Related Experiment Video
Updated: Jul 1, 2026
05:55
Detection of DNA Breaks in Dividing Human Cells by Neutral Comet Assay
Published on: August 23, 2024
53BP1-independent Shieldin-BRCA1 antagonism at replication-coupled double-strand breaks
Yi-Li Feng1,2, Meng Wang3,4, Ge Li3,4
1Key Laboratory of Laparoscopic Technology of Zhejiang Province, Department of General Surgery, Sir Run-Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, PR China. eric_feng@zju.edu.cn.
Nature Communications
|June 29, 2026
Summary
Loss of Shieldin complex proteins (Shld2/3) confers PARP inhibitor resistance in BRCA1-deficient cells by restoring homologous recombination. This 53BP1-independent Shieldin function offers new insights into PARPi resistance mechanisms.
Area of Science:
- DNA repair mechanisms
- Cancer therapeutics
- Molecular biology
Background:
- BRCA1 deficiency causes homologous recombination (HR) defects, leading to PARP inhibitor (PARPi) sensitivity.
- The 53BP1-Shieldin complex is known to inhibit DNA double-strand break (DSB) end resection, promoting PARPi sensitivity in BRCA1-deficient cells.
- The role of Shieldin in replication-coupled DSBs and its contribution to PARPi resistance is not fully understood.
Purpose of the Study:
- To investigate the role of the 53BP1-Shieldin complex in homologous recombination (HR) repair in BRCA1-deficient cells.
- To determine the impact of Shieldin loss on PARP inhibitor (PARPi) sensitivity in the context of BRCA1 deficiency.
- To elucidate the 53BP1-independent functions of Shieldin in DNA repair and PARPi resistance.
Main Methods:
- Utilized mouse embryonic stem cells (MESCs) with specific genetic modifications (BRCA1 BRCT domain mutations, Shld2/3 deletions, 53bp1 deletions).
- Assessed homologous recombination (HR) restoration, DNA double-strand break (DSB) repair pathways, and RAD51 loading.
- Investigated the role of the CST complex and residual BRCA1 activity in Shieldin-mediated HR regulation.
- Examined PARPi sensitivity in various BRCA1 and BARD1 mutant cell lines.
Main Results:
- Loss of Shieldin complex proteins (Shld2 or Shld3), but not 53BP1, conferred PARPi resistance in BRCA1-deficient MESCs.
- Shld2/3 deletion partially restored HR at replication-coupled DSBs, reduced insertion/deletion signatures, and promoted RAD51 loading in a 53BP1-independent manner.
- This Shieldin function requires the CST complex and counteracts residual BRCA1 activity, identifying a novel mechanism for HR deficiency maintenance.
Conclusions:
- Identified a 53BP1-independent function of the Shieldin complex in sustaining HR deficiency in BRCA1-deficient cells.
- Demonstrated that Shieldin loss can restore HR and confer PARPi resistance, providing new mechanistic insights into therapeutic resistance.
- These findings highlight Shieldin as a potential therapeutic target for overcoming PARPi resistance in BRCA1-deficient cancers.
Related Concept Videos
02:37Restarting Stalled Replication Forks
DNA replication is initiated at sites containing predefined DNA sequences known as origins of replication. DNA is unwound at these sites by the minichromosome maintenance (MCM) helicase and other factors such as Cdc45 and the associated GINS complex.The unwound single strands are protected by replication protein A (RPA) until DNA polymerase starts synthesizing DNA at the 5â end of the strand in the same direction as the replication fork. To prevent the replication fork from falling apart, a...
02:31Homologous Recombination
The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
01:02Long-patch Base Excision Repair
Since the discovery of the two BER pathways, there has been a debate about how a cell chooses one pathway over the other and the factors determining this selection. Numerous in vitro experiments have pointed out multiple determinants for the sub-pathway selection. These are:
01:03Single-Strand DNA Binding Proteins
For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...
02:04Fixing Double-strand Breaks
The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...
02:04Fixing Double-strand Breaks
The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...