title: Ubiquitin- and ATP-independent proteolytic turnover of p21 by the REGgamma-proteasome pathway.
abstract: We previously demonstrated that the proteasome activator REGgamma directs degradation of the steroid receptor coactivator SRC-3 by the 20S proteasome in an ATP- and ubiquitin-independent manner. Our efforts to identify additional endogenous direct targets of the REGgamma proteasome revealed that p21(Waf/Cip1), a central cyclin-dependent kinase inhibitor, is another endogenous target. Gain-of-function analysis, RNAi knockdown, REGgamma-deficient MEF analysis, and pulse-chase experiments substantiate that REGgamma promotes degradation of unbound p21. Cell-free proteasome proteolysis assays using purified REGgamma, p21, and the 20S proteasome confirm that REGgamma directly mediates degradation of free p21 in an ATP- and ubiquitin-independent manner. Depletion of REGgamma in a thyroid carcinoma cell line results in cell-cycle and proliferative alterations. Our study reveals that, in addition to degrading the SRC-3 growth coactivator, REGgamma also has a role in the regulation of the cell cycle through its ability to influence the level of a cell-cycle regulator(s).
authors.affiliation: Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
authors.forename: Xiaotao
authors.initials: X
authors.lastname: Li
authors.forename: Larbi
authors.initials: L
authors.lastname: Amazit
authors.forename: Weiwen
authors.initials: W
authors.lastname: Long
authors.forename: David M
authors.initials: DM
authors.lastname: Lonard
authors.forename: John J
authors.initials: JJ
authors.lastname: Monaco
authors.forename: Bert W
authors.initials: BW
authors.lastname: O'Malley
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001324:Autoantigens / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000235:genetics; D002474:Cell-Free System / Q000201:enzymology; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D051548:Histone Acetyltransferases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D056921:Nuclear Receptor Coactivator 3; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering; D013964:Thyroid Neoplasms / Q000201:enzymology / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*
chemical_list: D001324:Autoantigens; C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; C099558:Ki antigen; D034741:RNA, Small Interfering; D015534:Trans-Activators; D025801:Ubiquitin; D000255:Adenosine Triphosphate; D051548:Histone Acetyltransferases; C538866:NCOA3 protein, human; C538867:Ncoa3 protein, mouse; D056921:Nuclear Receptor Coactivator 3; D046988:Proteasome Endopeptidase Complex