牙缺失相关基因PAX9通过WNT信号通路调节口腔鳞状细胞癌的发生

Oral squamous cell carcinoma (OSCC) is a major subtype of oral cancer, accounting for approximately 90% of all oral cancer cases. Despite the progression in diagnosis and treatment of OSCC over the last three decades, it has a poor prognosis and remains one of the top ten cancers worldwide. In our attempt to identify key oncogenic regulator of OSCC, we focused on the transcriptional factors with a determining role during odontogenesis PAX9 (Paired box gene 9) is a master transcriptional factor in the establishment of the inductive capacity of the tooth mesenchyme, and in Pax9-deficient mice, embryos tooth development is arrested at the bud stage. In accordance, identification of new mutations in this gene has been recurrent theme in epidemiologic study of hypodontia. Interestingly, with a meta-analysis of PAX9 expression in various cancers, we found significant down-regulation of PAX9 in head and neck carcinomas compared with the normal tissue. Importantly, overexpression of PAX9 in human tongue squamous cell carcinoma (TSCC) cells inhibited cancer cell proliferation and growth. Pilot affinity purification and mass spectrometry revealed the composition of PAX9 associated repressive complex, and pinpoints the potential implication of WNT signaling pathway in PAX9-mediated transrepression. In support of the physical interaction of critical components of WNT pathway including TLEs (transducin-like enhancer of split) and beta-catenin with PAX9, transcriptional readout experiments suggest that PAX9 suppresses WNT-induced activation of TOPFLASH reporter and endogenous CCND1 promoter. Indeed, identification of SIRT1 deacetylatse and HDAC6 in PAX9 complex implied such trans-repression depends on epigenetic regulation on histone tails. Given by the critical function of WNT in a wide range of tumors, we believe this study would benefit our understanding on the molecular basis for oral cancer and elucidation of the role of PAX9 co-repression complex would provide new pharmacological targets in the therapy of OSCC.

口腔鳞状细胞癌是常见的头颈部恶性肿瘤，它具有恶性度高、易转移、预后差等特点。探索参与其发生与发展的关键基因是相应分子肿瘤学研究的重要内容。成对盒基因9（paired box gene9，PAX9）是哺乳动物牙齿发育过程中的一个主导转录因子，它的突变会导致非综合征型的牙齿缺失。通过对肿瘤表达谱数据库的分析，我们发现PAX9在头颈部肿瘤中的表达水平明显低于癌旁正常组织，同时实验表明在舌鳞癌细胞系中过表达PAX9会抑制细胞的增殖。通过蛋白质组学和质谱测序，我们分离鉴定了PAX9蛋白复合体，其组成包括beta-catenin和TLE类抑制子，提示它可能通过调节WNT信号通路来影响口腔鳞癌的发生。的确PAX9能够显著抑制WNT激活的TOPFLASH和细胞周期蛋白CCND1的启动子报告基因。本项目旨在探讨PAX9在口腔鳞癌发生中的作用及其中的分子机制，进而为口腔鳞状细胞癌的诊断和治疗提供新的分子靶点。

本项目立足于口腔肿瘤仍是世界范围内高发的肿瘤之一，着重探讨牙缺失相关基因PAX9在口腔鳞状细胞癌发生和发展过程中的作用及其分子机制。主要研究内容包括PAX9在正常口腔黏膜与口腔鳞癌组织及细胞水平上的表达差异，人为控制PAX9基因表达时对口腔鳞癌细胞生长增殖的影响，PAX9的相互作用蛋白鉴定及验证，PAX9对于WNT信号通路的调节机制探讨及其在口腔鳞癌发生中的作用机制。我们发现PAX9能够与beta-catenin等蛋白相互作用，且通过调节WNT信号通路来调节口腔鳞癌细胞的生长。这些数据为口腔鳞癌的发生发展分子机制提供了新颖的线索和视角，并为其临床治疗提供了新的分子靶点。项目研究过程中对研究内容进行了一定拓展，探讨了组蛋白去乙酰化酶HDAC6在牙周膜干细胞衰老中的作用，以及葡萄糖转运蛋白GLUT1在正畸牙齿移动中的作用，并发表了两篇SCI论文。这些结果将丰富我们对于表观遗传学在口腔相关疾病发生发展中的作用的认识，并为相关疾病的临床治疗提供理论和实验基础。