1,25-DIHYDROXYVITAMIN-D-3 STIMULATES DIFFERENTIATION OF COMMITTED MURINE BONE-MARROW-DERIVED MACROPHAGE PRECURSOR CELLS

1,25-Dihydroxyvitamin D-3 [1,25-(OH)(2)D-3] and macrophage colony-stimulating factor (M-CSF) both accelerate differentiation of marrow macrophages from which osteoclasts are derived. Previously, we showed that the steroid's effect on early macrophage precursors may be mediated through M-CSF, as the steroid enhances cytokine receptor expression. In contrast, 1,25-(OH)(2)D-3 blunts M-CSF receptor expression on more mature, yet still pluripotential, hematopoietic precursors. Extending these observations to marrow cells committed to macrophage differentiation, we found that 1,25-(OH)(2)D-3 causes a marked decrease in cellular proliferation despite a 2- to 3-fold increase in [I-125]M-CSF binding in a similar dose-dependent metabolite-specific manner. Scatchard analysis demonstrated that increased binding reflects increased receptor capacity without an alteration in affinity. Steroid-induced M-CSF receptor enhancement reflects acceleration of protein appearance rather than overexpression, as treated and untreated cells ultimately exhibit equivalent binding. Increased M-CSF receptor expression is mirrored by increased c-fms messenger RNA levels, and actinomycin D or cycloheximide experiments indicate that new receptor synthesis, rather than mobilization of intracellular pools, is required. Thus, 1,25-(OH)(2)D-3 differentially impacts on M-CSF receptor expression throughout the spectrum of bone marrow macrophage differentiation.