GCN5 and TADA2B constitutively regulate XRCC1 function during DNA repair to maintain cell survival

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• XRCC1 protein is central to DNA repair pathways like base excision repair (BER) and single-strand break repair (SSBR).
• Disruptions in XRCC1 function are linked to neurological disorders, such as spinocerebellar ataxia autosomal recessive 26 (SCAR26).
• While PARP1-mediated recruitment of XRCC1 is known, its constitutive regulation remains poorly understood.

Purpose of the Study:

• To identify novel binding partners of XRCC1 involved in its constitutive regulation.
• To elucidate the role of these partners in DNA repair localization and efficiency.
• To understand how these interactions influence cellular responses to genotoxic stress and disease pathology.

Main Methods:

• Co-immunoprecipitation assays to identify XRCC1 binding partners.
• Western blotting and immunofluorescence to assess protein localization and DNA repair foci.
• Cell viability assays and genotoxicity sensitivity tests following protein depletion.
• Analysis of XRCC1 mutants, including disease-associated mutations, to study binding interactions.

Main Results:

• GCN5 and TADA2B, components of the SAGA complex, were identified as novel XRCC1 binding partners.
• GCN5 and TADA2B bind distinct BRCT domains of XRCC1 (BRCT I and BRCT II, respectively), independent of DNA damage.
• Depletion of GCN5 or TADA2B impairs DNA repair, increases sensitivity to genotoxic stress, and elevates cell death.
• GCN5/TADA2B deficiency rescues defects in specific XRCC1 mutants, indicating context-dependent roles.
• The SCAR26 mutation disrupts TADA2B binding, with paradoxical inhibitory effects in the mutant context.

Conclusions:

• GCN5 and TADA2B provide constitutive regulation of XRCC1 localization, essential for efficient DNA repair and cell survival.
• These interactions establish a 'ready-for-action' model, preorganizing repair machinery before damage.
• Dysregulation of these constitutive interactions contributes to cellular dysfunction and potentially neurological diseases like SCAR26.