. Here, we report that the P2 promoter is regulated in a p53-dependent manner. Delta133p53 expression is increased in response to DNA damage by doxorubicin in p53 wild-type cell lines, but not in p53-mutated cells. Chromatin immunoprecipitation and luciferase assays using P2 promoter deletion constructs indicate that p53 binds functional response elements located within the P2 promoter. We also show that Delta133p53 does not bind specifically to p53 consensus DNA sequence in vitro, but competes with wild-type p53 in specific DNA-binding assays. Finally, we report that Delta133p53 counteracts p53-dependent growth suppression in clonogenic assays. These observations indicate that Delta133p53 is a novel target of p53 that may participate in a negative feedback loop controlling p53 function.
肿瘤抑制因子 p53 蛋白被遗传毒性应激激活，并调节与衰老、细胞凋亡和细胞周期停滞相关的基因。已经描述了 9 种 p53 同工型，它们可能调节经典 p53 蛋白的抑制功能。其中，Delta133p53 缺乏近端的 132 个残基，已被证明能调节 p53 诱导的细胞凋亡和细胞周期停滞。Delta133p53 由位于 TP53 基因内含子 1 和外显子 5 之间的替代启动子 P2 驱动，从特定的 mRNA p53I4 表达。在这里，我们报告 P2 启动子受 p53 依赖性调节。Delta133p53 的表达在 p53 野生型细胞系中，通过阿霉素引起的 DNA 损伤而增加，但在 p53 突变细胞中没有增加。使用 P2 启动子缺失构建体进行染色质免疫沉淀和荧光素酶测定表明，p53 结合位于 P2 启动子内的功能性反应元件。我们还表明，Delta133p53 不会在体外特异性结合 p53 共识 DNA 序列，但在特定的 DNA 结合测定中与野生型 p53 竞争。最后，我们报告说，Delta133p53 可以在集落形成测定中拮抗 p53 依赖性生长抑制。这些观察结果表明，Delta133p53 是 p53 的一个新靶点，可能参与控制 p53 功能的负反馈回路。
