New roles for p21 and p27 cell-cycle inhibitors: a function for each cell compartment?

Trends Cell Biol. 2003 Feb;13(2):65-70. doi: 10.1016/s0962-8924(02)00043-0.


Cell division relies on the activation of cyclins, which bind to cyclin-dependent kinases (CDKs) to induce cell-cycle progression towards S phase and later to initiate mitosis. Since uncontrolled cyclin-dependent kinase activity is often the cause of human cancer, their function is tightly regulated by cell-cycle inhibitors such as the p21 and p27 Cip/Kip proteins. Following anti-mitogenic signals or DNA damage, p21 and p27 bind to cyclin-CDK complexes to inhibit their catalytic activity and induce cell-cycle arrest. Interestingly, recent discoveries suggest that p21 and p27 might have new activities that are unrelated to their function as CDK inhibitors. The identification of new targets of Cip/Kip proteins as well as evidence of Cip/Kip cytoplasmic relocalization have revealed unexpected functions for these proteins in the control of CDK activation, in the regulation of apoptosis and in transcriptional activation. This article discusses recent insights into these possible additional functions of p21 and p27.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Apoptosis / physiology
  • Cell Compartmentation / physiology*
  • Cell Cycle / physiology*
  • Cell Cycle Proteins / metabolism*
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclin-Dependent Kinase Inhibitor p27
  • Cyclin-Dependent Kinases / metabolism
  • Cyclins / metabolism*
  • Cytoplasm / genetics
  • Cytoplasm / metabolism
  • Eukaryotic Cells / metabolism*
  • Humans
  • Transcriptional Activation / physiology
  • Tumor Suppressor Proteins / metabolism*


  • CDKN1A protein, human
  • Cell Cycle Proteins
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Tumor Suppressor Proteins
  • Cyclin-Dependent Kinase Inhibitor p27
  • Cyclin-Dependent Kinases