title: Commitment to the osteoblast lineage is not required for RANKL gene expression.
abstract: Differentiation of bone-resorbing osteoclasts from hematopoietic precursors depends upon expression of the cytokine receptor activator of NFkappaB ligand (RANKL) by fibroblastic stromal cells, which some evidence suggests are of the osteoblast lineage. We have shown previously that hormonal-responsiveness of the murine RANKL gene is mediated in part by a distal enhancer that binds Runx2, a transcription factor required for commitment to the osteoblast lineage, supporting the idea that osteoclast-supporting stromal cells may be osteoblasts or their progenitors. However, in this study we demonstrate that parathyroid hormone (PTH) stimulation of RANKL in mice is not affected by a significant reduction in the number of osteoblasts. Consistent with this, neither Runx2, nor Cbfb, a binding partner essential for Runx activity, are required for basal or PTH-stimulated RANKL expression in fibroblastic stromal cell models. Nonetheless, RANKL responsiveness to PTH was elevated in cultured calvaria cells expressing high levels of osterix, another transcription factor required for osteoblast differentiation, and this was associated with elevated PTH receptor expression. The responsiveness of RANKL to 1,25-dihydroxyvitamin D(3) was not elevated in the osterix-expressing cells. Together, these results suggest that commitment to the osteoblast lineage is not a requirement for RANKL gene transcription in fibroblastic stromal cells but may enhance responsiveness of this gene to specific hormones via control of their receptors.
authors.affiliation: Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and Central Arkansas Veterans Healthcare System, Little Rock, AR 72205, USA.
authors.forename: Carlo
authors.initials: C
authors.lastname: Galli
authors.forename: Qiang
authors.initials: Q
authors.lastname: Fu
authors.forename: Wenfang
authors.initials: W
authors.lastname: Wang
authors.forename: Bjorn R
authors.initials: BR
authors.lastname: Olsen
authors.forename: Stavros C
authors.initials: SC
authors.lastname: Manolagas
authors.forename: Robert L
authors.initials: RL
authors.lastname: Jilka
authors.forename: Charles A
authors.initials: CA
authors.lastname: O'Brien
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D019070:Cell Lineage / Q000502:physiology*; D050659:Core Binding Factor Alpha 1 Subunit / Q000502:physiology; D050658:Core Binding Factor beta Subunit / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D004622:Embryo, Mammalian / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression; D015151:Immunoblotting; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology; D053245:RANK Ligand / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012886:Skull / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017154:Stromal Cells / Q000187:drug effects / Q000378:metabolism; D014807:Vitamin D / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C493693:Cbfb protein, mouse; D050659:Core Binding Factor Alpha 1 Subunit; D050658:Core Binding Factor beta Subunit; D010281:Parathyroid Hormone; D053245:RANK Ligand; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C493716:Runx2 protein, mouse; C505689:Tnfsf11 protein, mouse; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D