title: Nucleophosmin/B23 interacts with p21WAF1/CIP1 and contributes to its stability.
abstract: The cyclin-dependent kinase inhibitor p21(WAF1/CIP1) is a critical regulator of cell cycle, and it is easily degraded by proteasome through ubiquitin-dependent and -independent pathway. The mechanism of the post-translational regulation of p21 stability remains to be further clarified. In the present study, we have identified nucleophosmin (NPM)/B23, a multifunctional protein that bound p21 and contributed to its stability. The direct interaction between p21 and NPM was confirmed by reciprocal co-immunoprecipitation and GST pull-down assay. Confocal microscopy showed that NPM partially co-localized with p21 in nucleoplasm and their co-localization increased treated with Act D which induces the nucleoplasmic translocation of NPM. We observed the half life of p21 was prolonged with overexpression of NPM or Act D treatment. Knockdown of NPM by siRNA resulted in downregulation of p21 and impaired upregulation of p21 treated with Act D. Further, we examined the effect of NPM expression on the ubiquitination of p21. Overexpression of NPM inhibited the ubiquitination of p21, and depletion of NPM remarkably improved the ubiquitination of p21. Altogether, we provide evidence for a direct binding between NPM and p21, and assign NPM as a positive post-translational regulator of p21.
authors.affiliation: Department of Pathology, Cancer Center of Sun Yat-sen University, Guangzhou, China.
authors.forename: Jianyong
authors.initials: J
authors.lastname: Xiao
authors.forename: Zhiyi
authors.initials: Z
authors.lastname: Zhang
authors.forename: George Gong
authors.initials: GG
authors.lastname: Chen
authors.forename: Meifang
authors.initials: M
authors.lastname: Zhang
authors.forename: Yuanjie
authors.initials: Y
authors.lastname: Ding
authors.forename: Jia
authors.initials: J
authors.lastname: Fu
authors.forename: Mingtao
authors.initials: M
authors.lastname: Li
authors.forename: Jing-Ping
authors.initials: JP
authors.lastname: Yun
mesh_terms: D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000187:drug effects / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D009687:Nuclear Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000090243:Nucleophosmin; D055550:Protein Stability; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D011500:Protein Synthesis Inhibitors; D034741:RNA, Small Interfering; D025801:Ubiquitin; D000090243:Nucleophosmin; D003609:Dactinomycin