CycT1调控SEC复合体组装的分子机制和功能研究

转录延伸是指处于启动子近端暂停的PolII重新启动并合成全长转录本的过程。激酶CDK9和调节亚基CycT1组成的P-TEFb是调控转录延伸的核心因子，若出现失调会导致病毒侵染、肿瘤等疾病发生。过去的研究多侧重于阐明P-TEFb相关复合体的转换调控机制，但对P-TEFb自身，特别是CycT1的功能及作用机制缺乏深入了解。超级转录延伸复合体（SEC）含有活化态P-TEFb，我们的前期研究阐释了CycT1与SEC骨架蛋白AFF1/4相互作用的分子基础，并据此建立了靶向干预SEC复合体组装的敲入系统。同时，我们还发现CycT1及SEC复合体在化疗药物响应下的动态特性。拟进行的工作将深入探讨SEC复合体下游靶基因的调控机制，揭示CycT1及其动态修饰对SEC复合体组装和肿瘤恶化进程的影响。本项目的研究将有助于我们更好地理解CycT1在转录延伸调控中的全新功能，为开发新型疾病治疗策略提供科学依据。

Transcriptional elongation control refers to the process where RNA polymerase (Pol) II is transited from the promoter-proximal paused state into productive elongation mode, leading to the synthesis of full-length RNA transcripts. Consisting of CDK9 and CycT1, the positive transcription elongation factor b (P-TEFb) is the master regulator of transcription elongation by Pol II. Given its essential role, the malfunction of P-TEFb regulation has been demonstrated to contribute to a variety of diseases such as HIV and cancer. While previous studies mainly focus on the mechanism of P-TEFb equilibrium within its complex cellular network, the function of CycT1, the cyclin partner of CDK9, in elongation control is not well understood. Our preliminary data identified the critical interface that mediates the direct interaction between CycT1 and SEC scaffolding protein AFF1/4. Based on that, we developed a knock-in system to disrupt the assembly of SEC complex without knocking down any SEC subunits, therefore providing us a unique platform to dissect the function of SEC in disease settings such as cancer progression. Moreover, we found that chemotherapy drug treatment induced dynamic post-translational modification of CycT1, which potentially affects the SEC assembly. In this proposal, we aim to elucidate the mechanism by which CycT1 modulates the SEC complex formation and stimulates gene expression at the elongation stage. The successful outcome of this work will not only deepen our mechanistic understanding of transcription elongation control but also illuminate novel therapy strategy targeting CycT1 for cancer treatment.