Interleukin-1α activates an NF-κB-like factor in osteoclast-like cells

We investigated the NF-κB transcription factor in osteoclast-like cells. Osteoclast-like cells were differentiated from mouse bone marrow cells in co- culture with mouse calvaria-derived primary osteoblasts in the presence of 1α,25-dihydroxyvitamin D₃ and prostaglandin E₂ in collagen gel-coated dishes. We enriched osteoclast-like cells from the co-cultures by Pronase treatment. When the enriched osteoclast-like cells were treated with phorbol 12-myristate 13-acetate, interleukin-1 (IL-1), calcitonin, or macrophage colony-stimulating factor, only IL-1 activated an NF-κB-like factor, which specifically bound to a κB motif DNA sequence, as detected by an electrophoretic mobility shift assay. IL-1 also activated NF-κB induction in osteoblasts. However, the NF-κB-like factor induced by IL-1-stimulated osteoclast-like cells is of smaller molecular size than the factor in osteoblasts, as shown by an electrophoretic mobility shift assay. The NF-κB activity of osteoclast-like cells was recognized completely by antibodies against the p50 subunit, and only partially by antibodies against the p65 subunit of NF-κB. Antibodies against c-Rel, Rel B, and p52 did not recognize the NF-κB-like factor. These results suggest that IL-1 activates an NF-κB- like factor in osteoclast-like cells, which contains p50 and p65-related proteins.