title: p27 is regulated independently of Skp2 in the absence of Cdk2.
abstract: Cyclin-dependent kinase 2 (Cdk2) is dispensable for mitotic cell cycle progression and Cdk2 knockout mice are viable due to the compensatory functions of other Cdks. In order to assess the role of Cdk2 under limiting conditions, we used Skp2 knockout mice that exhibit increased levels of Cdk inhibitor, p27(Kip1), which is able to inhibit Cdk2 and Cdk1. Knockdown of Cdk2 abrogated proliferation of Skp2(-/-) mouse embryonic fibroblasts, encouraging us to generate Cdk2(-/-)Skp2(-/-) double knockout mice. Cdk2(-/-)Skp2(-/-) double knockout mice are viable and display similar phenotypes as Cdk2(-/-) and Skp2(-/-) mice. Unexpectedly, fibroblasts generated from Cdk2(-/-)Skp2(-/-) double knockout mice proliferated at normal rates. The increased stability of p27 observed in Skp2(-/-) MEFs was not observed in Cdk2(-/-)Skp2(-/-) double knockout fibroblasts indicating that in the absence of Cdk2, p27 is regulated by Skp2-independent mechanisms. Ablation of other ubiquitin ligases for p27 such as KPC1, DDB1, and Pirh2 did not restore stability of p27 in Cdk2(-/-)Skp2(-/-) MEFs. Our findings point towards novel and alternate pathways for p27 regulation.
authors.affiliation: Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Proteos#3-09, Singapore 138673, Republic of Singapore; Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute-Frederick, Bldg. 560, 1050 Boyles Street, Frederick, MD 21702-1201, USA.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Kotoshiba
authors.affiliation: Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Proteos#3-09, Singapore 138673, Republic of Singapore.
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Gopinathan
authors.affiliation: Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Proteos#3-09, Singapore 138673, Republic of Singapore.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Pfeiffenberger
authors.affiliation: Institute of Medical Biology (IMB), A*STAR (Agency for Science, Technology and Research), 8A Biomedical Grove, Immunos, Singapore 138648, Republic of Singapore.
authors.forename: Anisa
authors.initials: A
authors.lastname: Rahim
authors.affiliation: Institute of Medical Biology (IMB), A*STAR (Agency for Science, Technology and Research), 8A Biomedical Grove, Immunos, Singapore 138648, Republic of Singapore; School of Biological Sciences, Nanyang Technological University, Singapore 639798, Republic of Singapore.
authors.forename: Leah A
authors.initials: LA
authors.lastname: Vardy
authors.affiliation: Tohoku University, Department of Developmental Genetics, Center for Translational and Advanced Animal Research, Graduate School of Medicine, Aoba-ku, Sendai, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Nakayama
authors.affiliation: Kyushu University, Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan; CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Keiichi I
authors.initials: KI
authors.lastname: Nakayama
authors.affiliation: Institute of Molecular and Cell Biology (IMCB), A*STAR (Agency for Science, Technology and Research), 61 Biopolis Drive, Proteos#3-09, Singapore 138673, Republic of Singapore; National University of Singapore (NUS), Department of Biochemistry, Singapore 117597, Republic of Singapore; Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute-Frederick, Bldg. 560, 1050 Boyles Street, Frederick, MD 21702-1201, USA. Electronic address: kaldis@imcb.a-star.edu.sg.
authors.forename: Philipp
authors.initials: P
authors.lastname: Kaldis
mesh_terms: D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism; D049628:Body Size; D049109:Cell Proliferation; D003433:Crosses, Genetic; D051357:Cyclin-Dependent Kinase 2 / Q000172:deficiency* / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D020868:Gene Silencing; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009929:Organ Size; D055550:Protein Stability; D044786:S-Phase Kinase-Associated Proteins / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D000952:Antigens, Polyomavirus Transforming; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D044767:Ubiquitin-Protein Ligases; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2
keywords: Cdk2; Cyclin-dependent kinase; Knockout mice; Skp2; p27