Human CST complex protects stalled replication forks by directly blocking MRE11 degradation of nascent-strand DNA.

Abstract

Degradation and collapse of stalled replication forks are main sources of genomic instability, yet the molecular mechanisms for protecting forks from degradation/collapse are not well understood. Here, we report that human CST (CTC1-STN1-TEN1) proteins, which form a single-stranded DNA-binding complex, localize at stalled forks and protect stalled forks from degradation by the MRE11 nuclease. CST deficiency increases MRE11 binding to stalled forks, leading to nascent-strand degradation at reversed forks and ssDNA accumulation. In addition, purified CST complex binds to 5' DNA overhangs and directly blocks MRE11 degradation in vitro, and the DNA-binding ability of CST is required for blocking MRE11-mediated nascent-strand degradation. Our results suggest that CST inhibits MRE11 binding to reversed forks, thus antagonizing excessive nascent-strand degradation. Finally, we uncover that CST complex inactivation exacerbates genome instability in BRCA2 deficient cells. Collectively, our findings identify the CST complex as an important fork protector that preserves genome integrity under replication perturbation.

• Authors: Xinxing Lyu, Kai-Hang Lei, Pau Biak Sang, Olga Shiva, Megan Chastain, Peter Chi, Weihang Chai
• Journal: The EMBO journal (EMBO J) Vol. 40 Issue 2 Pg. e103654 (01 15 2021) ISSN: 1460-2075 [Electronic] England
• PMID: 33210317 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: © 2020 The Authors.

Chemical References

• Ctc1 protein, human
• DNA, Single-Stranded
• DNA-Binding Proteins
• MRE11 protein, human
• Stn1 protein, human
• Telomere-Binding Proteins
• Ten1 protein, human
• MRE11 Homologue Protein
• DNA Helicases

Topics

• Cell Line
• Cell Line, Tumor
• DNA Breaks, Double-Stranded
• DNA Helicases (metabolism)
• DNA Repair (genetics)
• DNA Replication (genetics)
• DNA, Single-Stranded (genetics)
• DNA-Binding Proteins (metabolism)
• HCT116 Cells
• HEK293 Cells
• HeLa Cells
• Humans
• MRE11 Homologue Protein (metabolism)
• Protein Binding (genetics)
• Telomere-Binding Proteins (metabolism)