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p38 MAP Kinase Regulation of AP‐2 Binding in TGF‐β1‐Stimulated Chondrogenesis of Human Trabecular Bone‐Derived Cells
Author(s) -
TULI R.,
SEGHATOLESLAMI M. R.,
TULI S.,
HOWARD M. S.,
DANIELSON K. G.,
TUAN R. S.
Publication year - 2002
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.2002.tb03077.x
Subject(s) - microbiology and biotechnology , chondrogenesis , signal transduction , transforming growth factor , chemistry , osteoblast , kinase , p38 mitogen activated protein kinases , protein kinase a , transduction (biophysics) , biology , biochemistry , in vitro , mesenchymal stem cell
A bstract : 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‐β1 (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‐β1 and p38 during chondrogenesis of human trabecular bone‐derived multipotential cells. Both TGF‐β1 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‐β1 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‐β1‐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‐β1 and p38 MAP kinase signaling pathways and suggest a possible signal transduction cascade whereby TGF‐β1 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.