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Nbs1 is required for ATR-dependent phosphorylation events
Tom Stiff1, Caroline Reis, Gemma K Alderton
1Genome Damage and Stability Centre, University of Sussex, East Sussex, UK.
The EMBO Journal
|December 24, 2004
Summary
Nijmegen breakage syndrome (NBS) involves defects in Nbs1 protein, impacting both ATM and ATR signaling pathways. This study reveals Nbs1
Area of Science:
- Molecular Biology
- Genetics
- Cellular Biology
Background:
- Nijmegen breakage syndrome (NBS) is a genetic disorder characterized by microcephaly, developmental delay, immunodeficiency, and radiosensitivity.
- The Nbs1 protein, defective in NBS, is known to function in ATM-dependent signaling pathways.
- NBS shares clinical and molecular features with ataxia telangiectasia and ATR-Seckel syndrome, suggesting potential overlap in signaling pathways.
Purpose of the Study:
- To investigate the role of Nbs1 protein in ATR-dependent signaling pathways.
- To elucidate the functional consequences of Nbs1 deficiency in DNA replication stress response.
- To understand the contribution of combined ATM and ATR pathway defects to NBS clinical features.
Main Methods:
- Analysis of NBS cell lines for defects in ATR-dependent phosphorylation of substrates like Chk1, c-jun, and p53.
- Assessment of FANCD2 ubiquitination following hydroxyurea (HU) treatment in NBS cells.
- Evaluation of G2/M checkpoint arrest and DNA synthesis restart in NBS and ATR-Seckel cells after replication stress.
- Microscopy to examine ATR localization in NBS cells following HU treatment.
Main Results:
- NBS cell lines exhibit impaired ATR-dependent phosphorylation of key substrates in response to UV irradiation and HU-induced replication stalling.
- Defects in ATR-dependent FANCD2 ubiquitination were observed in NBS cells after HU treatment.
- NBS and ATR-Seckel cells display similar impairments in G2/M checkpoint arrest and DNA synthesis restart following replication stress.
- NBS cells show a failure to retain ATR in the nucleus after HU treatment and extraction.
Conclusions:
- Nbs1 protein plays a crucial role in facilitating ATR-dependent signaling, in addition to its known role in ATM signaling.
- The observed defects in ATR signaling contribute to the cellular phenotypes of NBS, including impaired replication stress response and checkpoint control.
- The clinical manifestations of NBS likely result from the combined functional deficits in both ATM and ATR signaling pathways mediated by Nbs1.