Involvement of the DNA Repair Protein hHR23 in p53 Degradation

Abstract

The stability of the tumor suppressor protein p53 is regulated via the ubiquitin-proteasome-dependent proteolytic pathway. Like most substrates of this pathway, p53 is modified by the attachment of polyubiquitin chains prior to proteasome-mediated degradation. However, the mechanism(s) involved in the delivery of polyubiquitylated p53 molecules to the proteasome are currently unclear. Here, we show that the human DNA repair protein hHR23 binds to polyubiquitylated p53 via its carboxyl-terminal ubiquitin-associated (Uba) domain shielding p53 from deubiquitylation in vitro and in vivo. In addition, downregulation of hHR23 expression within cells by RNA interference results in accumulation of p53. Since the Ubl domain of hHR23 has been shown to interact with the 26S proteasome, we propose that hHR23 is intrinsically involved in the delivery of polyubiquitylated p53 molecules to the proteasome. In this model, the Uba domain of hHR23 binds to polyubiquitin chains formed on p53 and protects them from deubiquitylation, while the Ubl domain delivers the polyubiquitylated p53 molecules to the proteasome.

ACKNOWLEDGMENTS

M.S. and C.B. share senior authorship of this work.

We are grateful to Helen Morrison for her comments on the manuscript; to David Lane, Jonathan Sleeman, and Christoph Englert for providing antibodies; and to Sibylle Mittnacht, Veronique Orian-Rousseau, Sakari Hietanen, Cecile M. Pickart, and Rohan T. Baker for providing plasmids.

This work was supported by grants from the Deutsche Forschungsgemeinschaft (C.B. and M.S.) and from Küln Fortune (M.S.) and by the Fonds der Chemischen Industrie (M.S.).