TOPBP1-PLK1 interaction preserves genome integrity during mitosis

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• TOPBP1 is crucial for genome integrity and DNA repair during mitosis, acting as a backup pathway in BRCA-deficient cells.
• Regulation of TOPBP1 during mitosis, particularly its interaction with mitotic kinases like PLK1, remains incompletely understood.

Purpose of the Study:

• To elucidate the molecular mechanism and functional significance of the interaction between TOPBP1 and the mitotic kinase PLK1.
• To investigate the role of this interaction in maintaining genome integrity during mitosis.

Main Methods:

• Identification and characterization of a conserved CDK1-primed binding site for PLK1 in TOPBP1.
• Site-directed mutagenesis to study the functional consequences of disrupting the TOPBP1-PLK1 interaction.
• Assessment of DNA damage transmission, DNA repair synthesis, DNA polymerase θ localization, and chromosomal abnormalities (anaphase bridges, micronucleation).
• Evaluation of TOPBP1-PLK1 complex formation dependency in BRCA2-depleted cells.

Main Results:

• A conserved CDK1-primed binding site for PLK1 in TOPBP1 was identified and characterized.
• Mutation of this site led to increased DNA damage transmission to daughter cells and impaired mitotic DNA repair synthesis.
• Mislocalization of DNA polymerase θ, increased anaphase bridges, and micronucleation were observed upon mutation.
• BRCA2-depleted cells showed a strong dependence on the TOPBP1-PLK1 complex for genome maintenance.

Conclusions:

• The study reveals the molecular details of TOPBP1-PLK1 complex formation, mediated by a CDK1-primed site.
• This interaction is critical for efficient mitotic DNA repair and preventing DNA damage carry-over to daughter cells.
• The TOPBP1-PLK1 complex plays a vital role in maintaining genome stability, especially in BRCA-deficient contexts.