RESUMO
The active metabolite of vitamin D3 , 1α,25-dihydroxyvitamin D3 , acts as a ligand for the vitamin D receptor (VDR) and activates VDR-mediated gene expression. Recently, we characterized 1α,25-dihydroxyvitamin D3 -26,23-lactams (DLAMs), which mimic vitamin D3 metabolites, as noncalcemic VDR ligands that barely activate the receptor. In this study, we present structural insights onto the regulation of VDR function by DLAMs. X-ray crystallographic analysis revealed that DLAMs induced a large conformational change in the loop region between helices H6 and H7 in the VDR ligand-binding domain. Our structural analysis suggests that targeting of the loop region may be a new mode of VDR regulation.
Assuntos
Calcitriol/análise , Lactamas/química , Simulação de Acoplamento Molecular , Receptores de Calcitriol/química , Animais , Sítios de Ligação , Calcitriol/química , Calcitriol/metabolismo , Linhagem Celular , Linhagem Celular Tumoral , Humanos , Ligação Proteica , Ratos , Receptores de Calcitriol/metabolismoRESUMO
The TGF-ß superfamily comprises pleiotropic cytokines that regulate SMAD and non-SMAD signaling. TGF-ß-SMAD signal transduction is known to be involved in tissue fibrosis, including renal fibrosis. Here, we found that 1,25-dihydroxyvitamin D3-bound [1,25(OH)2D3-bound] vitamin D receptor (VDR) specifically inhibits TGF-ß-SMAD signal transduction through direct interaction with SMAD3. In mouse models of tissue fibrosis, 1,25(OH)2D3 treatment prevented renal fibrosis through the suppression of TGF-ß-SMAD signal transduction. Based on the structure of the VDR-ligand complex, we generated 2 synthetic ligands. These ligands selectively inhibited TGF-ß-SMAD signal transduction without activating VDR-mediated transcription and significantly attenuated renal fibrosis in mice. These results indicate that 1,25(OH)2D3-dependent suppression of TGF-ß-SMAD signal transduction is independent of VDR-mediated transcriptional activity. In addition, these ligands did not cause hypercalcemia resulting from stimulation of the transcriptional activity of the VDR. Thus, our study provides a new strategy for generating chemical compounds that specifically inhibit TGF-ß-SMAD signal transduction. Since TGF-ß-SMAD signal transduction is reportedly involved in several disorders, our results will aid in the development of new drugs that do not cause detectable adverse effects, such as hypercalcemia.
