TRAF6在人结直肠癌中的功能及机制研究
文献类型：学位论文
| 作者 | 孙恒 |
| 学位类别 | 博士 |
| 答辩日期 | 2013-06 |
| 授予单位 | 中国科学院上海生命科学研究院营养科学研究所 |
| 授予地点 | 中国科学院上海生命科学研究院 |
| 导师 | 方靖 |
| 关键词 | 肿瘤坏死因子受体相关因子6 低氧诱导因子1-alpha 泛素化 结直肠癌 新血管生成 |
| 其他题名 | Functions and mechanisms of TRAF6 in colorectal cancer |
| 学位专业 | 生物化学与分子生物学 |
| 中文摘要 | TRAF6是肿瘤坏死因子受体相关因子家族（TNF receptor associated factors，TRAFs）的成员之一，最初发现于IL-1及CD40信号传导途径。TRAF6作为接头蛋白可以介导TNFR（tumor necrosis factor receptor）和IL-1R（interleukin-1 receptor）/TLR（Toll-like receptor）超家族的信号传递。作为泛素连接酶，TRAF6可以对其底物进行以Lys63连接的多聚泛素化修饰，而这种非降解的多聚泛素链可以促进底物激酶如TAK1和PKB（Akt）的活性。除了在先天和后天免疫，骨代谢，淋巴结发育中发挥着很重要的作用外，近来的研究发现TRAF6在癌症的发生发展过程中也扮演了重要的角色。低氧诱导因子1（hypoxia inducible factor-1，HIF-1）由受氧调节的alpha亚基和组成型表达的beta亚基构成。在氧气充足情况下，HIF-1被脯氨酸羟化酶（prolyl hydroxylases，PHDs）羟基化，再经pVHL（von Hipple Lindau protein）介导的VCB (pVHL-Elongin C-Elongin B) E3复合物泛素化而发生降解。在低氧情况下，HIF-1alpha的羟基化受到抑制，因此在蛋白水平得到积累。HIF-1作为重要的转录因子，从最初的EPO被报道以来，有越来越多的下游靶基因被发现，涉及血管生成、糖脂代谢、细胞生长、凋亡、迁移和炎症等多种生理过程，而这些跟肿瘤的发生发展有着十分紧密的联系。 结直肠癌是人类常见的消化道肿瘤，目前居癌症死因第3位。我们的工作主要是进行TRAF6在结直肠癌中功能的研究。我们通过研究分析70个配对的结直肠癌临床组织样本，发现了结直肠癌中TRAF6的表达水平明显高于正常结直肠粘膜组织，并且TRAF6在结直肠癌中的表达水平与肿瘤的恶性程度密切相关。而且，TRAF6的表达水平与HIF-1alpha的激活程度呈正相关趋势。细胞实验表明TRAF6可以在蛋白水平稳定HIF-1alpha，并激活其转录活性；抑制TRAF6则导致HIF-1alpha蛋白水平降低和转录活性抑制。TRAF6对HIF-1alpha的这种调节作用并不依赖于氧气。进一步的实验表明，TRAF6可以直接结合HIF-1alpha并对其进行以Lys63连接的多聚泛素化修饰。这可能是TRAF6稳定HIF-1alpha的主要原因。动物实验显示抑制TRAF6的表达可以明显阻止肿瘤生长和肿瘤新血管的生成。同时，我们还发现TRAF6可以通过诱导CCND1的表达促进结肠癌细胞的增殖。 我们的研究结果提示TRAF6可能是一个癌基因，并且发现了HIF-1alpha一个全新的泛素化修饰形式，丰富了对HIF-1alpha蛋白翻译后修饰的认识。TRAF6有可能通过调节HIF-1alpha在结肠肿瘤发生发展过程中发挥重要作用。这些结果不仅有助于深入了解结直肠癌的发病机制，并且也为将来的诊断和治疗提供了新的靶点和思路。 |
| 索取号 | D2011-011 |
| 英文摘要 | TRAF6 is a member of tumor necrosis factor receptor associated factors (TRAFs) family. It was first identified in the signal transduction pathways of IL-1 and CD40. TRAF6 functions as an adaptor protein to mediate signals from both the TNFR and the IL-1R/TLR superfamilies. Also, it works as an ubiquitin-ligase to mediate K63-linked polyubiquitination in the presence of the ubiquitin conjugation enzyme system, Ubc13 and Uev1A. These nondegradative polyubiquitin chains have been shown to be important in the activation of protein kinases such as TAK1 and PKB (Akt), which are direct targets of TRAF6. Besides its significant function in innate and adaptive immune responses, bone metabolism and lymph node development, recent studies indicate that TRAF6 also plays an important role in cancer. HIF-1 is a transcription factor that consists of an O2-regulated alpha subunit and a constitutively expressed beta subunit. In well-oxygenated cells, HIF-1alpha is hydroxylated by prolyl hydroxylases (PHDs). The hydroxylated HIF-1alpha is bound by the von Hippel-Lindau (VHL) tumor suppressor protein that recruits the Elongin C-Elongin B-Cullin 2-E3 ubiquitin-ligase complex, leading to proteasomal degradation of HIF-1alpha. Under hypoxia, HIF-1alpha hydroxylation is inhibited, leading to HIF-1alpha stabilization. HIF-1alpha is an important transcription factor and activates transcription of genes encoding proteins that are involved in key aspects of cancer biology, including angiogenesis, metabolism, proliferation, apoptosis, invasion, metastasis and inflammation. Colorectal cancer (CRC) is among the most common malignancy worldwide and the third leading cause of cancer death. Our work is focused on investigating the possible role and mechanism of TRAF6 in colorectal cancer. We found that the expression of TRAF6 is increased in colorectal cancer and the increased expression of TRAF6 is associated with higher tumor grade, indicating that TRAF6 is an oncogene in CRC. We found that the elevated TRAF6 is also correlated with the activation of HIF-1alpha. In vitro studies show that TRAF6 stabilized HIF-1alpha and induced its transcriptional activity; knockdown of TRAF6 reduced HIF-1alpha protein level and its transcriptional activity. Further studies indicated TRAF6 associated with HIF-1alpha and mediated its K63-linked polyubiquitination, which might result in its stabilization and activation. We also found that TRAF6 promtoed cell proliferation through inducing expression of CCND1. Furthermore, in vivo experiments showed that knockdown of TRAF6 obviously inhibited colorectal cancer cell angiogenesis and tumorigenesis. Our results suggest that TRAF6 is an oncogene. A novel K63-linked polyubiquitination of HIF-1alpha mediated by TRAF6 widens our knowledge of post-translational modification of HIF-1alpha. Activation of HIF-1alpha by TRAF6 may play an important role in colorectal cancer. So TRAF6 might be served as a therapeutic target of colorectal cancer. |
| 语种 | 中文 |
| 公开日期 | 2015-12-24 |
| 源URL | [http://202.127.25.144/handle/331004/376]  |
| 专题 | 中国科学院上海生命科学研究院营养科学研究所_营养与癌症研究组 |
| 推荐引用方式 GB/T 7714 | 孙恒. TRAF6在人结直肠癌中的功能及机制研究[D]. 中国科学院上海生命科学研究院. 中国科学院上海生命科学研究院营养科学研究所. 2013. |
入库方式： OAI收割
来源：上海营养与健康研究所
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