Rb/Cdk2/Cdk4 triple mutant mice elicit an alternative mechanism for regulation of the G1/S transition.
The G(1)/S-phase transition is a well-toned switch in the mammalian cell cycle. Cdk2, Cdk4, and the rate-limiting tumor suppressor retinoblastoma protein (Rb) have been studied in separate animal models, but interactions between the kinases and Rb in vivo have yet to be investigated. To further dissect the regulation of the G(1) to S-phase progression, we generated Cdk2(-/-)Cdk4(-/-)Rb(-/-) (TKO) mutant mice. TKO mice died at midgestation with major defects in the circulatory systems and displayed combined phenotypes of Rb(-/-) and Cdk2(-/-)Cdk4(-/-) mutants. However, TKO mouse embryonic fibroblasts were not only resistant to senescence and became immortal but displayed enhanced S-phase entry and proliferation rates similar to wild type. These effects were more remarkable in hypoxic compared with normoxic conditions. Interestingly, depletion of the pocket proteins by HPV-E7 or p107/p130 shRNA in the absence of Cdk2/Cdk4 elicited a mechanism for the G(1)/S regulation with increased levels of p27(Kip1) binding to Cdk1/cyclin E complexes. Our work indicates that the G(1)/S transition can be controlled in different ways depending on the situation, resembling a regulatory network.
Li
Weimin
W
Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute, Building 560/22-56, 1050 Boyles Street, Frederick, MD 21702-1201, USA.
Kotoshiba
Shuhei
S
Berthet
Cyril
C
Hilton
Mary Beth
MB
Kaldis
Philipp
P
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D049109:Cell Proliferation; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000235:genetics; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000172:deficiency*; D051358:Cyclin-Dependent Kinase 4 / Q000172:deficiency*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology*; D016193:G1 Phase; D000860:Hypoxia; D007399:Interphase / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D046912:Multiprotein Complexes / Q000502:physiology; D016160:Retinoblastoma Protein / Q000172:deficiency*; D016196:S Phase
C493961:Cdkn1b protein, mouse; D019927:Cyclin E; D046912:Multiprotein Complexes; D016160:Retinoblastoma Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016203:CDC2 Protein Kinase; C495893:Cdk2 protein, mouse; C495902:Cdk4 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4