title: MDM2 promotes p21waf1/cip1 proteasomal turnover independently of ubiquitylation.
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.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
authors.forename: Yetao
authors.initials: Y
authors.lastname: Jin
authors.forename: Hunjoo
authors.initials: H
authors.lastname: Lee
authors.forename: Shelya X
authors.initials: SX
authors.lastname: Zeng
authors.forename: Mu-Shui
authors.initials: MS
authors.lastname: Dai
authors.forename: Hua
authors.initials: H
authors.lastname: Lu
mesh_terms: D000230:Adenocarcinoma; D000818:Animals; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D007700:Kinetics; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009097:Multienzyme Complexes / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D034741:RNA, Small Interfering / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D013736:Testicular Neoplasms; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex