Biology subjects

Fajka-Boja, R.

Publications and source records attributed to Fajka-Boja, R..

2 recordsLinked to original sources

bioRxiv2025

Sustained poly(ADP-ribosyl)ation limits RPA loading and attenuates ATR-CHK1 signaling upon replication fork collapse

Poly(ADP-ribosyl)ation (PARylation) is a transient post-translational modification catalyzed by PARP enzymes and reversed by the glycohydrolase PARG. Inhibition of PARG causes sustained PARylation, a toxic state that could be exploited for cancer therapy. However, the mechanisms by which excessive PARylation drives toxicity and cell death remain incompletely understood. Here, we examined how persistent PARylation influences cellular responses to replication stress and DNA damage. We found that during replication stress, the decline of ATR checkpoint activity marks the transition from fork stalling to fork collapse, a context in which stabilized poly(ADP-ribose) reduces chromatin-bound RPA. This loss of RPA, a key activator of the checkpoint, further reduces ATR signaling, revealing a feedback loop between unrestrained PARylation and checkpoint control. Our results identify a checkpoint-dependent consequence of unregulated PARP activity during fork collapse and highlight the PARylation-RPA axis as a critical determinant of PARG inhibitor cytotoxicity.

cell biology↗

bioRxiv2023

The loss of DNA polymerase epsilon accessory subunits POLE3-POLE4 leads to BRCA1-independent PARP inhibitor sensitivity

The clinical success of PARP1/2 inhibitors prompts the expansion of their applicability beyond homologous recombination deficiency. Here, we demonstrate that the loss of the accessory subunits of DNA polymerase epsilon, POLE3 and POLE4, sensitizes cells to PARP inhibitors. We show that the sensitivity of POLE4 knockouts is not due to a compromised response to DNA damage or homologous recombination deficiency. Instead, POLE4 deletion generates replication stress with the accumulation of single-stranded DNA gaps upon PARP inhibitor treatment. In POLE4 knockouts, replication stress leads to elevated DNA-PK signaling revealing a role of POLE4 in regulating DNA-PK activation. Moreover, POLE4 knockouts show synergistic sensitivity to the co-inhibition of ATR and PARP. Finally, POLE4 loss enhances the sensitivity of BRCA1-deficient cells to PARP inhibitors and counteracts acquired resistance consecutive to restoration of homologous recombination. Altogether, our findings establish POLE4 as a promising target to improve PARP inhibitor driven therapies and hamper acquired PARP inhibitor resistance.

cell biology↗