PI 3 Kinase Related Kinases-Independent Proteolysis of BRCA1 Regulates Rad51 Recruitment during Genotoxic Stress in Human Cells
PI 3 Kinase Related Kinases-Independent Proteolysis of BRCA1 Regulates Rad51 Recruitment during Genotoxic Stress in Human Cells
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DOI：
10.1371/journal.pone.0014027
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发表时间：
2010-11-17
期刊：
影响因子：
3.7
通讯作者：
Affar, El Bachir
中科院分区：
文献类型：
--
作者：
Hammond-Martel, Ian;Pak, Helen;Affar, El Bachir
背景资料：BRCA 1在电离辐射中的功能，直接产生DNA双链断裂，已被广泛表征。然而，以前的研究产生了相互矛盾的数据，诱变剂，最初诱导其他类别的DNA加合物。由于了解BRCA 1功能的基本和临床的重要性，我们试图严格评估的作用，这种肿瘤抑制剂在应对不同形式的遗传毒性stress.Methodology/主要结果：我们调查了BRCA 1的稳定性和本地化在各种人类细胞处理模型诱变剂，触发不同的DNA损伤信号通路。我们确定，与电离辐射不同，UVC或甲磺酸甲酯（MMS）（分别产生大体积DNA加合物或烷基化碱基）诱导BRCA 1蛋白的瞬时下调，抑制PIKK既不能阻止也不能增强BRCA 1蛋白的下调。此外，我们发现蛋白酶体介导BRCA 1、BARD 1、BACH 1和Rad 52的早期降解，这意味着同源重组机制的关键组分需要在功能上被废除，作为对UV或MMS的早期反应的一部分。值得注意的是，我们发现BRCA 1/BARD 1下调的抑制伴随着这两种蛋白质与Rad 51一起沿着向染色质的非预定募集。因此，用MMS处理细胞导致Rad 51从预先形成的电离辐射诱导的病灶中完全分解。在BRCA 1/BARD 1下调的初始阶段之后，我们发现这些蛋白在病灶中的恢复与RPA和Rad 51病灶的形成相一致。这表明同源重组在细胞对MMS应答的后期被重新激活，最有可能修复由复制阻断产生的DSB。综上所述，我们的结果表明：（i）BRCA 1/BARD 1复合物的稳定性以诱变剂特异性方式调节，和（ii）表明可能需要防止冲突信号通路同时募集到DNA损伤位点的机制的存在。
Background: The function of BRCA1 in response to ionizing radiation, which directly generates DNA double strand breaks, has been extensively characterized. However previous investigations have produced conflicting data on mutagens that initially induce other classes of DNA adducts. Because of the fundamental and clinical importance of understanding BRCA1 function, we sought to rigorously evaluate the role of this tumor suppressor in response to diverse forms of genotoxic stress.Methodology/Principal Findings: We investigated BRCA1 stability and localization in various human cells treated with model mutagens that trigger different DNA damage signaling pathways. We established that, unlike ionizing radiation, either UVC or methylmethanesulfonate (MMS) (generating bulky DNA adducts or alkylated bases respectively) induces a transient downregulation of BRCA1 protein which is neither prevented nor enhanced by inhibition of PIKKs. Moreover, we found that the proteasome mediates early degradation of BRCA1, BARD1, BACH1, and Rad52 implying that critical components of the homologous recombinaion machinery need to be functionally abrogated as part of the early response to UV or MMS. Significantly, we found that inhibition of BRCA1/BARD1 downregulation is accompanied by the unscheduled recruitment of both proteins to chromatin along with Rad51. Consistently, treatment of cells with MMS engendered complete disassembly of Rad51 from pre-formed ionizing radiation-induced foci. Following the initial phase of BRCA1/BARD1 downregulation, we found that the recovery of these proteins in foci coincides with the formation of RPA and Rad51 foci. This indicates that homologous recombination is reactivated at later stage of the cellular response to MMS, most likely to repair DSBs generated by replication blocks.Conclusion/Significance: Taken together our results demonstrate that (i) the stabilities of BRCA1/BARD1 complexes are regulated in a mutagen-specific manner, and (ii) indicate the existence of mechanisms that may be required to prevent the simultaneous recruitment of conflicting signaling pathways to sites of DNA damage.