title: Osteoprotegerin expression and secretion are regulated by calcium influx through the L-type voltage-sensitive calcium channel.
abstract: Our previous studies showed that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] modulates the activity of the Ca(V1.2) alpha-subunit of the L-type voltage-sensitive calcium channel (VSCC) by two temporally distinct mechanisms. First, 1,25(OH)2D3 rapidly modulates local Ca2+ permeability in the plasma membrane of the proliferating osteoblast. Second, treatment with 1,25(OH)2D3 reduces biosynthesis of Ca(V1.2) such that transcript levels are half of original levels after 24 h. Osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) provide important regulatory mechanisms for controlling osteoclastogenesis and Ca2+ homeostasis. Because they often control Ca2+-activated secretion, we investigated the possibility that L-type VSCCs might regulate basal OPG and RANKL secretion in osteoblasts. We also studied 1,25(OH)2D3 effects on OPG and RANKL expression. To address this, we measured changes in expression and secretion of OPG and RANKL in MC3T3-E1 cells and calvarial organ cultures after treatment with 1,25(OH)2D3, VSCC inhibitors, and inhibitors of Ca2+-regulated signaling. RANKL production was increased in calvarial cultures by 1,25(OH)2D3 but was essentially undetectable in the medium of MC3T3-E1 cells. In contrast, OPG secretion in both systems was significantly reduced after 24 h treatment with 1,25(OH)2D3, by inhibitors of L-type VSCCs and calmodulin-sensitive protein kinases but not by inhibitors of protein kinase A, MAPKs, or other families of VSCCs. OPG secretion was abrogated by transfection with decoy cAMP response element binding sites. Our results suggest that OPG secretion is regulated through calmodulin-sensitive protein kinase signaling that depends on the activity of the L-type VSCC and is mediated through the cAMP response element-binding protein.
authors.affiliation: Department of Biological Sciences, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Joel J
authors.initials: JJ
authors.lastname: Bergh
authors.forename: Yihuan
authors.initials: Y
authors.lastname: Xu
authors.forename: Mary C
authors.initials: MC
authors.lastname: Farach-Carson
mesh_terms: D000818:Animals; D021461:Animals, Outbred Strains; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015536:Down-Regulation; D025461:Feedback, Physiological; D005260:Female; D015870:Gene Expression / Q000502:physiology; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D053244:Osteoprotegerin; D011247:Pregnancy; D053245:RANK Ligand; D012333:RNA, Messenger / Q000032:analysis; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics*; D018124:Receptors, Tumor Necrosis Factor; D012886:Skull / Q000166:cytology
chemical_list: D002120:Calcium Channel Agonists; D020746:Calcium Channels, L-Type; D002352:Carrier Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; C505687:Tnfrsf11a protein, mouse; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse; D017868:Cyclic AMP-Dependent Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D002117:Calcitriol; D002118:Calcium