Mre11 nuclease activity and Ctp1 regulate Chk1 activation by Rad3ATR and Tel1ATM checkpoint kinases at double-strand breaks

Area of Science:

• Molecular Biology
• Cellular Biology
• Genetics

Background:

• DNA double-strand breaks (DSBs) trigger checkpoint responses to maintain genomic integrity.
• Rad3 (ATR/Mec1) and Tel1 (ATM) are key kinases in DSB signaling pathways.
• DNA end processing factors, including Mre11 and Ctp1, are involved in DSB detection and signaling.

Purpose of the Study:

• To investigate the role of DNA end processing in the Rad3-Chk1 DSB checkpoint pathway in fission yeast.
• To identify alternative DSB signaling pathways that bypass Rad3.
• To elucidate the regulatory mechanisms coupling DSB detection to checkpoint activation.

Main Methods:

• Genetic analysis of fission yeast mutants (e.g., deletion of Ctp1).
• Analysis of checkpoint kinase activation (Rad3 and Tel1) and downstream signaling (Chk1).
• Investigation of protein complex roles (MRN, 9-1-1 clamp, Crb2) in DSB response.

Main Results:

• Mre11 nuclease activity and Ctp1 are essential for efficient Rad3-Chk1 signaling at DSBs.
• Deletion of Ctp1 activates a Tel1-Chk1 pathway that bypasses Rad3.
• This alternative pathway requires Mre11 nuclease activity, the 9-1-1 clamp, and Crb2.
• Ctp1 negatively regulates the Tel1-Chk1 pathway by controlling MRN complex localization.

Conclusions:

• Fission yeast DNA end processing is crucial for robust Rad3-Chk1 activation.
• A Tel1-Chk1 pathway operates at unresected DSBs, providing a mechanism for rapid Chk1 activation.
• These findings suggest conserved roles for ATM/Tel1 in directly and indirectly activating Chk1 in mammalian cells.