Al-Emam, Ahmed Mohamed Ahmed (2011)
Ph.D. thesis, University of Birmingham.
Restricted to Repository staff only until 01 December 2015.
XRCC4-like factor (XLF) is the most recently discovered core member of the nonhomologous end joining (NHEJ) machinery. XLF enhances ligation of DNA ends by DNA ligase IV (LIG4) and functionally interacts with KU70. Previous results showed that some polymorphic changes in LIG4 impact on the efficiency of double strand breaks (DSBs) repair. A random Caucasian population sample was screened for XLF polymorphic mutations with similar functional impact. This analysis identified two novel noncoding single nucleotide polymorphisms (SNPs). To address the regulation of XLF and KU70, the acetylation status of both proteins were analysed. It has been found that XLF undergoes acetylation both in vitro and in vivo and the acetylation sites were mapped in vitro by mass spectrometry. Preliminary analysis has indicated that XLF deacetylation might be histone-deacetylase (HDAC3) dependent. For KU70, it has been found that lysine residues K317, K331 and K338 are critical for NHEJ. Cells overexpressing aceto-mimicking or aceto-blocking mutants of these residues are radiosensitive and defective in DSBs repair (DSBR). This indicates that the dynamic regulation of the acetylation/deacetylation status of these residues is critical for DSBR in response to ionizing radiation. These findings establish the importance of non-histone repair protein acetylation in the regulation of NHEJ and define new possible therapeutic targets for cancer treatment.
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