Bcl-2 positively regulates Sox9-dependent chondrocyte gene expression by suppressing the MEK-ERK1/2 signaling pathway.
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 C alpha and NFkappaB 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.
Yagi
Rieko
R
Department of Anatomy, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272, USA
McBurney
Denise
D
Horton
Walter E
WE
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D061945:Caspase Inhibitors; D002454:Cell Differentiation; D002460:Cell Line; D019902:Chondrocytes / Q000378:metabolism*; D024043:Collagen Type II / Q000378:metabolism; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D006609:High Mobility Group Proteins / Q000378:metabolism*; D007763:Lac Operon; D008156:Luciferases / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D010641:Phenotype; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051571:Protein Kinase C-alpha; D011509:Proteoglycans / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055758:SOX9 Transcription Factor; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D001616:beta-Galactosidase / Q000378:metabolism
D002070:Butadienes; D061945:Caspase Inhibitors; D024043:Collagen Type II; D004791:Enzyme Inhibitors; D006609:High Mobility Group Proteins; D016328:NF-kappa B; D009570:Nitriles; D011509:Proteoglycans; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D055758:SOX9 Transcription Factor; D014157:Transcription Factors; C113580:U 0126; D008156:Luciferases; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020930:MAP Kinase Kinase Kinases; D001616:beta-Galactosidase