基因組DNA一直受到各種內(nèi)源及外源損傷因素的影響,，大多數(shù)的DNA損傷都能被多種DNA修復(fù)機制識別和修復(fù)。然而,，總有一些DNA損傷逃脫修復(fù)機制的監(jiān)控,，阻礙S期DNA復(fù)制。為了避免受阻的復(fù)制叉被破壞進而產(chǎn)生DNA雙鏈斷裂,，細(xì)胞進化出了跨損傷DNA合成（Translesion DNA synthesis,， TLS）途徑，利用特異的低保真度的DNA聚合酶直接在損傷的對面合成DNA,。
TLS分為無錯旁路途徑和易錯旁路途徑,，前者在對應(yīng)損傷的部位插入正確的核苷酸，而后者通常插入錯誤的核苷酸,。在細(xì)胞中,，易錯損傷旁路途徑是環(huán)境致癌物和其他DNA損傷試劑誘導(dǎo)基因組突變的主要機制，有效控制易錯途徑將有助于預(yù)防腫瘤發(fā)生,。然而對于TLS聚合酶是如何招募到受阻部位完成其功能的具體分子機制目前仍不十分清楚,。
近日，中科院北京基因組研究所重大疾病基因組與個體化醫(yī)療實驗室郭彩霞課題組首次發(fā)現(xiàn),，錯配修復(fù)關(guān)鍵蛋白MSH2能調(diào)控細(xì)胞內(nèi)紫外輻射損傷引發(fā)的TLS過程,。利用免疫共沉淀結(jié)合質(zhì)譜技術(shù),，研究人員發(fā)現(xiàn)MSH2與TLS聚合酶Kappa (Polκ)結(jié)合，并且MSH2還調(diào)控TLS聚合酶與紫外引發(fā)的受阻復(fù)制叉的結(jié)合,。
MSH2一方面通過影響泛素連接酶RAD18與染色質(zhì)的結(jié)合來調(diào)控PCNA單泛素化水平進而影響TLS聚合酶招募,，另一方面MSH2也可在敲低Rad18的細(xì)胞中通過PCNA單泛素化不依賴的方式，上調(diào)TLS聚合酶在受阻復(fù)制叉處的富集,。進一步研究發(fā)現(xiàn),，MSH2能夠促進紫外輻射后細(xì)胞跨越基因組上光產(chǎn)物損傷的TLS過程，表明了MSH2在紫外光損傷處理后細(xì)胞應(yīng)答方面具有新的作用,。
此外,，該課題組此前的研究發(fā)現(xiàn)MSH2還可調(diào)控氧化損傷后PCNA的單泛素化。這些研究成果有助于我們了解非傳統(tǒng)錯配修復(fù)導(dǎo)致基因組不穩(wěn)定性的內(nèi)在機制以及多種DNA損傷反應(yīng)通路的相互作用,，為預(yù)防癌癥發(fā)生,、增強腫瘤細(xì)胞對化療試劑的敏感性和降低腫瘤耐藥性突變的產(chǎn)生提供了重要的理論依據(jù)。
該項研究由中科院北京基因組研究所郭彩霞研究組和動物所生物膜與膜生物工程國家重點實驗室唐鐵山研究組合作完成,，相關(guān)論文于9月13日在線發(fā)表于Nucleic Acids Research,。
該項工作得到了中國科學(xué)院、科技部,、國家自然科學(xué)基金委的支持（生物谷Bioon.com）,。
生物谷推薦的英文摘要
Nucleic Acids Research doi：10.1093/nar/gkt793
Mismatch repair protein MSH2 regulates translesion DNA synthesis following exposure of cells to UV radiation
Lingna Lv1， Fengli Wang2,， Xiaolu Ma1,， Yeran Yang1， Zhifeng Wang1,， Hongmei Liu2,， Xiaoling Li2， Zhenbo Liu1,， Ting Zhang1， Min Huang1,， Errol C. Friedberg3,， Tie-Shan Tang2 and Caixia Guo1，*
Translesion DNA synthesis (TLS) can use specialized DNA polymerases to insert and/or extend nucleotides across lesions,， thereby limiting stalled replication fork collapse and the potential for cell death. Recent studies have shown that monoubiquitinated proliferating cell nuclear antigen (PCNA) plays an important role in recruitment of Y-family TLS polymerases to stalled replication forks after DNA damage treatment. To explore the possible roles of other factors that regulate the ultraviolet (UV)-induced assembly of specialized DNA polymerases at arrested replication forks,， we performed immunoprecipitation experiments combined with mass spectrometry and established that DNA polymerase kappa (Polκ) can partner with MSH2， an important mismatch repair protein associated with hereditary non-polyposis colorectal cancer. We found that depletion of MSH2 impairs PCNA monoubiquitination and the formation of foci containing Polκ and other TLS polymerases after UV irradiation of cells. Interestingly,， expression of MSH2 in Rad18-deficient cells increased UV-induced Polκ and REV1 focus formation without detectable changes in PCNA monoubiquitination,， indicating that MSH2 can regulate post-UV focus formation by specialized DNA polymerases in both PCNA monoubiquitination-dependent and -independent fashions. Moreover， we observed that MSH2 can facilitate TLS across cyclobutane pyrimidine dimers photoproducts in living cells,， presenting a novel role of MSH2 in post-UV cellular responses.
