Related Experiment Video
Updated: May 3, 2026
T-maze Forced Alternation and Left-right Discrimination Tasks for Assessing Working and Reference Memory in Mice
Published on: February 26, 2012
ATM dysfunction in Chinese hamster XRCC8 mutants
Piyawan Chailapakul1, Junko Maeda1, Takamitsu A Kato1
1Department of Environmental & Radiological Health Sciences, Colorado State University, Fort Collins, CO, 80523, USA.
Abstract:
XRCC8 is a member of the X-ray cross-complementing (XRCC) family, whose responsible gene has not been identified. Previous studies suggested ATM and other genes were potential candidates for XRCC8, but this was not confirmed. In this study, we characterized three V79-derived XRCC8 mutant cells: V-C4, V-E5, and V-G8. Western blot analysis showed reduced expression of the ATM protein in three XRCC8 mutants, and radiation-induced phosphorylated ATM foci were not detected by fluorescence immunocytochemistry. Both ATM knockout cells and XRCC8 mutants exhibited hypersensitivity to camptothecin. Through a cell fusion-based complementation test, we found that XRCC8 mutants were complemented by ATM-proficient cells, but not by ATM knockout cells, in terms of camptothecin sensitivity. Comprehensive sequencing of the ATM genome in XRCC8 mutants revealed unique mutations in each mutant. These results suggest that XRCC8 mutants carry ATM mutations, and their ATM is not properly functional, despite protein expression being detected. This is similar to missense mutations in some Ataxia Telangiectasia patients.
Insights
The gene responsible for XRCC8 mutations was identified as ATM. XRCC8 mutants exhibit ATM dysfunction, similar to Ataxia Telangiectasia, impacting DNA repair and camptothecin sensitivity.
Area of Science:
- Genetics
- Molecular Biology
- Cell Biology
Background:
- The gene responsible for XRCC8 mutations, a member of the X-ray cross-complementing (XRCC) family, remains unidentified.
- Previous studies suggested ATM as a potential candidate, but this was not confirmed.
Purpose of the Study:
- To identify the gene responsible for XRCC8 mutations.
- To characterize the functional consequences of XRCC8 mutations on ATM protein function and DNA repair.
Main Methods:
- Western blot analysis to assess ATM protein expression in XRCC8 mutants.
- Fluorescence immunocytochemistry to detect radiation-induced phosphorylated ATM foci.
- Camptothecin sensitivity assays.
- Cell fusion-based complementation tests.
- Comprehensive sequencing of the ATM gene in XRCC8 mutants.
Main Results:
- XRCC8 mutants showed reduced ATM protein expression and lacked radiation-induced phosphorylated ATM foci.
- Both ATM knockout cells and XRCC8 mutants displayed hypersensitivity to camptothecin.
- Cell fusion experiments confirmed that XRCC8 mutants were complemented by ATM-proficient cells but not ATM knockout cells regarding camptothecin sensitivity.
- Unique ATM gene mutations were identified in each XRCC8 mutant.
Conclusions:
- The results strongly suggest that XRCC8 mutants carry mutations in the ATM gene, leading to non-functional ATM protein despite its detectable expression.
- This functional deficit in ATM is similar to missense mutations observed in some Ataxia Telangiectasia patients, highlighting a conserved role in DNA repair pathways.
