LINE-1 protein localization and functional dynamics during the cell cycle.
LINE-1 protein localization and functional dynamics during the cell cycle.
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DOI：
10.7554/elife.30058
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发表时间：
2018-01-08
期刊：
影响因子：
7.7
通讯作者：
Boeke JD
中科院分区：
文献类型：
--
作者：
Mita P;Wudzinska A;Sun X;Andrade J;Nayak S;Kahler DJ;Badri S;LaCava J;Ueberheide B;Yun CY;Fenyö D;Boeke JD
LINE-1/L1反转录转座子序列占人类基因组的17%。在众多的移动的遗传元件中，L1是唯一一个至今仍在驱动人类基因组可塑性的自主反转录转座子。通过与人类基因组的共同进化，L1与宿主细胞生物学交织在一起。然而，对L1的生命周期以及限制其插入和基因组内传播的过程的清楚理解仍然是难以捉摸的。在这里，我们确定模式的L1蛋白进入细胞核，L1增殖的必要步骤。使用功能，生物化学和成像方法，我们还显示了一个明确的细胞周期的L1反转录偏置，在S期达到峰值。我们的观察提供了一个新的解释核和细胞质L1核糖核蛋白（RNP）的性质和DNA复制在L1反转录转座的潜在作用的基础。我们的遗传物质或基因组中只有2%被基因占据，而60- 70%由数十万个非常相似的DNA序列拷贝组成。这些重复序列是从称为转座子的遗传元件进化而来的。转座子通常被称为“跳跃基因”，因为它们可以在基因组内随机移动，从而产生可能导致癌症或其他遗传疾病的危险突变。LINE-1是人类中唯一剩下的活跃转座子，它通过一个称为“逆转录”的过程将自身复制和粘贴到新的位置来扩展。要做到这一点，它首先被转录成RNA -帮助制造蛋白质的分子-然后转化回相同的DNA序列。先前的研究表明，LINE-1可以与一系列蛋白质形成复合物，包括LINE-1 RNA本身编码的两种蛋白质：ORF 1 p和ORF 2 p。LINE-1复合物可以进入细胞核并将LINE-1的新拷贝插入基因组中。然而，直到现在还不知道他们是如何做到这一点的。为了进一步研究这一点，Mita等人使用在实验室中生长的人类癌细胞，并在细胞周期的不同阶段跟踪LINE-1。结果显示，当细胞开始分裂且细胞核膜破裂时，LINE-1进入细胞核。然后LINE-1复合物保留在细胞核中，同时细胞核的膜重新形成。后来，随着细胞复制其遗传物质，LINE-1开始复制和粘贴自己。Mita等人，与另一组研究人员一起，也发现在这个过程中，在细胞核中只发现LINE-1 RNA和ORF 2 p。这表明细胞周期决定了LINE-1复合物聚集的位置和LINE-1激活的时间。下一步将进一步研究LINE-1和两种LINE-1蛋白的“复制和粘贴”机制在细胞周期中是如何调节的。在未来，这可能有助于确定LINE-1在衰老或癌症等疾病中的作用。
LINE-1/L1 retrotransposon sequences comprise 17% of the human genome. Among the many classes of mobile genetic elements, L1 is the only autonomous retrotransposon that still drives human genomic plasticity today. Through its co-evolution with the human genome, L1 has intertwined itself with host cell biology. However, a clear understanding of L1’s lifecycle and the processes involved in restricting its insertion and intragenomic spread remains elusive. Here we identify modes of L1 proteins’ entrance into the nucleus, a necessary step for L1 proliferation. Using functional, biochemical, and imaging approaches, we also show a clear cell cycle bias for L1 retrotransposition that peaks during the S phase. Our observations provide a basis for novel interpretations about the nature of nuclear and cytoplasmic L1 ribonucleoproteins (RNPs) and the potential role of DNA replication in L1 retrotransposition. Only two percent of our genetic material or genome are occupied by genes, while between 60-70 percent are made up of hundreds of thousands of copies of very similar DNA sequences. These repetitive sequences evolved from genetic elements called transposons. Transposons are often referred to as ‘jumping genes’, as they can randomly move within the genome and thereby create dangerous mutations that may lead to cancer or other genetic diseases. LINE-1 is the only remaining active transposon in humans, and it expands by copying and pasting itself to new locations via a process called 'retrotransposition'. To do so, it is first transcribed into RNA – the molecules that help to make proteins – and then converted back into identical DNA sequences. Previous research has shown that LINE-1 can form complexes with a series of proteins, including the two encoded by LINE-1 RNA itself: ORF1p and ORF2p. The LINE-1 complexes can enter the nucleus of the cell and insert a new copy of LINE-1 into the genome. However, until now it was not known how they do this. To investigate this further, Mita et al. used human cancer cells grown in the lab and tracked LINE-1 during the different stages of the cell cycle. The results showed that LINE-1 enters the nucleus as the cell starts to divide and the membrane of the nucleus breaks down. The LINE-1 complexes are then retained in the nucleus while the membrane of the nucleus reforms. Later, as the cell duplicates its genetic material, LINE-1 starts to copy and paste itself. Mita et al., together with another group of researchers, also found that during this process, only LINE-1 RNA and ORF2p were found in the nucleus. This shows that the cell cycle dictates both where the LINE-1 complexes gather and when LINE-1 is active. A next step will be to further investigate how the ‘copy and paste’ mechanisms of LINE-1 and the two LINE-1 proteins are regulated during the cell cycle. In future, this may help to identify LINE-1’s role in processes like aging or in diseases such as cancer.