Tang, C. H. M. | Search bioRxiv

bioRxiv2026

PI3K-AKT activation determines oncogenic RAS-induced hypertranscription and replication stress

Hypertranscription and transcription-replication conflicts (TRCs) are frequent features of cancer cells. RAS oncogenes promote hypertranscription to allow cell growth and proliferation, which can the lead to TRCs. Here, we report that hyperactivation of the PI3K-AKT signalling pathway is required for TRCs induced by RAS oncogenes. Oncogenic HRAS causes more TRCs than oncogenic KRAS or BRAF, because HRAS hyperactivates PI3K. PI3K hyperactivation is associated with in glycogen synthase kinase-3{beta} (GSK3{beta}) inhibition, increased E2F and MYC transcription programmes, increased nascent transcription of ribosome biogenesis genes and small nucleolar RNAs (snoRNA) expression. Small molecule inhibition of PI3K signalling prevents RAS-induced replication stress, and small molecule PI3K activation promotes replication stress. RAS-induced TRCs require a cooperation of MAPK and Pi3K signalling, S phase entry and hypertranscription. Our findings suggest a mechanistic explanation for replication stress variability between RAS activation models and identify PI3K pathway activation as a potential new determinant of TRCs in cancer.

cancer biology↗

bioRxiv2024

Human RNase H2 upregulation counteracts oncogene- and chemotherapy-induced replication stress

RNase H2 is a heterotrimeric endoribonuclease that resolves RNA:DNA hybrids and genome-embedded ribonucleotides, which are implicated in DNA replication stress and cancer development. Protein and/or mRNA levels of individual RNase H2 subunits are elevated in some cancers, but little is known about the mechanisms or consequences of RNase H2 upregulation. We report that RNase H2 subunits are upregulated at the protein level in response to replication stress induced by oncogenes and chemotherapy drugs in human cancer and non-cancer cell lines. We show that inducible overexpression of the RNASEH2B subunit increases levels of the active RNase H2 heterotrimer. While causing only subtle changes to gene expression, RNASEH2B overexpression is unexpectedly associated with increased RNA:DNA hybrid levels. RNASEH2B overexpression prevents further increases in RNA:DNA hybrid levels by camptothecin or hydroxyurea and reduces replication fork stalling in presence of these drugs. Surprisingly, RNase H2 levels do not strongly impact survival of chemotherapy treatments but appear to have more subtle effects on genome instability and innate immune signalling. In contrast, increased RNase H2 levels in presence of oncogenic HRAS limit not only RAS-induced replication fork stalling but also cell death. Our findings shed new light on the functions of RNase H2 and suggest that upregulation of RNase H2 may be an important aspect of replication stress responses in cancer.

molecular biology↗