title: Down-regulation of p27Kip1 promotes cell proliferation of rat neonatal cardiomyocytes induced by nuclear expression of cyclin D1 and CDK4. Evidence for impaired Skp2-dependent degradation of p27 in terminal differentiation.
abstract: Mammalian cardiomyocytes lose their capacity to proliferate during terminal differentiation. We have previously reported that the expression of nuclear localization signal-tagged cyclin D1 (D1NLS) and its partner cyclin-dependent kinase 4 (CDK4) induces proliferation of rat neonatal cardiomyocytes. Here we show that the D1NLS/CDK4 cells, after their entry into the cell cycle, accumulated cyclin-dependent kinase inhibitor p27 in the nuclei and decreased the cyclin-dependent kinase 2 (CDK2) activity, leading to early cell cycle arrest. Biochemical analysis demonstrated that Skp2-dependent p27 ubiquitylation was remarkably suppressed in cardiomyocytes, whereas Skp2, a component of Skp1-Cullin-F-box protein ubiquitin ligase, was more actively ubiquitylated compared with proliferating rat fibroblasts. Specific degradation of p27 by co-expressing Skp2 or p27 small interfering RNA caused an increase of CDK2 activity and overrode the limited cell cycle. These data altogether indicate that the impaired Skp2-dependent p27 degradation is causally related to the loss of proliferation in cardiomyocytes. This provides a novel insight in understanding the molecular mechanism by which mammalian cardiomyocytes cease to proliferate during terminal differentiation.
authors.affiliation: Department of Biochemical Genetics, Medical Research Institute and Laboratory of Genome Structure and Regulation, School of Biomedical Science, Tokyo Medcal and Dental Universuty, Tokyo, Japan.
authors.forename: Mimi
authors.initials: M
authors.lastname: Tamamori-Adachi
authors.forename: Kentaro
authors.initials: K
authors.lastname: Hayashida
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Nobori
authors.forename: Chie
authors.initials: C
authors.lastname: Omizu
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Yamada
authors.forename: Naoya
authors.initials: N
authors.lastname: Sakamoto
authors.forename: Takumi
authors.initials: T
authors.lastname: Kamura
authors.forename: Keiichi
authors.initials: K
authors.lastname: Fukuda
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ogawa
authors.forename: Keiichi I
authors.initials: KI
authors.lastname: Nakayama
authors.forename: Shigetaka
authors.initials: S
authors.lastname: Kitajima
mesh_terms: D000818:Animals; D042846:CDC2-CDC28 Kinases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002455:Cell Division / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D019938:Cyclin D1 / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D015536:Down-Regulation; D032383:Myocytes, Cardiac / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D044786:S-Phase Kinase-Associated Proteins / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D044786:S-Phase Kinase-Associated Proteins; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; C495903:Cdk4 protein, rat; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases