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UV-damaged DNA-binding proteins are targets of CUL-4A-mediated ubiquitination and degradation

X Chen1, Y Zhang, L Douglas

  • 1Department of Pathology, Weill Medical College and Graduate School of Medical Sciences, Cornell University, New York, New York 10021, USA.

The Journal of Biological Chemistry
|October 24, 2001
PubMed

Insights

High levels of Cullin-4A (CUL-4A) in tumor cells degrade the p48 subunit of DNA damage-binding protein (DDB), impairing DNA repair. This links CUL-4A overexpression to reduced DNA repair capacity in cancer.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Cullin-4A (CUL-4A) is a ubiquitin ligase subunit overexpressed in many tumors.
  • The DNA damage-binding protein (DDB) complex, comprising p125 and p48 subunits, recognizes UV-damaged DNA.
  • DDB plays a crucial role in DNA repair pathways.

Purpose of the Study:

  • To investigate the role of CUL-4A in the regulation of DDB subunits.
  • To determine the impact of CUL-4A on DDB's DNA binding activity and DNA repair function.

Main Methods:

  • Ubiquitin-proteasome pathway analysis
  • Protein degradation assays
  • Immunoprecipitation and Western blotting
  • Analysis of DDB subunit stability and ubiquitination

Main Results:

  • CUL-4A overexpression stimulates p48 degradation via the ubiquitin-proteasome pathway, reducing DDB's UV-damaged DNA binding activity.
  • A xeroderma pigmentosum mutant p48 (R273H) resistant to CUL-4A-mediated degradation fails to bind CUL-4A.
  • CUL-4A stimulates p125 ubiquitination, but p125 levels are not significantly altered; UV irradiation inhibits p125 degradation and induces nuclear translocation.

Conclusions:

  • DDB subunits are substrates of the CUL-4A ubiquitination machinery.
  • Abnormal CUL-4A expression leads to decreased p48 levels, potentially impairing DDB-mediated DNA repair in tumor cells.
  • CUL-4A's role in regulating DDB suggests a mechanism by which cancer cells may evade DNA damage responses.

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