Abstract
AIMS
Glioblastoma (GBM) is the deadliest and most common primary brain tumour with median survival rates of less than two years. Inter- and intra-tumoral heterogeneity, cellular plasticity and de-regulated signalling pathways are plausible causes of resistance to existent therapies in GBM. As current therapies offer only limited survival benefits, the identification and validation of new approaches in glioblastoma management is of the highest importance
METHOD
• In silico analysis, RNA sequencing analysis after SPT6 depletion and analysis of R-loop formation after RAD52 depletion.
• Patient-Derived Xenografts and primary human glioblastoma cells
RESULTS
Our recent findings show significantly higher RAD52 mRNA levels in malignant gliomas compared to normal brain, where its levels negatively correlate with GBM patient survival. Experimental data show that the inhibition of RAD52 by 6-Hydroxy-DL-Dopa (6OH-Dopa) impairs GBM cell survival due to increased replication- transcription collisions leading to the accumulation of DNA damage. Transcriptional elongation factor SPT6 has previously been named an essential gene in GBM. We find that loss of SPT6 decreases the expression of HR proteins BRCA1, RAD51 and RAD52. RAD52 binds to single-strand DNA (ssDNA), plays a crucial role in most HR events, and restarts collapsed replication forks in response to oncogene-induced replication stress. Further investigation into the role of RAD52 showed depletion of RAD52 results in an increase of R-loops increasing genomic instability and DNA damage.
CONCLUSIONS
Based on our findings, we hypothesize that SPT6 modulates RAD52, which acts as a sensor of R-loops and plays a crucial role in R-loops’ resolution.