Low levels of p53 protein and chromatin silencing of p53 target genes repress apoptosis in Drosophila endocycling cells.
Low levels of p53 protein and chromatin silencing of p53 target genes repress apoptosis in Drosophila endocycling cells.
复制标题
DOI：
10.1371/journal.pgen.1004581
复制
发表时间：
2014-09
期刊：
影响因子：
4.5
通讯作者：
Calvi BR
中科院分区：
文献类型：
--
作者：
Zhang B;Mehrotra S;Ng WL;Calvi BR
细胞凋亡是对基因毒性应激的一种重要反应，可阻止肿瘤的发生。众所周知，组织的凋亡反应可能不同，但分子机制知之甚少。在这里，我们表明，果蝇多倍体内循环细胞（G/S周期）抑制DNA损伤的凋亡反应，通过至少两种机制。首先，所有果蝇p53蛋白亚型的表达在转录后步骤被强烈抑制。其次，p53调节的促凋亡基因在内循环细胞中表观遗传学沉默，防止通过p53依赖性或p53非依赖性途径激活暂停的RNA Pol II。过表达的p53 A亚型没有激活这个暂停RNA Pol II复合物内循环细胞，但过表达的p53 B亚型与较长的反式激活结构域，这表明抑制p53 B蛋白水平是至关重要的凋亡抑制。我们还发现，p53 A蛋白亚型是泛素化和降解的蛋白酶体在细胞内循环。在有丝分裂周期细胞中，p53 A是唯一的亚型表达到可检测的水平，其mRNA和蛋白水平增加照射后，但没有证据表明蛋白质的稳定性增加。然而，我们的数据表明，p53 A蛋白的稳定性在未照射的细胞中受到调节，这可能确保了在没有应激的情况下不会发生细胞凋亡。在没有辐射的情况下，p53 A蛋白和暂停的RNA pol II都预先结合到促凋亡基因的启动子上，为有丝分裂周期细胞对遗传毒性应激的快速凋亡反应做好准备。总之，我们的研究结果定义了发育中不同细胞调节其凋亡反应的分子机制，对哺乳动物中正常和癌症多倍体细胞的存活具有更广泛的意义。为了维持基因组的完整性，真核细胞已经进化出多种方式来应对DNA损伤应激。主要的细胞反应之一是细胞凋亡，在此期间细胞经历程序性细胞死亡，以防止受损基因组向子细胞的繁殖。虽然临床观察和其他研究表明，组织可以在他们的凋亡反应不同，这些差异的分子机制在很大程度上是未知的。我们已经在我们的模型系统果蝇中表明，内循环细胞不会响应DNA损伤而启动细胞死亡。内循环是广泛存在于自然界中并从植物到动物保守的细胞周期变异。在内循环期间，细胞复制其基因组DNA，但不进入有丝分裂以分离染色体，从而导致多倍体基因组内容。在这项研究中，我们调查如何凋亡反应的DNA损伤是阻遏内循环细胞。我们发现，果蝇直系同源的人类p53肿瘤抑制蛋白表达在非常低的水平内循环细胞。此外，由p53调控的下游促凋亡基因在内循环细胞中表观遗传学沉默。我们的研究结果提供了重要的见解，组织特异性细胞凋亡反应的发展，可能更广泛的影响，了解放射治疗反应和不同组织的癌症。
Apoptotic cell death is an important response to genotoxic stress that prevents oncogenesis. It is known that tissues can differ in their apoptotic response, but molecular mechanisms are little understood. Here, we show that Drosophila polyploid endocycling cells (G/S cycle) repress the apoptotic response to DNA damage through at least two mechanisms. First, the expression of all the Drosophila p53 protein isoforms is strongly repressed at a post-transcriptional step. Second, p53-regulated pro-apoptotic genes are epigenetically silenced in endocycling cells, preventing activation of a paused RNA Pol II by p53-dependent or p53-independent pathways. Over-expression of the p53A isoform did not activate this paused RNA Pol II complex in endocycling cells, but over-expression of the p53B isoform with a longer transactivation domain did, suggesting that dampened p53B protein levels are crucial for apoptotic repression. We also find that the p53A protein isoform is ubiquitinated and degraded by the proteasome in endocycling cells. In mitotic cycling cells, p53A was the only isoform expressed to detectable levels, and its mRNA and protein levels increased after irradiation, but there was no evidence for an increase in protein stability. However, our data suggest that p53A protein stability is regulated in unirradiated cells, which likely ensures that apoptosis does not occur in the absence of stress. Without irradiation, both p53A protein and a paused RNA pol II were pre-bound to the promoters of pro-apoptotic genes, preparing mitotic cycling cells for a rapid apoptotic response to genotoxic stress. Together, our results define molecular mechanisms by which different cells in development modulate their apoptotic response, with broader significance for the survival of normal and cancer polyploid cells in mammals. In order to maintain genome integrity, eukaryotic cells have evolved multiple ways to respond to DNA damage stress. One of the major cellular responses is apoptosis, during which the cell undergoes programmed cell death in order to prevent the propagation of the damaged genome to daughter cells. Although clinical observations and other studies have shown that tissues can differ in their apoptotic response, the molecular mechanisms underlying these differences are largely unknown. We have shown in our model system, Drosophila, that endocycling cells do not initiate cell death in response to DNA damage. The endocycle is a cell cycle variation that is widely found in nature and conserved from plant to animals. During the endocycle, cells duplicate their genomic DNA but do not enter mitosis to segregate chromosomes, resulting in a polyploid genome content. In this study, we investigate how the apoptotic response to DNA damage is repressed in endocycling cells. We find that the Drosophila ortholog of the human p53 tumor suppressor protein is expressed at very low levels in endocycling cells. Moreover, the downstream pro-apoptotic genes that are regulated by p53 are epigenetically silenced in endocycling cells. Our results provide important insights into tissue-specific apoptotic responses in development, with possible broader impact on understanding radiation therapy response and cancer of different tissues.
登录
查看更多内容
影响因子：
64.8
作者：
Di Micco, Raffaella;Fumagalli, Marzia;di Fagagna, Fabrizio d'Adda
通讯作者：
di Fagagna, Fabrizio d'Adda
影响因子：
1.6
作者：
Andreyenkova, Natalya G.;Kokoza, Elena B.;Zhimulev, Igor F.
通讯作者：
Zhimulev, Igor F.
影响因子：
4.6
作者：
Fox, Donald T.;Duronio, Robert J.
通讯作者：
Duronio, Robert J.
影响因子：
7.3
作者：
Coates, PJ;Lorimore, SA;Wright, EG
通讯作者：
Wright, EG
影响因子：
8
作者：
Bouvard, V;Zaitchouk, T;May, E
通讯作者：
May, E