title: S-phase lengthening induced by p16(INK4a) overexpression in malignant cells with wild-type pRb and p53.
abstract: The p16(INK4a) protein is considered to regulate the cell cycle progression mainly by inhibiting cyclin-dependent kinases (CDKs) 4 and 6 activity and leading to an arrest in G(0)/G(1). Here, we report that ectopic expression of p16(INK4a) in three p16-/pRb(Wt)/p53(Wt) human cancer cell lines MCF7, U2OS and U87 induces S-phase lengthening along with G(1) accumulation. S-phase lengthening is suggested by the discrepancy between the unchanged or even increased percentage of cells in S phase found by flow cytometry DNA content analysis and the drop of BrdU labelling, and demonstrated by IdU/BrdU double labelling. p16(INK4a) induces a profound decrease in the CDK4/6-mediated pRb phosphorylation on Ser-807/811, a downregulation of CDK2 and CDK1 protein expression independently of G(1) accumulation, and a decrease in Thr/Pro phosphorylation in part carried out by CDKs. In MCF7 cells, overexpression of the p16 G101W mutant, which is unable to inhibit CDK4/6 kinase activity and shows a modified subcellular localization, does not provoke the S-phase lengthening and the inhibition of Ser807/811-pRB and of Thr/Pro phosphorylation as wild-type p16(INK4a) does. Our results demonstrate that p16(INK4a) induces a S-phase lengthening independently of cellular origin. The CDK4/6 kinase activity inhibition together with the reduced expression of CDK2 and CDK1 acting downstream of G(1) phase may prevent cells from any possible kinasic compensatory mechanisms, and thus lead to a cell cycle progression inhibition.
authors: Université Claude Bernard Lyon 1, CNRS UMR 5239, ENS-HCL, Faculté de Médecine, Pierre-Bénite, France.
authors: Wei Wen
authors: WW
authors: Chien
authors: Carine
authors: C
authors: Domenech
authors: Régine
authors: R
authors: Catallo
authors: Gilles
authors: G
authors: Salles
authors: Martine
authors: M
authors: Ffrench
mesh_terms: D019943:Amino Acid Substitution; D045744:Cell Line, Tumor; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4 / Q000037:antagonists & inhibitors / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6 / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D016193:G1 Phase; D006801:Humans; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000378:metabolism*; D016196:S Phase; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; C495894:CDK2 protein, human; C495900:CDK4 protein, human; C495911:CDK6 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6