Human RAP1 specifically protects telomeres of senescent cells from DNA damage.

Area of Science:

• Cell Biology
• Genetics
• Molecular Biology

Background:

• Repressor/activator protein 1 (RAP1) is conserved across species and localizes to telomeres.
• Yeast Rap1 is crucial for telomere capping, preventing end-to-end chromosome fusions via non-homologous end joining (NHEJ).
• The in vivo role of RAP1 at mammalian telomeres remains debated.

Purpose of the Study:

• To investigate the function of human RAP1 at telomeres, specifically in replicative senescence.
• To determine if RAP1 prevents telomere uncapping and fusions in senescent human cells.
• To elucidate the molecular mechanisms underlying RAP1's anti-fusion effects.

Main Methods:

• Downregulation of RAP1 in human cells.
• Inducible CRISPR/Cas9 system for RAP1 depletion in HeLa cells.
• Telomere length analysis and fusion assays.
• Investigation of DNA ligase IV involvement.

Main Results:

• RAP1 downregulation in senescent human cells, but not in young cells, caused telomere uncapping and fusions.
• RAP1 depletion in HeLa cells induced telomere fusions only when telomerase activity was inhibited.
• Telomere fusions resulting from RAP1 loss were dependent on DNA ligase IV.

Conclusions:

• Human RAP1 plays a specific role in protecting critically short telomeres in senescent cells.
• RAP1 is essential for maintaining telomere integrity during cellular senescence.
• These findings highlight RAP1's importance in the context of telomere function in aging cells.