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1,2:3,4-二環(huán)氧丁烷誘導(dǎo)細(xì)胞DNA雙鏈斷裂損傷及其修復(fù)機(jī)制研究

發(fā)布時(shí)間:2018-08-26 19:16
【摘要】:研究背景1,3-丁二烯(1,3-butadiene,BD)是一種重要的工業(yè)原料,用于合成橡膠、塑料等石油化工和制造行業(yè)。美國(guó)將BD列為前40位重要的化學(xué)品之一,應(yīng)用范圍廣,職業(yè)接觸人群多。此外,汽車尾氣、香煙煙霧及食用油油煙中也發(fā)現(xiàn)BD普遍存在,屬于室內(nèi)具有慢性空氣危害的9種優(yōu)先污染物之一。因此BD不僅是一種職業(yè)暴露污染物,更是一種重要的環(huán)境空氣污染物,其危害范圍已從職業(yè)工人擴(kuò)展到普通人群。BD可以誘導(dǎo)嚙齒動(dòng)物多器官腫瘤的形成,人群研究也顯示出白血病發(fā)病相關(guān)的陽性結(jié)果,因而被IARC和EPA列為確定的人類致癌物(1組)。BD的致癌效應(yīng)主要來自于體內(nèi)代謝產(chǎn)生的環(huán)氧化產(chǎn)物:1,2-環(huán)氧-3-丁烯(EB),1,2-二羥基-3,4-環(huán)氧丁烯(EBD)和1,2:3,4-二環(huán)氧丁烯(DEB)。上述環(huán)氧化產(chǎn)物均能與DNA形成加合物,造成遺傳物質(zhì)的損傷,其中DEB的活性最強(qiáng),因而目前對(duì)BD致癌機(jī)制研究多聚焦于闡明其遺傳損傷效應(yīng)。既往研究發(fā)現(xiàn)BD及其代謝物可以誘導(dǎo)DNA雙鏈斷裂和染色體損傷,但是BD誘導(dǎo)DNA雙鏈斷裂損傷后的修復(fù)機(jī)制并不清楚。本課題組前期在人群研究中發(fā)現(xiàn)BD暴露與核質(zhì)橋(NPB)比例升高相關(guān)。NPB是染色體損傷的標(biāo)志和細(xì)胞癌變的重要環(huán)節(jié),研究BD誘導(dǎo)NPB形成的機(jī)制,將為闡明BD的致癌作用過程,預(yù)防和減少BD所誘導(dǎo)的染色體損傷和人群腫瘤的發(fā)生提供重要依據(jù)。有研究提示,NPB的形成可能與DNA雙鏈斷裂后,經(jīng)非同源末端連接(NHEJ)等錯(cuò)誤修復(fù)形成雙著絲粒染色體,在細(xì)胞分裂后期分別牽引到兩個(gè)子細(xì)胞核有關(guān)。由此我們推測(cè),BD及其代謝物誘導(dǎo)DNA雙鏈斷裂后,可能通過影響主要的DNA雙鏈斷裂修復(fù)通路,即HR和NHEJ修復(fù)通路,造成錯(cuò)誤修復(fù)效率的提高,從而引起NPB形成。因此,本課題以BD活性代謝物DEB為對(duì)象,在明確其誘導(dǎo)人淋巴母細(xì)胞DNA雙鏈斷裂和染色體損傷的條件下,研究DEB對(duì)DNA雙鏈斷裂修復(fù)通路的影響,進(jìn)一步驗(yàn)證修復(fù)通路在DEB致NPB形成中的作用,為深入探討B(tài)D的遺傳損傷機(jī)制提供依據(jù)。研究?jī)?nèi)容1.DEB的細(xì)胞毒性效應(yīng)研究建立DEB染毒處理的人淋巴母細(xì)胞TK6細(xì)胞模型模型。分別采用MTS和Ed U方法檢測(cè)DEB對(duì)細(xì)胞活性和增殖能力的影響。采用流式細(xì)胞儀分析技術(shù),分別以PI和Annix V-FITC/PI染色檢測(cè)DEB對(duì)細(xì)胞周期和細(xì)胞凋亡的影響。2.DEB誘導(dǎo)細(xì)胞遺傳損傷的檢測(cè)采用胞質(zhì)分裂阻滯微核試驗(yàn)(CBMNT)分析DEB對(duì)細(xì)胞染色體的損傷(微核率、核質(zhì)橋率、核芽突率及核分裂指數(shù));采用Western blot和免疫熒光技術(shù),檢測(cè)DNA雙鏈斷裂標(biāo)志物(γ-H2AX)的表達(dá)情況。3.DEB對(duì)細(xì)胞DNA雙鏈斷裂損傷修復(fù)的影響采用含有HR修復(fù)效率檢測(cè)報(bào)告底物的MCF-7細(xì)胞,檢測(cè)DEB處理后HR修復(fù)效率的變化。采用Cell-free方法,提取細(xì)胞總蛋白,與32P標(biāo)記的線性質(zhì)粒共同作用,檢測(cè)DEB處理后NHEJ修復(fù)效率的變化。采用Western blot、Slot blot或免疫熒光方法檢測(cè)DNA損傷修復(fù)通路關(guān)鍵分子ATM、p-ATM、γ-H2AX、Ku80、DKA-PKcs、XLF、DNA-ligase IV和BRCA1的表達(dá),以觀察DEB對(duì)DNA雙鏈斷裂修復(fù)通路分子表達(dá)的影響。4.NHEJ通路基因在DEB所致染色體損傷中的作用研究采用化學(xué)抑制劑Nu7026處理細(xì)胞以抑制DNA-PKcs的表達(dá),采用Sh RNA轉(zhuǎn)染細(xì)胞以抑制Ku80的表達(dá),通過CBMNT檢測(cè)細(xì)胞染色體損傷的變化,分析NHEJ通路在DEB所致DNA雙鏈斷裂損傷修復(fù)及NPB形成中的作用。研究結(jié)果1.DEB誘導(dǎo)TK6細(xì)胞增殖抑制、周期阻滯和細(xì)胞凋亡DEB可以抑制TK6細(xì)胞的活力,降低DNA的合成,具有劑量效應(yīng)關(guān)系。進(jìn)一步通過流式細(xì)胞儀分析發(fā)現(xiàn),DEB可以抑制TK6細(xì)胞的周期進(jìn)展,使細(xì)胞分裂阻滯在G2/M期。同時(shí),DEB處理可誘導(dǎo)TK6細(xì)胞凋亡,2.5~10μM DEB處理后48 h,細(xì)胞凋亡率均出現(xiàn)顯著升高(P0.01或0.001)。2.DEB誘導(dǎo)TK6細(xì)胞的染色體損傷及DNA雙鏈斷裂CBMNT檢測(cè)結(jié)果表明,DEB可誘導(dǎo)TK6細(xì)胞的微核率、核質(zhì)橋率及核芽突率升高,造成細(xì)胞的染色體損傷,同時(shí)引起核分裂指數(shù)降低,抑制細(xì)胞增殖。此外,Western Blot檢測(cè)發(fā)現(xiàn),10μM DEB處理細(xì)胞后,DNA雙鏈斷裂標(biāo)志物γ-H2AX蛋白的表達(dá)隨著時(shí)間的延長(zhǎng),先升高后降低,總體維持在一個(gè)高表達(dá)的水平。免疫熒光檢測(cè)也證實(shí),10μM DEB處理可誘導(dǎo)細(xì)胞γ-H2AX的大量表達(dá)。上述結(jié)果提示,DEB可造成TK6細(xì)胞的DNA雙鏈斷裂及染色體損傷。3.DEB影響HR和NHEJ修復(fù)效率及相關(guān)基因的表達(dá)采用含有p DR-GFP底物的細(xì)胞檢測(cè)DEB對(duì)HR修復(fù)效率的影響,結(jié)果顯示,DEB處理24 h后反映HR修復(fù)的熒光陽性細(xì)胞比例顯著降低,并存在劑量效應(yīng)關(guān)系,提示DEB可降低細(xì)胞的HR修復(fù)效率。體外NHEJ修復(fù)檢測(cè)結(jié)果表明,隨著DEB處理濃度增加,線性化質(zhì)粒DNA連接產(chǎn)物明顯增加,提示DEB可提高DNA雙鏈斷裂的NHEJ修復(fù)效率。此外,對(duì)DNA雙鏈斷裂損傷修復(fù)通路的蛋白表達(dá)檢測(cè)結(jié)果表明,HR通路BRCA1蛋白在DEB處理24 h時(shí)出現(xiàn)明顯降低。同時(shí),NHEJ通路蛋白DNA-PKcs、XLF和DNA-ligase IV的表達(dá)在DEB作用后4 h或24 h后開始出現(xiàn)顯著升高。Western blot檢測(cè)未發(fā)現(xiàn)NHEJ修復(fù)通路核心蛋白之一Ku80的表達(dá)改變,但是免疫熒光和Slot blot檢測(cè)顯示DEB處理細(xì)胞后4 h,Ku80蛋白形成聚焦灶,同時(shí)與DNA結(jié)合的Ku80含量顯著升高,并存在劑量效應(yīng)關(guān)系。上述結(jié)果提示DEB可降低HR修復(fù)通路效率及相關(guān)基因表達(dá),但是提高NHEJ修復(fù)通路效率,以及相關(guān)基因表達(dá)或轉(zhuǎn)移結(jié)合到DNA的能力。4.NHEJ通路參與DEB誘導(dǎo)的NPB形成采用化學(xué)抑制劑和sh RNA分別抑制DNA-PKcs和Ku80蛋白,通過CBMNT,觀察NHEJ通路在DEB誘導(dǎo)染色體損傷和NPB形成中的作用。檢測(cè)發(fā)現(xiàn),與單純DEB處理組相比,抑制DNA-PKcs表達(dá)可使DEB誘導(dǎo)的微核和核芽突比率顯著升高,而NPB比率顯著降低。同時(shí),與轉(zhuǎn)染陰性對(duì)照序列的細(xì)胞相比,在穩(wěn)定轉(zhuǎn)染Ku80 sh RNA的細(xì)胞中,DEB也能誘導(dǎo)微核和核芽突比率進(jìn)一步升高,而NPB比率則顯著降低。這些研究結(jié)果提示,抑制DNA-PKcs或Ku80蛋白的表達(dá)可加重DEB所誘導(dǎo)的微核及核芽突損傷,但減低了NPB損傷的發(fā)生。這一結(jié)果也提示NHEJ通路可能參與了DEB所誘導(dǎo)的NPB的形成。研究結(jié)論:DEB可誘導(dǎo)TK6細(xì)胞的DNA雙鏈斷裂和微核、核芽突以及核質(zhì)橋等染色體損傷,引起細(xì)胞增殖抑制、周期阻滯和凋亡。同時(shí),DEB引起DNA雙鏈斷裂損傷修復(fù)通路中HR修復(fù)通路的抑制和NHEJ修復(fù)通路的激活,NHEJ修復(fù)通路參與DEB誘導(dǎo)的核質(zhì)橋的形成。
[Abstract]:Background 1,3-butadiene (BD) is an important industrial raw material used in synthetic rubber, plastics and other petrochemical and manufacturing industries. The United States ranks BD as one of the top 40 important chemicals, with a wide range of applications and a large number of occupational contacts. BD is not only a kind of occupational exposure pollutant, but also an important environmental air pollutant. Its hazard range has expanded from professional workers to the general population. BD can induce the formation of multiple organ tumors in rodents. Population studies also show the incidence of leukemia. The carcinogenic effects of BD are mainly due to the epoxidation products produced by metabolism in vivo: 1,2-epoxy-3-butene (EB), 1,2-dihydroxy-3,4-epoxy-butene (EBD) and 1,2:3,4-dioxy-butene (DEB). Previous studies have found that BD and its metabolites can induce DNA double-strand breaks and chromosome damage, but the repair mechanism of BD-induced DNA double-strand breaks is not clear. NPB is a marker of chromosomal damage and an important link in cell carcinogenesis. Studying the mechanism of BD-induced NPB formation will provide important basis for clarifying the carcinogenic process of BD, preventing and reducing the chromosomal damage induced by BD and the occurrence of human tumors. After DNA double-strand breakage, it was repaired by non-homologous end-joining (NHEJ) and other erroneous repairs to form dicentric chromosomes, which were towed to two daughter nuclei at the late stage of cell division. In order to further verify the role of the repair pathway in the formation of DEB-induced NPB, we studied the effects of DEB on DNA double-strand break repair pathway in human lymphoblasts under the conditions of clear induction of DNA double-strand break and chromosome damage. The cytotoxic effects of DEB on human lymphoblasts TK6 cells were studied. MTS and Ed U methods were used to detect the effects of DEB on cell viability and proliferation. Flow cytometry was used to analyze the cytotoxic effects of DEB on human lymphoblasts TK6 cells. The effect of DEB on cell cycle and apoptosis was detected by color assay. 2. The cytokinesis block micronucleus test (CBMNT) was used to detect the damage of DEB to cell chromosome (micronucleus rate, nucleoplasmic bridge rate, nucleus germination rate and mitotic index); Western blot and immunofluorescence were used to detect DNA double-strand break markers (gamma-cleavage index). The effect of DEB on repair of DNA double strand breakage was detected by MCF-7 cells containing the substrate of HR repair efficiency test report, and the change of HR repair efficiency after DEB treatment was detected. Western blot, Slot blot or immunofluorescence were used to detect the expression of ATM, p-ATM, gamma-H2AX, Ku80, DKA-PKcs, XLF, DNA-ligase IV and BRCA1 in DNA damage repair pathway. 4. The role of NHEJ pathway gene in chromosome damage induced by DEB was studied by chemical inhibition. Nu7026 treated cells to inhibit the expression of DNA-PKcs, Sh RNA transfected cells to inhibit the expression of Ku80, and CBMNT was used to detect the changes of chromosome damage. The role of NHEJ pathway in DNA double-strand breakage repair and NPB formation induced by DEB was analyzed. Results 1. DEB induced TK6 cells proliferation inhibition, cell cycle arrest and cell apoptosis D EB could inhibit the activity of TK6 cells and decrease the synthesis of DNA in a dose-dependent manner. Further analysis by flow cytometry showed that DEB could inhibit the cycle progression of TK6 cells and block cell division in G2/M phase. At the same time, DEB treatment could induce apoptosis of TK6 cells, and the apoptosis rate increased significantly 48 hours after 2.5-10 Mu DEB treatment (P 0.05). DEB-induced chromosomal damage and DNA double strand breakage CBMNT assay showed that DEB could induce the micronucleus rate, nucleoplasmic bridge rate and nucleus budding rate of TK6 cells to increase, resulting in chromosomal damage, while causing a decrease in mitotic index and inhibiting cell proliferation. The expression of DNA double-strand break marker gamma-H2AX protein increased first and then decreased with the prolongation of time, and remained at a high level. Immunofluorescence assay also confirmed that the treatment of 10 mu DEB could induce a large expression of gamma-H2AX in TK6 cells. The repair efficiency of HR and NHEJ and the expression of related genes were detected by cells containing P DR-GFP substrates. The results showed that the percentage of fluorescent positive cells which could reflect HR repair decreased significantly after 24 hours of treatment with DEB, and there was a dose-effect relationship, suggesting that DEB could reduce the repair efficiency of HR cells. The results showed that the linearized plasmid DNA junction products increased significantly with the increase of DEB concentration, suggesting that DEB could improve the repair efficiency of DNA double strand breaks. In addition, the expression of BRCA1 protein in DNA double strand breaks repair pathway was significantly decreased after 24 hours of DEB treatment. Western blot showed no change in the expression of Ku80, one of the core proteins of the NHEJ repair pathway. However, immunofluorescence and Slot blot showed that Ku80 protein formed a foci 4 hours after DEB treatment and the Ku80 content bound to DNA increased significantly. These results suggest that DEB can decrease the efficiency of HR repair pathway and related gene expression, but increase the efficiency of NHEJ repair pathway and the ability of related gene expression or transfer to DNA. 4. NHEJ pathway participates in the formation of DEB-induced NPB by inhibiting DNA-PKcs and Ku80 proteins by chemical inhibitors and sh RNA, respectively. CBMNT, observed the role of NHEJ pathway in DEB-induced chromosomal damage and NPB formation. Inhibition of DNA-PKcs expression significantly increased the DEB-induced micronucleus and nucleus-bud ratio, while significantly decreased the NPB ratio. Meanwhile, compared with the cells transfected with negative control sequence, the cells transfected with Ku80 sh RNA were stably transfected. These results suggest that inhibiting the expression of DNA-PKcs or Ku80 proteins may aggravate DEB-induced micronucleus and nuclear bud damage, but reduce the occurrence of NPB damage. These results also suggest that NHEJ pathway may be involved in DEB-induced NPB damage. CONCLUSION: DEB can induce DNA double strand breakage and micronucleus, nucleus bud and nucleoplasmic bridge damage in TK6 cells, which can inhibit cell proliferation, cycle arrest and apoptosis. At the same time, DEB can inhibit HR repair pathway and activate NHEJ repair pathway in DNA double strand breakage repair pathway. NHEJ repair pathway participates in DEB-induced DNA double strand breakage repair pathway. The formation of nuclear bridges.
【學(xué)位授予單位】:第三軍醫(yī)大學(xué)
【學(xué)位級(jí)別】:碩士
【學(xué)位授予年份】:2017
【分類號(hào)】:R114

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