Stability of p21Waf1/Cip1 CDK inhibitor protein is responsive to RhoA-mediated regulation of the actin cytoskeleton

Oncogene. 2006 May 4;25(19):2708-16. doi: 10.1038/sj.onc.1209322.


The proto-oncogene Ras GTPase stimulates transcription of p21Waf1/Cip1 (p21), which is repressed by the RhoA GTPase. We previously showed that Ras also elevates p21 protein levels by reducing its proteasome-mediated degradation. Therefore, we investigated whether RhoA also influenced p21 protein degradation. Pulse-chase analysis of p21 protein stability revealed that inhibitors of Rho function, which disrupt filamentous actin (F-actin), drastically slowed p21 degradation. Direct F-actin disruption mimicked Rho inhibition to stabilize p21. We found that Rho inhibition, or F-actin disruption, activated the JNK stress-activated protein kinase, and that interfering with JNK signalling, but not p38, abrogated p21 stabilization by Rho inhibition or F-actin-disrupting drugs. In addition, Ras-transformation led to increased constitutive JNK activity that contributed to the elevated p21 protein levels. These data suggest that p21 stability is influenced by a mechanism that monitors F-actin downstream of Rho, and which acts through a pathway involving activation of JNK. These results may have significant implications for therapies that target Rho-signalling pathways to induce p21-mediated cell-cycle arrest.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism*
  • Animals
  • Blotting, Northern
  • Blotting, Western
  • Cell Transformation, Neoplastic
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism*
  • Cytoskeleton / metabolism*
  • Enzyme Stability
  • Fibroblasts / cytology
  • Fibroblasts / metabolism
  • MAP Kinase Kinase 4 / metabolism
  • Mice
  • NIH 3T3 Cells
  • Signal Transduction
  • Swiss 3T3 Cells
  • p38 Mitogen-Activated Protein Kinases / metabolism
  • ras Proteins / pharmacology
  • rhoA GTP-Binding Protein / genetics
  • rhoA GTP-Binding Protein / metabolism*


  • Actins
  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • p38 Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase 4
  • ras Proteins
  • rhoA GTP-Binding Protein