Cytoplasmic relocalization and inhibition of the cyclin-dependent kinase inhibitor p27(Kip1) by PKB/Akt-mediated phosphorylation in breast cancer

Nat Med. 2002 Oct;8(10):1136-44. doi: 10.1038/nm762. Epub 2002 Sep 16.


The cyclin-dependent kinase inhibitor p27(kip1) is a putative tumor suppressor for human cancer. The mechanism underlying p27(kip1) deregulation in human cancer is, however, poorly understood. We demonstrate that the serine/threonine kinase Akt regulates cell proliferation in breast cancer cells by preventing p27(kip1)-mediated growth arrest. Threonine 157 (T157), which maps within the nuclear localization signal of p27(kip1), is a predicted Akt-phosphorylation site. Akt-induced T157 phosphorylation causes retention of p27(kip1) in the cytoplasm, precluding p27(kip1)-induced G1 arrest. Conversely, the p27(kip1)-T157A mutant accumulates in cell nuclei and Akt does not affect p27(kip1)-T157A-mediated cell cycle arrest. Lastly, T157-phosphorylated p27(kip1) accumulates in the cytoplasm of primary human breast cancer cells coincident with Akt activation. Thus, cytoplasmic relocalization of p27(kip1), secondary to Akt-mediated phosphorylation, is a novel mechanism whereby the growth inhibitory properties of p27(kip1) are functionally inactivated and the proliferation of breast cancer cells is sustained.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cell Line
  • Cell Nucleus / metabolism
  • Cyclin-Dependent Kinase Inhibitor p27
  • Cyclin-Dependent Kinases / antagonists & inhibitors*
  • Enzyme Inhibitors / metabolism
  • Female
  • Genes, Tumor Suppressor
  • Humans
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphorylation
  • Protein Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt
  • Threonine / metabolism
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism*


  • Cell Cycle Proteins
  • Enzyme Inhibitors
  • Proto-Oncogene Proteins
  • Tumor Suppressor Proteins
  • Cyclin-Dependent Kinase Inhibitor p27
  • Threonine
  • AKT1 protein, human
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Cyclin-Dependent Kinases