Initiation of genome instability and preneoplastic processes through loss of Fhit expression.
Initiation of genome instability and preneoplastic processes through loss of Fhit expression.
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DOI：
10.1371/journal.pgen.1003077
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发表时间：
2012
期刊：
影响因子：
4.5
通讯作者：
Huebner K
中科院分区：
文献类型：
--
作者：
Saldivar JC;Miuma S;Bene J;Hosseini SA;Shibata H;Sun J;Wheeler LJ;Mathews CK;Huebner K
基因组的不稳定性驱动肿瘤发生，但它是如何在散发性肿瘤启动是未知的。在早期癌前病变中，由于DNA复制应激，染色体脆性位点发生改变。一个常见的，也许是最早的，在癌前病变的遗传改变是脆性FRA 3B/FHIT基因座内的缺失，导致Fhit蛋白表达的损失。由于常见的染色体脆性位点对复制应激非常敏感，因此有人提出，癌细胞中它们的克隆改变是由于应激敏感性，而不是由于脆性基因产物表达丧失所赋予的选择性优势。在这里，我们表明，在正常的，转化的，和癌症衍生的细胞系，Fhit-耗竭导致复制应激诱导的DNA双链断裂。使用DNA梳理，我们观察到Fhit缺陷细胞中复制叉进展的缺陷，其主要源于叉停滞和崩溃。Fhit在复制叉进展中的作用的可能机制是通过调节胸苷激酶1表达和胸苷三磷酸池水平;值得注意的是，核苷酸平衡的恢复挽救了DNA复制缺陷并抑制了Fhit缺陷细胞中的DNA断裂。Fhit的耗尽不会激活DNA损伤反应，也不会引起细胞周期停滞，从而允许持续的细胞增殖和持续的染色体不稳定性。这一发现与体内研究雅阁，因为Fhit敲除小鼠组织未显示细胞周期停滞或衰老的证据，但在复制应激敏感基因座处显示出许多体细胞DNA拷贝数畸变。此外，从Fhit敲除组织建立的细胞显示出快速永生化和DNA缺失和扩增的选择，包括Mdm 2基因的扩增，表明Fhit缺失诱导的基因组不稳定性促进转化。我们认为，癌前病变中Fhit表达的丧失是基因组不稳定性启动的第一步，将常见脆性位点的改变与基因组不稳定性的起源联系起来。正常细胞具有强大的机制来维持其DNA的正确序列;在癌细胞中，这些机制受到损害，导致肿瘤DNA的复杂变化。这种基因组不稳定性是如何开始的尚未确定，除非是家族性癌症，这种癌症通常在称为“看守”基因的基因中发生突变，这是保持DNA稳定性所必需的。我们已经确定了一个机制，基因组不稳定性的非家族性肿瘤，发生零星的人口。我们DNA的某些脆弱区域在细胞分裂过程中更难复制，并且容易断裂。脆性区FRA 3B位于FHIT基因内，并且FRA 3B内的缺失在癌前细胞中是常见的，导致Fhit蛋白表达的丧失。我们发现Fhit蛋白的缺失导致DNA复制缺陷，导致进一步的DNA断裂。在没有Fhit的情况下继续DNA复制的细胞发展出许多染色体畸变。重要的是，从缺失Fhit的小鼠组织中建立的细胞经历了增加DNA改变的选择，这些改变可以促进永生，这是癌细胞的标志。因此，癌前细胞中Fhit表达的丧失是启动基因组不稳定性的第一步，并促进癌症发展。
Genomic instability drives tumorigenesis, but how it is initiated in sporadic neoplasias is unknown. In early preneoplasias, alterations at chromosome fragile sites arise due to DNA replication stress. A frequent, perhaps earliest, genetic alteration in preneoplasias is deletion within the fragile FRA3B/FHIT locus, leading to loss of Fhit protein expression. Because common chromosome fragile sites are exquisitely sensitive to replication stress, it has been proposed that their clonal alterations in cancer cells are due to stress sensitivity rather than to a selective advantage imparted by loss of expression of fragile gene products. Here, we show in normal, transformed, and cancer-derived cell lines that Fhit-depletion causes replication stress-induced DNA double-strand breaks. Using DNA combing, we observed a defect in replication fork progression in Fhit-deficient cells that stemmed primarily from fork stalling and collapse. The likely mechanism for the role of Fhit in replication fork progression is through regulation of Thymidine kinase 1 expression and thymidine triphosphate pool levels; notably, restoration of nucleotide balance rescued DNA replication defects and suppressed DNA breakage in Fhit-deficient cells. Depletion of Fhit did not activate the DNA damage response nor cause cell cycle arrest, allowing continued cell proliferation and ongoing chromosomal instability. This finding was in accord with in vivo studies, as Fhit knockout mouse tissue showed no evidence of cell cycle arrest or senescence yet exhibited numerous somatic DNA copy number aberrations at replication stress-sensitive loci. Furthermore, cells established from Fhit knockout tissue showed rapid immortalization and selection of DNA deletions and amplifications, including amplification of the Mdm2 gene, suggesting that Fhit loss-induced genome instability facilitates transformation. We propose that loss of Fhit expression in precancerous lesions is the first step in the initiation of genomic instability, linking alterations at common fragile sites to the origin of genome instability. Normal cells have robust mechanisms to maintain the proper sequence of their DNA; in cancer cells these mechanisms are compromised, resulting in complex changes in the DNA of tumors. How this genome instability begins has not been defined, except in cases of familial cancers, which often have mutations in genes called “caretaker” genes, necessary to preserve DNA stability. We have defined a mechanism for genome instability in non-familial tumors that occur sporadically in the population. Certain fragile regions of our DNA are more difficult to duplicate during cell division and are prone to breakage. A fragile region, FRA3B, lies within the FHIT gene, and deletions within FRA3B are common in precancer cells, causing loss of Fhit protein expression. We find that loss of Fhit protein causes defective DNA replication, leading to further DNA breaks. Cells that continue DNA replication in the absence of Fhit develop numerous chromosomal aberrations. Importantly, cells established from tissues of mice that are missing Fhit undergo selection for increasing DNA alterations that can promote immortality, a cancer cell hallmark. Thus, loss of Fhit expression in precancer cells is the first step in the initiation of genomic instability and facilitates cancer development.
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影响因子：
64.8
作者：
Bartkova, J;Horejsi, Z;Bartek, J
通讯作者：
Bartek, J
影响因子：
64.8
作者：
Bartkova, Jirina;Rezaei, Nousin;Gorgoulis, Vassilis G.
通讯作者：
Gorgoulis, Vassilis G.
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：
30.8
作者：
Hollander, MC;Sheikh, MS;Fornace, AJ
通讯作者：
Fornace, AJ
影响因子：
64.8
作者：
通讯作者：
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