Mre11-Rad50-Nbs1-dependent processing of DNA breaks generates oligonucleotides that stimulate ATM activity

Area of Science:

• Molecular Biology
• DNA Repair Mechanisms
• Cell Signaling

Background:

• DNA double-strand breaks (DSBs) are critical DNA lesions.
• The Mre11-Rad50-Nbs1 (MRN) complex is crucial for DSB processing and ATM activation.
• The precise molecular link between MRN and ATM activation remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms by which the MRN complex activates ATM following DSBs.
• To identify novel signaling molecules involved in DSB-induced ATM activation.

Main Methods:

• Utilized Xenopus laevis egg extracts for in vitro studies of DSB processing.
• Isolated and analyzed MRN complexes bound to DNA fragments.
• Quantified single-stranded DNA oligonucleotides (ssDNA oligos) using biochemical assays.
• Investigated ATM activation in response to ssDNA oligos in human cells.

Main Results:

• MRN-dependent processing of DSBs generates short ssDNA oligos.
• MRN complex isolated from DSB-containing extracts is bound to ssDNA oligos and stimulates ATM.
• Elimination of ssDNA oligos abolishes ATM activity.
• ssDNA oligos are found in human cells post-ionizing radiation.
• Synthetic ssDNA oligos induce ATM activation in undamaged cells.

Conclusions:

• MRN-dependent generation of ssDNA oligos is a key mechanism for stimulating ATM activity.
• ssDNA oligos serve as a unique signal of ongoing DSB repair.
• This pathway represents a novel aspect of DNA damage response not previously recognized in normal DNA metabolism.