Cdk4 disruption renders primary mouse cells resistant to oncogenic transformation, leading to Arf/p53-independent senescence

• Published in: Genes & development Vol. 16; no. 22; pp. 2923 - 2934
• Main Authors: Zou, Xianghong, Ray, Dipankar, Aziyu, Aileen, Christov, Konstantin, Boiko, Alexander D., Gudkov, Andrei V., Kiyokawa, Hiroaki
• Format: Journal Article
• Language: English
• Published: United States Cold Spring Harbor Laboratory Press 15.11.2002
• Subjects: ADP-Ribosylation Factor 1 - genetics; ADP-Ribosylation Factor 1 - metabolism; Animals; Carcinogenicity Tests; Cell Transformation, Neoplastic; Cells, Cultured; Cellular Senescence - physiology; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase Inhibitor p16 - genetics; Cyclin-Dependent Kinase Inhibitor p16 - metabolism; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinases - genetics; Cyclin-Dependent Kinases - metabolism; Cyclins - genetics; Cyclins - metabolism; Fibroblasts - pathology; Mice; Mice, Inbred Strains; Mice, Mutant Strains; Mice, Nude; Oncogene Proteins, Viral - genetics; Oncogene Proteins, Viral - metabolism; Papillomavirus E7 Proteins; Proto-Oncogene Proteins; ras Proteins - genetics; ras Proteins - metabolism; Research Paper; RNA, Small Interfering - metabolism; Tumor Suppressor Protein p53 - genetics; Tumor Suppressor Protein p53 - metabolism
• ISSN: 0890-9369; 1549-5477
• DOI: 10.1101/gad.1033002

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.