PKB/Akt phosphorylates p27, impairs nuclear import of p27 and opposes p27-mediated G1 arrest.
Mechanisms linking mitogenic and growth inhibitory cytokine signaling and the cell cycle have not been fully elucidated in either cancer or in normal cells. Here we show that activation of protein kinase B (PKB)/Akt, contributes to resistance to antiproliferative signals and breast cancer progression in part by impairing the nuclear import and action of p27. Akt transfection caused cytoplasmic p27 accumulation and resistance to cytokine-mediated G1 arrest. The nuclear localization signal of p27 contains an Akt consensus site at threonine 157, and p27 phosphorylation by Akt impaired its nuclear import in vitro. Akt phosphorylated wild-type p27 but not p27T157A. In cells transfected with constitutively active Akt(T308DS473D)(PKB(DD)), p27WT mislocalized to the cytoplasm, but p27T157A was nuclear. In cells with activated Akt, p27WT failed to cause G1 arrest, while the antiproliferative effect of p27T157A was not impaired. Cytoplasmic p27 was seen in 41% (52 of 128) of primary human breast cancers in conjunction with Akt activation and was correlated with a poor patient prognosis. Thus, we show a novel mechanism whereby Akt impairs p27 function that is associated with an aggressive phenotype in human breast cancer.
Liang
Jiyong
J
Molecular and Cell Biology, Sunnybrook and Women's College Health Sciences Centre, St. Mary's Hospital, McGill University, Montreal, Quebec.
Zubovitz
Judit
J
Petrocelli
Teresa
T
Kotchetkov
Rouslan
R
Connor
Michael K
MK
Han
Kathy
K
Lee
Jin-Hwa
JH
Ciarallo
Sandra
S
Catzavelos
Charles
C
Beniston
Richard
R
Franssen
Edmee
E
Slingerland
Joyce M
JM
D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D005260:Female; D016193:G1 Phase / Q000502:physiology*; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015996:Survival Rate; D013912:Threonine / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins; D019927:Cyclin E; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases; D004791:Enzyme Inhibitors; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011993:Recombinant Fusion Proteins; D013912:Threonine; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; C494918:AKT1 protein, human; C495894:CDK2 protein, human