張卿義，張櫻子，沈凱，張舒羽，曹建平

?

組蛋白泛素化修飾及其在DNA損傷應(yīng)答中的作用

張卿義1，張櫻子2，沈凱1，張舒羽2，曹建平2

1. 蘇州大學(xué)醫(yī)學(xué)部第一臨床醫(yī)學(xué)院，蘇州 215123 2. 蘇州大學(xué)醫(yī)學(xué)部放射醫(yī)學(xué)與防護(hù)學(xué)院，蘇州 215123

泛素化修飾是真核生物細(xì)胞內(nèi)重要的翻譯后修飾類型，通過(guò)調(diào)節(jié)蛋白質(zhì)活性、穩(wěn)定性和亞細(xì)胞定位廣泛參與細(xì)胞內(nèi)各項(xiàng)信號(hào)傳導(dǎo)與代謝過(guò)程，對(duì)維持正常生命活動(dòng)具有重要意義。組蛋白作為染色質(zhì)中主要的蛋白成分，與DNA復(fù)制轉(zhuǎn)錄、修復(fù)等行為密切相關(guān)，是研究翻譯后修飾的熱點(diǎn)。DNA損傷后，組蛋白泛素化修飾通過(guò)調(diào)節(jié)核小體結(jié)構(gòu)、激活細(xì)胞周期檢查點(diǎn)、影響修復(fù)因子的招募與裝配等諸多途徑參與損傷應(yīng)答。同時(shí)，組蛋白泛素化修飾還能調(diào)節(jié)其他位點(diǎn)翻譯后修飾，并通過(guò)這種串?dāng)_(crosstalk)作用調(diào)節(jié)DNA損傷應(yīng)答。本文介紹了組蛋白泛素化修飾的主要位點(diǎn)和相關(guān)組分(包括E3連接酶、去泛素化酶與效應(yīng)分子)，以及這些修飾作用共同編譯形成的信號(hào)網(wǎng)絡(luò)在DNA損傷應(yīng)答中的作用，最后總結(jié)了目前該領(lǐng)域研究所面臨的一些問(wèn)題，以期為科研人員進(jìn)一步探索組蛋白密碼在DNA損傷應(yīng)答中的作用提供參考。

組蛋白；泛素化修飾；DNA損傷應(yīng)答；串?dāng)_

DNA是真核生物遺傳信息的載體，其遺傳保守性是維持物種相對(duì)穩(wěn)定的基礎(chǔ)。然而，各種內(nèi)源性或外源性因素造成的DNA損傷如不能及時(shí)修復(fù)，將導(dǎo)致細(xì)胞凋亡甚至癌變。因此，生物體在進(jìn)化過(guò)程中形成了復(fù)雜的DNA損傷應(yīng)答(DNA damage response, DDR)機(jī)制，以應(yīng)對(duì)各種DNA損傷壓力。組蛋白是真核生物染色質(zhì)中主要的蛋白成分，包括H1、H2A、H2B、H3和H4五種類型。約146 bp的DNA通過(guò)左手螺旋的方式環(huán)繞由2分子H2A-H2B二聚體和1分子H3-H4四聚體組成的核心顆粒1.75圈，形成核小體輔助DNA折疊[1,2]。

組蛋白N端含有大量精氨酸、賴氨酸殘基，是主要的翻譯后修飾位點(diǎn)。組蛋白在各修飾酶、去修飾酶共同編譯下形成組蛋白密碼(histone code)，構(gòu)成了DDR中精密的信號(hào)網(wǎng)絡(luò)[3]。近年來(lái)，組蛋白泛素化修飾在DDR中的作用愈發(fā)受到關(guān)注。組蛋白泛素化修飾可以通過(guò)調(diào)節(jié)核小體結(jié)構(gòu)、激活細(xì)胞周期檢查點(diǎn)、影響修復(fù)因子的招募與裝配等途徑參與DDR。此外，組蛋白修飾之間還存在交互作用，一位點(diǎn)修飾能促進(jìn)或抑制其他位點(diǎn)的修飾[4,5]。組蛋白泛素化修飾同樣可以通過(guò)這種串?dāng)_(crosstalk)作用調(diào)節(jié)其他類型翻譯后修飾作用于DDR。本文介紹了組蛋白泛素化修飾的各主要位點(diǎn)和相關(guān)的E3連接酶、去泛素化酶與效應(yīng)分子，以及這些修飾作用共同編譯形成的信號(hào)網(wǎng)絡(luò)在DDR中的作用。

1 泛素與泛素化修飾

泛素(ubiquitin, ub)是由76個(gè)氨基酸組成的多肽，廣泛存在于真核生物體內(nèi)。泛素分子高度保守，在動(dòng)物、植物和酵母菌中其一級(jí)結(jié)構(gòu)僅有1~3個(gè)氨基酸殘基不同，三級(jí)結(jié)構(gòu)基本相同[6]。泛素分子在激活酶(E1)、結(jié)合酶(E2)和連接酶(E3)的作用下連接于底物，形成單泛素化修飾。泛素分子還可依次連接于前一泛素分子的賴氨酸或甲硫氨酸殘基形成泛素鏈，稱多聚泛素化修飾。連接位點(diǎn)有第6、11、27、29、33、48、63位賴氨酸殘基和第1位甲硫氨酸殘基(K6/11/27/29/33/48/63-linked and M1-linked) 8種類型。

泛素化修飾是泛素–蛋白酶體途徑(ubiquitin- proteasome pathway, UPP)的重要步驟，介導(dǎo)了細(xì)胞內(nèi)短壽蛋白和錯(cuò)誤折疊蛋白通過(guò)26S蛋白酶體降解。此外，泛素化修飾還能調(diào)節(jié)蛋白在細(xì)胞內(nèi)的定位與活性，廣泛參與DNA復(fù)制轉(zhuǎn)錄、損傷應(yīng)答、炎癥反應(yīng)、免疫應(yīng)答、細(xì)胞周期與凋亡、囊泡運(yùn)輸?shù)戎T多生理過(guò)程[7~11]。不同的效應(yīng)往往與泛素鏈不同的拓?fù)浣Y(jié)構(gòu)有關(guān)，例如K11/48連接的泛素鏈主要參與蛋白質(zhì)降解，K63連接的泛素鏈主要參與DNA損傷應(yīng)答與信號(hào)轉(zhuǎn)導(dǎo)，而M1連接的泛素鏈則主要參與免疫應(yīng)答與炎癥反應(yīng)[12]。

2 H2A多位點(diǎn)泛素化修飾參與DDR

H2A泛素化修飾最早于1975年發(fā)現(xiàn)，首個(gè)修飾位點(diǎn)定位于K119 (第119位賴氨酸，同下)，后又陸續(xù)在K13/15和K127/129等位點(diǎn)發(fā)現(xiàn)泛素化修飾[13,14]。H2A各位點(diǎn)泛素化修飾介導(dǎo)多種生物學(xué)效應(yīng)，對(duì)修復(fù)進(jìn)程進(jìn)行調(diào)控，在DNA雙鏈斷裂(double-strand br-eaks, DSBs)和紫外線造成的DNA損傷(UV-induced DNA damage)應(yīng)答中起重要作用。

2.1 沉默損傷周?chē)?/h3>

哺乳動(dòng)物細(xì)胞核內(nèi)約5%~15%的H2A處于單泛素化修飾狀態(tài)，其中以H2AK119單泛素化修飾為主。H2AK119單泛素化修飾參與抑制RNA Pol Ⅱ延伸、多梳蛋白家族(polycomb group proteins, PcG)基因沉默、X染色體失活和抑制趨化因子基因表達(dá)等諸多生理過(guò)程[15~17]。多梳抑制復(fù)合體1 (polycomb repressive complex 1, PRC1)是PcG家族成員，其亞基環(huán)指蛋白2 (ring finger protein 2, RING2)是單泛素化修飾H2AK119的E3連接酶，通過(guò)第98位精氨酸殘基嵌入H2A-H2B二聚體間縫隙定位催化反應(yīng)。由于缺乏活性精氨酸/賴氨酸殘基，RING2還需與PRC1另一亞基BMI-1結(jié)合形成異二聚體才能充分發(fā)揮其催化活性。異二聚體形成有助于穩(wěn)定E2~ub結(jié)構(gòu)，促進(jìn)泛素分子傳遞，BMI-1缺失將嚴(yán)重影響RING2活性[18]。

H2AK119單泛素化修飾可與PcG家族另一成員PRC2催化的H3K27三甲基化修飾相互串?dāng)_，即PRC1的CBX亞基識(shí)別H3K27三甲基化修飾定位，單泛素化修飾H2AK119；PRC2的JARID2亞基識(shí)別H2AK119單泛素化修飾定位，三甲基化修飾H3K27[19]。這種交叉招募可極大地提高損傷位點(diǎn)附近H2AK119單泛素化修飾水平。

近年來(lái)，已有關(guān)于RING2/BMI-1催化的H2AK119單泛素化修飾參與DSBs修復(fù)的研究報(bào)道，如在損傷早期調(diào)節(jié)γH2AX生成、影響修復(fù)因子招募以及輔助DNA定位于核仁周?chē)龋唧w機(jī)制尚未明確[20,21]。目前，H2AK119 單泛素化修飾在DSBs修復(fù)中較為明確的作用是實(shí)現(xiàn)損傷位點(diǎn)周?chē)鷶?shù)千堿基對(duì)范圍內(nèi)基因沉默，抑制損傷區(qū)域的復(fù)制、轉(zhuǎn)錄行為，減少錯(cuò)誤產(chǎn)物的生成，為DNA修復(fù)創(chuàng)造條件[22,23]。然而，Chandler等[24]在AsiSI限制酶誘導(dǎo)的DSBs周?chē)⑽窗l(fā)現(xiàn)PRC1聚集，對(duì)上述理論提出挑戰(zhàn)。此外，還有證據(jù)表明除參與DSBs修復(fù)外，細(xì)胞核內(nèi)儲(chǔ)備的K119單泛素化修飾的H2A還可在分子伴侶CAF-1的輔助下定位于UV損傷周?chē)⑼ㄟ^(guò)共濟(jì)失調(diào)毛細(xì)血管擴(kuò)張癥Rad3相關(guān)蛋白激酶(ATM and Rad3 related kinase, ATR)依賴的途徑參與核苷酸切除修復(fù)(nucle-otide excision repair, NER)后染色質(zhì)重塑[25,26]。

2.2 調(diào)節(jié)DNA斷端剪切

同源重組修復(fù)(homologous recombination, HR)和非同源斷端連接(non-homologous end joining, NHEJ)是細(xì)胞修復(fù)DSBs的兩種重要方式。BRCA1和53BP1分別是HR和NHEJ中重要的效應(yīng)分子，二者相互競(jìng)爭(zhēng)，又彼此協(xié)同。BRCA1通過(guò)易化DNA斷端剪切，促進(jìn)HR；相反，53BP1則在DNA斷端兩側(cè)限制DNA剪切長(zhǎng)度，防止過(guò)度剪切造成的DNA單鏈復(fù)性和染色體重排，易化NHEJ。BRCA1和53BP1在不同位點(diǎn)被招募并級(jí)聯(lián)不同的后續(xù)效應(yīng)，共同決定兩種修復(fù)方式間的平衡[27](圖1A)。

環(huán)指蛋白8 (ring finger protein 8, RNF8)和環(huán)指蛋白168 (ring finger protein 168, RNF168)催化的H2A/H2AXK13/15泛素化修飾，是BRCA1和53BP1招募過(guò)程中的重要信號(hào)。RNF8和RNF168的聚集，依賴于ATM和DNA損傷檢測(cè)點(diǎn)介質(zhì)1 (mediator of DNA damage checkpoint 1, MDC1)的作用。ATM檢測(cè)到DSBs后，磷酸化修飾H2AX和MDC1。磷酸化MDC1的BRCT結(jié)構(gòu)域識(shí)別γH2AX定位于損傷位點(diǎn)，作為腳手架招募RNF8[28,29]。早期認(rèn)為由RNF8直接多聚泛素化修飾H2A/H2AXK13/15招募修復(fù)因子[30]，或首先由RNF8單泛素化修飾H2A/H2AXK13/ 15招募RNF168，再由RNF168延伸K63連接的泛素鏈招募修復(fù)因子[31]。然而實(shí)驗(yàn)中發(fā)現(xiàn)RNF8在體內(nèi)對(duì)核小體中H2A/H2AX缺乏親和力，卻具有延伸K63連接的泛素鏈的能力。近年來(lái)的研究對(duì)這一過(guò)程逐漸有了清晰的認(rèn)識(shí)：RNF8被招募至損傷位點(diǎn)后首先多聚泛素化修飾H1(K63連接的泛素鏈)招募RNF168，由后者單泛素化修飾H2A/H2AXK13/15，最后再由RNF8延伸K63連接的泛素鏈，招募修復(fù)因子[32,33]。

BRCA1是H2A/H2AXK13/15多聚泛素化修飾招募的修復(fù)因子之一，實(shí)際上BRCA1與RAP80、Abraxas、MERIT40、BRCC36、BRCC45和BARD1形成BRCA-A復(fù)合體共同被招募[34]。該復(fù)合體以Abraxas為核心組裝，RAP80負(fù)責(zé)識(shí)別泛素鏈定位[35]。BRCA1-A復(fù)合體能限制DNA斷端剪切，防止HR過(guò)度激活[34]。去泛素化酶BRCC36清除K63連接的泛素鏈，被認(rèn)為在該過(guò)程中發(fā)揮主要作用[36]。53BP1是另一個(gè)被招募的修復(fù)因子，與BRCA1不同，53BP1通過(guò)識(shí)別H2AK15單泛素化修飾定位[37,38]。53BP1可在損傷位點(diǎn)與剪切酶競(jìng)爭(zhēng)，調(diào)整DNA斷端剪切長(zhǎng)度。同時(shí)，53BP1還可作為腳手架，促進(jìn)修復(fù)因子組裝[39]。BRCA1-A復(fù)合體和53BP1的協(xié)同作用有效避免了DNA斷端過(guò)度剪切，使細(xì)胞傾向于通過(guò)NHEJ途徑修復(fù)DSBs。

K127/129單泛素化修飾是新近發(fā)現(xiàn)的第3個(gè)參與DSBs修復(fù)的H2A泛素化修飾類型，由BRCA1-C復(fù)合體催化。BRCA1-C復(fù)合體包含BRCA1/BARD1二聚體、DNA內(nèi)切酶CtIP和MRN復(fù)合體3種成分，BRCA1是主要的E3活性單位[40]。與RING2/BMI-1二聚體相似，BRCA1需與BARD1結(jié)合才能充分發(fā)揮其催化活性[41]。BRCA1/BARD1在異染色質(zhì)蛋白HP1的輔助下定位至損傷中心區(qū)域催化H2AK127/ 129單泛素化修飾，后者可被SMARCAD1的CUE結(jié)構(gòu)域識(shí)別[42]。SMARCAD1依賴其ATP酶活性將53BP1重新定位于損傷外圍，易化CtIP在MRN復(fù)合體輔助下剪切DNA斷端，促進(jìn)以高保真的HR修復(fù)DSBs[41,43~45]。值得一提的是，BRCA1還可形成BRCA1-B/D復(fù)合體，分別通過(guò)調(diào)節(jié)細(xì)胞周期和促進(jìn)鏈侵入的方式參與DDR[34]。

圖1 H2A各位點(diǎn)泛素化修飾在HR/NHEJ與NER中的作用

A：H2A多位點(diǎn)泛素化修飾共同參與DSBs修復(fù)；B：H2AK119單泛素化修飾參與NER。

2.3 輔助起始NER

除RING2/BMI-1外，H2AK119單泛素化修飾還可由DDB1-CUL4DDB2復(fù)合體催化，輔助起始NER[46]。NER是應(yīng)對(duì)UV造成的DNA損傷的主要方式，除修復(fù)環(huán)丁烷嘧啶二聚體(cyclobutane pyrim-idine dimers, CPDs)和6-4光產(chǎn)物[(6-4) photoproducts, 6-4 PPs]外，NER還可廣泛地識(shí)別多種損傷，與其特殊的識(shí)別機(jī)制有關(guān)。XPC是全基因組NER中主要的識(shí)別因子，可識(shí)別DNA發(fā)生修飾(損傷)且Waston-Crick堿基配對(duì)破壞時(shí)形成的不穩(wěn)定結(jié)構(gòu)，而非損傷本身[47]。CPDs本身不足以引起DNA螺旋結(jié)構(gòu)的不穩(wěn)定，因此還需DDB1-CUL4DDB2復(fù)合體的輔助才能激活NER。該復(fù)合體由E3連接酶CUL4和紫外線損傷DNA結(jié)合蛋白(UV-damaged DNA-binding protein, UV-DDB)組成，其中UV-DDB包括DDB1與DDB2兩種類型，DDB1位于CUL4的N端，是連接CUL4與DDB2的橋梁。DDB2通過(guò)WD40結(jié)構(gòu)域識(shí)別CPDs后招募DDB1-CUL4至損傷位點(diǎn)[48]。正常情況下，CUL4的活性受COP9信號(hào)體抑制，激活則依賴NEDD8類泛素化修飾[49]。

正常細(xì)胞在UV損傷后H2AK119單泛素化修飾水平迅速下降，DDB1-CUL4DD2復(fù)合體在H2AK119單泛素化修飾水平的恢復(fù)中起重要作用。H2AK119單泛素化修飾能有效促進(jìn)H2A/H2A-H2B從核小體解離，加劇DNA螺旋結(jié)構(gòu)的不穩(wěn)定性，促進(jìn)XPC識(shí)別[50]。同時(shí)，DDB2、XPC均是DDB1- CUL4DDB2泛素化修飾的底物，DDB2泛素化修飾后可被分子伴侶VCP/p97識(shí)別，介導(dǎo)DDB2通過(guò)UPP降解，解除位阻效應(yīng)，促進(jìn)后續(xù)NER進(jìn)程[51,52]。XPC泛素化修飾可增強(qiáng)其與DNA的親和力，促進(jìn)其與損傷DNA結(jié)合[52,53](圖1B)。

目前認(rèn)為，DDB1-CUL4DDB2單泛素化修飾H2AK119是發(fā)生在NER早期的事件，輔助XPC對(duì)損傷DNA的識(shí)別，激活NER。RING2/BMI-1單泛素化修飾H2AK119則更多的以剪切后事件的形式發(fā)生于NER后期，通過(guò)CAF-1和ATR依賴的途徑參與染色質(zhì)重塑[25,26]。

3 H2B單泛素化修飾串?dāng)_其他修飾

RNF20-RNF40催化的H2BK120單泛素化修飾是參與哺乳動(dòng)物DDR的主要類型[54]。在正常細(xì)胞中，H2BK120單泛素化修飾還參與了基因轉(zhuǎn)錄的起始、延伸和轉(zhuǎn)錄后mRNA的剪切，并能選擇性地促進(jìn)或抑制基因的表達(dá)[55~57]。轉(zhuǎn)錄相關(guān)的H2BK120單泛素化修飾高背景為研究H2B泛素化修飾在DDR中的作用提高了難度，直至2011年Moyal等[58]才證實(shí)DNA損傷可提高局部H2BK120單泛素化修飾水平，確認(rèn)了H2BK120單泛素化修飾同樣參與DDR。

H2BK120單泛素化修飾參與DDR，與組蛋白翻譯后修飾間的串?dāng)_作用密切相關(guān)。以串?dāng)_H3K79甲基化修飾為例，H2BK120單泛素化修飾能促進(jìn)H3K79甲基化修飾，特別是H3K79二甲基化修飾，對(duì)53BP1等修復(fù)因子的招募具有重要意義[59,60]。關(guān)于H2BK120單泛素化修飾是如何串?dāng)_H3K79甲基化修飾的，Zhou等[61]提出了“占位誘導(dǎo)”學(xué)說(shuō)，即H2BK120單泛素化修飾在空間上封閉核小體表面無(wú)功能位點(diǎn)，促進(jìn)類端粒沉默干擾體1 (disruptor of telomeric silencing 1-like, Dot1L)在效應(yīng)位點(diǎn)聚集并甲基化修飾H3K79。同時(shí)，H2BK120單泛素化修飾通過(guò)串?dāng)_作用還能改變?nèi)旧|(zhì)高度壓縮的結(jié)構(gòu)，例如串?dāng)_H3K4甲基化修飾可協(xié)同染色質(zhì)重塑因子SNF2h調(diào)節(jié)核小體結(jié)構(gòu)[62,63]；串?dāng)_H4K16乙酰化修飾可開(kāi)放約30 nm長(zhǎng)度的染色質(zhì)纖維[64,65]；串?dāng)_H3K56乙?；揎椡瑯涌梢源龠M(jìn)促轉(zhuǎn)錄因子復(fù)合體FACT調(diào)節(jié)染色質(zhì)結(jié)構(gòu)，為修復(fù)因子裝配提供條件[66,67]。

相似的作用同樣存在于酵母菌中，由E3連接酶Bre1催化的H2BK123單泛素化修飾同樣可以提高Dot1甲基化修飾H3K79的效率，促進(jìn)53BP1、Ku80和XRCC4的招募[68,69]。同時(shí)，H3K79甲基化修飾還可作為修復(fù)因子的?？课稽c(diǎn)參與NER[70]。H2BK123單泛素化修飾還參與了復(fù)制過(guò)程中DNA損傷耐受機(jī)制的調(diào)控，可能同樣與調(diào)節(jié)核小體結(jié)構(gòu)，促進(jìn)復(fù)制叉恢復(fù)與缺損區(qū)段DNA的填補(bǔ)有關(guān)[71,72]。

另一方面，H2BK120單泛素化修飾在DDR中的作用還體現(xiàn)在激活細(xì)胞周期檢查點(diǎn)中。Kari等[66]敲除RNF40并采用新制霉菌素處理細(xì)胞后發(fā)現(xiàn)，與對(duì)照組相比，G2/M:G1從5.02下降至2.29，S期占比從2.93%升至5.66%，提出H2BK120單泛素化修飾對(duì)細(xì)胞周期檢查點(diǎn)的激活和維持具有重要作用。但Moyal等[58]在實(shí)驗(yàn)中沉默RNF20后并未發(fā)現(xiàn)細(xì)胞周期檢查點(diǎn)激活異常，認(rèn)為RNF20-RNF40并非通過(guò)激活細(xì)胞周期檢查點(diǎn)的方式參與DDR。上述差異可能與分別沉默RNF40和RNF20有關(guān)，其具體作用還有待進(jìn)一步研究。

4 H3、H4泛素化修飾協(xié)同參與DDR

正常生理狀態(tài)下細(xì)胞內(nèi)僅有約0.3%的H3和0.1%的H4處于泛素化修飾狀態(tài)。UV損傷后，H3、H4泛素化修飾水平迅速升高，并于1~2 h內(nèi)達(dá)到峰值[73]。

Wang等[73]通過(guò)層析與質(zhì)譜分析，提純并確認(rèn)了泛素化修飾H3和H4的E3連接酶復(fù)合體——CUL4- DDB-ROC1 (即DDB1-CUL4DDB2復(fù)合體)。UV損傷后，泛素化修飾的H3在胞漿和核漿中比例分別從5%升至19%，12%升至40%；相應(yīng)地，在核顆粒中的比例從83%跌至41%，表明泛素化修飾可促進(jìn)H3從核小體解離，易化XPC識(shí)別，激活NER[73]。除上述作用外，CUL4-DDB-ROC1復(fù)合體還可促進(jìn)NER后H3K56乙酰化修飾水平恢復(fù)，促進(jìn)核小體組裝[74]；以及在修復(fù)前輔助H3.3在損傷部位沉積，為修復(fù)后轉(zhuǎn)錄恢復(fù)打下基礎(chǔ)[75]。

通常認(rèn)為，組蛋白修飾位點(diǎn)位于伸出核小體外的肽鏈N端，但近年來(lái)研究發(fā)現(xiàn)組蛋白核心區(qū)域也是翻譯后修飾的熱點(diǎn)部位[76]。H4K91處于H2A-H2B二聚體與H3-H4四聚體連接的核心區(qū)域，可由B細(xì)胞淋巴瘤和BAL相關(guān)蛋白(B-lymphoma and BAL- associated protein, BBAP)單泛素化修飾。H4K91單泛素化修飾可串?dāng)_H4K20甲基化修飾影響53BP1的招募[77]。實(shí)驗(yàn)表明H4K91單泛素化修飾可以提高賴氨酸甲基轉(zhuǎn)移酶PR-Set7/Set8的聚集效率，促進(jìn)H4K20二甲基化修飾。BBAP敲除后，53BP1在損傷部位的聚集顯著降低。

此外，BBAP還可通過(guò)多聚泛素化修飾底物招募修復(fù)因子，并且這是一種獨(dú)立于RNF8/RNF168軸介導(dǎo)的H2A/H2AXK13/15多聚泛素化修飾的招募模式[63]。該過(guò)程中，多聚ADP-核糖聚合酶1 [poly (ADP-ribose) polymerase 1, PARP1]首先識(shí)別DNA損傷，在損傷部位多聚ADP-核糖基化修飾底物，后者可被BBAP在BAL1的輔助下識(shí)別并定位，再由BBAP催化產(chǎn)生泛素鏈，招募BRCA1等修復(fù)因子[78](圖2B)。分析認(rèn)為，BBAP催化的多聚泛素化修飾發(fā)生于DNA損傷早期，較RNF8/RNF168催化的H2A/H2AXK13/15多聚泛素化修飾更為簡(jiǎn)單快捷。

圖2 H2B和H4泛素化修飾在DNA損傷應(yīng)答中的作用

A: H2BK120單泛素化修飾串?dāng)_H3K79甲基化修飾；B: H4泛素化修飾招募修復(fù)因子。

5 組蛋白去泛素化修飾

組蛋白密碼編譯過(guò)程中，修飾與去修飾總是對(duì)應(yīng)存在的。無(wú)一例外地，DDR過(guò)程中泛素化修飾也必然伴隨著去泛素化修飾。上調(diào)去泛素化酶(deub-iquitinating enzymes, DUBs)能抑制修復(fù)因子的招募，延緩DDR進(jìn)程；下調(diào)DUBs則引起自發(fā)性染色體斷裂，更加強(qiáng)調(diào)了泛素化修飾與去泛素化修飾間動(dòng)態(tài)平衡在維持基因組穩(wěn)定性中的重要性[79]。

泛素特異性蛋白酶(ubiquitin-specific proteases, USPs)是DUBs家族中成員最多的一類。USPs的3個(gè)結(jié)構(gòu)域空間構(gòu)象類似于“手指-手掌-拇指”(fingers-palm-thumb)，其中palm和thumb構(gòu)成活性中心，fingers負(fù)責(zé)定位[80]。H2AK119可由USP16去泛素化修飾，USP16敲除將抑制修復(fù)完成后轉(zhuǎn)錄的重啟[22,81]。BAP1是另一個(gè)作用于H2AK119的DUB，其C端與核小體結(jié)合，可在ASXL1的輔助下完成去泛素化修飾[82]。在最新的研究中，Jullien等[83]還發(fā)現(xiàn)USP21亦能解除H2AK119單泛素化修飾產(chǎn)生的基因抵抗作用。USP3、USP51均是參與H2A/H2AXK13/15去泛素修飾的DUBs，區(qū)別在于USP3過(guò)表達(dá)能降低RNF168在損傷位點(diǎn)的招募[84]；而USP51依賴于RNF168定位，過(guò)表達(dá)僅影響RNF168下游修復(fù)因子如53BP1、BRCA1的招募，不影響上游分子ATM、MDC1、RNF168的聚集[85]。USP3、USP51產(chǎn)生不同效應(yīng)或與拮抗不同的E3連接酶有關(guān)：USP3可能直接拮抗RNF8，抑制H1多聚泛素化修飾而影響RNF168的招募及后續(xù)修飾，USP51則可能與RNF168拮抗，影響H2A/H2AXK13/ 15單泛素化修飾。USP48是新近發(fā)現(xiàn)的DUB，去泛素化修飾H2AK127/129，通過(guò)限制MARCAD1對(duì)53BP1的重定位限制DNA斷端的剪切，對(duì)HR起負(fù)性調(diào)控作用[86]。值得注意的是，USP48的激活還需H2A上其他位點(diǎn)泛素化修飾的輔助，可能與改變USP48構(gòu)象形成活性中心有關(guān)[86]。

轉(zhuǎn)錄輔助復(fù)合體SAGA是參與DDR過(guò)程中H2BK120 (H2BK123)去泛素化修飾的DUB。在哺乳動(dòng)物中SAGA亞基USP22起主要催化作用，而在酵母菌中以Ubp8為主[87]。實(shí)驗(yàn)表明敲除USP22將嚴(yán)重影響細(xì)胞通過(guò)HR或NHEJ修復(fù)DSBs，表明H2BK120去泛素化修飾在DDR中同樣起重要作用[88]。

6 結(jié)語(yǔ)與展望

DDR是一個(gè)復(fù)雜的過(guò)程，涵蓋了損傷位點(diǎn)的識(shí)別、細(xì)胞周期檢查點(diǎn)激活、DNA修復(fù)和染色質(zhì)重塑等諸多環(huán)節(jié)，組蛋白翻譯后修飾在該過(guò)程中扮演重要角色。本文總結(jié)了組蛋白泛素化修飾/去泛素化修飾的各位點(diǎn)和相關(guān)組分，以及這些修飾作用共同編譯形成的信號(hào)網(wǎng)絡(luò)在DDR中的作用(表1)。

近年來(lái)，人們對(duì)于組蛋白泛素化修飾在DDR中的作用有了深入的了解。這得益于研究手段的進(jìn)步與高度特異性抗體的制備，使人們能夠排除高背景的干擾，直接觀察局部DNA損傷后細(xì)胞的應(yīng)答情況[58]。方法的創(chuàng)新也同樣至關(guān)重要，在組蛋白上人為連接泛素分子為探究位阻效應(yīng)在組蛋白翻譯后修飾間的串?dāng)_作用提供了新的思路[61,68]。然而，現(xiàn)階段的研究還存在一定的問(wèn)題：某些泛素化修飾的位點(diǎn)、類型尚未確定[77]；某些泛素化修飾的具體作用仍不夠清晰[40]；泛素化與去泛素化修飾間關(guān)系混亂[79]；與其他翻譯后修飾間串?dāng)_的具體作用及機(jī)制不明等。此外，從現(xiàn)有的研究來(lái)看，仍有其他泛素化修飾位點(diǎn)尚未發(fā)現(xiàn)[86]。對(duì)于上述問(wèn)題的深入研究，必將為全面系統(tǒng)地闡述組蛋白密碼在DDR中的作用奠定堅(jiān)實(shí)的基礎(chǔ)。

表1 組蛋白泛素化/去泛素化修飾在DNA損傷應(yīng)答中的作用

續(xù)表

?表示修飾位點(diǎn)暫不明確。

[1] Mari?oramírez L, Kann MG, Shoemaker BA, Landsman D. Histone structure and nucleosome stability., 2005, 2(5): 719–729.

[2] Luger K, M?der AW, Richmond RK, Sargent DF, Richmond TJ. Crystal structure of the nucleosome core particle at 2.8?? resolution., 1997, 389(6648): 251–260.

[3] Strahl BD, Allis CD. The language of covalent histone modifications., 2000, 403(6765): 41–45.

[4] Suganuma T, Workman JL. Crosstalk among histone modifications., 2008, 135(4): 604–607.

[5] Lee JS, Smith E, Shilatifard A. The language of histone crosstalk., 2010, 142(5): 682–685.

[6] Hershko A, Ciechanover A. The ubiquitin system., 1998, 67(1): 425–479.

[7] Herrmann J, Lerman LO, Lerman A. Ubiquitin and ubiquitin-like proteins in protein regulation., 2007, 100(9): 1276–1291.

[8] Shaid S, Brandts CH, Serve H, Dikic I. Ubiquitination and selective autophagy., 2013, 20(1): 21–30.

[9] Wagner SA, Beli P, Weinert BT, Nielsen ML, Cox J, Mann M, Choudhary C. A proteome-wide, quantitative survey ofubiquitylation sites reveals widespread regulatory roles., 2011, 10(10): M111.013284.

[10] Welchman RL, Gordon C, Mayer RJ. Ubiquitin and ubiquitin-like proteins as multifunctional signals., 2005, 6(8): 599–609.

[11] Schnell JD, Hicke L. Non-traditional functions of ubiquitin and ubiquitin-binding proteins., 2003, 278(38): 35857–35860.

[12] Komander D, Rape M. The Ubiquitin Code., 2012, 81: 203–229.

[13] Goldknopf IL, Taylor CW, Baum RM, Yeoman LC, Olson MO, Prestayko AW, Busch H. Isolation and charac-terization of protein A24, a "histone-like" non-histone chromosomal protein., 1975, 250(18): 7182– 7187.

[14] Goldknopf IL, Busch H. Isopeptide linkage between nonhistone and histone 2A polypeptides of chromosomal conjugate-protein A24., 1977, 74(3): 864–868.

[15] Wang H, Wang L, Erdjument-Bromage H, Vidal M, Tempst P, Jones RS, Zhang Y. Role of histone H2A ubiquitination in polycomb silencing., 2004, 431 (7010): 873–878.

[16] Fang J, Chen TB, Li E, Zhang Y. Ring1b-mediated H2A ubiquitination associates with inactive X chromosomes and is involved in initiation of X inactivation., 2004, 279(51): 52812–52815.

[17] Zhou W, Zhu P, Wang J, Pascual G, Ohgi KA, Lozach J, Glass CK, Rosenfeld MG. Histone H2A monoubiquitin-ation represses transcription by inhibiting RNA polymer-rase II transcriptional elongation., 2008, 29(1): 69–80.

[18] Ginjala V, Nacerddine K, Kulkarni A, Oza J, Hill SJ, Yao M, Citterio E, Lohuizen MV, Ganesan S. BMI1 is recruited to DNA breaks and contributes to DNA damage-induced H2A ubiquitination and repair., 2011, 31(10): 1972–1982.

[19] Blackledge NP, Farcas AM, Kondo T, King HW, McGouran JF, Hanssen LL, Ito S, Cooper S, Kondo K, Koseki Y, Ishikura T, Long HK, Sheahan TW, Brockdorff N, Kessler BM, Koseki H, Klose RJ. Variant PRC1 complex-dependent H2A ubiquitylation drives PRC2 recruitment and polycomb domain formation., 2014, 157(6): 1445–1459.

[20] Ismail IH, Andrin C, Mcdonald D, Hendzel MJ. BMI1- mediated histone ubiquitylation promotes DNA double- strand break repair., 2010, 191(1): 45–60.

[21] Chitale S, Richly H. Nuclear organization of nucleotide excision repair is mediated by RING1B dependent H2A- ubiquitylation., 2017, 8(19): 30870–30887.

[22] Shanbhag NM, Rafalska-Metcalf IU, Balane-Bolivar C, Janicki SM, Greenberg RA. ATM-dependent chromatin changes silence transcription in cis to DNA double-strand breaks., 2010, 141(6): 970–981.

[23] Kakarougkas A, Ismail A, Chambers AL, Riballo E, Herbert AD, Künzel J, L?brich M, Jeggo PA, Downs JA. Requirement for PBAF in transcriptional repression and repair at DNA breaks in actively transcribed regions of chromatin., 2014, 55(5): 723–732.

[24] Chandler H, Patel H, Palermo R, Brookes S, Matthews N, Peters G. Role of polycomb group proteins in the DNA damage response – a reassessment., 2014, 9(7): e102968.

[25] Bergink S, Salomons FA, Hoogstraten D, Groothuis TA, De WH, Wu J, Yuan L, Citterio E, Houtsmuller AB, Neefjes J, Hoeijmakers JH , Vermeulen W , Dantuma NP. DNA damage triggers nucleotide excision repair-dependent monoubiquitylation of histone H2A., 2006, 20(10): 1343–1352.

[26] Zhu Q, Wani G, Arab HH, El-Mahdy MA, Ray A, Wani AA. Chromatin restoration following nucleotide excision repair involves the incorporation of ubiquitinated H2A at damaged genomic sites., 2009, 8(2): 262– 273.

[27] Uckelmann M, Sixma TK. Histone ubiquitination in the DNA damage response., 2017, 56: 92–101.

[28] Stucki M, Clapperton JA, Mohammad D, Yaffe MB, Smerdon SJ, Jackson SP. MDC1 directly binds phosphor-rylated histone H2AX to regulate cellular responses to DNA double-strand breaks., 2005, 123(7): 1213– 1226.

[29] Huen MS, Grant R, Manke I, Minn K, Yu X, Yaffe MB, Chen J.transduces the DNA-damage signal via histone ubiquitylation and checkpoint protein assembly., 2007, 131(5): 901–914.

[30] Mailand N, Bekker-Jensen S, Faustrup H, Melander F, Bartek J, Lukas C, Lukas J.ubiquitylates histones at DNA double-strand breaks and promotes assembly of repair proteins., 2007, 131(5): 887–900.

[31] Doil C, Mailand N, Bekker-Jensen S, Menard P, Larsen DH, Pepperkok R, Ellenberg J, Panier S, Durocher D, Bartek J.binds and amplifies ubiquitin conjugates on damaged chromosomes to allow accumulation of repair proteins., 2009, 136(3): 435–446.

[32] Mattiroli F, Vissers JH, van Dijk WJ, Ikpa P, Citterio E, Vermeulen W, Marteijn JA, Sixma TK. RNF168 ubiquitinateson H2A/H2AX to drive DNA damage signaling., 2012, 150(6): 1182–1195.

[33] Thorslund T, Ripplinger A, Hoffmann S, Wild T, Uckelmann M, Villumsen B, Narita T, Sixma TK, Choudhary C, Bekkerjensen S, Mailand N. Histone H1 couples initiation and amplification of ubiquitin signalling after DNA damage., 2015, 527(7578): 389–393.

[34] Savage KI, Harkin DP. BRCA1, a 'complex' protein involved in the maintenance of genomic stability., 2015, 282(4): 630–646.

[35] Sobhian B, Shao G, Lilli DR, Culhane AC, Moreau LA, Xia B, Livingston DM, Greenberg RA. RAP80 targets BRCA1 to specific ubiquitin structures at DNA damage sites., 2007, 316(5828): 1198–1202.

[36] Ng HM, Wei LZ, Lan L, Huen MSY. The Lys63- deubiquitylating enzyme BRCC36 limits DNA break processing and repair., 2016, 291(31): 16197–16207.

[37] Fradetturcotte A, Canny MD, Escribanodíaz C, Orthwein A, Leung CC, Huang H, Landry MC, Kitevskileblanc J, Noordermeer SM, Sicheri F, Durocher D. 53BP1 is a reader of the DNA-damage-induced H2A lys 15 ubiquitin mark., 2013, 499(7456): 50–54.

[38] Wilson MD, Benlekbir S, Fradet-Turcotte A, Sherker A, Julien JP, Mcewan A, Noordermeer SM, Sicheri F, Rubinstein JL, Durocher D. The structural basis of modified nucleosome recognition by., 2016, 536(7614): 100–103.

[39] Ochs F, Somyajit K, Altmeyer M, Rask MB, Lukas J, Lukas C. 53BP1 fosters fidelity of homology-directed DNA repair., 2016, 23(8): 714–721.

[40] Kalb R, Mallery D, Larkin C, Huang JJ, Hiom K. BRCA1 is a histone-H2A-specific ubiquitin ligase., 2014, 8(4): 999–1005.

[41] Densham RM, Morris JR. The BRCA1 ubiquitin ligase function sets a new trend for remodelling in DNA repair., 2017, 8(2): 116–125.

[42] Densham RM, Garvin AJ, Stone HR, Strachan J, Baldock RA, Daza-Martin M, Fletcher A, Blair-Reid S, Beesley J, Johal B, Pearl LH, Neely R, Keep NH, Watts FZ, Morris JR. Human BRCA1–BARD1 ubiquitin ligase activity counteracts chromatin barriers to DNA resection., 2016, 23(7): 647–655.

[43] Gieni RS, Ismail IH, Campbell S, Hendzel MJ. Polycomb group proteins in the DNA damage response: a link between radiation resistance and "stemness"., 2011, 10(6): 883–894.

[44] Cruz-García A, López-Saavedra A, Huertas P. BRCA1 accelerates CtIP-mediated DNA-end resection., 2014, 9(2): 451–459.

[45] Polato F, Callen E, Wong N , Faryabi R, Bunting S, Chen HT, Kozak M, Kruhlak MJ, Reczek CR, Lee WH, Ludwig T, Baer R, Feigenbaum L, Jackson S, Nussenzweig A. CtIP-mediated resection is essential for viability and can operate independently of BRCA1., 2014, 211(6): 1027–1036.

[46] Hannah J, Zhou P. Distinct and overlapping functions of the cullin E3 ligase scaffolding proteins CUL4A and CUL4B., 2015, 573(1): 33–45.

[47] Hess MT, Schwitter U, Petretta M, Giese B, Naegeli H. Bipartite substrate discrimination by human nucleotide excision repair., 1997, 94(13): 6664–6669.

[48] Lan L, Nakajima S, Kapetanaki MG, Hsieh CL, Fagerburg M, Thickman K, Rodriguez-Collazo P, Leuba SH, Levine AS, Rapi?-Otrin V. Monoubiquitinated histone H2A destabilizes photolesion-containing nucleosomes with concomitant release of UV-damaged DNA-binding protein E3 ligase., 2012, 287(15): 12036–12049.

[49] Hannah J, Zhou P. Regulation of DNA damage response pathways by the cullin-RING ubiquitin ligases., 2009, 8(4): 536–543.

[50] Kapetanaki MG, Guerrero-Santoro J, Bisi DC, Hsieh CL, Rapi?-Otrin V, Levine AS. The DDB1-CUL4ADDB2ubiquitin ligase is deficient in xeroderma pigmentosum group E and targets histone H2A at UV-damaged DNA sites., 2006, 103(8): 2588–2593.

[51] Puumalainen MR, Lessel D, Rüthemann P, Kaczmarek N, Bachmann K, Ramadan K, Naegeli H. Chromatin retention of DNA damage sensors DDB2 and XPC through loss of p97 segregase causes genotoxicity., 2014, 5: 3695.

[52] El-Mahdy MA, Zhu Q, Wang QE, Wani G, Praetorius-Ibba M, Wani AA. Cullin 4A-mediated proteolysis of DDB2 protein at DNA damage sites regulateslesion recognition by XPC., 2006, 281(19): 13404– 13411.

[53] Sugasawa K, Okuda Y, Saijo M, Nishi R, Matsuda N, Chu G, Mori T, Iwai S, Tanaka K, Tanaka K, Hanaoka F. UV-induced ubiquitylation of XPC protein mediated by UV-DDB-ubiquitin ligase complex., 2005, 121(3): 387–400.

[54] Meas R, Mao P. Histone ubiquitylation and its roles in transcription and DNA damage response., 2015, 36: 36–42.

[55] Shiloh Y, Shema E, Moyal L, Oren M. RNF20-RNF40: A ubiquitin-driven link between gene expression and the DNA damage response., 2011, 585(18): 2795–2802.

[56] Hérissant L, Moehle EA, Bertaccini D, Dorsselaer AV, Schaefferreiss C, Guthrie C, Dargemont C. H2B ubiquityl-ation modulates spliceosome assembly and function in budding yeast., 2014, 106(4): 126–138.

[57] Weake VM, Workman JL. Histone ubiquitination: triggering gene activity., 2008, 29(6): 653–663.

[58] Moyal L, Lerenthal Y, Gana-Weisz M, Mass G, So S, Wang SY, Eppink B, Chung YM, Shalev G, Shema E, Shkedy D, Smorodinsky NI, van Vliet N, Kuster B, Mann M, Ciechanover A, Dahm-Daphi J, Kanaar R, Hu MC, Chen DJ, Oren M, Shiloh Y. Requirement of ATM- dependent monoubiquitylation of histone H2B for timely repair of DNA double-strand breaks., 2011, 41(5): 529–542.

[59] Huyen Y, Zgheib O, Ditullio RA, Gorgoulis VG, Zacharatos P, Petty TJ, Sheston EA, Mellert HS, Stavridi ES, Halazonetis TD. Methylated lysine 79 of histone H3 targets 53BP1 to DNA double-strand breaks., 2004, 432(7015): 406–411.

[60] Wakeman TP, Wang Q, Feng J, Wang XF. Bat3 facilitates H3K79 dimethylation by DOT1L and promotes DNA damage-induced 53BP1 foci at G1/G2 cell-cycle phases., 2012, 31(9): 2169–2181.

[61] Zhou LJ, Holt MT, Ohashi N, Zhao AS, Muller MM, Wang BY, Muir TW. Evidence that ubiquitylated H2B corrals hDot1L on the nucleosomal surface to induce H3K79 methylation., 2016, 7:10589.

[62] Kato A, Komatsu K. RNF20-SNF2H pathway of chromatin relaxation in DNA double-strand break repair., 2015, 6(3): 592–606.

[63] Kim J, Guermah M, McGinty RK, Lee J-S, Tang Z, Milne TA, Shilatifard A, Muir TW, Roeder RG. RAD6-mediated transcription-coupled H2B ubiquitylation directly stimulates H3K4 methylation in human cells., 2009, 137(3): 459–471.

[64] Fierz B, Chatterjee C, McGinty RK, Bar-Dagan M, Raleigh DP, Muir TW. Histone H2B ubiquitylation disrupts local and higher-order chromatin compaction., 2011, 7(2): 113–119.

[65] Robinson PJJ, An W, Routh A, Martino F, Chapman L, Roeder RG, Rhodes D. 30 nm chromatin fibre decompaction requires both H4-K16 acetylation and linker histone eviction., 2008, 381(4): 816–825.

[66] Kari V, Shchebet A, Neumann H, Johnsen SA. The H2B ubiquitin ligase RNF40 cooperates with SUPT16H to induce dynamic changes in chromatin structure during DNA double-strand break repair., 2011, 10(20): 3495–3504.

[67] Nair DM, Ge Z, Mersfelder EL, Parthun MR. Genetic interactions between POB3 and the acetylation of newly synthesized histones., 2011, 57(4): 271–286.

[68] Vlaming H, van Welsem T, de Graaf EL, Ontoso D, Altelaar AF, San-Segundo PA, Heck AJ, van Leeuwen F. Flexibility in crosstalk between H2B ubiquitination and H3 methylation in vivo., 2014, 15(10): 1077– 1084.

[69] Nakanishi S, Lee JS, Gardner KE, Gardner JM, Takahashi Y, Chandrasekharan MB, Sun ZW, Osley MA, Strahl BD, Jaspersen SL, Shilatifard A. Histone H2BK123 monoub-iquitination is the critical determinant for H3K4 and H3K79 trimethylation by COMPASS and Dot1., 2009, 186(3): 371–377.

[70] Tatum D, Li S. Evidence that the histone methyltr-ansferase Dot1 mediates global genomic repair by methylating histone H3 on lysine 79., 2011, 286(20): 17530–17535.

[71] Hung SH, Wong RP, Ulrich HD, Kao CF. Monoubiq-uitylation of histone H2B contributes to the bypass of DNA damage during and after DNA replication., 2017, 114(11): E2205–E2214.

[72] Northam MR, Trujillo KM. Histone H2B mono- ubiquitylation maintains genomic integrity at stalled replication forks., 2016, 44(19): 9245–9255.

[73] Wang H, Zhai L, Xu J, Joo HY, Jackson S, Erdjument- Bromage H, Tempst P, Xiong Y, Zhang Y. Histone H3 and H4 ubiquitylation by the CUL4-DDB-ROC1 ubiquitin ligase facilitates cellular response to DNA damage., 2006, 22(3): 383–394.

[74] Zhu QZ, Wei SC, Sharma N, Wani G, He JS, Wani AA. Human CRL4DDB2ubiquitin ligase preferentially regulates post-repair chromatin restoration of H3K56Ac through recruitment of histone chaperon CAF-1., 2017, 8(61): 104525–104542.

[75] Adam S, Polo SE, Almouzni G. Transcription recovery after DNA damage requires chromatin priming by the H3.3 histone chaperone HIRA., 2013, 155(1): 94– 106.

[76] Tropberger P, Schneider R. Scratching the (lateral) surface of chromatin regulation by histone modifications., 2013, 20(6): 657–661.

[77] Yan Q, Dutt S, Xu R, Graves K, Juszczynski P, Manis JP, Shipp MA. BBAP monoubiquitylates histone H4 at lysine 91 and selectively modulates the DNA damage response., 2009, 36(1): 110–120.

[78] Yan Q, Xu R, Zhu L, Cheng X, Wang Z, Manis J, Shipp MA. BAL1 and its partner E3 ligase, BBAP, link poly (ADP-ribose) activation, ubiquitylation, and double-strand DNA repair independent of ATM, MDC1, and RNF8., 2013, 33(4): 845–857.

[79] Lancini C, van den Berk PC, Vissers JH, Gargiulo G, Song JY, Hulsman D, Serresi M, Tanger E, Blom M, Vens C, van Lohuizen M, Jacobs H, Citterio E. Tight regulation of ubiquitin-mediated DNA damage response by USP3 preserves the functional integrity of hematopoietic stem cells., 2014, 211(9): 1759–1777.

[80] Hu M, Li P, Li M, Li W, Yao T, Wu JW, Gu W, Cohen RE, Shi Y. Crystal structure of a UBP-family deubiquitinating enzyme in isolation and in complex with ubiquitin aldehyde., 2002, 111(7): 1041–1054.

[81] Joo HY, Zhai L, Yang C, Nie S, Erdjument-Bromage H, Tempst P, Chang C, Wang H. Regulation of cell cycle progression and gene expression by H2A deubiquitination., 2007, 449(7165): 1068–1072.

[82] Sahtoe DD, van Dijk WJ, Ekkebus R, Ovaa H, Sixma TK. BAP1/ASXL1 recruitment and activation for H2A deubiquitination., 2016, 7: 10292.

[83] Jullien J, Vodnala M, Pasque V, Oikawa M, Miyamoto K, Allen G, David SA, Brochard V, Wang S, Bradshaw C, Koseki H, Sartorelli V, Beaujean N, Gurdon J. Gene resistance to transcriptional reprogramming following nuclear transfer is directly mediated by multiple chromatin- repressive pathways., 2017, 65(5): 873–884.e8.

[84] Sharma N, Zhu Q, Wani G, He J, Wang QE, Wani AA. USP3 counteracts RNF168 via deubiquitinating H2A and γH2AX at lysine 13 and 15., 2014, 13(1): 106–114.

[85] Wang ZQ, Zhang HL, Liu J, Cheruiyot A, Lee JH, Ordog T, Lou ZK, You ZS, Zhang ZG. USP51 deubiquitylates H2AK13,15ub and regulates DNA damage response., 2016, 30(8): 946–959.

[86] Uckelmann M, Densham RM, Baas R, Winterwerp HHK, Fish A, Sixma TK, Morris JR. USP48 restrains resection by site-specific cleavage of the BRCA1 ubiquitin mark from H2A., 2018, 9: 229.

[87] Morgan MT, Haj-Yahya M, Ringel AE, Bandi P, Brik A, Wolberger C. Structural basis for histone H2B deubiqui-tination by the SAGA DUB module., 2016, 351(6274): 725–728.

[88] Ramachandran S, Haddad D, Li C, Le MX, Ling AK, So CC, Nepal RM, Gommerman JL, Yu K, Ketela T, Moffat J, Martin A. The SAGA deubiquitination module promotes DNA repair and class switch recombination through ATM and DNAPK-mediated γH2AX ormation., 2016, 15(7): 1554–1565.

Histone ubiquitylation and its roles in DNA damage response

Qingyi Zhang1, Yingzi Zhang2, Kai Shen1, Shuyu Zhang2, Jianping Cao2

Ubiquitylation is an essential type of protein post-translational modifications (PTMs) in eukaryotes, which mediates various biological processes by regulating the subcellular localization, activity, and stability of proteins. Histones, as the main protein ingredients of chromatin, are closely coupled with DNA activities such as replication, transcription and repair, and therefore are the hotspots of PTMs. After DNA damage, histone ubiquitylations are involved in DNA damage response (DDR) by regulating nucleosome structure, activating cell cycle checkpoints, remodeling the nucleosome, and the recruitment and assembly of repair factors. Meanwhile, histone ubiquitylations can also crosstalk with other types of PTMs to regulate DDR processes. In this review, we summarize how the site-specific histone ubiquitylation forms signal network and contributes to DDR, which may shed light on the further study of how histone codes formed by histone PTMs affect the entire DDR processes.

histone; ubiquitylation; DNA damage response (DDR); crosstalk

2018-07-10;

2018-09-04

國(guó)家級(jí)大學(xué)生創(chuàng)新創(chuàng)業(yè)訓(xùn)練計(jì)劃(編號(hào)：201610285039Z，201610285045Z)資助[Supported by the National Students’ Platform for Innovation and Entrepreneurship Training Program (Nos. 201610285039Z, 201610285045Z)]

張卿義，本科在讀，專業(yè)方向：臨床醫(yī)學(xué)。E-mail: zhangqingyi@outlook.com

曹建平，教授，博士生導(dǎo)師，研究方向：放射生物學(xué)。E-mail: jpcao@suda.edu.cn

10.16288/j.yczz.18-112

2018/10/20 14:54:00

URI: http://kns.cnki.net/kcms/detail/11.1913.R.20181020.1453.004.html

(責(zé)任編委: 朱衛(wèi)國(guó))