title: Rapamycin inhibits cdk4 activation, p 21(WAF1/CIP1) expression and G1-phase progression in transformed mouse fibroblasts.
abstract: Rapamycin, a bacterial macrolide antibiotic, is a potent immunosuppressant agent that blocks cell proliferation by inhibiting the G1/S transition in several cell types. In sensitive cells, rapamycin inhibits the phosphorylation of p70 S6K and of Rb; however, the precise mechanisms involved have not been elucidated. In the mouse BP-A31 fibroblasts, synchronised in G0/G1 phase by serum starvation and induced to reinitiate the G1-phase progression, rapamycin inhibited the entry into S phase. The effect of rapamycin was situated in early G1 phase. The assembly of the cyclin D1/cdk4 complexes that phosphorylate Rb early in the G1 phase was not modified by the drug. Nevertheless, an inhibition of the activation of cyclin D1/cdk4 and cyclin E/cdk2 as well as of Rb phosphorylation accompanied the cell cycle arrest. Remarkably, rapamycin reduced the level of total p21(WAF1/CIP1) as well as that of p21(WAF1/CIP1) associated with the cyclin D1/cdk4 complexes. Besides its inhibitory activity toward cdk, p21(WAF1/CIP1) has been recently found to participate in the formation/stabilisation/nuclear translocation of cyclin D1/cdk4 complexes. We propose that the inhibition of the expression of p21(WAF1/CIP1) is a mechanism by which rapamycin inhibits the triggering of the cdk cascade in the BP-A31 cells.
authors.affiliation: INSERM U 482, Hôpital St-Antoine, Paris, France. gaben@adr.st-antoine.inserm.fr
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Gaben
authors.forename: Cecile
authors.initials: C
authors.lastname: Saucier
authors.forename: Monique
authors.initials: M
authors.lastname: Bedin
authors.forename: Véronique
authors.initials: V
authors.lastname: Barbu
authors.forename: Jan
authors.initials: J
authors.lastname: Mester
mesh_terms: D016475:3T3 Cells / Q000187:drug effects; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D002461:Cell Line, Transformed; D019938:Cyclin D1 / Q000378:metabolism; D019927:Cyclin E / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D005347:Fibroblasts / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects*; D051379:Mice; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D016196:S Phase / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology*
chemical_list: D000903:Antibiotics, Antineoplastic; C493957:Cdkn1a protein, mouse; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D019938:Cyclin D1; D019893:Ribosomal Protein S6 Kinases; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D020123:Sirolimus