PARG is essential for Polθ-mediated DNA end-joining by removing repressive poly-ADP-ribose marks.

Area of Science:

• Molecular Biology
• DNA Repair Mechanisms
• Biochemistry

Background:

• DNA polymerase theta (Polθ)-mediated end-joining (TMEJ) is crucial for repairing DNA double-strand breaks and conferring resistance to genotoxic agents.
• The precise molecular regulation of Polθ in TMEJ remains largely uncharacterized, hindering a comprehensive understanding of its function.

Purpose of the Study:

• To elucidate the molecular mechanisms governing the regulation of DNA polymerase theta (Polθ) during TMEJ.
• To investigate the roles of PARP1 and PARG in modulating Polθ activity and TMEJ pathway function.

Main Methods:

• Investigated the interaction between Polθ and PARP1, focusing on PARylation status and its effect on Polθ activity.
• Utilized biochemical assays to assess DNA binding and end-joining activities of modified Polθ.
• Examined the spatiotemporal recruitment of PARP1 and PARG to DNA damage sites and correlated it with TMEJ activation.

Main Results:

• Identified a novel interaction where PARP1 PARylates Polθ in a HPF1-independent manner, leading to Polθ recruitment to DNA damage sites.
• Demonstrated that PARylation by PARP1 inactivates Polθ's DNA binding and TMEJ activities.
• Showed that PARG-mediated de-PARylation reactivates Polθ, restoring its DNA binding and end-joining capabilities, and is essential for TMEJ.

Conclusions:

• Established a two-step spatiotemporal regulatory mechanism for TMEJ involving PARP1 and PARG.
• PARP1 acts as an initial regulator, recruiting and inactivating Polθ via PARylation at DNA damage sites.
• PARG serves as the crucial activator, removing repressive PAR marks to enable Polθ-mediated DNA repair.