Abstract
The present study demonstrates 1alpha,25-dehydroxyvitamin D3 (1alpha-25-(OH)2D3) synergism toward transforming growth factor (TGF)-beta1-induced activation protein-1 (AP-1) activity in mouse osteoblastic MC3T3-E1 cells via the nuclear receptor of the vitamin. 1alpha-25-(OH)2D3 synergistically stimulated TGF-beta1-induced expression of the c-jun gene in the cells but not that of the c-fos gene. We actually showed by a gel mobility shift assay 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced AP-1 binding to the 12-(O-tetradecanoylphorbol-13-acetate response element (TRE). 1alpha-25-(OH)2D3 markedly stimulated the transient activity of TGF-beta1-induced AP-1 in the cells transfected with a TRE-chloramphenicol acetyltransferase (CAT) reporter gene. Also, a synergistic increase in TGF-beta1-induced CAT activity was observed in the cells cotransfected with an expression vector encoding vitamin D3 receptor (VDR) and the reporter gene. However, the synergistic CAT activity was inhibited by pretreatment with VDR antisense oligonucleotides. In addition, in a Northern blot assay, we observed 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced expression of the c-jun gene in the cells transfected with the VDR expression vector and also found that the synergistic action was clearly blocked by VDR antisense oligonucleotide pretreatment. The present study strongly suggests a novel positive regulation by 1alpha-25-(OH)2D3 of TGF-beta1-induced AP-1 activity in osteoblasts via "genomic action."
Highlights
The present study demonstrates 1␣,25-dehydroxyvitamin D3 (1␣-25-(OH)2D3) synergism toward transforming growth factor (TGF)-1-induced activation protein-1 (AP-1) activity in mouse osteoblastic MC3T3-E1 cells via the nuclear receptor of the vitamin. 1␣-25-(OH)2D3 synergistically stimulated TGF-1-induced expression of the c-jun gene in the cells but not that of the c-fos gene
We showed by a gel mobility shift assay 1␣-25(OH)2D3 synergism of TGF-1-induced AP-1 binding to the 12-(O-tetradecanoylphorbol-13-acetate response element (TRE). 1␣-25-(OH)2D3 markedly stimulated the transient activity of TGF-1-induced AP-1 in the cells transfected with a TRE-chloramphenicol acetyltransferase (CAT) reporter gene
Since AP-1 typically appeared when the cells were treated for 3 h with TGF-1 at 1 ng/ml, in this study we investigated the regulatory action of 1␣-25(OH)2D3 on TGF-1-induced AP-1 activity in the cells under these experimental conditions
Summary
The present study demonstrates 1␣,25-dehydroxyvitamin D3 (1␣-25-(OH)2D3) synergism toward transforming growth factor (TGF)-1-induced activation protein-1 (AP-1) activity in mouse osteoblastic MC3T3-E1 cells via the nuclear receptor of the vitamin. 1␣-25-(OH)2D3 synergistically stimulated TGF-1-induced expression of the c-jun gene in the cells but not that of the c-fos gene. A synergistic increase in TGF-1-induced CAT activity was observed in the cells cotransfected with an expression vector encoding vitamin D3 receptor (VDR) and the reporter gene. In a Northern blot assay, we observed 1␣-25(OH)2D3 synergism of TGF-1-induced expression of the c-jun gene in the cells transfected with the VDR expression vector and found that the synergistic action was clearly blocked by VDR antisense oligonucleotide pretreatment. Many studies (20 –26) have shown that the hormone binds to its receptor, VDR, in the cell nucleus and acts via binding of this complex to the VDR response element This VDR-dependent action is referred to as the “genomic action” of the hormone. Other recent studies [27,28,29,30,31,32,33,34,35,36,37] have suggested that the hormone is able to induce several biological activities via protein kinase C, ceramide signaling pathways, and via an increase in the intracellular calcium concentration, which are called “nongenomic action.”
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