Sp1协同GABPA激活突变TERT启动子的机制研究及其相应的治疗策略

Two cancer-specific somatic mutations (C228T and C250T) in the TERT promoter(TERTp) have been found in different types of cancer such as melanoma, glioblastoma, hepatocellular carcinoma, urothelial bladder carcinoma and thyroid carcinoma. These mutations can upregulate TERT expression through creatinga novel ETS transcription factor binding motif (such as GABPA), contributing to tumorigenesis. Although a previous study has reported that these mutations reactivate TERT expression through long-range chromatin interactions via transcription factor GABPA, the molecular mechanisms remain largely unclear.Our preliminary datashowed thatGABPA was significantly upregulated in glioma tissues compared to normal brain tissues. Knocking down GABPA expression in TERTp mutated cell linessignificantly inhibited cell proliferation. In addition, we also demonstrated thatGABPA recruited phosphorylated ERK onto TERTp to promoteSp1 phosphorylation, thereby resulting in enrichment of active histone marks on these promoters. Subsequently, phosphorylated Sp1 further recruitedGABPAonto TERTp. Based on these findings, in this project, we attempt to explore the molecular mechanism underlying TERT activation through chromatin remodeling via TERTp mutations, and screen small molecular inhibitors specifically targeting TERTp mutations through CADD (computer aided drug design) strategy. Our findings will provide a potential therapeutic strategy for tumors carrying these mutations.

多种恶性肿瘤中均证实存在高频率的TERT启动子突变，该突变可产生新的ETS转录因子结合位点（如GABPA），进而上调TERT的表达、促进肿瘤的进展。尽管先前已有研究证实，GABPA可介导长距离的染色体相互作用，激活TERT表达，但仍有许多机制尚不明确。我们前期的研究发现，GABPA在胶质瘤患者中表达上调，敲减GABPA可显著降低肿瘤细胞的增殖能力。此外，我们还证实GABPA可介导磷酸化的ERK特异性结合到TERT启动子区，并磷酸化Sp1，进而引起染色质重塑；同时，磷酸化Sp1进一步促进GABPA在TERT启动子区富集。本项目拟在前期工作的基础上，深入研究TERT启动子突变通过引起染色质重塑，上调TERT表达的分子机制，并利用CADD（computer aided drug design）技术在小分子库中筛选针对TERT启动子突变的小分子化合物，为携带该突变的肿瘤提供新的治疗策略。

多种恶性肿瘤中均证实存在高频率的TERT启动子突变，该突变可产生新的ETS转录因子结合位点（如GABPA），进而上调TERT的表达促进肿瘤的进展。尽管先前已有研究证实GABPA可介导长距离的染色体相互作用激活TERT表达，但仍有许多机制尚不明确。我们的前期研究发现GABPA在胶质瘤患者中表达上调，敲减GABPA可显著降低肿瘤细胞的增殖能力。此外，我们还证实GABPA可介导磷酸化的ERK特异性结合到TERT启动子区，并磷酸化Sp1，进而引起染色质重塑；同时，磷酸化Sp1进一步促进GABPA在TERT启动子区富集。本项目深入研究了TERT启动子突变通过引起染色体重塑上调TERT表达的分子机制。我们发现，转录因子GABPA特异性结合到突变的启动子区后，可确切招募ERK，并启动表观遗传激活。pERK可进一步促进GABPA在TERT启动子区的结合能力，形成了一个正反馈环路；Sp1可能介导了pERK对GABPA结合能力的调控。Sp1磷酸化会导致Sp1与GABPA的结合能力增强，HDAC1的空间位阻作用减低了GBAPA与Sp1之间的作用。Sp1磷酸化对GABPA结合能力与TERT基因的激活至关重要。Sp1与GABPA可以协同激活TERT启动子突变。总之，我们的工作证明了，对肿瘤（尤其是BRAFV600E驱动的恶性肿瘤），TERT启动子突变对这一类肿瘤的发生与进展有重要影响，GABPA与Sp1是可以协同激活TERT启动子突变的；我们证实，的确存在这样一种直接的机制，该机制可以较好地阐明BRAFV600E、TERT启动子突变这样两个原癌基因的改变，会如何发生关联。我们的工作有望为为携带该突变的肿瘤提供新的治疗策略。

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