A POSSIBLE NEW ROLE FOR VITAMIN-D-BINDING PROTEIN IN OSTEOCLAST CONTROL - INHIBITION OF EXTRACELLULAR CA2+ SENSING AT LOW PHYSIOLOGICAL CONCENTRATIONS

Upon removal of its sialic acid or galactose residue, vitamin D-bindin g protein (DBP) becomes a potent macrophage-activating factor, DBP-MAF . Here we document a new function of DBP-MAF and its parent molecule, DBP, in osteoclast control. We show that all DBPs potently inhibit ext racellular Ca2+ (cation) sensing at low nanomolar concentrations with the following rank order of potency: native DBP = sialidase-treated DB P > beta-galactosidase-treated DBP. This attenuation remains unaffecte d despite co-incubation either with the native DBP ligand, 1,25-dihydr oxyvitamin D-3, Or with an asialoglycoprotein receptor modulator, asia loorosomucoid. Taken together, the results suggest that circulating DB P may play a role in the systemic control of osteoclastic bone resorpt ion, a hitherto unrecognized action of the protein, (C) 1998 Academic Press.