Characterization and hormonal modulation of IL-1 binding in neonatal mouse osteoblastlike cells

Considerable evidence indicates that interleukin-1 (IL-1) is a potent regulator of bone cell activity. Consequently, we studied its binding to neonatal mouse osteoblastlike cells. Purified, labeled recombinant IL-1α bound specifically to neonatal mouse osteoblastlike cells with a dissociation constant of 30-200 pM at 22°C. There were 3000-15,000 receptors per cell. IL-1 bound to cell surfaces at 4°C was rapidly internalized when the temperature was raised to 37°C. Receptor specificity was confirmed by demonstrating that, among a series of 11 polypeptides, only IL-1 inhibited 125I-IL-1 binding. Treatment of surface-bound 125I-IL-1α with a bivalent water-soluble cross-linker identified a membrane peptide of Mr 70,000 cross-linked to IL-1. The apparent IL-1 receptor was solubilized from a plasma membrane-enriched fraction using 3-[(3-cholamido-propyldimethylammonio]-1-propanesulfonate (CHAP). The resulting material exhibited specific IL-1 binding. Preincubation of cells with IL-1, retinoic acid, transforming growth factor s (TGF-s), or phorbol ester caused a reduction in apparent receptor numbers per cell, while preincubation with epidermal growth factor (EGF), dexamethasone, or parathyroid hormone (PTH) increased receptor numbers per cell. Preincubation with insulin, vitamin D, prostaglandin E2 (PGE2), interferon-γ (IFN-γ), and 17s-estradiol had no effect. These results suggest that specific, high-affinity IL-1 receptors are present on osteoblastlike cells and that the receptor number can be modified by various osteotropic agents. Regulation of bone cell IL-1 receptors may contribute to the control of bone remodeling.