MDM2 promotes p21waf1/cip1 proteasomal turnover independently of ubiquitylation.
Journal: 2004/February - EMBO Journal
ISSN: 0261-4189
Abstract:
The CDK inhibitor p21waf1/cip1 is degraded by a ubiquitin-independent proteolytic pathway. Here, we show that MDM2 mediates this degradation process. Overexpression of wild-type or ring finger-deleted, but not nuclear localization signal (NLS)-deleted, MDM2 decreased p21waf1/cip1 levels without ubiquitylating this protein and affecting its mRNA level in p53(-/-) cells. This decrease was reversed by the proteasome inhibitors MG132 and lactacystin, by p19(arf), and by small interfering RNA (siRNA) against MDM2. p21waf1/cip1 bound to MDM2 in vitro and in cells. The p21waf1/cip1-binding-defective mutant of MDM2 was unable to degrade p21waf1/cip1. MDM2 shortened the half-life of both exogenous and endogenous p21waf1/cip1 by 50% and led to the degradation of its lysine-free mutant. Consequently, MDM2 suppressed p21waf1/cip1-induced cell growth arrest of human p53(-/-) and p53(-/-)/Rb(-/-)cells. These results demonstrate that MDM2 directly inhibits p21waf1/cip1 function by reducing p21waf1/cip1 stability in a ubiquitin-independent fashion.
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EMBO J 22(23): 6365-6377

MDM2 promotes p21<sup>waf1/cip1</sup> proteasomal turnover independently of ubiquitylation

Department of Biochemistry and Molecular Biology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA
Corresponding author e-mail: ude.usho@hul
Received 2003 Jun 30; Revised 2003 Oct 10; Accepted 2003 Oct 13.

Abstract

The CDK inhibitor p21 is degraded by a ubiquitin-independent proteolytic pathway. Here, we show that MDM2 mediates this degradation process. Overexpression of wild-type or ring finger-deleted, but not nuclear localization signal (NLS)-deleted, MDM2 decreased p21 levels without ubiquitylating this protein and affecting its mRNA level in p53 cells. This decrease was reversed by the proteasome inhibitors MG132 and lactacystin, by p19, and by small interfering RNA (siRNA) against MDM2. p21 bound to MDM2 in vitro and in cells. The p21-binding-defective mutant of MDM2 was unable to degrade p21. MDM2 shortened the half-life of both exogenous and endogenous p21 by 50% and led to the degradation of its lysine-free mutant. Consequently, MDM2 suppressed p21-induced cell growth arrest of human p53 and p53/Rbcells. These results demonstrate that MDM2 directly inhibits p21 function by reducing p21 stability in a ubiquitin-independent fashion.

Keywords: MDM2/p21 /proteasome/stability/ubiquitin
Abstract

Acknowledgements

We thank David M.Keller and Jayme Gallegos for proofreading this manuscript. We also thank Guillinao Lozano, Wafik S.el-Deiry, Jiandong Chen, Charles J.Sherr, Yue Xiong, Bruce E.Clurman and Anindya Dutta for generously providing us with cell lines, antibodies and plasmids. This work is supported by grants to H.L. from the NIH ({"type":"entrez-nucleotide","attrs":{"text":"CA095441","term_id":"34948748","term_text":"CA095441"}}CA095441, CA93614 and {"type":"entrez-nucleotide","attrs":{"text":"CA079721","term_id":"34931993","term_text":"CA079721"}}CA079721).

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