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。PP2A在ras突变型癌症中经常失活，要么通过PP2A亚基突变，要么通过PP2A内源性抑制剂的过表达。永生化细胞的恶性转化需要PP2A失活和RAS信号的过度激活。然而，目前尚不清楚哪些细胞途径受到PP2A失活的影响。RAS突变促进转录失调和转录过程中形成的r环、RNA/DNA杂交的积累，导致复制应激和基因组不稳定。有趣的是，PP2A的活性也调节转录和r环。我们将探讨PP2A失活是否会失调转录和r环，从而促进和/或增加ras突变癌细胞的复制应激和基因组不稳定性。为了实现这一目标，我们将使用PROTAC靶向降解方法快速降解PP2A复合物的亚基，以灭活或重新激活PP2A活性。我们将把这种PROTAC方法与尖端的基因组学和蛋白质组学以及DNA复制、复制应激和基因组不稳定性分析相结合，以了解PP2A的主要功能以及PP2A失活在ras突变癌症中的后果。该项目将提供PP2A再激活与PROTACs作为治疗ras突变癌症的潜在策略的重要数据。

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.