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1α,25 Dihydroxyvitamin D3 Rapidly Regulates the Mouse Osteoprotegerin Gene Through Dual Pathways

2004; Oxford University Press; Volume: 19; Issue: 9 Linguagem: Inglês

10.1359/jbmr.040604

1523-4681

Takeshi Kondo, Riko Kitazawa, Sakan Maeda, Sohei Kitazawa,

S100 Proteins and Annexins

1 alpha,25(OH)(2)D(3) rapidly and transiently suppressed OPG gene expression both by accelerating the degradation of mRNA and by suppressing promoter activity. The latter process was mediated through the AP-1 binding site by a reduction in the proportion of phospho-c-Jun in a JNK-independent manner.Osteoclastogenesis is regulated by an integrated network of numerous bone metabolic factors, among which 1 alpha,25-dihydroxyvitamin D(3) [1 alpha,25(OH)(2)D(3)] promotes osteoclastogenesis by reciprocally upregulating the expression of RANKL and downregulating that of osteoprotegerin (OPG).To analyze the mechanism by which 1 alpha,25(OH)(2)D(3) suppresses OPG, we characterized cis-acting elements of the mouse OPG gene and assessed the post-transcriptional modifications by actinomycin D assays.1 alpha,25(OH)(2)D(3) rapidly and transiently suppressed OPG expression and shortened the half-life of OPG mRNA; additionally, the c-Jun homodimer bound to the AP-1 binding site (TGACTGA, -293/-287) and maintained steady-state transcription of the OPG gene. Furthermore, mutation of the AP-1 site negated 1 alpha,25(OH)(2)D(3)-driven OPG suppression. Moreover, 1 alpha,25(OH)(2)D(3) treatment of ST2 cells decreased the amount of phosphorylated c-Jun protein (phospho-c-Jun), while the total amount of c-Jun remained constant; however, the amount of phosphorylated Jun N-terminal kinase (JNK) was nearly unchanged by 1 alpha,25(OH)(2)D(3) treatment.Taken together with the observation that the OPG promoter has no consensus negative vitamin D-responsive elements, these data suggest that 1 alpha,25(OH)(2)D(3) transrepresses mouse OPG by reducing the proportion of phospho-c-Jun in a JNK-independent manner. Our data indicated that short-term treatment with 1 alpha,25(OH)(2)D(3) effectively downregulated OPG expression both by accelerating the degradation of OPG mRNA and by transrepressing the OPG gene through its AP-1 binding site in the catabolic phase. The OPG gene became insensitive to 1 alpha,25(OH)(2)D(3) treatment, however, and reverted to its steady-state expression level over time, leading to the anabolic phase of the effect of 1 alpha,25(OH)(2)D(3) on bone.