Akt-dependent phosphorylation of p27Kip1 promotes binding to 14-3-3 and cytoplasmic localization.
In many human cancers, the cyclin-dependent kinase inhibitor p27(Kip1) is expressed at low or undetectable levels. The decreased p27(Kip1) expression allows cyclin-dependent kinase activity to cause cells to enter into S phase and correlates with poor patient survival. Inhibition of serine/threonine kinase Akt signaling by some pharmacological agents or by PTEN induces G(1) arrest, in part by up-regulating p27(Kip1). However, the role of Akt-dependent phosphorylation in p27(Kip1) regulation is not clear. Here, we show that Akt bound directly to and phosphorylated p27(Kip1). Screening p27(Kip1) phosphorylation sites identified the COOH-terminal Thr(198) residue as a novel site. Further analysis revealed that 14-3-3 proteins bound to p27(Kip1) through Thr(198) only when it was phosphorylated by Akt. Although Akt also phosphorylated p27(Kip1) at Ser(10) and Thr(187), these two sites were not involved in the binding to 14-3-3 proteins. p27(Kip1) phosphorylated at Thr(198) exists only in the cytoplasm. Therefore, Akt promotes cell-cycle progression through the mechanisms of phosphorylation-dependent 14-3-3 binding to p27(Kip1) and cytoplasmic localization.
Fujita
Naoya
N
Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0032, Japan.
Sato
Saori
S
Katayama
Kazuhiro
K
Tsuruo
Takashi
T
D048948:14-3-3 Proteins; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27; D003593:Cytoplasm / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D013912:Threonine / Q000737:chemistry; D014162:Transfection; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D048948:14-3-3 Proteins; D018797:Cell Cycle Proteins; D010455:Peptides; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D013912:Threonine; D014446:Tyrosine 3-Monooxygenase; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt