- Paper Report
- Open Access
Nuclear-cytoplasmic shuttling of p21Cip1/WAF1is regulated by Akt
- Karen L Schmeichel1
© Biomed Central Ltd 2001
- Received: 30 April 2001
- Accepted: 20 August 2001
- Published: 1 December 2001
- Cellular models, Pathogenesis and cell biology
The serine-threonine kinase Akt is a central component of signaling pathways controlling both cellular proliferation and apoptosis. In previous studies the authors showed that overexpression of HER-2/neu, a membrane tyrosine kinase whose upregulation correlates with some breast and ovarian cancers, activates signaling through Akt in NIH3T3 cells. By studying the cellular and molecular consequences of Akt activation in the context of these HER-2/neu overexpressing cells, the authors set out to reveal fundamental information regarding the signaling mechanisms altered during malignant progression.
Akt activation induces cellular proliferation, but does not alter apoptotic events. Akt interacts with the cell cycle inhibitor p21Cip1/WAF1 and phosphorylates a threonine residue that resides in the molecule's carboxy-terminal nuclear localization sequence (NLS). Total levels of p21Cip1/WAF1 were not altered by Akt activation, but its subcellular distribution was altered: when p21Cip1/WAF1 NLS phosphorylation is reduced the protein is predominantly nuclear, but when p21Cip1/WAF1 is phosphorylated it is cytoplasmic. Collectively these findings suggest a model in which cell proliferation can be influenced by HER-2/neu-Akt signaling pathways by altering the subcellular localization of specific cell cycle regulators. In this case, activated Akt phosphorylates the cell-cycle inhibitor p21Cip1/WAF1, thereby causing it to shuttle to the cytoplasm where it is sequestered from its targets in the nuclear cell cycle machinery.
Cell proliferation assays, phosphoaminoacid analysis, coimmunoprecipitation, immunoblotting, transient transfections, immunofluorescence, colony-formation assay, cellular fractionation (cytosol/nucleus), BrdU incorporation.