胚胎干細(xì)胞（embryonic stem cells,ESCs）來(lái)源于著床前囊胚的內(nèi)細(xì)胞團(tuán),具有自我更新和發(fā)育全能性這兩大特性,，該特性決定了其具有巨大的研究?jī)r(jià)值和廣泛的臨床應(yīng)用前景,。近年來(lái),，由體細(xì)胞重編程為與ESCs特性相似的誘導(dǎo)性多能干細(xì)胞(induced pluripotent stem cells,iPS cells）的建立更進(jìn)一步拉進(jìn)了干細(xì)胞和臨床疾病治療的距離。已有的大量研究表明,，轉(zhuǎn)錄因子Oct4和Sox2對(duì)于維持ESCs以及iPS細(xì)胞的建立都起著重要的作用,，它們蛋白水平的微小改變都可以影響到其下游靶基因的正常表達(dá)，進(jìn)而導(dǎo)致ESCs分化,。然而,，至今仍不是很清楚Oct4和Sox2以及其下游靶基因在ESCs及其分化過(guò)程中是如何被精密調(diào)控的。
中科院上海生命科學(xué)院/上海交通大學(xué)醫(yī)學(xué)院健康科學(xué)研究所干細(xì)胞生物重點(diǎn)實(shí)驗(yàn)室高芙蓉博士研究生在導(dǎo)師金穎研究員的指導(dǎo)下,，以O(shè)ct4和Sox2的一個(gè)下游靶基因,，成纖維生長(zhǎng)因子4（fibroblast growth factor 4,FGF4），的增強(qiáng)子的一段寡核苷酸（含有Oct4和Sox2結(jié)合序列）為餌,，通過(guò)親和層析和蛋白質(zhì)質(zhì)譜分析發(fā)現(xiàn)了一個(gè)與Oct4和Sox2共同特異性調(diào)控FGF4表達(dá)的核蛋白,，PARP1,。PARP1是一個(gè)NAD+依賴的多聚ADP-核糖轉(zhuǎn)移酶,，參與多種重要的細(xì)胞功能的調(diào)控。她們的研究發(fā)現(xiàn),，PARP1可直接結(jié)合于FGF4的增強(qiáng)子上,，在ESCs分化過(guò)程中，PARP1通過(guò)對(duì)Sox2進(jìn)行多聚ADP-核糖修飾,，使Sox2從FGF4增強(qiáng)子上解離并降解,，從而正調(diào)控FGF4的表達(dá)。當(dāng)PARP1缺失或處于低活性時(shí),，Sox2的多聚ADP-核糖修飾降低,，使得Sox2與FGF4增強(qiáng)子的結(jié)合多于正常水平。同時(shí),，Sox2蛋白水平也增加,，最終造成FGF4的表達(dá)下降。FGF4對(duì)于ESCs誘導(dǎo)的分化細(xì)胞的生長(zhǎng)或存活是必需的,，而加入外源的FGF4生長(zhǎng)因子可以部分恢復(fù)因由PARP1-/- ESCs來(lái)源的分化細(xì)胞的生長(zhǎng)或存活的異常,。該研究工作首次闡明蛋白翻譯后修飾對(duì)于Sox2蛋白水平及其功能的重要調(diào)控作用，同時(shí)揭示了在ESCs分化過(guò)程中,，PARP1對(duì)Sox2的蛋白水平和FGF4的轉(zhuǎn)錄的動(dòng)態(tài)調(diào)控是必需的,。這些發(fā)現(xiàn)有助于我們進(jìn)一步闡明ESCs維持其自我更新和發(fā)育全能性的機(jī)制，并且對(duì)于研究體細(xì)胞重編程的分子機(jī)制有促進(jìn)作用,。
這項(xiàng)研究工作于2009年8月發(fā)表在《生物化學(xué)雜志》 (The Journal of Biological Chemistry)上,，該研究工作得到了國(guó)家自然科學(xué)基金,、上海市優(yōu)秀學(xué)科帶頭人計(jì)劃、上海市教育委員會(huì)重點(diǎn)學(xué)科建設(shè)項(xiàng)目和科學(xué)院創(chuàng)新項(xiàng)目等的支持,。（生物谷Bioon.com）
生物谷推薦原始出處：
J. Biol. Chem., Vol. 284, Issue 33, 22263-22273, August 14, 2009
PARP1 Poly(ADP-ribosyl)ates Sox2 to Control Sox2 Protein Levels and FGF4 Expression during Embryonic Stem Cell Differentiation*
Furong Gao?, Sung Won Kwon||, Yingming Zhao||, and Ying Jin1
From the From the Key Laboratory of Stem Cell Biology, Institute of Health Sciences, Shanghai Institute of Biological Sciences, Chinese Academy of Sciences/Shanghai JiaoTong University School of Medicine, Shanghai 200025, China, , Shanghai Stem Cell Institute, Shanghai JiaoTong University School of Medicine, Shanghai 200025, China, , the ||Ben May Department for Cancer Research, University of Chicago, Chicago, Illinois 60637, and , ?Graduate School of Chinese Academy of Sciences, Beijing 100000, China
Transcription factors Oct4 and Sox2 are key players in maintaining the pluripotent state of embryonic stem cells (ESCs). Small changes in their levels disrupt normal expression of their target genes. However, it remains elusive how protein levels of Oct4 and Sox2 and expression of their target genes are precisely controlled in ESCs. Here we identify PARP1, a DNA-binding protein with an NAD+-dependent enzymatic activity, as a cofactor of Oct4 and Sox2 to regulate expression of their target gene FGF4. We demonstrate for the first time that PARP1 binds the FGF4 enhancer to positively regulate FGF4 expression. Our data show that PARP1 interacts with and poly(ADP-ribosyl)ates Sox2 directly, which may be a step required for dissociation and degradation of inhibitory Sox2 proteins from the FGF4 enhancer. When PARP1 activity is inhibited or absent, poly(ADP-ribosyl)ation of Sox2 decreases and association of Sox2 with FGF4 enhancers increases, accompanied by an elevated level of Sox2 proteins and reduced expression of FGF4. Significantly, specific knockdown of Sox2 expression by RNA interference can considerably abrogate the inhibitory effect of the poly(ADP- ribose) polymerase inhibitor on FGF4 expression. Interestingly, PARP1 deficiency does not affect undifferentiated ESCs but compromises cell survival and/or growth when ESCs are induced into differentiation. Addition of FGF4 can partially rescue the phenotypes caused by PARP1 deficiency during ESC differentiation. Taken together, this study uncovers new mechanisms through which Sox2 protein levels and FGF4 expression are dynamically regulated during ESC differentiation and adds a new member to the family of proteins regulating the properties of ESCs.
