DNA损伤应答相关蛋白Bclaf1在HIF1低氧应激系统中的作用

The hypoxia-inducible factor 1 (HIF1) is the master regulator of the cellular response to hypoxia, which have important physiological functions and are intimately related to tumor progression. The HIF1 system has a great potential as drug targets in anti-tumor therapies. However, how HIF1 is regulated in hypoxic condition is not well understood. Bclaf1 (Bcl2 associated transcription factor) is a protein that is involved in apoptosis, DNA damage response and tumorigenesis, and yet its exact function in tumorigenesis is no clear. We found in our preliminary studies that Bclaf1 was upregulated in response to hypoxic treatment in multiple cancer cell lines, and that knockdown of Bclaf1 greatly reduced the stability of HIF1 in hypoxic condition. We therefore speculate that the activity of HIF1 in hypoxic condition requires a positive feedback mechanism to maintain, in which Bclaf1 plays a critical role. In this proposal we plan to test this hypothesis aiming to elucidate the role of Bclaf1 in hypoxic response and the underlying mechanism. Specifically, we plan to investigate: 1) the mechanism that is responsible for Bclaf1 upregulation in hypoxic treatment; 2) the mechanism that induces HIF1 degradation in hypoxic condition and the role of Bclaf1 antagonizing this action; and 3) the role of Bclaf1 in cell and tumor growth and its relationship to HIF1. These studies will provide insights into HIF1 regulation and role of Bclaf1 in tumorigenesis.

HIF1介导的低氧应激体系，不仅具有重要的生理功能，而且该系统的失调在肿瘤的发展中起着重要作用，是肿瘤治疗中十分具有前景的靶系统，但HIF1的活性在低氧条件是如何受到有效调控的还不清楚。Bclaf1是一个和细胞凋亡、DNA损伤应答以及肿瘤发生密切相关的重要蛋白，但其在肿瘤发生中的具体作用也不清楚。我们前期的一些实验结果显示Bclaf1是一个表达受低氧调控的蛋白，而且有可能参与了低氧条件下HIF1稳定性调控。我们推测HIF1的稳定性在低氧条件需要一种正反馈机制来加以维持，而Bclaf1在该过程中起着关键作用。在本申请项目中我们拟深入研究Bclaf1在低氧应激中的作用和机制。具体研究内容包括：1）低氧刺激上调Bclaf1的分子机制；2）HIF1在低氧条件下的降解机制以及Bclaf1对该机制的拮抗作用；3）Bclaf1在细胞及肿瘤生长中的作用及与HIF1的关系。

HIF-1信号通路是低氧应答的重要通路，与肿瘤的发生发展密切相关。HIF-1alpha是HIF-1信号通路的关键调控因子，其稳定性受氧气浓度的调控。在低氧刺激下，HIF-1alpha稳定性提高，进而入核转录上调低氧应答的系列基因。HIF-1alpha的失调则和肿瘤的发生发展密切相关。在本基金的资助下，本研究发现了一个调控HIF-1信号通路的新因子Bclaf1，并解析了Bclaf1在HIF-1信号通路中发挥的具体作用和分子机制。Bclaf1在低氧刺激的多种细胞系中发生了转录上调，而且直接受HIF-1的转录调控。Bclaf1上调后将与入核的HIF-1alpha发生直接的相互结合，这种相互结合可以保护HIF-1alpha不受细胞降解机制的降解。在Bclaf1缺乏的细胞中，HIF-1alpha在低氧刺激下的稳定性不能持续维持，导致HIF-1诱导基因的的转录整体下降，从而导致了低氧应答通路的缺陷。这些研究表明HIF-1alpha与Bclaf1形成了一个正反馈环路，Bclaf1通过对低氧下HIF-1alpha稳定性的维持，对HIF-1信号通路进行了正调控。此外，课题还研究了Bclaf1在肿瘤生长中的作用，并在裸鼠肿瘤模型中证明Bclaf1在肿瘤生长中具一定的促进作用，而且在Bclaf1缺失的肿瘤组织中，HIF1信号通路受到抑制，表明Bclaf1的促肿瘤作用与其对HIF1信号通路的调控有一定的关联。项目按研究计划实施，实现了研究目标，揭示了低氧刺激上调Bclaf1及Bclaf1调控低氧应答通路的分子机制，对深入认识HIF-1信号通路的调控网络及揭示Bclaf1在肿瘤发生中的作用奠定了理论基础。在本基金的资助下，课题发表了SCI论文三篇，包括Oncogene（2020）、J Mol Cell Biol.（2020，封面文章）和gene（2020）各一篇。