title: Fos plays an essential role in the upregulation of RANK expression in osteoclast precursors within the bone microenvironment.
abstract: Fos plays essential roles in the osteoclastic differentiation of precursor cells generated by colony-stimulating factor 1 (CSF-1) and receptor activator of NF-κB ligand (RANKL; also known as tumor necrosis factor ligand superfamily member 11, Tnsf11). RANKL-deficient (RANKL(-/-)) mice and Fos(-/-) mice exhibit osteopetrosis due to an osteoclast deficiency. We previously reported that RANK-positive osteoclast precursors are present in bone of RANKL(-/-) mice but not Fos(-/-) mice. Here we report the role of Fos in RANK expression in osteoclast precursors. Medullary thymic epithelial cells and intestinal antigen-sampling microfold cells have been shown to express RANK. High expression of RANK was observed in some epithelial cells in the thymic medulla and intestine but not in osteoclast precursors in Fos(-/-) mice. RANK mRNA and protein levels in bone were lower in Fos(-/-) mice than RANKL(-/-) mice, suggesting that Fos-regulated RANK expression is tissue specific. When wild-type bone marrow cells were inoculated into Fos(-/-) mice, RANK-positive cells appeared along bones. RANK expression in wild-type macrophages was upregulated by coculturing with RANKL(-/-) osteoblasts as well as wild-type osteoblasts, suggesting that cytokines other than RANKL expressed by osteoblasts upregulate RANK expression in osteoclast precursors. CSF-1 receptor-positive cells were detected near CSF-1-expressing osteoblastic cells in bone in Fos(-/-) mice. CSF-1 upregulated RANK expression in wild-type macrophages but not Fos(-/-) macrophages. Overexpression of Fos in Fos(-/-) macrophages resulted in the upregulation of RANK expression. Overexpression of RANK in Fos(-/-) macrophages caused RANKL-induced signals, but failed to recover the RANKL-induced osteoclastogenesis. These results suggest that Fos plays essential roles in the upregulation of RANK expression in osteoclast precursors within the bone environment.
authors.affiliation: Institute for Oral Science, Matsumoto Dental University, Nagano 399-0781,  Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Arai
authors.forename: Toshihide
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Suguru
authors.initials: S
authors.lastname: Harada
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Nakamichi
authors.forename: Hisataka
authors.initials: H
authors.lastname: Yasuda
authors.forename: Josef M
authors.initials: JM
authors.lastname: Penninger
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Yamada
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Udagawa
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Takahashi
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000378:metabolism; D001842:Bone and Bones / Q000378:metabolism*; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010010:Osteoclasts / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism; D053246:Receptor Activator of Nuclear Factor-kappa B / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B