端粒酶催化亚基 hTERT调控VEGF的分子机制及生物学意义

Telomerase plays a pivotal role in aging and cancer by maintaining genome integrity, controlling cell proliferation and regulating tissue homeostasis. However, accumulating evidence indicates that telomerase reverse transcriptase exerts fundamental biological functions independent of its enzymatic activity in telomere maintenance. The molecular mechanisms of the functions of TERT beyond telomeres are poorly understood. Sp1 is the first discovered and cloned transcription factor, and it plays important roles in maintaining normal body development as well as physiological functions. By regulating target gene transcription, Sp1 influences tumor growth, invasion, angiogenesis, etc. We recently found that hTERT can interact with Sp1 and strengthen its activity of transcription, leading to elevated VEGF expression and thus enhanced tube formation ability of human umbilical vein endothelial cell (HUVEC). This project aims to systematically investigate the molecular mechanism and biological significance of the VEGF gene transcription by hTERT through its interaction with Sp1 at the biochemical, molecular and cellular levels, to further confirm in TERT-/- mice model. This project will advance our understanding on the biological function and the role in angiogenesis and tumorigenesis mechanism of telomerase. This may provide theoretical basis for discovering the new potential drug targets for cardiovascular diseases, cancer, and other related diseases, as well as the drug development.

端粒酶与细胞增殖、衰老及癌变密切相关。近年来研究发现端粒酶催化亚基hTERT在肿瘤发生、基因转录及基因组稳定性等方面具有独立于端粒之外的重要生物学功能，目前这些新功能的分子机制尚未阐明。核转录因子Sp1是最早被发现和克隆的转录因子，对维持机体正常发育及生理活动起重要作用，并通过调控下游基因转录参与调节肿瘤生长、侵袭及血管生成等多种生物学行为。我们的前期工作发现：hTERT调控血管内皮生长因子VEGF基因转录依赖转录因子Sp1；hTERT能够与Sp1相互作用并增强 Sp1转录因子活性；在内皮细胞HUVEC中过表达hTERT，能够上调VEGF表达并促进HUVEC形成管腔结构。本项目拟从生化、细胞及动物水平上系统地研究hTERT与Sp1相互作用调控VEGF基因转录的分子机制及其生物学意义，为进一步揭示端粒酶新的生物学功能及其在血管新生及肿瘤发生中的作用机制提供新的线索与思路。

血管生成被认为是癌症发生发展的一个重要标志。虽然端粒酶已经被证明参与了肿瘤血管生成的过程，但其潜在的证据及分子机制并没有被阐述清楚。在本项目中，我们用一系列严谨的分子水平、细胞水平、基因敲除动物模型及人体样本实验证明了：端粒酶逆转录酶催化亚基（hTERT）可以通过与转录因子Sp1的相互作用，共同结合血管内皮生长因子（VEGF）启动子，从而激活血管内皮生长因子（VEGF）基因的表达；hTERT在体内和体外都能够与Sp1相互作用，促进血管生成，这种调控在某种程度上依赖Sp1转录因子；利用TERT基因敲除小鼠成瘤模型试验，我们证明了TERT基因缺失可以明显抑制肿瘤的生长，抑制肿瘤中VEGF的表达；此外，我们还收集了多例人的胃癌样本，检测发现TERT基因的表达水平与血管内皮生长因子VEGF及标记物CD31基因的表达水平呈正相关。综上，我们的研究结果阐明了端粒酶催化亚基hTERT可以通过直接与Sp1转录因子相互作用上调VEGF的表达从而促进肿瘤血管生成。这些研究结果为我们理解hTERT独立于端粒之外，在肿瘤血管生成和肿瘤发育中所起的生物学功能提供了理论依据；为治疗端粒酶所调控的人类肿瘤提供了非常重要的见解和策略。