TRAF7/AKT/β-catenin/TCF正反馈调控环路异常在胶质瘤发生发展中的作用及分子机制研究

Malignant gliomas are the most frequent primary brain tumors, which are highly recurrent and lethal malignant neoplasms. The abnormal expression and the ubiquitination modulation of TRAFs (tumor necrosis factor receptor-associated factors) protein family may be important post-translational regulators of gliomagenesis and malignant progression. Our previous work showed that TRAF7 expression was higher in gliomas than that in the control, and its expression was significantly increased with the elevation of glioma grades and was the highest in glioblastoma. Moreover, its expression was positively correlation with the proliferation index of Ki-67 expression. Endogenous TRAF7 knockdown with siRNAs could significantly suppress the G1/S-phase transition and cell proliferation and promote the apoptosis of glioblastoma cells. According to these results, we propose the hypothesis that there is an abnormal positive feedback loop of TRAF7/AKT/β-catenin/TCF crosstalk regulation in glioblastoma cells, which may promote the gliomagenesis and malignant progression. The following parts are the central idea of this project: ① clearing the effects of the expression level of TRAF7 on tumorigenesis of glioblastoma and assessing whether they can be used as potential evaluation index of grading and prognosis for malignant gliomas; ②conforming the molecular mechanisms of aberrant activation of AKT protein kinase in malignant gliomas and discussing the roles of aberrant up-regulation of TRAF7 in the regulatory process; ③revealing the roles of aberrant feedback loop of TRAF7/AKT/β-catenin/TCF pathway in the tumorigenesis and malignant progression of glioma. Through the research of this subject, we try to provide additional proof for the molecular mechanisms for tumorigenesis and malignant progression of glioma, and we also hope we could provide more theoretical evidence for developing new technology of the diagnosis and treatment for glioblastoma.

恶性胶质瘤是最常见的高致死性颅内原发性肿瘤，TRAFs家族蛋白表达及其泛素化调控异常与胶质瘤发生发展密切相关。我们前期研究发现胶质瘤普遍有TRAF7过表达且随肿瘤良恶性级别升高而增加；在胶质瘤细胞中TRAF7与AKT共定位，并通过激活AKT信号通路促进/抑制其增殖和凋亡。据此提出胶质瘤细胞存在TRAF7/AKT/β-catenin/TCF正反馈调控环路，该环路调控紊乱是导致胶质瘤发生发展重要分子机制的研究假说。本项目拟解决的关键科学问题是：①明确胶质瘤TRAF7表达水平与其分级和发生发展的关系及对评估肿瘤生物学行为和患者预后的实用价值；②了解胶质瘤细胞TRAF7过表达对AKT泛素化激活的影响及在胶质瘤发生发展的作用；③确定TRAF7/AKT/β-catenin/TCF正反馈调控环路异常在胶质瘤发生发展的作用及其分子机制。旨在为阐明胶质瘤发病机制提供新线索，为研发诊疗新技术提供客观参考依据。

肿瘤的发生发展常伴随蛋白质异常泛素化修饰，尤其是E3泛素连接酶的失调在胶质瘤的发病机制中起着至关重要的作用。肿瘤坏死因子受体相关因子7（TRAF7）是一类具有E3 泛素连接酶活性的细胞内接头分子，迄今为止，其与胶质瘤发生发展的关系尚无报道。通过本项目研究，我们发现TRAF7在胶质瘤中高表达，其表达水平随胶质瘤良恶性级别升高而相应升高，其高表达与胶质瘤患者预后不良显著相关，可作为评价胶质瘤良恶性级别及患者预后的重要参考指标。机制上，TRAF7通过与AKT相互作用促进AKT的K63形式泛素化修饰，增加AKT蛋白的细胞膜富集和激酶活性，进而通过AKT/β-catenin/ORAI1途径影响细胞内钙离子水平和线粒体功能，从而促进胶质瘤细胞增殖；TRAF7还通过AKT/LIMK/Cofilin通路影响胶质瘤细胞侵袭能力，并诱导细胞骨架重排，最终促进胶质瘤的发生发展。上述研究揭示了TRAF7是胶质瘤发生发展的重要促瘤因子，其通过调控AKT的K63形式泛素化修饰，增强p-AKT的细胞膜富集和激酶活性，促进胶质瘤的发生发展，可作为潜在的恶性胶质瘤治疗的特异性靶点，为研发恶性胶质瘤诊疗新技术提供客观的实验依据。