Abstract
The 4-1BB is a costimulatory molecule similar to the receptor activator of NF-kappaB ligand (RANKL), both of which are key factors for the differentiation of osteoclasts and are expressed mainly by activated T cells. The 4-1BB shares common signaling pathways with RANK, suggesting a potential role in osteoclastogenesis. In this study, the role of 4-1BB and 4-1BB ligand (4-1BBL) in osteoclastogenesis was investigated using 4-1BB(-/-) and 4-1BB(+/+) mice. Osteoclast precursors normally express 4-1BB and 4-1BBL after exposure to RANKL, which was confirmed by semi-quantitative RT-PCR and flow cytometry. The 4-1BB(-/- )mice had a slightly increased bone mass accompanied by a reduced osteoclastogenic ability of 4-1BB(-/-) bone marrow-derived macrophages (BMM) ex vivo. In addition, 4-1BB(-/-) BMM demonstrated hypophosphorylation of JNK and p38 and decreased induction of c-Fos in response to RANKL stimulation. Retroviral transduction of wild-type as well as partial-length 4-1BB, which lacks TNF receptor-associated factor 2-binding sites for signaling, restored the osteoclastogenic ability of 4-1BB(-/-) BMM. Furthermore, both recombinant 4-1BB and 4-1BBL enhanced RANKL-induced osteoclastogenesis by 4-1BB(+/+) BMM and the induction of c-Fos and NFATc1.Together, these results indicate that 4-1BBL and 4-1BB expressed on osteoclast precursors enhance RANKL-induced osteoclastogenesis via bi-directional signaling, findings that may delineate the complex nature of the 4-1BBL and 4-1BB interaction.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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4-1BB Ligand / genetics
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4-1BB Ligand / physiology*
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Acid Phosphatase / metabolism
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Animals
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Bone Marrow Cells / cytology
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Bone Marrow Cells / drug effects
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Bone Marrow Cells / metabolism
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Cell Differentiation / drug effects
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Cell Differentiation / physiology*
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Gene Expression / drug effects
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Gene Expression / genetics
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Macrophage Colony-Stimulating Factor / pharmacology
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Macrophages / cytology
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Macrophages / drug effects
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Macrophages / metabolism
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Mice
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Mice, Inbred C57BL
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Mice, Knockout
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Mitogen-Activated Protein Kinase 8 / metabolism
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Models, Biological
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NFATC Transcription Factors / genetics
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Osteoclasts / cytology*
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Osteoclasts / drug effects
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Osteoclasts / metabolism
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Phosphorylation / drug effects
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Proto-Oncogene Proteins c-fos / genetics
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RANK Ligand / pharmacology*
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Recombinant Proteins / pharmacology
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Retroviridae / genetics
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Signal Transduction / drug effects
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Signal Transduction / physiology*
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Tibia / anatomy & histology
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Transduction, Genetic
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Tumor Necrosis Factor Receptor Superfamily, Member 9 / genetics
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Tumor Necrosis Factor Receptor Superfamily, Member 9 / physiology*
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p38 Mitogen-Activated Protein Kinases / metabolism
Substances
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4-1BB Ligand
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NFATC Transcription Factors
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Nfatc1 protein, mouse
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Proto-Oncogene Proteins c-fos
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RANK Ligand
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Recombinant Proteins
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Tumor Necrosis Factor Receptor Superfamily, Member 9
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Macrophage Colony-Stimulating Factor
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Mitogen-Activated Protein Kinase 8
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p38 Mitogen-Activated Protein Kinases
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Acid Phosphatase