Bone morphogenetic protein 2-induced osteoblast differentiation requires Smad-mediated down-regulation of Cdk6.
Because a temporal arrest in the G(1) phase of the cell cycle is thought to be a prerequisite for cell differentiation, we investigated cell cycle factors that critically influence the differentiation of mouse osteoblastic MC3T3-E1 cells induced by bone morphogenetic protein 2 (BMP-2), a potent inducer of osteoblast differentiation. Of the G(1) cell cycle factors examined, the expression of cyclin-dependent kinase 6 (Cdk6) was found to be strongly down-regulated by BMP-2/Smads signaling, mainly via transcriptional repression. The enforced expression of Cdk6 blocked BMP-2-induced osteoblast differentiation to various degrees, depending on the level of its overexpression. However, neither BMP-2 treatment nor Cdk6 overexpression significantly affected cell proliferation, suggesting that the inhibitory effect of Cdk6 on cell differentiation was exerted by a mechanism that is largely independent of its cell cycle regulation. These results indicate that Cdk6 is a critical regulator of BMP-2-induced osteoblast differentiation and that its Smads-mediated down-regulation is essential for efficient osteoblast differentiation.
Ogasawara
Toru
T
Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan.
Kawaguchi
Hiroshi
H
Jinno
Shigeki
S
Hoshi
Kazuto
K
Itaka
Keiji
K
Takato
Tsuyoshi
T
Nakamura
Kozo
K
Okayama
Hiroto
H
D000818:Animals; D015153:Blotting, Western; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002453:Cell Cycle; D002454:Cell Differentiation; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases / Q000096:biosynthesis*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D005434:Flow Cytometry; D016193:G1 Phase; D051379:Mice; D008954:Models, Biological; D010006:Osteoblasts / Q000378:metabolism*; D011233:Precipitin Tests; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051785:Smad Proteins; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; D051785:Smad Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C495912:Cdk6 protein, mouse; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases; D001973:Bromodeoxyuridine