title: Non-CDK-bound p27 (p27(NCDK)) is a marker for cell stress and is regulated through the Akt/PKB and AMPK-kinase pathways.
abstract: p27Kip1 (p27) tumour suppressor protein is regulated by multiple mechanisms including its turnover, localization and complex formation with its key targets, cyclin-dependent kinases (CDK) and cyclins. We have earlier shown that p27 exists in cells in a form that lacks cyclin/CDK interactions (hence non-CDK, p27(NCDK)) but the nature of p27(NCDK) has remained unresolved. Here we demonstrate that the epitope recognized by the p27(NCDK)-specific antibody resides in the p27 CDK-interaction domain and that p27(NCDK) is regulated by the balance of CDK inhibitors and cyclin-CDK complexes. We find that signalling by cellular growth promoting pathways, like phosphoinositol 3-kinase (PI3K) and specifically Akt/PKB kinase, inversely correlates with p27(NCDK) levels whereas total p27 levels are unaffected. p27(NCDK), but not total p27, is increased by cellular perturbations such as hyperosmotic and metabolic stress and activation of AMP-activated protein kinase (AMPK). By using AMPK catalytic subunit proficient and deficient cells we further demonstrate that the AMPK pathway governs p27(NCDK) responses to metabolic stress and PI3K inhibition. These results indicate that p27(NCDK) is a sensitive marker for both cell stress and proliferation over and above p27 and is regulated by Akt/PKB and AMPK pathways.
authors.affiliation: Molecular Cancer Biology Program, Biomedicum Helsinki and Haartman Institute, University of Helsinki, Helsinki, Finland.
authors.forename: Mia A
authors.initials: MA
authors.lastname: Björklund
authors.forename: Kari
authors.initials: K
authors.lastname: Vaahtomeri
authors.forename: Karita
authors.initials: K
authors.lastname: Peltonen
authors.forename: Benoît
authors.initials: B
authors.lastname: Viollet
authors.forename: Tomi P
authors.initials: TP
authors.lastname: Mäkelä
authors.forename: Arja M
authors.initials: AM
authors.lastname: Band
authors.forename: Marikki
authors.initials: M
authors.lastname: Laiho
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D015415:Biomarkers / Q000378:metabolism*; D002460:Cell Line; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012265:Ribonucleotides / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013312:Stress, Physiological
chemical_list: D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide; D015415:Biomarkers; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases; D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D010455:Peptides; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D021122:Protein Subunits; D051057:Proto-Oncogene Proteins c-akt; D012265:Ribonucleotides; C031143:AICA ribonucleotide