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Updated: Mar 15, 2026
Visualization of DNA Repair Proteins Interaction by Immunofluorescence
Published on: June 26, 2020
MRNIP/C5orf45 Interacts with the MRN Complex and Contributes to the DNA Damage Response
Christopher J Staples1, Giancarlo Barone1, Katie N Myers1
1Sheffield Institute for Nucleic Acids (SInFoNiA), Department of Oncology and Metabolism, Academic Unit of Molecular Oncology, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK.
Abstract:
Through an RNAi-based screen for previously uncharacterized regulators of genome stability, we have identified the human protein C5orf45 as an important factor in preventing the accumulation of DNA damage in human cells. Here, we functionally characterize C5orf45 as a binding partner of the MRE11-RAD50-NBS1 (MRN) damage-sensing complex. Hence, we rename C5orf45 as MRNIP for MRN-interacting protein (MRNIP). We find that MRNIP is rapidly recruited to sites of DNA damage. Cells depleted of MRNIP display impaired chromatin loading of the MRN complex, resulting in reduced DNA end resection and defective ATM-mediated DNA damage signaling, a reduced ability to repair DNA breaks, and radiation sensitivity. Finally, we show that MRNIP phosphorylation on serine 115 leads to its nuclear localization, and this modification is required for MRNIP's role in promoting genome stability. Collectively, these data reveal that MRNIP is an important component of the human DNA damage response.
Insights
Researchers identified C5orf45, now named MRNIP, as crucial for preventing DNA damage. MRNIP interacts with the MRN complex, aiding DNA repair and maintaining genome stability in human cells.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Genome stability is essential for preventing diseases like cancer.
- The MRE11-RAD50-NBS1 (MRN) complex is a key sensor of DNA double-strand breaks.
- Uncharacterized proteins regulating DNA damage response pathways are actively sought.
Purpose of the Study:
- To identify novel regulators of genome stability.
- To functionally characterize the role of C5orf45 in DNA damage response.
- To elucidate the mechanism by which C5orf45 contributes to genome maintenance.
Main Methods:
- RNA interference (RNAi)-based screening in human cells.
- Co-immunoprecipitation to identify protein binding partners.
- Immunofluorescence microscopy to track protein recruitment to DNA damage sites.
- Analysis of DNA repair, DNA damage signaling, and radiation sensitivity in depleted cells.
Main Results:
- C5orf45 was identified as a novel genome stability factor and renamed MRN-interacting protein (MRNIP).
- MRNIP directly binds to the MRN complex and is rapidly recruited to DNA damage sites.
- MRNIP depletion impairs MRN complex loading, DNA end resection, ATM signaling, DNA repair, and increases radiation sensitivity.
- Phosphorylation of MRNIP at serine 115 is required for its nuclear localization and genome-stabilizing function.
Conclusions:
- MRNIP is a critical component of the human DNA damage response pathway.
- MRNIP functions by facilitating MRN complex recruitment and activity at DNA breaks.
- MRNIP's phosphorylation-dependent nuclear localization is essential for its role in maintaining genome stability.
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