title: Requirement of calcium and phosphate ions in expression of sodium-dependent vitamin C transporter 2 and osteopontin in MC3T3-E1 osteoblastic cells.
abstract: Osteoclasts dissolve mineralized bone matrix at bone resorption sites and release large amounts of calcium (Ca(2+)) and phosphate (PO(4)(3-)) ions into the extracellular fluid. However, the exact nature of Ca(2+) and PO(4)(3-) on osteoblasts remains unclear. We proposed that Ca(2+) and PO(4)(3-) ions are required for the expression of sodium-dependent vitamin C transporter (SVCT) 2 and a differentiation marker, osteopontin (OPN), in osteoblasts as a response to the osteoclastic degradation. Results from Northern blotting indicated that a deficiency of Ca(2+) or PO(4)(3-) inhibited both SVCT2 and OPN expression in a time-dependent manner, whereas elevated Ca(2+) (1 to 4 mM) or PO(4)(3-) (1 to 4 mM) dose-dependently induced SVCT2, OPN expression and OPN promoter activity. In addition, the L-type calcium channel blocker, nifedipine (5 to 20 micro M) and the phosphate transporter inhibitor, foscarnet (0.15 to 0.6 mM), dose-dependently abolished Ca(2+)- and PO(4)(3-)-induced SVCT2, OPN expression and OPN promoter activity. Furthermore, the results from L-ascorbic acid uptake assay and Western blotting indicated that the stimulatory effect of Ca(2+) and PO(4)(3-) on functional SVCT2 protein expression. These findings suggested that Ca(2+) and PO(4)(3-) regulate osteoblastic phenotype by entering into cells to stimulate SVCT2 and OPN expression.
authors.affiliation: Department of Toxicology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamada-oka, Suita, Osaka 565-0871, Japan.
authors.forename: Ximei
authors.initials: X
authors.lastname: Wu
authors.forename: Norio
authors.initials: N
authors.lastname: Itoh
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Nakanishi
authors.forename: Keiichi
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D015415:Biomarkers; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D017245:Foscarnet / Q000494:pharmacology; D051379:Mice; D009543:Nifedipine / Q000494:pharmacology; D029363:Organic Anion Transporters, Sodium-Dependent / Q000187:drug effects / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D053495:Osteopontin; D010710:Phosphates / Q000502:physiology*; D012795:Sialoglycoproteins / Q000378:metabolism*; D060347:Sodium-Coupled Vitamin C Transporters; D027981:Symporters / Q000187:drug effects / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D029363:Organic Anion Transporters, Sodium-Dependent; D010710:Phosphates; D012795:Sialoglycoproteins; C555165:Slc23a2 protein, mouse; D060347:Sodium-Coupled Vitamin C Transporters; C506896:Spp1 protein, mouse; D027981:Symporters; D053495:Osteopontin; D017245:Foscarnet; D009543:Nifedipine; D002118:Calcium