多胺參與DNA雙股斷裂修復中的作用機制

Abstract

存在細胞中的小分子是如何影響DNA基因體的完整性，一直是研究癌症生物學裡很有趣的課題。和正常細胞相比，多胺小分子在許多種類的癌細胞裡會被大量製造，來維持癌細胞的存活及快速增生，使得多胺小分子被認為影響腫瘤發展的過程。在此博士論文裡，我們團隊證明了多胺尚未被研究發現的新穎功能：參與雙股DNA斷裂修補機制。並且我們的研究結果顯示，多胺只會專一性的促進同源重組反應(homologous recombination)所催化的DNA雙股斷裂修補，而不影響DNA雙股斷裂修補中的另一種修補機制：非同源重組端接合(non-homologous DNA end-joining)。藉由生化特性分析，證明了多胺可大幅刺激同源重組酶(recombinase) RAD51蛋白的DNA股交換活性，更進一步研究顯示，此刺激機轉源自於多胺分子可提高同源重組酶RAD51蛋白在進行同源搜尋(homology search)尋找同源的修補模板DNA時，增加其捕獲雙股DNA的碰撞反應，而利用了動物實驗分析，我們也證明了多胺分子在活體細胞內對於DNA雙股斷裂的修補扮演著重要的角色。我們的研究經由深入探討後提供了一重要的發現：多胺分子可利用調控同源重組修補反應來維持基因體的穩定性。

How naturally occurring cellular small chemicals impact upon genome integrity is of great interests in cancer biology. Many cancers synthesize elevated levels of polyamines to sustain cell growth and proliferation, thus implicating these compounds in tumorigenesis. Here, we document a novel function of polyamines in DNA double-strand break (DSB) repair. Specifically, we show that polyamines facilitate homologous recombination-mediated DSB repair without affecting non-homologous DNA end-joining. Biochemical reconstitution and functional analyses demonstrate that polyamines significantly enhance the DNA strand exchange activity of RAD51. The stimulatory effect of polyamines by RAD51 stems from the enhancement of duplex DNA capture in the DNA homology search process. We also reveal the importance of polyamines to DSB repair in an animal model. Our findings thus furnish valuable insights into the role of polyamines in genome maintenance via homology-directed DNA repair.