title: Inhibition of Cdk6 expression through p38 MAP kinase is involved in differentiation of mouse prechondrocyte ATDC5.
abstract: Because a temporal arrest in the G1-phase of the cell cycle is a prerequisite for cell differentiation, this study investigated the involvement of cell cycle factors in the differentiation of cultured mouse prechondrocyte cell line ATDC5. Among the G1 cell cycle factors examined, both protein and mRNA levels of cyclin-dependent kinase (Cdk6) were downregulated during the culture in a differentiation medium. The protein degradation of Cdk6 was not involved in this downregulation because proteasome inhibitors did not reverse the protein level. When inhibitors of p38 MAPK, ERK-1/2, and PI3K/Akt were added to the culture, only a p38 MAPK inhibitor SB203580 blocked the decrease in the Cdk6 protein level by the differentiation medium, indicating that the Cdk6 inhibition was mediated by p38 MAPK pathway. In fact, p38 MAPK was confirmed to be phosphorylated during differentiation of ATDC5 cells. Enforced expression of Cdk6 in ATDC5 cells blocked the chondrocyte differentiation and inhibited Sox5 and Sox6 expressions. However, the Cdk6 overexpression did not affect the proliferation or the cell cycle progression, suggesting that the inhibitory effect of Cdk6 on the differentiation was exerted by a mechanism largely independent of its cell cycle regulation. These results indicate that Cdk6 may be a regulator of chondrocyte differentiation and that its p38-mediated downregulation is involved in the efficient differentiation.
authors.affiliation: Department of Sensory and Motor System Medicine, Faculty of Medicine, University of Tokyo, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Moro
authors.forename: Toru
authors.initials: T
authors.lastname: Ogasawara
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Chikuda
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Ikeda
authors.forename: Naoshi
authors.initials: N
authors.lastname: Ogata
authors.forename: Zenjiro
authors.initials: Z
authors.lastname: Maruyama
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Komori
authors.forename: Kazuto
authors.initials: K
authors.lastname: Hoshi
authors.forename: Ung-Il
authors.initials: UI
authors.lastname: Chung
authors.forename: Kozo
authors.initials: K
authors.lastname: Nakamura
authors.forename: Hiroto
authors.initials: H
authors.lastname: Okayama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawaguchi
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D019902:Chondrocytes / Q000166:cytology* / Q000201:enzymology* / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D015870:Gene Expression; D051379:Mice; D015398:Signal Transduction; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: C495912:Cdk6 protein, mouse; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases; D048051:p38 Mitogen-Activated Protein Kinases