缺氧环境下HMGB1通过诱导线粒体生物合成促进肝癌发病的机制研究

Mitophagy and mitochondrial biogenesis represent two opposing, but coordinated processes. The balance of mitochondrial biogenesis and mitophagy, response to physiological and pathological stressors, regulates the content, structure, and function of mitochondria within cells. Several studies have shown that HMGB1 plays an oncogene role in hepatocarcinogenesis. HMGB1 not only regulates the cell cycle, induces angiogenesis, but also removes disfunctional mitochondrial by activating mitophagy, to support continued proliferation. To date, the role of HMGB1 induces new mitochondria formation by activating mitochondrial biogenesis, maintain and restore mitochondrial homeostasis under stress microenvironment in carcinogenesis has been largely ignored. We found, during hypoxia, when cells were transfected with HMGB1 siRNA, hepatocellular carcinoma (HCC) cell line proliferation and mitochondrial biogenesis were inhibited. In vivo study, male hepatic HMGB1 conditional knockout mice (HMGB1 KO) and age- and sex-matched littermate controls were given a single intraperitoneal N-nitrosodiethylamine (DEN), a well-known hepatocarcinogen, injection and followed for 6-12 months for hepatic tumors. HMGB1 KO mice showed significantly decrease in susceptibility to DEN-induced tumorigenesis and mitochondrial biogenesis. While we now know that HMGB1 is important for mitochondrial biogenesis in hypoxia environment. We also want to determine its potential mechanisms, that is during hypoxia, HMGB1 regulates PGC -1α expression, protein localization or post-translational modifications, to result in the synthesis of both nDNA-encoded mitochondrial proteins and mitochondrial transcriptional regulators such as TFAM, which in turn functions to increase mitochondrial number, stabilize mtDNA, and promote the augmentation of mitochondrial respiratory capacity. To begin addressing these alternative hypotheses, we first detect the correlation between mitochondrial biogenesis and development, progress, prognosis of hepatocellular carcinoma tissues. Gain of function and loss of function strategy were applied to analysis the effect of HMGB1 on mitochondrial quality control in hypoxia microenvironment. Our study will provide a brand-new molecular mechanism to illustrate how HMGB1 regulates hepatocellular carcinoma growth, it will also be developed as potential new target for the therapy of HCC.

线粒体自噬和线粒体生物合成共同调节使细胞内线粒体保持数量、形态和功能的动态平衡。研究发现在肝癌发病中扮演癌基因角色的HMGB1除了调控细胞周期、促进肿瘤新生血管生产外，还通过诱导线粒体自噬清除功能受损线粒体。HMGB1能否同时激活粒体生物合成诱导新生线粒体形成，维持和恢复应激刺激下肝癌细胞的线粒体稳态却鲜有报道。我们发现缺氧环境下干扰HMGB1表达后，细胞增殖速度和线粒体生物合成受限；腹腔注射化学诱癌剂DEN后，肝脏敲除HMGB1小鼠的肝癌发生率和线粒体生物合成显著下降。本课题拟在上述研究基础上检测线粒体生物合成与肝癌发生、进展和预后的相关性；采用功能获得/缺失策略分析缺氧环境下HMGB1对细胞内线粒体质量控制的影响；从蛋白质互作及翻译后修饰角度研究HMGB1调控PGC-1α表达的可能机制，为阐明HMGB1如何调控肝癌生长提供一个新观点，并为寻找肿瘤治疗新靶点打下坚实基础。

线粒体自噬和线粒体生物合成两者协同调节使线粒体的数量、形态和功能保持动态平衡，以产生充足能量供细胞生命活动所需。在原发性肝细胞癌(HCC)发病中扮演癌基因角色的核蛋白HMGB1除了调控细胞周期和凋亡、诱导肿瘤新生血管形成外，还通过激活线粒体自噬清除功能受损线粒体。HMGB1能否激活粒体生物合成诱导新生线粒体形成，维持和恢复应激微环境刺激下肝癌细胞的线粒体稳态却鲜有报道。本课题拟通过检测线粒体生物合成与肝癌发生、进展和预后的相关性；采用功能获得/缺失策略分析缺氧环境下HMGB1对细胞内线粒体质量控制的影响；从蛋白质互作及翻译后修饰角度研究HMGB1调控线粒体生物合成关键分子PGC-1α表达的可能机制。结果：①缺氧的人HCC组织、细胞系中HMGB1和线粒体生物合成相关分子(PGC-1α、NRF1、TFAM)表达增加。②缺氧条件下HMGB1从胞核向胞浆易位并与胞浆中的Toll样受体(TLR)-9结合，导致p38激活及PGC-1α的磷酸化修饰和转录激活，从而促进线粒体生物合成。③缺氧肝癌细胞系中HMGB1的沉默抑制PGC-1α的活化和线粒体生物合成，最终导致ATP生成明显减少，细胞增殖变慢，凋亡增加。我们的研究表明：缺氧时HMGB1通过激活PGC-1α，促进线粒体生物合成，使肝癌细胞在低氧应激微环境中得以无限增殖、浸润和转移。上述研究为阐明HMGB1如何调控肝癌生长提供一个新颖的分子机制，并为寻找肝癌靶向治疗新途径打下坚实基础。