【作者】 赵洁；

【导师】 张学敏；

【作者基本信息】 中国人民解放军军事医学科学院 ， 细胞生物学， 2009， 博士

【摘要】 本项工作主要研究了CUEDC2和SOX4蛋白质在肿瘤细胞生长调控中的作用,并发现了上述蛋白质的重要新功能:(一)CUEDC2是一个包含CUE结构域,但功能尚不明确的基因。CUE结构域,约含40个氨基酸残基的保守结构,广泛存在于真核细胞的蛋白质中。它能与泛素结合,既能识别单泛素也能识别多泛素,并能够促进分子内的单泛素化。我们在发现CUEDC2能够与孕激素受体(PR)结合,促进孕激素依赖的PR泛素化降解基础上(The EMBO Journal,2007),进一步研究了CUEDC2对雌激素受体α(ERα)功能的调控。研究发现CUEDC2可以通过雌激素非依赖的方式与ERα发生相互作用,并通过泛素-蛋白酶体通路促进ERα的降解。通过比较MCF-7对照细胞和MCF-7 CUEDC2干涉细胞中ERα的蛋白量,我们发现CUEDC2的干涉与ERα蛋白质水平的上调正相关。进一步的结果显示,CUEDC2抑制了ERα介导的下游靶基因的转录,并且染色质免疫沉淀实验进一步证明CUEDC2能够减少ERα与靶基因启动子区域雌激素反应元件的结合。与这些结果一致的是,CUEDC2能够抑制雌激素诱导的乳腺癌细胞增殖。以上显示,CUEDC2促进ERα蛋白质的泛素化降解,并抑制ERα功能,在乳腺癌细胞生长中发挥了重要作用。(二)SOX4在许多发育进程中发挥了关键作用,如胚胎心脏发育、胸腺发育和神经系统发育等。越来越多的研究还表明,SOX4蛋白质在许多肿瘤细胞中过量表达,并与疾病预后相关。但是到目前为止,SOX4在肿瘤发生和发展中的作用机制还不明确。在本研究中,我们发现SOX4蛋白质表达水平被DNA损伤信号诱导上调;更为重要的是,利用RNA干涉技术干涉内源SOX4的表达能显著抑制p53抑癌蛋白质在DNA损伤反应中的激活。以上提示,SOX4参与了DNA损伤反应中p53的激活。通过进一步研究,我们发现SOX4能结合p53,并且其相互作用随DNA损伤信号的刺激而增强。更深入的研究发现,SOX4干扰了Mdm2与p53的相互作用,抑制p53泛素化降解进而使p53稳定性增加。我们还发现,SOX4能结合p300/CBP并促进其与p53的相互作用,从而促进p53乙酰化修饰。综上,我们发现SOX4在DNA损伤激活p53的过程中发挥了关键作用及其机制,为今后更深入研究SOX4在DNA损伤和肿瘤发生中的作用提供了重要线索。更多还原

【Abstract】 In this work,we study the roles of CUEDC2 and SOX4 in regulating the growth of tumor cells,and our findings provide novel function of these proteins.(1) CUEDC2 is a CUE domain-contained gene,whose function is not clear. Identified as ubiquitin binding motifs,the CUE domains are small, moderately-conserved domains of about 40 amino acid residues that are found in a variety of eukaryotic proteins.CUE domains interact with both mono- and poly-ubiquitin,and have a dual role in mono- and poly-ubiquitin recognition as well as in facilitating intramolecular monoubiquitination.Based on the finding that CUEDC2 interacts with progesterone receptor(PR) and promotes progesterone-dependent PR degradation by the ubiquitin-proteasome pathway,we further investigate the regulation of estrogen receptorα(ERα) function by CUEDC2.In this study,we identified that CUEDC2 interacts with ERαand promotes ERαdegradation through the ubiquitin-proteasome pathway in a ligand independent manner.Assessment of ERαlevels in the MCF-7/Control shRNA and MCF-7/CUE shRNA cells demonstrated that knocking down CUEDC2 is associated with increased ERαexpression level.We also show that CUEDC2 represses the transcription of ERαtarget genes,and chromatin immunoprecipitation assays further demonstrate that CUEDC2 associates with the reduced occupancy of ERαto ERE.In concern with these results,we show that CUEDC2 inhibites estrogen-mediated proliferation of breast cancer cells.These findings provide evidence that CUEDC2 promotes the ubiquitination and degradation of ERα,inhibits its transcriptional activity and that this protein is of importance in regulating the growth of breast cancer cells.(2) SOX4 plays important roles in many developmental processes,such as embryonic cardiac development,thymocyte development and nervous system development.Recently,increasing evidence has shown that SOX4 is highly up-regulated in a number of tumors and correlates with better survival in some tumor patients.However,the precise mechanism by which SOX4 is involved in tumorigenesis remains largely unknown.Here we show that SOX4 protein level is elevated following DNA damage treatment.Notably,knocking down of endogenous SOX4 by RNA interfering inhibits the stabilization and activation of p53 tumor suppressor in response to DNA damage.SOX4 interacts with p53 under normal conditions and DNA damage signals enhance their interaction.SOX4 stabilizes p53 protein by blocking Mdm2-mediated p53 ubiquitination and degradation.Furthermore,SOX4 enhances p53 acetylation by interacting with p300/CBP and facilitating p300/CBP/p53 complex formation.Thus,SOX4 may be a novel critical protein involved in the regulation of p53 stability and activity upon DNA damage.In conclusion,our findings provide insight into the roles of SOX4 in the complicated regulation network of p53 in response to DNA damage,and drugs targeting SOX4 may be a potential anti-cancer therapeutic approach for future studies.更多还原