title: 1,25-dihydroxyvitamin D3 receptors and hormonal responses in cloned human skeletal muscle cells.
abstract: Although skeletal muscle is a major calcium-regulated organ, there remains uncertainty about whether muscle is a target organ for the action of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. In this study we examine pure populations of clonally derived human muscle cells for the presence of 1,25-(OH)2D3 receptors and direct responses to the hormone. All of the clones tested exhibited specific [3H]1,25-(OH)2D3 binding, with values ranging from 5-70 fmol/mg protein. Scatchard analysis of binding data revealed a dissociation constant (approximately 100 pM) comparable to that of classical receptors in other target organs. The 1,25-(OH)2D3 receptors sedimented at 3.3S on hypertonic sucrose gradients. Specificity for [3H]1,25-(OH)2D3 was demonstrated on gradients by substantially better competition by 1,25-(OH)2D3 than 25-hydroxyvitamin D3 for the 3.3S receptor binding peak. The 1,25-(OH)2D3 receptor complex bound to DNA-cellulose and eluted as a single peak at 0.2 M KCl. Myoblasts and myotubes did not show significant differences in either the amount or characteristics of the 1,25-(OH)2D3 receptor. In addition to the presence of receptors, cells were tested for functional responsiveness to 1,25-(OH)2D3. Both cell types exhibited a dose-dependent induction of 25-hydroxyvitamin D3-24-hydroxylase enzyme activity after treatment of monolayers with 1,25-(OH)2D3. Incorporation of both leucine and thymidine into growing myoblasts and fused myotubes was inhibited in a dose-dependent fashion after treatment with 1,25-(OH)2D3. In summary, cloned human skeletal muscle cells contain a binding protein compatible with classical 1,25-(OH)2D3 receptors as well as functional responsiveness to 1,25-(OH)2D3 at physiological concentrations of hormone.
mesh_terms: D002117:Calcitriol / Q000378:metabolism; D002455:Cell Division; D002482:Cellulose / Q000031:analogs & derivatives; D002499:Centrifugation, Density Gradient; D002999:Clone Cells / Q000378:metabolism; D004247:DNA / Q000031:analogs & derivatives; D004261:DNA Replication / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism; D014176:Protein Biosynthesis; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000378:metabolism*; D013936:Thymidine / Q000378:metabolism
chemical_list: C033190:DNA-cellulose; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D002482:Cellulose; D004247:DNA; D002117:Calcitriol; D007930:Leucine; D013936:Thymidine