Resection of DNA double-strand breaks activates Mre11-Rad50-Nbs1- and Rad9-Hus1-Rad1-dependent mechanisms that...

Area of Science:

• Molecular Biology
• Genetics
• Cellular Biology

Background:

• DNA double-strand breaks (DSBs) are critical DNA lesions that threaten genome stability.
• The ATM and ATR checkpoint pathways are essential for sensing and responding to DSBs.
• The Mre11-Rad50-Nbs1 (MRN) complex and the Rad9-Hus1-Rad1 (9-1-1) clamp are key DNA structure sensors.

Purpose of the Study:

• To investigate the mechanisms regulating ATR activation and DNA end resection in response to DSBs.
• To elucidate the roles of MRN, 9-1-1, and Topbp1 in ATR signaling pathways.
• To understand how different DNA structures trigger specific ATR activation subpathways.

Main Methods:

• Utilized DNA substrates mimicking extensively resected DSBs in Xenopus egg extracts.
• Investigated the roles of MRN, 9-1-1, Dna2, Topbp1, ATM, and ATR in DNA processing.
• Analyzed protein loading, phosphorylation, and dissociation events during checkpoint activation.

Main Results:

• MRN and 9-1-1 redundantly stimulate Dna2-dependent long-range end resection and ATR activation.
• MRN acts as a platform for ATM, promoting Dna2 and Topbp1 loading, but MRN-mediated processing is largely ATM-independent.
• Topbp1 loading is interdependent with 9-1-1, and ATR activation leads to Mre11 phosphorylation and ATM dissociation.

Conclusions:

• Long-range end resection activates two redundant pathways that enhance ATR checkpoint signaling and DNA processing.
• This study uncovers a complex interplay between MRN, 9-1-1, ATM, and ATR in vertebrate DNA repair.
• The findings provide new insights into the regulation of DNA double-strand break repair pathways.