Impact of HIPK2 and posttranslational p53 modification on B[a]P/BPDE induced cell death and senescence

遗传毒性应激导致DNA损伤，可能导致突变和致癌作用的积累。为了抵消这些影响，DNA修复机制已经进化，以消除或容忍DNA损伤。除了DNA修复之外，还存在其他机制参与保护免受致癌作用。这些是通过细胞凋亡和坏死诱导细胞死亡，短暂的细胞周期停滞为适当的修复提供时间，以及诱导衰老形式的“不可逆”细胞周期停滞。预测暴露于遗传毒性应激的结果的一个问题是基于这样一个事实，即所有途径可以单独或同时激活，这取决于应激的量。在我们以前的工作中，我们表明，在无毒浓度的环境致癌物苯并（a）芘（B[a]P）及其活性代谢物苯并（a）芘9，10-二醇-7，8-环氧化物（BPDE），诱导核苷酸切除修复的p53依赖性转录激活和错配修复和同源重组的p53/p21介导的转录抑制，以及诱导衰老。尽管这些机制仅在无毒浓度下观察到，但在无毒和毒性浓度下观察到p53的活化和几种p53依赖性促凋亡因子的诱导。有趣的是，在无毒浓度下，p53介导存活和衰老，而在毒性浓度下，它介导细胞死亡。虽然DNA损伤反应的初始激活在毒性和无毒浓度之间没有区别，但在稍后的时间点，毒性浓度引起DNA损伤反应的变化，这现在导致细胞死亡。总的来说，这些发现表明存在特定的阈值，在该阈值处，p53依赖性促生存信号传导转变为促死亡信号传导。该项目的主要重点是确定DNA损伤反应改变的分子机制，并阐明饱和DNA修复的阈值是否与代表从促生存信号转换为促死亡信号的阈值相关。因此，我们将集中在p53的翻译后修饰的作用和蛋白激酶HIPK 2的作用，在生活和死亡之间的决定后，B[a]P/BPDE曝光。

Genotoxic stress causes DNA damage that might lead to the accumulation of mutations and carcinogenesis. To counteract these effects, DNA repair mechanisms have evolved in order to remove or tolerate DNA lesions. Besides DNA repair, additional mechanisms involved in protection against carcinogenesis exist. These are the induction of cell death via apoptosis and necrosis, transient cell cycle arrest providing time for proper repair and the induction of “irreversible” cell cycle arrest in form of senescence. A problem in predicting the outcome of an exposure to genotoxic stress is based on the fact, that all pathways can be activated separately or simultaneously, depending on the amount of stress.In our previous work, we showed that at non-toxic concentrations of the environmental carcinogen benzo(a)pyrene (B[a]P) and its active metabolite benzo(a)pyrene 9,10-diol-7,8-epoxide (BPDE), induces a p53-dependend transcriptional activation of the nucleotide excision repair and a p53/p21-mediated transcriptional repression of mismatch repair and homologous recombination, as well as induction of senescence. Whereas these mechanisms are only observed at non-toxic concentrations, activation of p53 and induction of several p53 dependent pro-apoptotic factors is observed at non-toxic and toxic concentrations. Interestingly, at non-toxic concentrations, p53 mediates survival and senescence, whereas at toxic concentrations it mediates cell death. While the initial activation of the DNA damage response does not differ between toxic and non-toxic concentrations, at later time points toxic concentrations cause a change in the DNA damage response, which now leads to cell death. Overall, these findings suggest the existence of specific thresholds at which the p53-dependent pro-survival signalling turns into pro-death signalling. The main focus of this project is to identify the molecular mechanisms by which the DNA damage response is changed and to elucidate whether the threshold for saturated DNA repair correlates to the threshold representing the switch from pro-survival signalling into pro-death signalling. Thus, we will focus on the role of posttranslational modification of p53 and the role of the protein kinase HIPK2 in the decision between live and death upon B[a]P/BPDE exposure.