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The ubiquitin ligase COP1 is a critical negative regulator of p53


COP1 (constitutively photomorphogenic 1) is a RING-finger-containing protein that functions to repress plant photomorphogenesis, the light-mediated programme of plant development. Mutants of COP1 are constitutively photomorphogenic, and this has been attributed to their inability to negatively regulate the proteins LAF1 (ref. 1) and HY5 (ref. 2). The role of COP1 in mammalian cells is less well characterized3. Here we identify the tumour-suppressor protein p53 as a COP1-interacting protein. COP1 increases p53 turnover by targeting it for degradation by the proteasome in a ubiquitin-dependent fashion, independently of MDM2 or Pirh2, which are known to interact with and negatively regulate p53. Moreover, COP1 serves as an E3 ubiquitin ligase for p53 in vitro and in vivo, and inhibits p53-dependent transcription and apoptosis. Depletion of COP1 by short interfering RNA (siRNA) stabilizes p53 and arrests cells in the G1 phase of the cell cycle. Furthermore, we identify COP1 as a p53-inducible gene, and show that the depletion of COP1 and MDM2 by siRNA cooperatively sensitizes U2-OS cells to ionizing-radiation-induced cell death. Overall, these results indicate that COP1 is a critical negative regulator of p53 and represents a new pathway for maintaining p53 at low levels in unstressed cells.

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Figure 1: COP1 and its interaction with p53.
Figure 2: COP1 negative regulation of p53.
Figure 3: siRNA ablation of COP1 causes an accumulation of p53 protein and induces a G1 arrest.
Figure 4: COP1, Pirh2 and MDM2 ablation by siRNA stabilizes and activates p53.
Figure 5: COP1 is a p53-inducible gene.


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We would like to thank T. Hupp for his contribution of reagents and thought-provoking discussions, G. Lozano for p53-/-/MDM2-/- MEFs, S. Benchimol for the Pirh2 antibody and cDNA, J. Chen for H1299 cells, B. Henzel for mass spectrometry support, C. Reed for the generation of COP1 monoclonal antibodies, M. Vasser and P. Ng for oligonucleotide synthesis and purification, A. Waugh for Bioinformatics support, Genentech Protein Engineering and core DNA sequencing facility for support services, and P. Polakis and members of the Dixit lab for advice and encouragement. I.W. is supported by a PSTP fellowship from the University of California, Davis.

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Correspondence to Vishva M. Dixit.

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Supplementary Figure S1: COP1 maintains the ability to degrade p53 in the absence of MDM2 or Pirh2; Supplementary Figure S2: COP1 negative regulation of p53 transactivation activity; Supplementary Figure S3: Ablation of COP1 by two further distinct siRNA oligos causes an accumulation of p53 at the protein level. (PDF 303 kb)

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Dornan, D., Wertz, I., Shimizu, H. et al. The ubiquitin ligase COP1 is a critical negative regulator of p53. Nature 429, 86–92 (2004).

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