Dock180结合蛋白TRAF6调节神经胶质瘤生长与侵袭的分子机制

A hallmark of human glioblastomas is that oncogenic signalings stimulated by overexpressed genes such as PDGFRa is aberrantly active, rendering these tumors highly malignant, and inherently resistant to combination therapies, resulting in an extremely poor prognosis of patients with malignant gliomas. However, a major barrier of this challenge is the lack of a complete understanding of the mechanisms underlying the aggressiveness of these tumors and ineffectiveness of therapies for gliomas. Exploring these mechanisms would further reduce the replase rate and improve prognosis of patients. The applicant had ever found that Dock180 is a downstream effector of PDGFRa signal in USA.To further explore the roles of Dock180 in gliomagenesis, TRAF6 is found as a new Dock180-binding protein by proteomic method, and their association is increased by PDGF-A stimulation. Moreover, knockdown of TRAF6 markedly inhibits the glioma cell proliferation and invasion stimulated by PDGFRa signal. Based on these observations, in this project, we will use in vitro and in vivo animal models and human clinical samples to elucidate the functions and mechanisms by which TRAF6 augments PDGFRa-stimulated glioma tumorigenesis and the relative of the expression of TRAF6 and PDGFRa with clinical patient prognosis. We also will explore the impact of TRAF6 on glioma stem cell self renewal and the efficacies of chemotherapeutic agents on PDGFRa-expressing glioblastomas. Elucidation of this novel mechanism holds promise to a better understanding of the oncogenic signaling promoted glioma tumorigenesis and to overcome the insidious glioma resistance to current therapies. This project also addresses an urgent challenge in neuro-oncology and offers an enormous potential for developing novel therapies that could prove effective, thus eliminating the major barrier in treating patients with malignant glioblastomas.

恶性胶质瘤是中枢神经系统最常见的脑瘤，因其恶性程度高、侵袭性强，至今缺乏有效的治疗手段。尽管目前研究发现PDGFRa过表达是其主要特征之一，但分子机制尚不清楚。深入研究PDGFRa信号通路调节胶质瘤生长与侵袭的分子机制，对筛选新的恶性胶质瘤治疗靶点、提高治疗效率意义重大。申请人曾在国外研究发现Dock180是PDGFRa信号下游的重要信号分子。通过免疫共沉淀联质谱发现泛素化连接酶TRAF6是Dock180新结合蛋白，并且其结合受PDGFRa信号调节；敲除TRAF6可以抑制由PDGFRa调节的胶质瘤生长与侵袭。本课题将在此基础上，利用体外实验和体内动物模型及临床标本，进一步揭示TRAF6对PDGFRa调节胶质瘤生长与侵袭的作用及分子机制，探究其作为新的肿瘤治疗靶点的潜能；并探讨TRAF6对胶质瘤干细胞的干性维持及其对化疗药敏感性的影响，探索以抑制TRAF6信号为靶点的联合化疗治疗新策略。

脑肿瘤是全球十大恶性肿瘤之一，而其中胶质瘤患者生存期更差。表皮生长因子EGFR和血小板生长因子受体PDGFRA是驱动胶质瘤恶性增殖和弥漫性侵袭的主要信号通路，深入揭示其调控增殖及侵袭的分子机制，对临床治疗显得极为重要和迫切。..通过本项目的研究，取得如下成果：1）我们不仅揭示肿瘤坏死因子受体相关因子TRAF6与类似血管再生因子家族蛋白-DCBLD2 膜受体结合，参与表皮生长因子EGFR/AKT信号调控的胶质瘤发生发展，而且参与调节肿瘤干细胞的增殖。相关的研究成果发表在国际一流医学转化杂志Journal Clinical Investigation (2014,IF 13.2)； 2）在先前揭示鸟核苷酸交换因子Dock180/Rac1参与调节胶质瘤侵袭的基础上，我们进一步揭示Dock80-S1250位点能被PKA磷酸化，该位点的磷酸化增强Rac1的活性，从而促进EGFR和PDGFRA驱动的胶质瘤的侵袭{Oncogene(2014,IF 8.5)和Neuro-Oncology(2015,IF 7.4)}；3) 上皮间质转化（EMT）在调控肿瘤转移和肿瘤干细胞干性维持中具有非常重要的作用。我们的研究发现PDGFRA调控胶质瘤间质转化和肿瘤干细胞干性的新的信号通路-miR-200-ZEB1，揭示胶质瘤细胞的侵袭和胶质瘤干细胞干性维持与EMT相关{Oncogene(2016,IF 7.9)}；4）以往研究表明表观遗传学修饰如组蛋白乙酰化，在发育和肿瘤中具有重要的作用。本研究发现EGFR及其胶质瘤中常见突变体EGFRvⅢ的激活特异上调组蛋白H3K23乙酰化，招募三基序家族蛋白TRIM24与染色质结合。而TRIM24作为转录因子共激活子，通过其N端结构域与细胞核STAT3结合，稳定并激活STAT3转录活性，增强STAT3下游通路的活化，导致胶质瘤的恶性增殖{Nature Communications （2017，IF 12.1）和Cancer Res 2017（2017，IF 9.1）}。..总之，我们做出了世界前列的研究成果，揭示了新的胶质瘤恶性增殖和弥漫性侵袭的分子机制，发现多个新的有益于临床预后分析的分子标记物和靶向治疗靶点。这将极大促进临床研究和治疗。