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Antagonistic roles of canonical and Alternative-RPA in disease-associated tandem CAG repeat instability

Terence Gall-Duncan1, Jennifer Luo1, Carla-Marie Jurkovic2

  • 1Genetics & Genome Biology, The Hospital for Sick Children, Toronto, ON, Canada; Molecular Genetics, University of Toronto, Toronto, ON, Canada.

Cell
|October 12, 2023
PubMed

Insights

Replication protein A (RPA) and Alternative-RPA (Alt-RPA) complexes are upregulated in repeat expansion diseases. RPA suppresses expansions, while Alt-RPA promotes them, suggesting a disease-driving role for Alt-RPA.

Area of Science:

  • Genetics
  • Molecular Biology
  • Neuroscience

Background:

  • Repeat DNA expansions cause over 70 diseases, with worsening symptoms due to ongoing expansions in the brain.
  • During expansion mutations, single-stranded DNA (ssDNA) forms, leading to slipped-DNA structures.

Purpose of the Study:

  • To investigate the roles of canonical Replication Protein A (RPA) and Alternative-RPA (Alt-RPA) in repeat expansion diseases.
  • To determine how RPA and Alt-RPA influence CAG repeat instability and disease progression.

Main Methods:

  • Analyzing RPA and Alt-RPA expression in patient brains (Huntington disease, SCA1).
  • Characterizing protein interactomes of RPA and Alt-RPA.
  • Assessing the in vitro and in vivo effects of RPA and Alt-RPA on CAG repeat expansions and DNA repair.
  • Evaluating RPA overexpression in SCA1 mouse models.

Main Results:

  • RPA and Alt-RPA are upregulated in Huntington disease and SCA1 patient brains.
  • RPA enhances the repair of slipped-CAGs and protects against CAG expansions in human cells.
  • RPA overexpression in SCA1 mouse brains reduced CAG expansions, ATXN1 aggregation, DNA damage, and improved neurological function.
  • Alt-RPA was found to inhibit the repair of slipped-CAGs and promote CAG expansions.

Conclusions:

  • A functional interplay exists between RPA and Alt-RPA, with Alt-RPA potentially counteracting RPA's protective effects against repeat expansions.
  • Alt-RPA may promote disease-associated repeat expansions and contribute to disease pathogenesis, with implications for other DNA processes.
Keywords:
Alternative replication protein A (Alt-RPA)BioID protein interactomeDNA repair (FAN1, MSH2, MSH3, MSH6, HTT)Huntington's disease (HD)RPA1, RPA2, RPA3, RPA4Replication protein A (RPA)Spinocerebellar ataxia type 1 (SCA1)slipped-DNAtandem repeat expansionstrinucleotide CAG repeat expansions

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