Combined Loss of Cdk2 and Cdk4 Results in Embryonic Lethality and Rb Hypophosphorylation

• Published in: Developmental cell 2006-05, Vol.10 (5), p.563-573
• Main Authors: Berthet, Cyril, Klarmann, Kimberly D., Hilton, Mary Beth, Suh, Hyung Chan, Keller, Jonathan R., Kiyokawa, Hiroaki, Kaldis, Philipp
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cell differentiation, maturation, development, hematopoiesis; Cell physiology; Cell Proliferation; CELLCYCLE; Cells, Cultured; Cyclin-Dependent Kinase 2 - deficiency; Cyclin-Dependent Kinase 2 - genetics; Cyclin-Dependent Kinase 4 - deficiency; Cyclin-Dependent Kinase 4 - genetics; DEVBIO; E2F Transcription Factors - antagonists & inhibitors; Embryo, Mammalian - abnormalities; Fibroblasts - cytology; Fundamental and applied biological sciences. Psychology; Gene Silencing; Hematopoiesis; Mice; Mice, Inbred C57BL; Mice, Knockout; Molecular and cellular biology; Oncogene Proteins, Viral - metabolism; Papillomavirus E7 Proteins; Phenotype; Phosphorylation; Retinoblastoma Protein - antagonists & inhibitors; Retinoblastoma Protein - chemistry; Retinoblastoma Protein - metabolism
• ISSN: 1534-5807; 1878-1551
• DOI: 10.1016/j.devcel.2006.03.004

Mouse knockouts of Cdk2 and Cdk4 have demonstrated that, individually, these genes are not essential for viability. To investigate whether there is functional redundancy, we have generated double knockout (DKO) mice. Cdk2 −/−Cdk4 −/− DKOs die during embryogenesis around E15 as a result of heart defects. We observed a gradual decrease of Retinoblastoma protein (Rb) phosphorylation and reduced expression of E2F-target genes, like Cdc2 and cyclin A2, during embryogenesis and in embryonic fibroblasts (MEFs). DKO MEFs are characterized by a decreased proliferation rate, impaired S phase entry, and premature senescence. HPV-E7-mediated inactivation of Rb restored normal expression of E2F-inducible genes, senescence, and proliferation in DKO MEFs. In contrast, loss of p27 did not rescue Cdk2 −/−Cdk4 −/− phenotypes. Our results demonstrate that Cdk2 and Cdk4 cooperate to phosphorylate Rb in vivo and to couple the G1/S phase transition to mitosis via E2F-dependent regulation of gene expression.