硫氧还蛋白调控缺氧诱导因子-2α促进肝癌转移的机制研究

Metastasis and recurrence seriously affect the long-term prognosis of patients with hepatocellular carcinoma (HCC), while hypoxia is deeply involved in this malignant behavior. Our preliminary data showed that high expression level of HIF-2α predicted poor prognosis in HCC patients and highly metastatic potential in HCC cell lines. Metastasis-related protein, Thioredoxin (TXN) could protect highly metastatic HCC cells from DNA damage under hypoxia and increase tolerance for hypoxia. Knocking down the expression of TXN would down-regulate not only the expression of HIF-2α but the expression of its specific target gene. It has been proved that TXN can inhibit the degradation of HIF-1α through regulating its post-translational sumoylation and ubiquitination. However, whether and how TXN regulates HIF-2α is still unknown. The aim of this proposal is to determine the biological function of TXN and HIF-2α in HCC, and explore the regulating and post-translational modificating mechanisms. It will provide strong supports for novel methods in targeting therapy of HCC.

肝癌的转移复发严重影响肝癌远期疗效，缺氧与其关系密切。前期工作发现，缺氧诱导因子HIF-2α的高表达与肝癌患者的预后差及肝癌细胞的高转移潜能相关。转移相关分子硫氧还蛋白（TXN）有助于高转移肝癌细胞在缺氧环境中的DNA损伤修复，提高对缺氧的耐受能力；敲减TXN，不仅引起HIF-2α的表达下调，还可导致HIF-2α下游靶基因的表达下调。已证实，TXN可调节HIF-1α翻译后的SUMO化及泛素化，抑制其蛋白降解，维持HIF-1α的稳定性。TXN调控HIF-2α的作用机制尚不清楚。本课题拟在前期工作的基础上，深入研究TXN及HIF-2α对肝癌细胞生物学行为的影响，探索其可能的调控机制及翻译后修饰机制，为肝癌转移的分子靶向干预提供理论依据。

肝癌的转移复发严重影响肝癌远期疗效，前期研究表明，TXN及HIF-2α的高表达可能与肝癌细胞转移密切相关。TXN可调控HIF-1α的表达，主要与减少其降解有关，对HIF-2α存在调控作用，但机制尚不清楚。HIF-2α对肝癌细胞生物学行为的影响存在争议，如何维持其在肝癌细胞中的稳定性及活性则是问题的关键。我们利用已有的肝癌转移模型平台，深入研究HIF-2α在肝癌细胞转移过程中的作用及其调控机制。结果表明，TXN及HIF-2α不仅促进肝癌细胞增殖，还可通过HIF-2α-CDCP1-PKCδ通路介导，促进肝癌细胞运动侵袭；miR-182负向调控HIF-2α的表达，敲减或过表达TXN可改变miR-182及HIF-2α的表达，进而影响HIF-2α的下游分子CDCP1的表达。免疫共沉淀方法明确TXN与HIF-2α存在直接结合作用关系，通过抑制HIF-2α的降解，TXN可维持HIF-2α的稳定；TXN可通过SENP1调控 HIF-2α翻译后的SUMO化修饰，影响HIF-2α的降解，从而对HIF-2α的转录活性产生影响；TXN还可通过SENP1的SUMO化修饰调节影响SIRT1的去乙酰化酶活性，从而间接对HIF-2α的乙酰化及转录活性产生影响。本课题首次发现TXN/HIF-2α对肝癌细胞运动侵袭能力的影响，部分阐明TXN调控HIF-2α的翻译后修饰调节机制，进一步加深了对肝癌转移机制的认识。