title: Cdk4 disruption renders primary mouse cells resistant to oncogenic transformation, leading to Arf/p53-independent senescence.
abstract: A large number of human cancers display alterations in the Ink4a/cyclin D/Cdk4 genetic pathway, suggesting that activation of Cdk4 plays an important role in oncogenesis. Here we report that Cdk4-null mouse embryonic fibroblasts are resistant to transformation in response to Ras activation with dominant-negative (DN) p53 expression or in the Ink4a/Arf-null background, judged by foci formation, anchorage-independent growth, and tumorigenesis in athymic mice. Cdk4-null fibroblasts proliferate at normal rates during early passages. Whereas Cdk4(+/+)Ink4a/Arf(-/-) cells are immortal in culture, Cdk4(-/-)Ink4a/Arf(-/-) cells undergo senescence during continuous culture, as do wild-type cells. Activated Ras also induces premature senescence in Cdk4(-/-)Ink4a/Arf(-/-) cells and Cdk4(-/-) cells with DNp53 expression. Thus, Cdk4 deficiency causes senescence in a unique Arf/p53-independent manner, which accounts for the loss of transformation potential. Cdk4-null cells express high levels of p21(Cip1/Waf1) with increased protein stability. Suppression of p21(Cip1/Waf1) by small interfering RNA (siRNA), as well as expression of HPV-E7 oncoprotein, restores immortalization and Ras-mediated transformation in Cdk4(-/-)Ink4a/Arf(-/-) cells and Cdk4(-/-) cells with DNp53 expression. Therefore, Cdk4 is essential for immortalization, and suppression of Cdk4 could be a prospective strategy to recruit cells with inactive Arf/p53 pathway to senescence.
authors.affiliation: Department of Molecular Genetics, University of Illinois College of Medicine, Chicago, Illinois 60607, USA.
authors.forename: Xianghong
authors.initials: X
authors.lastname: Zou
authors.forename: Dipankar
authors.initials: D
authors.lastname: Ray
authors.forename: Aileen
authors.initials: A
authors.lastname: Aziyu
authors.forename: Konstantin
authors.initials: K
authors.lastname: Christov
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Boiko
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Gudkov
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kiyokawa
mesh_terms: D020823:ADP-Ribosylation Factor 1 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015197:Carcinogenicity Tests; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000235:genetics* / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000473:pathology*; D051379:Mice; D008815:Mice, Inbred Strains; D008817:Mice, Mutant Strains; D008819:Mice, Nude; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism; D050725:Papillomavirus E7 Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C493957:Cdkn1a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; C059731:oncogene protein E7, Human papillomavirus type 16; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D020823:ADP-Ribosylation Factor 1; D018631:ras Proteins