COP9 signalosome-specific phosphorylation targets p53 to degradation by the ubiquitin system

In higher eukaryotic cells, the p53 protein is degraded by the ubiquitin-26 S proteasome system mediated by Mdm2 or the human papilloma virus E6 protei n. Here we show that COP9 signalosome (CSN)-specific phosphorylation target s human p53 to ubiquitin-26S proteasome-dependent degradation. As visualize d by electron microscopy, p53 binds with high affinity to the native CSN co mplex. p53 interacts via its N-terminus with CSN subunit 5/Jab1 as shown by far-western and pull-down assays. The CSN-specific phosphorylation sites w ere mapped to the core domain of p53 including Thr155. A phosphorylated pep tide, Delta p53(145-164), specifically inhibits CSN-mediated phosphorylatio n and p53 degradation. Curcumin, a CSN kinase inhibitor, blocks E6-dependen t p53 degradation in reticulocyte lysates. Mutation of Thr155 to valine is sufficient to stabilize p53 against E6-dependent degradation in reticulocyt e lysates and to reduce binding to Mdm2. The p53T155V mutant accumulates in both HeLa and HL 60 cells and exhibits a mutant (PAb 240+) conformation. I t induces the cyclin-dependent inhibitor p21, In HeLa and MCF-7 cells, inhi bition of CSN kinase by curcumin or Delta p53(145-164) results in accumulat ion of endogenous p53.