Bcl-2 Positively Regulates Sox9-dependent Chondrocyte Gene Expression by Suppressing the MEK-ERK1/2 Signaling Pathway

• Published in: The Journal of biological chemistry Vol. 280; no. 34; pp. 30517 - 30525
• Main Authors: Yagi, Rieko, McBurney, Denise, Horton, Walter E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 26.08.2005; American Society for Biochemistry and Molecular Biology
• Subjects: Adenoviridae - genetics; Animals; Apoptosis; beta-Galactosidase - metabolism; Blotting, Western; Butadienes - pharmacology; Caspase Inhibitors; Cell Differentiation; Cell Line; Chondrocytes - metabolism; Collagen Type II - metabolism; Down-Regulation; Enzyme Inhibitors - pharmacology; Fibroblasts - metabolism; Gene Expression Regulation; High Mobility Group Proteins - metabolism; Lac Operon; Luciferases - metabolism; MAP Kinase Kinase Kinases - metabolism; Microscopy, Fluorescence; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; NF-kappa B - metabolism; Nitriles - pharmacology; Phenotype; Phosphorylation; Promoter Regions, Genetic; Protein Kinase C - antagonists & inhibitors; Protein Kinase C-alpha; Proteoglycans - metabolism; Proto-Oncogene Proteins c-bcl-2 - metabolism; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - metabolism; RNA, Small Interfering - metabolism; Signal Transduction; SOX9 Transcription Factor; Time Factors; Transcription Factors - metabolism; Transcription, Genetic; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M502751200

Bcl-2 is an anti-apoptotic protein that has recently been shown to regulate other cellular functions. We previously reported that Bcl-2 regulates chondrocyte matrix gene expression, independent of its anti-apoptotic function. Here, we further investigate this novel function of Bcl-2 and examine three intracellular signaling pathways likely to be associated with this function. The present study demonstrates that the activity of Sox9, a master transcription factor that regulates the gene expression of chondrocyte matrix proteins, is suppressed by Bcl-2 small interference RNA in the presence of caspase inhibitors. This effect was attenuated by prior exposure of chondrocytes to an adenoviral vector expressing sense Bcl-2. In addition, the down-regulation of Bcl-2, Sox9, and chondrocyte-specific gene expression by serum withdrawal in primary chondrocytes was reversed by expressing Bcl-2. Inhibition of the protein kinase Cα and NFκB pathways had no effect on the maintenance of Sox9-dependent gene expression by Bcl-2. In contrast, whereas the MEK-ERK1/2 pathway negatively regulated the differentiated phenotype in wild type chondrocytes, inhibition of this pathway reversed the loss of differentiation markers and fibroblastic phenotype in Bcl-2-deficient chondrocytes. In conclusion, the present study identifies a specific signaling pathway, namely, MEK-ERK1/2, that is downstream of Bcl-2 in the regulation of Sox9-dependent chondrocyte gene expression and phenotype.