Does inactivation of protein phosphatase PP2A contribute to genomic instability in RAS-mutant cancers?

蛋白磷酸酶PP2A是参与细胞周期、代谢、DNA复制和转录等多种细胞途径的主要酶。在RAS突变的癌症中，PP2A经常被失活，要么是通过PP2A亚单位的突变，要么是通过PP2A内源性抑制物的过度表达。PP2A失活和RAS信号过度激活是永生化细胞恶性转化所必需的。然而，目前还不清楚PP2A失活会影响哪些细胞通路。RAS突变促进转录失调和转录过程中形成的R-环、RNA/DNA杂交体的积累，导致复制压力和基因组不稳定。有趣的是，PP2A活性也调节转录和R-环。我们将讨论PP2A失活是否会扰乱转录和R-环，从而促进和/或增加RAS突变癌细胞的复制压力和基因组不稳定性。为了实现这一目标，我们将使用PROTAC靶向降解方法来快速降解PP2A复合体的亚基，以灭活或重新激活PP2A活性。我们将把这种PROTAC方法与前沿基因组学和蛋白质组学以及DNA复制、复制压力和基因组不稳定性的分析结合起来，以了解PP2A的主要功能和Ras突变癌症中PP2A失活的后果。该项目将为用PROTAC重新激活PP2A作为治疗RAS突变癌症的潜在策略提供重要数据。

Protein phosphatase PP2A is a major enzyme involved in different cellular pathways, including cell cycle, metabolism, DNA replication, and transcription. PP2A is frequently inactivated in RAS-mutant cancers, either via mutations in PP2A subunits or by overexpression of PP2A endogenous inhibitors. PP2A inactivation and hyperactivation of RAS signalling are required for malignant transformation of immortalized cells. However, it remains unclear which cellular pathways are affected by PP2A inactivation. RAS mutations promote transcriptional dysregulation and accumulation of R-loops, RNA/DNA hybrids formed during transcription, resulting in replication stress and genomic instability. Interestingly, PP2A activity also regulates transcription and R-loops. We will address whether PP2A inactivation dysregulates transcription and R-loops and thus promotes and/or increases replication stress and genomic instability in RAS-mutant cancer cells. To accomplish this, we will use a PROTAC targeted degradation approach to quickly degrade subunits of PP2A complexes to inactivate or reactivate PP2A activity. We will couple this PROTAC approach with cutting-edge genomics and proteomics and analysis of DNA replication, replication stress, and genomic instability to understand the primary functions of PP2A and the consequences of PP2A inactivation in RAS-mutant cancers. This project will provide important data on PP2A reactivation with PROTACs as a potential strategy to treat RAS-mutant cancers.