title: Ras-stimulated extracellular signal-related kinase 1 and RhoA activities coordinate platelet-derived growth factor-induced G1 progression through the independent regulation of cyclin D1 and p27.
abstract: Platelet-derived growth factor (PDGF)-induced Ras activation is required for G1 progression in Chinese hamster embryo fibroblasts (IIC9 cells). Ras stimulates both extracellular signal-related kinase (ERK) activation and RhoA activation in response to PDGF stimulation. Inhibition of either of these Ras-stimulated pathways results in growth arrest. We have shown previously that Ras-stimulated ERK activation is essential for the induction and continued G1 expression of cyclin D1. In this study we examine the role of Ras-induced RhoA activity in G1 progression. Unstimulated IIC9 cells expressed high levels of the G1 cyclin-dependent kinase inhibitor p27(KIP1). Stimulation with PDGF resulted in a dramatic decrease in p27(KIP1) protein expression. This decrease was attributed to increased p27(KIP1) protein degradation. Overexpression of dominant-negative forms of Ras or RhoA completely blocked PDGF-induced p27(KIP1) degradation, but only dominant-negative Ras inhibited cyclin D1 protein expression. C3 transferase also inhibited PDGF-induced p27(KIP1) degradation, thus further implicating RhoA in p27(KIP1) regulation. Overexpression of dominant-negative ERK resulted in inhibition of PDGF-induced cyclin D1 expression but had no effect on PDGF-induced p27(KIP1) degradation. These data suggest that Ras coordinates the independent regulation of cyclin D1 and p27(KIP1) expression by the respective activation of ERK and RhoA and that these pathways converge to determine the activation state of complexes of cyclin D1 and cyclin-dependent kinase in response to mitogen.
authors.affiliation: Department of Cell and Molecular Biology, St. Louis University, St. Louis, Missouri 63104, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Weber
authors.forename: W
authors.initials: W
authors.lastname: Hu
authors.forename: S C
authors.initials: SC
authors.lastname: Jefcoat
authors.forename: D M
authors.initials: DM
authors.lastname: Raben
authors.forename: J J
authors.initials: JJ
authors.lastname: Baldassare
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism; D000818:Animals; D001905:Botulinum Toxins; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D018797:Cell Cycle Proteins; D006224:Cricetinae; D019938:Cyclin D1 / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D003599:Cytoskeleton / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism*; D016193:G1 Phase; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D025521:Tumor Suppressor Proteins; D018631:ras Proteins / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein
chemical_list: D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D046911:Macromolecular Substances; D008869:Microtubule-Associated Proteins; D010982:Platelet-Derived Growth Factor; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D018844:Cyclin-Dependent Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D018631:ras Proteins; D020742:rhoA GTP-Binding Protein