Kermi, C. | Search bioRxiv

bioRxiv2025

KDM5 demethylases suppress R-loop-mediated viral mimicry and DNA damage in breast cancer cells

Tumors with low expression of Interferon-Stimulated Genes (ISG) and Antigen Presentation (AP) genes respond relatively poorly to current immunotherapies. One of the early hallmarks of cancer is DNA hypomethylation in genomic repeat regions, resulting in the expression of normally silenced endogenous "viral" elements. Such epigenetic changes have the potential to augment anti-tumor immune responses as well as reduce tumor cell fitness through the generation of aberrant nucleic acid species (NAS) and consequent activation of NAS-sensing pathways. Therefore, tumor evolution should favor additional selective events that suppress NAS generation, possibly yielding specific therapeutic vulnerabilities. Here, we show that the Lysine Demethylase 5 (KDM5) family of epigenetic regulatory enzymes suppress R-loop formation in genomic repeat regions in cancer cells. We find that KDM5 inhibition in luminal breast cancer cells results in R-loop-mediated DNA damage, reduced cell fitness and an increase in ISG and AP signatures as well as cell surface Major Histocompatibility Complex (MHC) class I, mediated by RNA:DNA hybrid activation of the CGAS/STING pathway. KDM5 inhibition does not result in DNA damage or activation of the CGAS/STING pathway in normal breast epithelial cells, suggesting that KDM5 inhibitors may enable a wide therapeutic window in this setting, as compared to STING agonists or Type I Interferons. These findings provide new insights into the interplay between epigenetic regulation of genomic repeats, R-loop formation, innate immunity, and cell fitness in the context of cancer evolution and therapeutic vulnerability.

cancer biology↗

bioRxiv2024

A non-catalytic function for Rad18 in sustaining glioblastoma proliferation

The Rad18 E3 ubiquitin ligase, a non-essential gene, is a key regulator of DNA damage tolerance that also functions in repair of DNA double strand breaks. Rad18 is overexpressed in the aggressive brain cancer glioblastoma (GBM) and its downregulation sensitizes glioblastoma cells to DNA damaging agents. Here we show that Rad18 has an essential role in GBM cells proliferation in the absence of external damage, surprisingly independent of its catalytic activity. Rad18 downregulation leads to cell cycle arrest in the G1 phase in the absence of apparent DNA damage. We also show that Rad18 sustains GBM stem cells self-renewal and survival, as well as the growth of tumor orthotropic xenografts in mice. We also show that increased Rad18 expression enhances the growth of non-transformed cells and induces features of oncogenic transformation. Mechanistically, we show that Rad18 downregulation negatively regulates the Hippo pathway by interfering with the nuclear retention of the YAP1 transcription factor. Altogether, these data show that Rad18 has an essential, non-catalytic function, in GBM proliferation, and propose Rad18 as a key target to sensitize GBM to therapy.

cancer biology↗