title: Transforming growth factor (TGF)-beta-activated kinase 1 mimics and mediates TGF-beta-induced stimulation of type II collagen synthesis in chondrocytes independent of Col2a1 transcription and Smad3 signaling.
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.
authors.affiliation: Orthopaedic Hospital, Los Angeles, J. Vernon Luck, Sr., M.D. Research Center and UCLA-Orthopaedic Hospital Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA, University of California, Los Angeles, California 90095, USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Qiao
authors.forename: Silvia R
authors.initials: SR
authors.lastname: Padilla
authors.forename: Paul D
authors.initials: PD
authors.lastname: Benya
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D053674:Aggrecans; D000818:Animals; D015153:Blotting, Western; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D002356:Cartilage / Q000378:metabolism; D002358:Cartilage, Articular / Q000166:cytology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D003094:Collagen / Q000378:metabolism; D024043:Collagen Type II / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D017930:Genes, Reporter; D005822:Genetic Vectors; D006609:High Mobility Group Proteins / Q000378:metabolism; D047468:Immunoprecipitation; D037181:Lectins, C-Type; D008156:Luciferases / Q000378:metabolism; D048669:MAP Kinase Kinase 6 / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism / Q000502:physiology*; D016328:NF-kappa B / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D011509:Proteoglycans / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D012260:Ribonucleases / Q000378:metabolism; D055758:SOX9 Transcription Factor; D015398:Signal Transduction; D051900:Smad3 Protein; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D000099151:MAP Kinase Kinase Kinase 7
chemical_list: D053674:Aggrecans; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D003094:Collagen; D024043:Collagen Type II; D004268:DNA-Binding Proteins; D016326:Extracellular Matrix Proteins; D006609:High Mobility Group Proteins; D037181:Lectins, C-Type; D008156:Luciferases; D048669:MAP Kinase Kinase 6; D020930:MAP Kinase Kinase Kinases; D016328:NF-kappa B; D017395:Plasminogen Activator Inhibitor 1; D011509:Proteoglycans; D012313:RNA; D012333:RNA, Messenger; D012260:Ribonucleases; D055758:SOX9 Transcription Factor; D051900:Smad3 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D000099151:MAP Kinase Kinase Kinase 7; C508320:Acan protein, mouse; C525719:Bmp2 protein, mouse; C527933:Sox9 protein, mouse; C508961:Tgfb1 protein, mouse; C482567:Map2k6 protein, mouse