Ki-67 is necessary during DNA replication for fork protection and genome stability

Area of Science:

• Cell Biology
• Molecular Biology
• Genomics

Background:

• The proliferation antigen Ki-67 is vital for cancer staging but its biological functions remain under-investigated.
• Known roles include regulating chromosome structure, mitosis, heterochromatin organization, and gene transcription.
• Understanding Ki-67's cell cycle coordination is limited by available protein depletion tools.

Purpose of the Study:

• To investigate the uncharacterized functions of the proliferation antigen Ki-67.
• To develop a system for rapid and acute depletion of Ki-67 protein.
• To elucidate Ki-67's role in DNA replication and genome maintenance.

Main Methods:

• Utilized a doxycycline-inducible E3 ligase and auxin-inducible degron system for rapid Ki-67 degradation in HCT116 cells.
• Employed APEX2 proximity labeling and phospho-proteomics for comprehensive analysis.
• Assessed DNA replication, DNA damage response, and interferon signaling pathways.

Main Results:

• Rapid Ki-67 depletion severely delays DNA replication and unloads the replication machinery.
• Absence of Ki-67 leads to DNA damage not sensed by canonical pathways and dependent on HUWE1 ligase.
• Replication defects, sister chromatid cohesion issues, and cGAS/STING-mediated interferon response were observed.

Conclusions:

• Unveiled a novel function of Ki-67 in DNA replication and genome maintenance.
• Demonstrated a role for Ki-67 independent of its known functions in mitosis and gene regulation.
• Highlighted the importance of Ki-67 in preventing replication stress and maintaining genomic integrity.