Cloning of an osteoblastic cell line involved in the formation of osteoclast‐like cells

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Abstract
Experiments have been carried out to determine the mechanisms involved in the formation of osteoclast‐like cells from spleen cells in mice. Osteoclasts were defined as tartrate‐resistan. acid phosphatase‐positive multinucleated cells (TRACP‐positive MNCs) in which specific calcitonin receptors were identified by autdradiography with labeled salmon calcitonin. Furthermore, cultures rich in these cells produced resorption pits when grown on dentine slices. Several clonal cell lines were obtained from fetal mouse calvariae and screened for their ability to induce TRACP‐positive MNCs in response to 1α, 25‐dihydroxyvitamin D3 “1α,25(OH)2D3” in co‐cultures with spleen cells. A cell line, KS‐4, was identified with the greatest potency in inducing osteolast‐like cell formation in co‐culture with spleen cells. The capacity of KS‐4 cells to produce this effect was much greater than that of two bone marrow‐derived stromal cell lines (MC3T3‐G2/PA6 and ST2 cells), which we have previously shown to be effective in this system but to require treatment with dexamethasone in addition to 1α25(OH)2D3 (Udagawa et al.: Endocrinology 125:1805–1813, 1989). Parathyroid hormone (PTH) in creased cAMP production in KS‐4 cells, and PTH and interleukin‐1α also induced TRACP‐positive MNCs in co‐cultures with spleen cells. Contact between living KS‐4 and spleen cells was necessary for osteoclast formation to take place, since this did not occur when the two populations were separated by a membrane filter, or when the KS‐4 cells were killed by fixation. Separate cultures of either spleen cells or KS‐4 cells formed no TRACP‐positive MNCs. KS‐4 cells synthesized predominantly type I collagen, formed bone nodules without added of β‐glycerophosphate in a long‐term culture, and expressed increasing alkaline phosphatase activity after confluence in culture. These results indicate that the KS‐4 cells have properties consistent with progression toward the osteoblast phenotype, and represent a single cell line with the ability to promote osteoclast formation by a contact‐requiring process.