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Two- and Three-Dimensional Live Cell Imaging of DNA Damage Response Proteins
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The DNA damage response in DNA-dependent protein kinase-deficient SCID mouse cells: replication protein A

L M Fried1, C Koumenis, S R Peterson

  • 1Department of Radiation Oncology, Stanford University School of Medicine, CA 94305, USA.

Proceedings of the National Academy of Sciences of the United States of America
|November 26, 1996
PubMed

Insights

Severe combined immunodeficient (SCID) mice show radiation sensitivity due to DNA repair defects. DNA-dependent protein kinase (DNA-PK) is implicated, but its exact role in the p53 and RPA DNA damage response remains unclear.

Area of Science:

  • Molecular Biology
  • Radiation Biology
  • Cellular Biology

Background:

  • Severe combined immunodeficient (SCID) mice exhibit heightened sensitivity to ionizing radiation, linked to impaired DNA double-strand break repair.
  • The catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) is a prime suspect for the SCID gene mutation.
  • DNA-PK phosphorylates key proteins like p53 and replication protein A (RPA) in vitro, which are crucial for DNA damage response.

Purpose of the Study:

  • To investigate if p53 and RPA are in vivo substrates of DNA-PK following DNA damage.
  • To compare the DNA damage response in SCID mice and human DNA-PKcs-deficient MO59J cells versus their wild-type counterparts.

Main Methods:

  • Ionizing radiation exposure of SCID and MO59J cells and their wild-type controls.
  • Analysis of p53 levels and RPA p34 phosphorylation status post-irradiation.
  • Assessment of RPA binding to single-stranded DNA in cellular extracts.

Main Results:

  • p53 levels increased in SCID cells after ionizing radiation.
  • RPA p34 showed hyperphosphorylation in both SCID and MO59J cells post-irradiation.
  • Hyperphosphorylation of RPA p34 correlated with reduced RPA binding to single-stranded DNA.

Conclusions:

  • The DNA damage response involving p53 and RPA is not directly linked to the DNA repair defect in SCID cells.
  • DNA-PK is not the sole kinase responsible for RPA phosphorylation in vivo.
  • The critical physiological substrate(s) of DNA-PK essential for DNA repair remain unidentified.

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