1. Transforming Growth Factor (TGF)-β-activated Kinase 1 Mimics and Mediates TGF-β-induced Stimulation of Type II Collagen Synthesis in Chondrocytes Independent of Col2a1 Transcription and Smad3 Signaling
- Author
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Bo Qiao, Silvia R. Padilla, and Paul D. Benya
- Subjects
Cartilage, Articular ,TGF alpha ,Time Factors ,Transcription, Genetic ,Bone Morphogenetic Protein 2 ,MAP Kinase Kinase 6 ,Biochemistry ,Genes, Reporter ,Transforming Growth Factor beta ,Aggrecans ,Phosphorylation ,Luciferases ,Promoter Regions, Genetic ,Cells, Cultured ,Extracellular Matrix Proteins ,R-SMAD ,High Mobility Group Proteins ,NF-kappa B ,SOX9 Transcription Factor ,MAP Kinase Kinase Kinases ,DNA-Binding Proteins ,Phenotype ,Bone Morphogenetic Proteins ,Proteoglycans ,Collagen ,Rabbits ,Signal transduction ,Plasmids ,Signal Transduction ,Blotting, Western ,Genetic Vectors ,Type II collagen ,Biology ,Transfection ,Bone morphogenetic protein ,Bone morphogenetic protein 2 ,Adenoviridae ,Transforming Growth Factor beta1 ,Chondrocytes ,Ribonucleases ,Plasminogen Activator Inhibitor 1 ,Animals ,Immunoprecipitation ,Lectins, C-Type ,RNA, Messenger ,Smad3 Protein ,Collagen Type II ,Molecular Biology ,Cell Biology ,Molecular biology ,CTGF ,Cartilage ,Protein Biosynthesis ,Trans-Activators ,RNA ,Protein Processing, Post-Translational ,Transcription Factors ,Transforming growth factor - Abstract
Transforming growth factor (TGF)-beta, bone morphogenetic protein (BMP), and interleukin-1beta activate TGF-beta-activated kinase 1 (TAK1), which lies upstream of the p38 MAPK, JNK, and NF-kappaB pathways. Our knowledge remains incomplete of TAK1 target genes, requirement for cooperative signaling, and capacity for shared or segregated ligand-dependent responses. We show that adenoviral overexpression of TAK1a in articular chondrocytes stimulated type II collagen protein synthesis 3-6-fold and mimicked the response to TGF-beta1 and BMP2. Both factors activated endogenous TAK1 and its activating protein, TAB1, and the collagen response was inhibited by dominant-negative TAK1a. Isoform-specific antibodies to TGF-beta blocked the response to endogenous and exogenous TGF-beta but not the response to TAK1a. Expression of Smad3 did not stimulate type II collagen synthesis or enhance that caused by TGF-beta1 or TAK1a, in contrast to its effects on its endogenous targets, CTGF and plasminogen-activated inhibitor-1. TAK1a, overexpressed alone and immunoprecipitated, phosphorylated MKK6 and stimulated the plasminogen-activated inhibitor-1 promoter following transient transfection; both effects were enhanced by TAB1 coexpression, but type II collagen synthesis was not. Stimulation by TAK1a or TGF-beta did not require increased Col2a1 mRNA, and TAK1 actually reduced Col2a1 mRNA in parallel with the cartilage markers, SRY-type HMG box 9 (Sox9) and aggrecan. Thus, TAK1 increased target gene expression (Col2a1) by translational or posttranslational mechanisms as a Smad3-independent response shared by TGF-beta1 and BMP2.
- Published
- 2005