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Molecular and Cellular Biology, October 2003, p. 7305-7314, Vol. 23, No. 20
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.20.7305-7314.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Degradation of Transcription Repressor ZBRK1 through the Ubiquitin-Proteasome Pathway Relieves Repression of Gadd45a upon DNA Damage

Jeanho Yun and Wen-Hwa Lee{dagger}*

Department of Molecular Medicine and Institute of Biotechnology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78245

Received 19 March 2003/ Returned for modification 22 May 2003/ Accepted 16 July 2003

Induction of gene expression in response to DNA damage is important for repairing damaged DNA for cell survival. Previously, we identified a novel zinc finger protein, ZBRK1, which contains a KRAB domain at the N terminus, eight zinc fingers at the center, and a BRCA1-binding region at the C terminus. In a BRCA1-dependent manner, ZBRK1 represses Gadd45a transcription through binding to a specific sequence in intron 3. In addition, ZBRK1-binding sequences are located at the regulatory region of many DNA damage-inducible genes, suggesting that ZBRK1 may have a role in DNA damage response. However, it is unclear how transcription repression by ZBRK1 is relieved subsequent to DNA damage. Here we report that ZBRK1 is rapidly degraded upon treatment with the DNA-damaging agents UV and methyl methanesulfonate. Specific proteasome inhibitors block DNA damage-induced degradation of ZBRK1, and the polyubiquitinated form of ZBRK1 is detectable, suggesting that the ubiquitin-proteasome pathway mediates the degradation of ZBRK1. In both BRCA1-proficient and -deficient cells, ZBRK1 is degraded with similar efficiencies independent of BRCA1 E3 ligase activity. By analysis of a series of ZBRK1 mutants, a 44-amino-acid element located between the N-terminal KRAB domain and the eight zinc fingers was found to be sufficient for the DNA damage-induced degradation of ZBRK1. Cells expressing a ZBRK1 mutant lacking the 44-amino-acid element are hypersensitive to DNA damage and are compromised for Gadd45a derepression. These results indicate that ZBRK1 is a novel target for DNA damage-induced degradation and provide a mechanistic explanation of how ZBRK1 is regulated in response to DNA damage.


* Corresponding author. Present address: Department of Biological Chemistry, 124 Sprague Hall, University of California, Irvine, Irvine, CA 92697. Phone: (949) 824-4492. Fax: (949) 824-4493. E-mail: whlee{at}uci.edu.

{dagger} Present address: Department of Biological Chemistry, University of California, Irvine, Irvine, CA 92697.


Molecular and Cellular Biology, October 2003, p. 7305-7314, Vol. 23, No. 20
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.20.7305-7314.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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