title: p38 MAP kinase regulation of AP-2 binding in TGF-beta1-stimulated chondrogenesis of human trabecular bone-derived cells.
abstract: Collagenase-treated, explanted human trabecular-bone chips are an excellent source of osteoblast-like cells. We have recently shown the multiple differentiation potential of these cells; in addition to osteogenesis and adipogenesis, these cells also undergo chondrogenesis when maintained as high-density pellet cultures (250,000 cells/pellet) in a serum-free, chemically defined medium stimulated with TGF-beta1 (10 ng/mL). In this investigation, we have analyzed how transactivating nuclear transcription factors, specifically AP-2 and SP-1, may interact with common cis-acting elements found in the regulatory region of cartilage-specific genes as part of the signal transduction mechanism of TGF-beta1 and p38 during chondrogenesis of human trabecular bone-derived multipotential cells. Both TGF-beta1 stimulation and p38 MAP kinase activation affect the binding of AP-2 as well as SP-1 to oligonucleotides with sequence similarity to the overlapping AP-2/SP-1 sites found in the putative 52-bp immediate upstream regulatory region and the 5'-untranslated region of the human aggrecan gene. Electrophoretic mobility shift assays show that TGF-beta1 treatment of the bone-derived cells inhibits AP-2 DNA binding but enhances the DNA binding ability of SP-1. Additionally, treatment of these TGF-beta1-stimulated cells with p38 MAP kinase inhibitor, SB203580, rescued the AP-2 DNA binding but did not affect SP-1 DNA binding. These findings indicate that AP-2 DNA binding is the target of both TGF-beta1 and p38 MAP kinase signaling pathways and suggest a possible signal transduction cascade whereby TGF-beta1 induction of chondrogenesis involves the activation of p38 MAP kinase and the subsequent inhibition of DNA binding by AP-2, thereby preventing the transcriptional repression of the aggrecan gene.
authors.affiliation: Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases/NIH, 50 South Drive, Building 50 Room 1503, Bethesda, MD 20892, USA.
authors.forename: R
authors.initials: R
authors.lastname: Tuli
authors.forename: M R
authors.initials: MR
authors.lastname: Seghatoleslami
authors.forename: S
authors.initials: S
authors.lastname: Tuli
authors.forename: M S
authors.initials: MS
authors.lastname: Howard
authors.forename: K G
authors.initials: KG
authors.lastname: Danielson
authors.forename: R S
authors.initials: RS
authors.lastname: Tuan
mesh_terms: D001846:Bone Development; D001842:Bone and Bones / Q000166:cytology / Q000378:metabolism*; D002454:Cell Differentiation; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D019902:Chondrocytes / Q000166:cytology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008648:Mesoderm / Q000166:cytology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology*; D011725:Pyridines / Q000494:pharmacology; D012313:RNA / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016329:Sp1 Transcription Factor / Q000378:metabolism; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007093:Imidazoles; D011725:Pyridines; D016329:Sp1 Transcription Factor; C508960:TGFB1 protein, human; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D012313:RNA; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580