title: Identification of 1,25-dihydroxyvitamin D3 receptors and activities in muscle.
abstract: Cytosols from cultured myoblast cells (G-8 and H9c2) prepared in high salt (0.3 M KCl) possesses receptor like proteins for 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) that sediment in the 3.2 S region of sucrose gradients. These receptors were characterized as having high affinity (Kd less than 0.1 nM) for 1,25-(OH)2D3 and are in low capacity (less than 80 fmol/mg of cytosol protein). Analog competition for receptor binding revealed that 1,25-(OH)2D3 was more potent than 24,25-(OH)2D3, or 25-(OH)2D3 for displacement of 1,25-(OH)2[3H]D3 from these 3.2 S region sedimenting receptors. Furthermore, the receptor proteins had affinity for DNA and eluted from Sephacryl S-200 as a macromolecule with Stokes radius (Rs) of 32 A. High salt cytosol from collagenase-dispersed skeletal muscle cells was also found to possess a 3.2 S 1,25-(OH)2D3 receptor-like protein. The 1,25-(OH)2D3 receptor concentration in both G-8 and H9c2 myoblast lines was found to down-regulate by 50-70% when cells were stimulated to differentiate to myotubes by lowering fetal calf serum to 5% of the medium. Moreover, we demonstrated that 1,25-(OH)2D3 can inhibit DNA synthesis and cell proliferation of the G-8 myoblast cells in a dose-dependent manner. 1,25-(OH)2D3 was more potent at inhibiting cell proliferation in cells grown in 5% serum than in 20% serum. The data suggest that 1,25-(OH)2D3 can act directly on muscle myoblast via a 1,25-(OH)2D3 receptor that is similar to those found in intestine and bone. The data support the possibility that muscle is a target tissue for 1,25-(OH)2D3 and the hormone may act to initiate terminal differentiation of myoblast cells.
authors.forename: R U
authors.initials: RU
authors.lastname: Simpson
authors.forename: G A
authors.initials: GA
authors.lastname: Thomas
authors.forename: A J
authors.initials: AJ
authors.lastname: Arnold
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002850:Chromatography, Gel; D003201:Computers; D004247:DNA / Q000096:biosynthesis; D051379:Mice; D009132:Muscles / Q000032:analysis* / Q000166:cytology / Q000187:drug effects; D011869:Radioligand Assay; D051381:Rats; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000032:analysis*; D014316:Tritium; D014808:Vitamin D Deficiency / Q000378:metabolism
chemical_list: D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D014316:Tritium; D004247:DNA; D002117:Calcitriol; D002118:Calcium