TAZ/TEAD4-SOX2调控轴参与口腔鳞癌肿瘤干细胞干性维持的机制研究

Stemness maintenance of cancer stem cell (CSC) represents a key biological event underlying oral squamous cell carcinoma initiation and progression, which is intricately associated with tumor recurrence, metastasis and therapeutic resistance. However, the molecular mechanism underlying oral CSCs stemness remained incompletely defined. Our previous studies have established that TAZ (transcriptional coactivator with PDZ-binding motif) is a novel regulator involved in the stemness maintenance of oral CSCs；SOX2 is identified as the putative downstream target of TAZ by transcriptional profiling assay. Our preliminary experiments and bioinformatics analyses have revealed the initial results as follows: the stemness factor SOX2 (Sry related HMG box-2) was significantly enriched in oral CSC subpopulation; its knockdown resulted in significantly less tumorsphere and lower CSC ratio; TAZ combined with TEAD4 to form a complex which in turn bind to the promoter region of SOX2 and facilitated its transcription. In the present study, we aim to identify the regulatory mechanisms underlying oral CSCs stemness by focusing on TAZ/TEAD4-SOX2 axis. A series of in vitro and in vivo experiments including gene overexpression knockdown, rescue experiment, animal models and clinical samples by ChIP, luciferase report assays are scheduled to unravel the regulatory mechanisms mediated by TAZ/TEAD4-SOX2 axis driving oral CSCs stemness maintenance. Taken together, these findings might provide the novel therapeutic target by eradicating CSCs for oral cancer treatment.

肿瘤干细胞（cancer stem cell, CSC）干性维持是口腔鳞癌发生发展过程中的核心生物学事件，与肿瘤复发、转移等密切相关。我们前期研究发现：TAZ是参与口腔鳞癌CSC干性维持新的关键分子；SOX2是通过转录组芯片技术筛选获得的、受TAZ调控的候选靶基因。预实验和生物信息学研究提示：SOX2在口腔鳞癌CSC亚群中富集表达, 其沉默明显抑制体外肿瘤球形成，降低CSC亚群比例；TAZ和TEAD4结合形成复合体后，可能通过与SOX2基因启动子区发生结合后激活其转录表达。本课题拟以口腔鳞癌CSC干性维持为切入点，以TAZ/TEAD4-SOX2调控轴为研究对象，采取过表达、沉默、挽救实验、动物模型构建以及临床标本检测等策略，应用ChIP、荧光素酶报告等技术进行研究，旨在阐明TAZ/TEAD4-SOX2调控轴在口腔鳞癌CSC干性维持过程中的作用和机制，为研发口腔鳞癌新型治疗策略提供潜在靶标。

Hippo-TAZ通路已成为肿瘤干细胞（CSCs）干性调控的基本信号通路，与头颈部鳞状细胞癌（HNSCC）的局部复发和转移密切相关。但是，TAZ调控HNSCC CSCs干性维持的分子机制仍不清楚。前期预实验确定SOX2可能是TAZ调控的下游靶标。本研究证实TAZ调控SOX2表达参与HNSCC CSCs干性维持及致癌作用。流式细胞分选法表明TAZ和SOX2在以CD44+CD133+标记双阳性的Cal27和Fadu细胞亚群中富集表达。通过基因沉默实验显著降低了SOX2在细胞中mRNA和蛋白质的表达水平，而其异位过表达实验显著增加了其在HNSCC细胞中的丰度。SOX2的过表达可以逆转因TAZ表达沉默所导致的肿瘤成球能力及致瘤能力的降低。具体机制方面，研究证实TAZ主要通过与TEAD4形成的转录复合物后被募集到SOX2启动子区中的至少两个结合位点上，进而直接转录激活HNSCC细胞中SOX2的表达。通过HNSCC临床样本检测发现，TAZ和SOX2的在肿瘤组织中均呈显著高表达且两者表达水平呈显著正相关，且高表达的TAZ和SOX2与患者不良生存预后密切相关。综上所述，我们的数据揭示了TAZ和SOX2之间的内在联系，证实SOX2是TAZ调控HNSCC CSCs干性维持过程下游靶基因，发挥了调节HNSCC中CSC的自我更新和干性维持的作用。这些发现表明针对TAZ/TEAD4-SOX2轴可能是HNSCC的一种新型有效的靶向治疗靶点。