title: Maintenance of differentiated phenotype of articular chondrocytes by protein kinase C and extracellular signal-regulated protein kinase.
abstract: The differentiated phenotype of chondrocyte is rapidly lost during in vitro culture by a process designated "dedifferentiation." In this study, we investigate the roles of protein kinase C (PKC) and extracellular signal-regulated protein kinase (ERK) in the maintenance of the differentiated chondrocyte phenotype. Chondrocytes isolated from rabbit articular cartilage underwent dedifferentiation upon serial monolayer culture with cessation of type II collagen expression and proteoglycan synthesis, which was reversed by culturing dedifferentiated cells in alginate gel. The expression pattern of PKC alpha was essentially the same as that of type II collagen during de- and redifferentiation, in that expression was decreased during dedifferentiation and increased during redifferentiation. In contrast to PKC alpha, ERK activity increased 15-fold during dedifferentiation. This enhanced activity was terminated during redifferentiation. Down-regulation of PKC alpha in passage 0 chondrocytes resulted in dedifferentiation. However, overexpression of PKC alpha did not affect type II collagen levels, suggesting that PKC alpha expression is not sufficient to maintain the differentiated phenotype. However, inhibition of ERK by PD98059 enhanced type II collagen expression and proteoglycan synthesis in passage 0 cells, retarded dedifferentiation during monolayer cultures, and reversed dedifferentiation caused by down-regulation of PKC. Unlike PKC-dependent ERK regulation of chondrogenesis, PKC and ERK independently modulated chondrocyte dedifferentiation, as confirmed by observations that PKC down-regulation and ERK inhibition did not alter ERK phosphorylation and PKC expression, respectively. In addition, expression of N-cadherin, alpha-catenin, and beta-catenin, which are oppositely regulated to type II collagen during phenotype alterations, were modulated by PKC and ERK during chondrogenesis but not dedifferentiation, supporting distinct mechanisms for the regulation of chondrocyte differentiation and maintenance of differentiated phenotype by these two protein kinases.
authors.affiliation: National Research Laboratory, Department of Life Science, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea.
authors.forename: Young-Mee
authors.initials: YM
authors.lastname: Yoon
authors.forename: Song-Ja
authors.initials: SJ
authors.lastname: Kim
authors.forename: Chun-Do
authors.initials: CD
authors.lastname: Oh
authors.forename: Jung-Won
authors.initials: JW
authors.lastname: Ju
authors.forename: Woo Keun
authors.initials: WK
authors.lastname: Song
authors.forename: Yung Joon
authors.initials: YJ
authors.lastname: Yoo
authors.forename: Tae-Lin
authors.initials: TL
authors.lastname: Huh
authors.forename: Jang-Soo
authors.initials: JS
authors.lastname: Chun
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D015820:Cadherins / Q000096:biosynthesis; D002358:Cartilage, Articular / Q000201:enzymology*; D002454:Cell Differentiation; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000201:enzymology* / Q000502:physiology; D003094:Collagen / Q000096:biosynthesis; D003598:Cytoskeletal Proteins / Q000096:biosynthesis; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D007527:Isoenzymes / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D010641:Phenotype; D010766:Phosphorylation; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D011817:Rabbits; D013997:Time Factors; D015534:Trans-Activators; D051178:alpha Catenin; D051176:beta Catenin
chemical_list: D015820:Cadherins; D003598:Cytoskeletal Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007527:Isoenzymes; D015534:Trans-Activators; D051178:alpha Catenin; D051176:beta Catenin; D003094:Collagen; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one