title: Interaction with cyclin-dependent kinases and PCNA modulates proteasome-dependent degradation of p21.
abstract: The cyclin-dependent kinase (CDK) inhibitor p21(Cip1/Waf1) plays an essential role in the control of cell proliferation by modulating the activity of cyclin/CDK complexes in response to various intracellular or extracellular signals. Small variations in p21 expression levels may determine whether it acts as an inhibitor or an assembly factor for cyclin/CDK complexes. It is therefore critical to better characterize the mechanisms regulating p21 abundance. Here, we show, using a tetracycline-regulated system in p53-deficient DLD-1 human colon cancer cells, that p21 protein levels and stability are regulated by the proteasome-dependent degradation pathway and by association with its partners, CDKs and PCNA. A p21 mutant deficient for interaction with CDKs, p21CDK-, displayed an enhanced stability and greatly reduced sensitivity to proteasome-mediated proteolysis, indicating that association with cyclin/CDK complexes may trigger p21 degradation. In contrast, a p21 mutant impaired in the interaction with PCNA, p21PCNA-, exhibited a decreased stability, suggesting that association with PCNA protects p21 from proteasome-dependent degradation. Furthermore, the abundance of p21 itself, in addition to protein-protein interactions, may also modulate p21 stability since we found that high levels of p21 expression overcome proteasome-dependent regulation of p21 accumulation.
authors.affiliation: I.P.B.S.-C.N.R.S Université Paul Sabatier, Toulouse, France.
authors.forename: C
authors.initials: C
authors.lastname: Cayrol
authors.forename: B
authors.initials: B
authors.lastname: Ducommun
mesh_terms: D003110:Colonic Neoplasms / Q000473:pathology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D009097:Multienzyme Complexes / Q000378:metabolism*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D018809:Proliferating Cell Nuclear Antigen; D016159:Tumor Suppressor Protein p53; D018844:Cyclin-Dependent Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex