Speckle Cdk12信号调控P-TEFb应激活化的功能机制

Positive transcription elongation factor P-TEFb is a kinase composed of Cdk9 and its partner CyclinT1, and plays a central role in regulating the transition elongation of signal inducible genes. Its activity regulation consists of three steps: stress-induced release, activation and recruitment. Our previous reports have revealed the mechanisms of stress-induced P-TEFb release and recruitment. However, how the stress-induced P-TEFb activation is regulated still remains unclear. Our previous data suggest that the recruitment factors Brd4 and AFF might play a role in stress-induced P-TEFb activation, and this activation might be regulated by Speckle Cdk12 signaling. Therefore, we will study the molecular mechanism of recruitment factor-induced P-TEFb activation, and the role of Cdk12 signaling-controlled Speckle SRSF phosphorylation in stress-induced P-TEFb activation. We expect to reveal how and where the stress-induced P-TEFb activation is regulated inside the nuclear, thereby providing intact picture of P-TEFb activity regulation.

正性转录延伸因子P-TEFb由Cdk9激酶及其调节亚基CyclinT1组成，是调控应激性基因转录延伸的核心因子。P-TEFb活性调控过程包括应激释放、应激活化和应激募集等环节，我们的报道已基本阐明P-TEFb应激释放和应激募集的信号和分子调控机制，但对P-TEFb的应激活化调控机制仍不了解。我们的前期结果提示：“募集因子Brd4及AFF诱导P-TEFb应激活化”，以及“Cdk12信号调控P-TEFb应激活化”，可能是细胞内P-TEFb应激活化的两个核心模式。本项目拟通过阐明募集因子诱导P-TEFb应激活化的分子机制，探讨Cdk12调控Speckle核心组分SRSF蛋白磷酸化的机制、及其对募集因子诱导P-TEFb应激活化的调控作用和机制，从而解决P-TEFb应激活化的信号和分子调控机制，为完善P-TEFb活性调控模式提供依据。

真核细胞中基因转录调控存在两大限速调控平台：转录起始和转录延伸。在转录延伸早期RNA聚合酶II暂停在基因启动子区下游，生长、发育或者应激信号等会刺激细胞迅速重新启动转录延伸，从而调节胚胎发育和细胞应激反应等相关事件。P-TEFb作为调控延伸重启的核心因子，通过与多种正性或负性调控因子结合影响RNA聚合酶II的延伸活性。无转录活性的P-TEFb主要存在于核浆的7SK snRNP复合体中，有转录活性的P-TEFb与募集因子Brd4或SEC结合形成活化复合体并定位在染色质上。从无转录活性的7SK snRNP复合体向活化P-TEFb复合体（Brd4/P-TEFb或SEC/P-TEFb）转换决定了全局性基因转录的活性。在本项目中，我们已完成项目申请所计划的研究的内容。我们揭示了在应激和细胞周期进程中，磷酸酶PP1a作用于核浆7SK snRNP复合体，导致核心P-TEFb彻底解离成单体CyclinT1和T186去磷酸化的Cdk9；募集因子Brd4和SEC协助核心P-TEFb重新形成以及Cdk9-T186自磷酸化；随后，活化的Brd4/P-TEFb和SEC/P-TEFb复合体在染色质上激活全局性基因的转录延伸。同时，我们拓展研究了Brd4/P-TEFb在幽门螺杆菌感染及随后引发胃癌的潜在病理功能。