Cytoplasmic p27Kip1 counteracts the pro-apoptotic function of the open conformation of PTEN by retention and destabilization of PTEN outside of the nucleus.
The tumor suppressor activity of p27Kip1 takes place in the cell nucleus by inhibitory binding to cyclin/CDK complexes. p27Kip1 can also be localized in the cytoplasm, where it has been proposed to have oncogenic properties. Here, we describe a novel role for cytoplasmic p27Kip1 which could account for its activity as an oncoprotein by negative regulation of the PTEN tumor suppressor. p27Kip1 physically interacted with the open conformation of PTEN, which is competent to enter the nucleus. In mammalian cells, cytoplasmic p27Kip1 retained to nuclear-targeted PTEN in the cytoplasm. This retention was exerted by the C-terminal p27Kip1 region, and was independent of cyclin/CDK-binding. The nuclear accumulation of PTEN triggered by pro-apoptotic TNFα treatment was abolished by cytoplasmic p27Kip1. Furthermore, conformationally-open PTEN displayed diminished protein stability and pro-apoptotic activity in the presence of cytoplasmic p27Kip1. Our results support a conformationally-dependent model of cytoplasmic retention and negative regulation of the activity of nuclear PTEN by oncogenic cytoplasmic p27Kip1, and suggest the existence of reciprocal mechanisms to regulate the levels of both p27Kip1 and PTEN.
Centro de Investigación Príncipe Felipe, Valencia 46013, Spain.
Amparo
A
Andrés-Pons
Centro de Investigación Príncipe Felipe, Valencia 46013, Spain.
Anabel
A
Gil
Centro de Investigación Príncipe Felipe, Valencia 46013, Spain.
María D
MD
Oliver
Centro de Investigación Príncipe Felipe, Valencia 46013, Spain.
Natalia-Soledad
NS
Sotelo
Centro de Investigación Príncipe Felipe, Valencia 46013, Spain. Electronic address: rpulido@cipf.es.
Rafael
R
Pulido
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D019556:COS Cells; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D020014:K562 Cells; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D010957:Plasmids; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
C436291:CDKN1B protein, human; D018797:Cell Cycle Proteins; D014409:Tumor Necrosis Factor-alpha; D050760:Cyclin-Dependent Kinase Inhibitor p27; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human