title: PDK1-dependent activation of atypical PKC leads to degradation of the p21 tumour modifier protein.
abstract: p21(WAF1/CIP1) Contributes to positive and negative growth control on multiple levels. We previously mapped phosphorylation sites within the C-terminal domain of p21 that regulate proliferating cell nuclear antigen binding. In the current study, a kinase has been fractionated from mammalian cells that stoichiometrically phosphorylates p21 at the Ser146 site, and the enzyme has been identified as an insulin-responsive atypical protein kinase C (aPKC). Expression of PKCzeta or activation of the endogenous kinase by 3-phosphoinositide dependent protein kinase-1 (PDK1) decreased the half-life of p21. Conversely, dnPKCzeta or dnPDK1 increased p21 protein half-life, and a PDK1-dependent increase in the rate of p21 degradation was mediated by aPKC. Insulin stimulation gave a biphasic response with a rapid transient decrease in p21 protein levels during the initial signalling phase that was dependent on phosphatidylinositol 3- kinase, PKC and proteasome activity. Thus, aPKC provides a physiological signal for the degradation of p21. The rapid degradation of p21 protein during the signalling phase of insulin stimulation identifies a novel link between energy metabolism and a key modulator of cell cycle progression.
authors.affiliation: Cancer Research UK Laboratories, University of Dundee Medical School, Dundee DD1 9SY, UK.
authors.forename: Mary T
authors.initials: MT
authors.lastname: Scott
authors.forename: Angela
authors.initials: A
authors.lastname: Ingram
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Ball
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D002455:Cell Division; D002460:Cell Line; D002850:Chromatography, Gel; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D004797:Enzyme-Linked Immunosorbent Assay; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D007328:Insulin / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D000099221:Protein Kinase C zeta
chemical_list: D064413:3-Phosphoinositide-Dependent Protein Kinases; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D007328:Insulin; D010455:Peptides; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011994:Recombinant Proteins; D012694:Serine; D000099221:Protein Kinase C zeta; C493956:CDKN1A protein, human; C578562:PDPK1 protein, human; C115015:PKC-3 protein