USP1 inhibition promotes RAD18-dependent PCNA degradation and BRCA1 synthetic lethality

Area of Science:

• Molecular Biology
• DNA Repair Mechanisms
• Cancer Biology

Background:

• Proliferating cell nuclear antigen (PCNA) is vital for DNA replication and repair.
• PCNA ubiquitination by RAD6-RAD18 initiates translesion synthesis, a DNA damage tolerance pathway.
• The interaction between RAD18 and PCNA is critical but not fully understood.

Purpose of the Study:

• To elucidate the molecular basis of RAD18's interaction with PCNA.
• To investigate the role of this interaction in DNA damage tolerance and BRCA1-deficient cell synthetic lethality.
• To explore potential drug resistance mechanisms related to PCNA ubiquitination.

Main Methods:

• Combined computational and structural biology approaches.
• Identified and characterized a PCNA-interacting peptide (PIP) motif in RAD18.
• Utilized cell-based assays to assess the impact of mutations on PCNA ubiquitination, ssDNA gap accumulation, and drug sensitivity.

Main Results:

• A PCNA-interacting peptide (PIP) motif in RAD18 was identified and structurally characterized.
• This PIP motif is essential for RAD18-dependent DNA damage-induced PCNA ubiquitination and turnover.
• Mutating the RAD18-PCNA interface reduced single-stranded DNA gap accumulation and sensitivity to USP1 inhibitors in BRCA1-deficient cells.

Conclusions:

• The study defines a critical molecular interface between RAD18 and PCNA required for mono-ubiquitination.
• This interface is a key determinant of USP1 inhibitor-induced synthetic lethality in BRCA1-deficient cells.
• Deregulation of RAD18 contributes to drug resistance, which can be overcome by ATR kinase inhibition.