Related Experiment Videos
Identification of a defect in DNA ligase IV in a radiosensitive leukaemia patient
E Riballo1, S E Critchlow, S H Teo
1MRC Cell Mutation Unit, University of Sussex, Brighton, BN1 9RR, UK.
Abstract:
The major mechanism for the repair of DNA double-strand breaks (DSBs) in mammalian cells is non-homologous end-joining (NHEJ), a process that involves the DNA-dependent protein kinase [1] [2], XRCC4 and DNA ligase IV [3] [4] [5] [6]. Rodent cells and mice defective in these components are radiation-sensitive and defective in V(D)J-recombination, showing that NHEJ also functions to rejoin DSBs introduced during lymphocyte development [7] [8]. 180BR is a radiosensitive cell line defective in DSB repair, which was derived from a leukaemia patient who was highly sensitive to radiotherapy [9] [10] [11]. We have identified a mutation within a highly conserved motif encompassing the active site in DNA ligase IV from 180BR cells. The mutated protein is severely compromised in its ability to form a stable enzyme-adenylate complex, although residual activity can be detected at high ATP concentrations. Our results characterize the first patient with a defect in an NHEJ component and suggest that a significant defect in NHEJ that leads to pronounced radiosensitivity is compatible with normal human viability and does not cause any major immune dysfunction. The defect, however, may confer a predisposition to leukaemia.
Insights
Researchers identified a DNA ligase IV mutation in a radiosensitive leukemia patient, revealing a defect in DNA double-strand break repair. This finding characterizes the first human non-homologous end-joining defect, compatible with normal viability but potentially predisposing to leukemia.
Area of Science:
- Molecular Biology
- Genetics
- Radiation Biology
Background:
- Non-homologous end-joining (NHEJ) is the primary mechanism for repairing DNA double-strand breaks (DSBs) in mammalian cells.
- Defects in NHEJ components lead to radiation sensitivity and impaired V(D)J recombination during lymphocyte development.
- The 180BR cell line, derived from a radiotherapy-sensitive leukemia patient, exhibits a defect in DSB repair.
Purpose of the Study:
- To identify the genetic basis of the radiosensitivity in the 180BR cell line.
- To characterize the functional consequences of the identified mutation in DNA ligase IV.
- To understand the clinical implications of defects in the NHEJ pathway.
Main Methods:
- Mutation analysis of DNA ligase IV in 180BR cells.
- Biochemical assays to assess the enzymatic activity of the mutated DNA ligase IV.
- Clinical correlation with patient history and cellular phenotype.
Main Results:
- A mutation was identified in a conserved active site motif of DNA ligase IV in 180BR cells.
- The mutated DNA ligase IV showed severely compromised ability to form a stable enzyme-adenylate complex.
- Residual enzymatic activity was detectable at high ATP concentrations.
Conclusions:
- This study characterizes the first identified patient with a defect in a non-homologous end-joining component (DNA ligase IV).
- A significant defect in NHEJ can cause pronounced radiosensitivity while remaining compatible with normal human viability and immune function.
- The identified NHEJ defect may predispose individuals to leukemia.