title: p21 (CDKN1A) is a negative regulator of p53 stability.
abstract: Cell cycle arrest in response to DNA damage involves protein stabilization and consequent upregulation of p53, which induces transcription of cyclin-dependent kinase inhibitor p21 (CDKN1A). We now show that p21 acts as a negative regulator of the cellular levels of p53. p21 knockdown by short hairpin RNA strongly increased p53 upregulation by a DNA-damaging drug doxorubicin in HT1080 fibrosarcoma cells. A protease inhibitor N-Ac-Leu-Leu-norleucinal (ALLN) drastically increased the amount of p53 in HCT116 colon carcinoma cells, but it had no effect on the already high p53 level in a p21(-/-) derivative of this cell line. Inhibition of transcription, which increases p53 levels in different cell lines due to the degradation of p53-destabilizing proteins such as Mdm2, failed to increase but instead decreased the amount of p53 in p21(-/-) cells, despite a drastic decrease in the level of Mdm2. These results indicate that p21 acts as a negative regulator of p53 stability in different cell types. p53 regulation by p21 may provide a negative regulatory loop that limits p53 induction.
authors.affiliation: Cancer Center, Ordway Research Institute, Albany, New York 12208, USA.
authors.forename: Eugenia V
authors.initials: EV
authors.lastname: Broude
authors.forename: Zoya N
authors.initials: ZN
authors.lastname: Demidenko
authors.forename: Claire
authors.initials: C
authors.lastname: Vivo
authors.forename: Mari E
authors.initials: ME
authors.lastname: Swift
authors.forename: Brian M
authors.initials: BM
authors.lastname: Davis
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Blagosklonny
authors.forename: Igor B
authors.initials: IB
authors.lastname: Roninson
mesh_terms: D002453:Cell Cycle / Q000502:physiology*; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D004249:DNA Damage; D004317:Doxorubicin / Q000633:toxicity; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D015151:Immunoblotting; D007976:Leupeptins / Q000494:pharmacology; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D007976:Leupeptins; D016159:Tumor Suppressor Protein p53; C063261:acetylleucyl-leucyl-norleucinal; D004317:Doxorubicin; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2