title: Stability of p21Waf1/Cip1 CDK inhibitor protein is responsive to RhoA-mediated regulation of the actin cytoskeleton.
abstract: 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.
authors.affiliation: The Wellcome Trust Centre for Human Genetics, Oxford, UK.
authors.forename: M L
authors.initials: ML
authors.lastname: Coleman
authors.forename: R M
authors.initials: RM
authors.lastname: Densham
authors.forename: D R
authors.initials: DR
authors.lastname: Croft
authors.forename: M F
authors.initials: MF
authors.lastname: Olson
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002471:Cell Transformation, Neoplastic; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism*; D004795:Enzyme Stability; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D000090063:Proto-Oncogene Mas; D015398:Signal Transduction; D041701:Swiss 3T3 Cells; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D018631:ras Proteins / Q000494:pharmacology; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D018631:ras Proteins; D020742:rhoA GTP-Binding Protein