title: MAP kinase cascade is required for p27 downregulation and S phase entry in fibroblasts and epithelial cells.
abstract: The present report delineates the critical pathway in the G(1) phase involved in downregulation of p27(Kip1), a cyclin-dependent kinase inhibitor, which plays a pivotal role in controlling entry into the S phase of the cell cycle. In resting CCL39 fibroblasts and IEC-6 intestinal epithelial cells, protein levels of p27(Kip1) were elevated but dramatically decreased on serum stimulation, along with hyperphosphorylation of pRb and increased CDK2 activity. In both cell types, expression of ras resulted in an increase of basal and serum-stimulated E2F-dependent transcriptional activity and a reduction in p27(Kip1) protein levels as well. The role of the mitogen-activated protein (MAP) kinase cascade in p27(Kip1) reduction and S phase reentry was reinforced by the blockades of serum-induced E2F-dependent transcriptional activity and p27(Kip1) downregulation with the MKK-1/2 inhibitor PD-98059. In both cell lines, downregulation of p27(Kip1) was associated with a repression of its synthesis, an event mediated by the p42/p44 MAP kinase pathway. Using an antisense approach, we demonstrated that p27(Kip1) may control cell cycle exit in both cell types. These data indicate that activation of the MAP kinase cascade is required for S phase entry and p27(Kip1) downregulation in fibroblasts and epithelial cells.
authors.affiliation: Groupe du Conseil de Recherches Médicales sur le Développement Fonctionnel et la Physiopathologie du Tube Digestif, Département d'Anatomie et Biologie Cellulaire, Quebec J1H 5N4, Canada. nrivard@courrier.usherb.ca
authors.forename: N
authors.initials: N
authors.lastname: Rivard
authors.forename: M J
authors.initials: MJ
authors.lastname: Boucher
authors.forename: C
authors.initials: C
authors.lastname: Asselin
authors.forename: G
authors.initials: G
authors.lastname: L'Allemain
mesh_terms: D000818:Animals; D001790:Blood Physiological Phenomena; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D015536:Down-Regulation; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008934:Mitogens / Q000494:pharmacology; D020559:Monomeric GTP-Binding Proteins / Q000502:physiology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D016160:Retinoblastoma Protein / Q000378:metabolism; D016196:S Phase / Q000502:physiology*; D025521:Tumor Suppressor Proteins; D018631:ras Proteins / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000502:physiology
chemical_list: C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D008869:Microtubule-Associated Proteins; D008934:Mitogens; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D020928:Mitogen-Activated Protein Kinases; D020559:Monomeric GTP-Binding Proteins; D018631:ras Proteins; D020742:rhoA GTP-Binding Protein