USP1 Is Required for Replication Fork Protection in BRCA1-Deficient Tumors

Area of Science:

• Molecular Biology
• Cancer Biology
• Genetics

Background:

• BRCA1-deficient tumors exhibit homologous-recombination repair defects and replication fork instability, leading to PARP inhibitor sensitivity.
• Upregulation of USP1 (a deubiquitinase) is observed in tumors with BRCA1 mutations.

Purpose of the Study:

• To investigate the role of USP1 in BRCA1-deficient cells and its potential as a therapeutic target.
• To elucidate the mechanism by which USP1 influences replication fork stability and cell viability.

Main Methods:

• Knockdown and inhibition of USP1 in BRCA1-deficient cells.
• Assessment of replication fork stability and cell viability.
• Analysis of USP1's interaction with and activation by fork DNA.
• Investigation of PCNA ubiquitination at replication forks.

Main Results:

• USP1 knockdown or inhibition led to replication fork destabilization and reduced viability in BRCA1-deficient cells, indicating a synthetic lethal interaction.
• USP1 binds to and is activated by fork DNA, protecting replication forks.
• Absence of USP1 resulted in persistent monoubiquitinated PCNA at replication forks, causing cell death.

Conclusions:

• USP1 is activated by DNA at the replication fork, where it protects fork stability and promotes survival in BRCA1-deficient cells.
• USP1 inhibition represents a potential therapeutic strategy for PARP-inhibitor-resistant BRCA1-deficient tumors.
• Targeting USP1 may overcome acquired resistance to PARP inhibitors by re-sensitizing tumors through replication fork destabilization.