慢性乙型肝炎病毒（HBV）感染是肝癌發生的重要因素，其中乙肝病毒X蛋白（HBx）在這一過程起著關鍵作用。研究發現，一些HBV變體和HBx突變具有更高致癌風險，而且這些變體和突變存在地區差異。香港是HBV感染高發地帶，因此本研究目的是從這一地區120個肝癌組織標本中篩查出HBx突變位點。我們用巢式PCR從84.16% (101/120)的標本中提取和擴增了HBx，並進行基因測序。三種HBx突變被檢測出，包括點突變，遠端羧基端截斷和缺失突變。其中點突變位點有39個，特別的是在50%的標本中檢測出A1630G/G1721A 和 A1762T/G1764A雙突變。在31.68% (32/101)的標本中發現遠端羧基端截斷，以及在2.97% (3/101)的標本中檢測出缺失突變。總之，大多數突變集中在HBx轉錄啟動域，表明這些突變在肝癌發生中可能起著重要作用。 / 缺氧誘導因數-1α（HIF-1α）在肝癌的發生和發展中也起著重要作用。研究發現，野生型HBx可以啟動HIF-1α，但是變異型HBx和HIF-1α的關係還沒有研究清楚。我們研究表明HBx轉錄啟動域是必需而且足夠啟動HIF-1α的。在這個區域的突變中，雙突變K130M/V131Z增強HBx對HIF-1α的活性，但遠端羧基端截斷和缺失突變削弱其功能。進一步研究發現，羧基端特別是119-140氨基酸對HBx的穩定和功能非常重要。肝癌標本中，我們也發現HBx和HIF-1α的表達呈正相關。因此，雖然不同的突變對於HBx的功能有不同的影響，但總的來說這些突變可以促進HIF-1α的表達和啟動，進而導致肝癌患者的預後不良。 / 靶向治療在肝癌綜合治療中扮演重要角色。索拉菲尼（Sorafenib）是一種多激酶抑制劑，臨床實驗發現它對晚期肝癌治療有效，但其抑制腫瘤血管生成機制還不完全清楚。我們研究發現Sorafenib明顯而且劑量依賴性地降低HIF-1α的表達和活化，進而抑制血管內皮生長因數（VEGF）的表達。Sorafenib抑制mTOR, ERK, p70S6K, RP-S6, eIF4E和4E-BP1等翻譯起始因數的磷酸化，從而抑制HIF-1α的合成而不影響其降解。體外實驗進一步發現Sorafenib降低HIF-1α和VEGF的表達，從而抑制腫瘤的血管形成和生長。總之，我們的研究表明sorafenib可能通過阻斷mTOR/p70S6K/4E-BP1 和 ERK 信號通路來抑制HIF-1α的合成，從而發揮其抗腫瘤血管生成作用。 / Chronic HBV infection is the leading cause of hepatocellular carcinoma (HCC) and HBx plays a crucial role in the molecular pathogenesis of HBV-related HCC. Previous investigations have indicated that some variations of HBV or mutations of HBx are associated with higher risk of HCC development, whereas the mutations profiles may be disparate in different regions. In the present studies, we thus aim to screen and identify the HBx mutation hotspots in 120 HCC tissues from Hong Kong, a region with HBV hyper-endemic. HBV DNAs were successfully isolated and amplified in 84.16% (101/120) HCC specimens via nest-PCR, and then subjected to gene sequencing. Three types of HBx mutations, including point mutations, distal carboxyl-terminal truncations and deletion mutations, were discovered. Among the point mutations, 39 mutation hotspots were indentified, with two double mutations (A1630G/G1721A and A1762T/G1764A) occurring in approximate 50% of 101 HCC cases. Distal C-terminal truncated mutations were discovered in 31.68% (32/101) of HCC cases, whereas deletion mutations were detected in 2.97% (3/101) of them. Overall, majority of identified mutations were located at the transactivation domain of HBx, suggesting the crucial roles of these mutations in HCC development. / Hypoxia-inducible factor-1α (HIF-1α) also closely involves in the development and progression of HCC. Wild-type HBx has been shown to activate HIF-1α. But the relationship between HBx mutants and activation of HIF-1α has not been fully elucidated. We here revealed that the transactivaiton domain of HBx was necessary and sufficient to activate HIF-1α. Double mutations K130M/V131Z in this domain enhanced the functionality of HBx in upregulating the expression and the activation of HIF-1α, whereas C-terminal truncations and deletion mutations weakened this prosperity of HBx. We further uncovered that the C-terminus, especially the region of amino acids 119-140, was essential for the stability and transactivation of HBx. The positive association between the HBx mutants and HIF-1α was found in the HCC tissue samples. Therefore, although mutations exerted different effects on the functionality of HBx, the overall activity of HBx mutants was suggested to upregulate HIF-1α, whose level is related to poor prognosis of HCC patients. / The therapy targeting a critical molecule in the development of HCC such as HIF-1α may be a potential and effective treatment regimen for HCC patients. Sorafenib, a multikinase inhibitor, has demonstrated promising results for the treatment of advanced HCC in clinical trials, but the mechanism that accounts for the anti-angiogenic efficiency of this agent has not been fully elucidated. We here revealed that sorafenib remarkably and dose-dependently decreased the expression and the transcriptional activity of HIF-1α, and its target gene, vascular endothelial grow factor (VEGF). Further analysis revealed that this reduction of HIF-1α by sorafenib was caused by the inhibition of HIF-1α protein synthesis rather than by the promotion of HIF-1α protein degradation. Moreover, the phosphorylated levels of mTOR, ERK, p70S6K, RP-S6, eIF4E and 4E-BP1 were significantly suppressed by sorafenib. In vivo studies further confirmed the inhibitory effect of sorafenib on the expression of HIF-1α and VEGF proteins, leading to a decrease of tumor vascularisation and growth. Collectively, our data suggest that sorafenib may exhibit anti-angiogenic activity by inhibiting HIF-1α synthesis, which is likely to be achieved through suppressing the phosphorylation of mTOR/p70S6K/4E-BP1 and ERK. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Liu, Liping. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 133-154). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Abstract --- p.I / 摘要 --- p.IV / Publications --- p.VI / Acknowledgements --- p.VII / Abbreviations --- p.IX / List of Figures --- p.XI / List of Tables --- p.XIII / Table of Contents --- p.XIV / Chapter Chapter I --- General Introduction --- p.1 / Chapter 1.1 --- Overview of Hepatocellular Carcinoma --- p.1 / Chapter 1.2 --- HBV Infection and HCC Development --- p.6 / Chapter 1.3 --- Overview on Hepatitis B virus X Protein --- p.10 / Chapter 1.4 --- Roles of Hypoxia-inducible Factors in HCC --- p.17 / Chapter 1.5 --- Targeted Therapies and Sorafenib --- p.27 / Chapter Chapter II --- Identification of HBx Mutation Hotspots in HCC Tissues --- p.31 / Chapter 2.1 --- Abstract --- p.31 / Chapter 2.2 --- Introduction --- p.32 / Chapter 2.3 --- Materials and Methods --- p.35 / Chapter 2.4 --- Results --- p.40 / Chapter 2.5 --- Discussion --- p.53 / Chapter Chapter III --- The Relationship between HBx Mutants and HIF-1α --- p.59 / Chapter 3.1 --- Abstract --- p.59 / Chapter 3.2 --- Introduction --- p.60 / Chapter 3.3 --- Materials and Methods --- p.63 / Chapter 3.4 --- Results --- p.70 / Chapter 3.5 --- Discussion --- p.91 / Chapter Chapter IV --- The Effects of Sorafenib on Hypoxia-inducible Factor-1α --- p.96 / Chapter 4.1 --- Abstract --- p.96 / Chapter 4.2 --- Introduction --- p.98 / Chapter 4.3 --- Materials and Methods --- p.101 / Chapter 4.4 --- Results --- p.108 / Chapter 4.5 --- Discussion --- p.124 / Chapter Chapter V --- Conclusion and Future Plans --- p.129 / Chapter 5.1 --- Conclusion --- p.129 / Chapter 5.2 --- Future Plans --- p.131 / References --- p.133
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_328259 |
| Date | January 2012 |
| Contributors | Liu, Liping, Chinese University of Hong Kong Graduate School. Division of Surgery. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography |
| Format | electronic resource, electronic resource, remote, 1 online resource (xv, 154 leaves) : ill. (some col.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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