Inhibitors of cyclin-dependent kinases induce features of replicative senescence in early passage human diploid fibroblasts.
After a limited number of population doublings (PDs), cultures of normal mammalian diploid cells undergo an irreversible growth arrest known as replicative senescence [1]. As well as contributing to cellular ageing, senescence is viewed as an important mechanism of tumour suppression by preventing the emergence of immortal cell clones [2-4]. Senescent cells have a number of characteristics that distinguish them from cycling or quiescent cells including elevated levels of two cyclin-dependent kinase (Cdk) inhibitors, p16INK4a and p21CIP1 [5-11]. Here, we demonstrate that both of these Cdk inhibitors, as well as other members of their protein families (the INK4 and CIP/KIP families, respectively [12]), induce several facets of the senescent phenotype when ectopically expressed in young human diploid fibroblasts. These include a reduced proliferative capacity, an altered size and shape, the presence of underphosphorylated retinoblastoma protein (pRb), increased expression of plasminogen activator inhibitor (PAI-1) and the appearance of senescence-associated beta-galactosidase (SA-beta-gal) activity [2,3,13-15]. A 20 amino acid peptide from p16INK4a that inhibits Cdks active in the G1 phase of the cell cycle [16] produces similar effects in a dose-dependent manner suggesting that, in primary fibroblasts, inhibition of G1-specific Cdk activity is sufficient to induce phenotypic changes that normally occur at the end of their finite lifespan.
McConnell
B B
BB
Imperial Cancer Research Fund, London, UK.
Starborg
M
M
Brookes
S
S
Peters
G
G
D000818:Animals; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D016213:Cyclins / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D005347:Fibroblasts / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010641:Phenotype; D012313:RNA; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism; D025521:Tumor Suppressor Proteins
C493956:CDKN1A protein, human; C493966:CDKN2B protein, human; D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D012313:RNA; D018844:Cyclin-Dependent Kinases