title: Evidence for a 1 alpha,25-dihydroxyvitamin D3 receptor/binding protein in a membrane fraction isolated from a chick tibial fracture-healing callus.
abstract: Previous biological studies have implicated two vitamin D metabolites, 1 alpha,25(OH)2-vitamin D3[1 alpha,25(OH)2-D3] and 24R,25(OH)2-vitamin D3 [24R,25(OH)2D3] in the process of skeletal fracture-healing. While a nuclear receptor for 1 alpha,25(OH)2D3 is known to be present in osteoblast and absent in osteoclast cell lines, no systematic study has been carried out on the callus tissue which is formed during fracture-healing. The present report shows that a binding protein/receptor for 1 alpha,25(OH)2D3 resides both in a postnuclear membrane fraction and in a high speed cytosol fraction of the callus tissue obtained 10 days after imposition of a tibial fracture. The dissociation constant, KD, for 1 alpha,25(OH)2D3 was 0.83 +/- 0.34 M and 0.66 +/- 0.38 nM respectively, for the membrane and cytosol fractions. Results from a panel of steroid competition assays indicate that both receptor/binding proteins greatly prefer 1 alpha-hydroxylated ligands as compared to 1 alpha-deoxy or 24-hydroxylated ligands. The presence of 1 alpha,25(OH)2D3 receptors in the fracture-healing callus is consistent with the known biological effects of the metabolite on the fracture-healing process.
authors.affiliation: Department of Biochemistry, University of California, Riverside 92521, USA.
authors.forename: A
authors.initials: A
authors.lastname: Kato
authors.forename: J E
authors.initials: JE
authors.lastname: Bishop
authors.forename: A W
authors.initials: AW
authors.lastname: Norman
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002146:Bony Callus / Q000378:metabolism*; D002117:Calcitriol / Q000378:metabolism*; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000737:chemistry; D002645:Chickens; D002762:Cholecalciferol / Q000031:analogs & derivatives; D003600:Cytosol / Q000737:chemistry; D017102:Fracture Healing; D008297:Male; D018167:Receptors, Calcitriol / Q000302:isolation & purification / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013977:Tibia
chemical_list: D002352:Carrier Proteins; D018167:Receptors, Calcitriol; D002762:Cholecalciferol; D002117:Calcitriol