Activation of the Janus kinase/STAT (signal transducer and activator of transcription) signal transduction pathway by interleukin-6-type cytokines promotes osteoblast differentiation.
We have previously established that stromal/osteoblastic cells collectively express receptors for all members of the cytokine subfamily that share the gp130 signal transducer and that different receptor repertoires may be expressed at different stages of differentiation of this lineage. We have now used human (MG-63) and murine (MC3T3-E1) osteoblastic cell lines as well as primary murine calvaria cells to test the hypothesis that these receptors mediate effects of the cytokines on the biology of osteoblasts. We report that as in other cell types, all of the osteoblastic cell models responded to interleukin-6 (IL-6)-type cytokines with activation of both the JAK/STAT (Janus kinase/signal transducer and activator of transcription) and the mitogen-activated protein kinase (MAPK) pathways. In addition, IL-6-type cytokines stimulated alkaline phosphatase activity and osteocalcin expression and inhibited (MG-63), stimulated (MC3T3-E1), or had no effect (calvaria cells) on the rate of cell proliferation. The ability of a given cell type to respond to a particular member of this family of cytokines was strictly dependent on the presence of the corresponding ligand-binding subunit (alpha) of the cytokine receptor, and the magnitude of all the effects was closely correlated with the concentration of this subunit. The relative contribution of the JAK/STAT and MAPK pathways to the biological effects of the cytokines was evaluated using kinase inhibitors. Cytokine-mediated modulation of cell proliferation as well as stimulation of alkaline phosphatase activity were abrogated by tyrosine kinase inhibitors as well as a threonine/serine kinase inhibitor, but were only minimally affected by a specific inhibitor of MAPK phosphorylation. These results demonstrate that IL-6-type cytokines, besides their osteoclastogenic properties, promote differentiation of committed osteoblastic cells toward a more mature phenotype and that this action is mediated primarily via the activation of the JAK/STAT pathway.
Bellido
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T
Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the McClellan Veterans Administration Medical Center, Little Rock 72205, USA. TMBELLIDO@LIFE.UAMS.EDU
Borba
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VZ
Roberson
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P
Manolagas
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SC
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D020934:Ciliary Neurotrophic Factor; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology*; D053605:Leukemia Inhibitory Factor; D008222:Lymphokines / Q000494:pharmacology; D051379:Mice; D009419:Nerve Tissue Proteins / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*
D020934:Ciliary Neurotrophic Factor; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D006131:Growth Inhibitors; D015850:Interleukin-6; C507837:LIF protein, human; D053605:Leukemia Inhibitory Factor; C507838:Lif protein, mouse; D008222:Lymphokines; D009419:Nerve Tissue Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494080:Stat1 protein, mouse; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000469:Alkaline Phosphatase