Non-CDK-bound p27 (p27 NCDK) is a marker for cell stress and is regulated through the Akt/PKB and AMPK-kinase pathways

• Published in: Experimental cell research 2010-03, Vol.316 (5), p.762-774
• Main Authors: Björklund, Mia A., Vaahtomeri, Kari, Peltonen, Karita, Viollet, Benoît, Mäkelä, Tomi P., Band, Arja M., Laiho, Marikki
• Format: Article
• Language: English
• Subjects: 60 APPLIED LIFE SCIENCES; Akt/PKB; Amino Acid Sequence; Aminoimidazole Carboxamide - analogs & derivatives; Aminoimidazole Carboxamide - metabolism; AMP; AMP-Activated Protein Kinases - genetics; AMP-Activated Protein Kinases - metabolism; AMPK; Animals; ANTIBODIES; Biomarkers - metabolism; Cell Line; CELL PROLIFERATION; Cellular biology; Cyclin dependent kinases; Cyclin-Dependent Kinase Inhibitor p27 - genetics; Cyclin-Dependent Kinase Inhibitor p27 - metabolism; Cyclin-Dependent Kinases - antagonists & inhibitors; Cyclin-Dependent Kinases - metabolism; Enzyme Activation; Enzyme Inhibitors - metabolism; FIBROBLASTS; GROWTH FACTORS; Humans; Hypoglycemic Agents - metabolism; INHIBITION; Kinases; Metabolic stress; Mice; Mice, Knockout; Molecular Sequence Data; p27; Peptides - genetics; Peptides - metabolism; PERTURBATION THEORY; Phosphatidylinositol 3-Kinases - antagonists & inhibitors; Phosphatidylinositol 3-Kinases - metabolism; PHOSPHOTRANSFERASES; Protein Subunits - genetics; Protein Subunits - metabolism; Proteins; Proto-Oncogene Proteins c-akt - antagonists & inhibitors; Proto-Oncogene Proteins c-akt - genetics; Proto-Oncogene Proteins c-akt - metabolism; Ribonucleotides - metabolism; Signal transduction; Signal Transduction - physiology; Stress; Stress, Physiological
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1016/j.yexcr.2009.12.014

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.