Abstract
Recent studies of intracellular signal transduction mechanisms for the transforming growth factor-beta (TGF-beta) superfamily have focused on Smad proteins, but have paid little attention to mitogen-activated protein (MAP) kinase cascades. Here we demonstrate that growth/differentiation factor-5 (GDF-5), but neither bone morphogenetic protein-2 (BMP-2) nor TGF-beta1, fully promotes the early phase of the chondrogenic response by inducing cellular condensation followed by cartilage nodule formation in a mouse chondrogenic cell line, ATDC5. We investigated which, if any, of the three major types of MAP kinase plays a functional role in the promotion of chondrogenesis induced by GDF-5. GDF-5 induced phosphorylation of p38 MAP kinase and extracellular signal-regulated kinase (ERK) but not that of c-Jun N-terminal kinase (JNK). The phosphorylation of p38 MAP kinase was also induced by BMP-2 and TGF-beta1. An inhibitor of p38 and p38 beta MAP kinase, SB202190, showed complete inhibition of cartilage nodule formation but failed to affect alkaline phosphatase (ALP) activity induced by GDF-5. Expression of the type II collagen gene, a hallmark of chondrogenesis in vertebrates, was also induced by GDF-5 treatment and strongly suppressed by SB202190. On the other hand, although an inhibitor of MAP/ERK kinase, PD98059, inhibited the rapid phosphorylation of ERK by GDF-5, it inhibited neither ALP activity nor cartilage nodule formation induced by GDF-5. These results strongly suggest that the p38 MAP kinase cascade is involved in GDF-5 signaling pathways and that a role of the p38 MAP kinase pathway is necessary over a longer period to promote chondrogenesis in ATDC5 cells.
Copyright 1999 Academic Press.
MeSH terms
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Alkaline Phosphatase / metabolism
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Animals
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Bone Morphogenetic Protein 2
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Bone Morphogenetic Proteins / pharmacology
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Calcium-Calmodulin-Dependent Protein Kinases / antagonists & inhibitors
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Calcium-Calmodulin-Dependent Protein Kinases / metabolism*
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Carcinoma, Embryonal
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Cartilage / drug effects
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Cartilage / metabolism
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Cell Differentiation / drug effects
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Cell Size / drug effects
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Chondrogenesis / drug effects*
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Collagen / genetics
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Dose-Response Relationship, Drug
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Enzyme Induction / drug effects
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Growth Differentiation Factor 5
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Growth Substances / pharmacology*
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Humans
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JNK Mitogen-Activated Protein Kinases
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MAP Kinase Kinase 1
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Mice
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Mitogen-Activated Protein Kinase Kinases*
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Mitogen-Activated Protein Kinases*
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Phosphorylation / drug effects
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Protein Serine-Threonine Kinases / antagonists & inhibitors
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Protein Serine-Threonine Kinases / metabolism
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Protein-Tyrosine Kinases / antagonists & inhibitors
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Protein-Tyrosine Kinases / metabolism
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Signal Transduction / drug effects
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Transforming Growth Factor beta / pharmacology
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Tumor Cells, Cultured
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p38 Mitogen-Activated Protein Kinases
Substances
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BMP2 protein, human
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Bmp2 protein, mouse
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Bone Morphogenetic Protein 2
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Bone Morphogenetic Proteins
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GDF5 protein, human
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Gdf5 protein, mouse
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Growth Differentiation Factor 5
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Growth Substances
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RNA, Messenger
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Transforming Growth Factor beta
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Collagen
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Protein-Tyrosine Kinases
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Protein Serine-Threonine Kinases
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Calcium-Calmodulin-Dependent Protein Kinases
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JNK Mitogen-Activated Protein Kinases
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Mitogen-Activated Protein Kinases
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p38 Mitogen-Activated Protein Kinases
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MAP Kinase Kinase 1
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MAP2K1 protein, human
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Map2k1 protein, mouse
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Mitogen-Activated Protein Kinase Kinases
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Alkaline Phosphatase