Treacle and TOPBP1 control replication stress response in the nucleolus

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Replication stress is a major driver of genome instability in eukaryotic cells.
• The replication stress response (RSR) is well-studied in the nucleus, but its role in the nucleolus remains largely unknown.
• Understanding nucleolar RSR is crucial for comprehending overall genome maintenance.

Purpose of the Study:

• To investigate the mechanisms of replication stress response within the nucleolus.
• To identify key proteins involved in nucleolar RSR and their interactions.
• To elucidate the functional significance of nucleolar RSR in maintaining genome stability.

Main Methods:

• Drug-induced replication stress models in eukaryotic cells.
• Immunofluorescence microscopy to visualize protein localization (RPA, TOPBP1, ATR, Treacle).
• Co-immunoprecipitation assays to study protein-protein interactions (Treacle-TOPBP1).
• Assessment of ATR signaling and checkpoint activation within the nucleolus.

Main Results:

• Replication stress response factors (RPA, TOPBP1, ATR) are recruited to the nucleolus.
• TOPBP1 interacts with the nucleolar protein Treacle (TCOF1), forming Treacle-TOPBP1 foci.
• Treacle-TOPBP1 facilitates ATR signaling and checkpoint activation at stalled replication forks within the nucleolus.
• These interactions promote the recruitment of downstream RSR proteins to the nucleolus.

Conclusions:

• The nucleolus is an active site for replication stress response.
• Treacle and TOPBP1 form a molecular platform within the nucleolus to enhance ATR signaling and checkpoint activation.
• This nucleolar platform plays a critical role in maintaining genome stability during replication stress.