Akiko Murayama

Positive and Negative Regulations of the Renal 25-Hydroxyvitamin D3 1α-Hydroxylase Gene by Parathyroid Hormone, Calcitonin, and 1α,25(OH)2D3 in Intact Animals1

Reflecting the prime role of 1α,25(OH)2D3 in calcium homeostasis, the activity of 25-hydroxyvitamin D3 1α-hydroxylase, a key enzyme for 1α,25(OH)2D3 biosynthesis, is tightly regulated by 1α,25(OH)2D3, PTH and calcitonin. Its significant activity is found in kidney, though the enzymatic activity is also reported in extra-renal tissues. In the present study, we found that the 1α-hydroxylase gene abundantly expresses in kidney, and at low levels in other tissues and in some cell lines. Positive and negative regulations of 1α-hydroxylase gene by PTH, calcitonin, or 1α,25(OH)2D3 were observed at transcriptional levels in kidneys of animals and in a mouse proximal tubule cell line. Moreover, the protein kinase A inhibitor abrogated the PTH-mediated positive regulation. In mice lacking the vitamin D receptor, the 1α-hydroxylase gene expression was overinduced, and the inducible effect of either PTH or calcitonin, but not the repression by 1α,25(OH)2D3, was evident. Thus, vitamin D receptor is essential for the n...

Selective Interaction of Vitamin D Receptor with Transcriptional Coactivators by a Vitamin D Analog

ABSTRACT The nuclear vitamin D receptor (VDR) is a member of a nuclear receptor superfamily and acts as a ligand-dependent transcription factor. A family of cotranscriptional activators (SRC-1, TIF2, and AIB-1) interacts with and activates the transactivation function of nuclear receptors in a ligand-dependent way. We examined interaction of VDR with these coactivators that was induced by several vitamin D analogs, since they exert differential subsets of the biological action of vitamin D through unknown mechanisms. Unlike other vitamin D analogs tested, OCT (22-oxa-1α,25-dihydroxyvitamin D3) induced interaction of VDR with TIF2 but not with SRC-1 or AIB-1. Consistent with these interactions, only TIF2 was able to potentiate the transactivation function of VDR bound to OCT. Thus, the present findings suggest that the structure of VDR is altered in a vitamin D analog-specific way, resulting in selective interactions of VDR with coactivators. Such selective interaction of coactivators with VDR may specify the array of biological actions of a vitamin D analog like OCT, possibly through activating a particular set of target gene promoters.

Ligand type-specific Interactions of Peroxisome Proliferator-activated Receptor γ with Transcriptional Coactivators

Ligand type-specific interactions of peroxisome proliferator-activated receptor with transcriptional coactivators. Yasuo Kodera, Ken-ichi Takeyama, Akiko Murayama, Miyuki Suzawa, Yoshikazu Masuhiro, and Shigeaki Kato This article has been withdrawn by the authors. THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 288, NO. 42, p. 30505, October 18, 2013

Transrepression by a liganded nuclear receptor via a bHLH activator through co-regulator switching

Vitamin D receptor (VDR) is essential for ligand-induced gene repression of 25(OH)D3 1α-hydroxylase (1α(OH)ase) in mammalian kidney, while this gene expression is activated by protein kinase A (PKA) signaling downstream of the parathyroid hormone action. The mapped negative vitamin D response element (1αnVDRE) in the human 1α(OH)ase gene promoter (around 530 bp) was distinct from those of the reported DR3-like nVDREs, composed of two E-box-like motifs. Unlike the reported nVDREs, no direct binding of VDR/RXR heterodimer to 1αnVDRE was detected. A bHLH-type factor, designated VDIR, was identified as a direct sequence-specific activator of 1αnVDRE. The transactivation function of VDIR was further potentiated by activated-PKA signaling through phosphorylation of serine residues in the transactivation domains, with the recruitment of a p300 histone acetyltransferase co-activator. The ligand-dependent association of VDR/RXR heterodimer with VDIR bound to 1αnVDRE caused the dissociation of p300 co-activators from VDIR, and the association of HDAC co-repressor complex components resulting in ligand-induced transrepression. Thus, the present study deciphers a novel mechanism of ligand-induced transrepression by nuclear receptor via co-regulator switching.

In vivo function of VDR in gene expression-VDR knock-out mice

Vitamin D exerts many biological actions through nuclear vitamin D receptor (VDR)-mediated gene expression. The transactivation function of VDR is activated by binding 1alpha,25-dihydroxyvitamin D3[1alpha,25(OH)2D3], an active form of vitamin D. Conversion from 25(OH)D3 is finely regulated in kidney by 25(OH)D3 1alpha-hydroxylase[25(OH)D 1alpha-hydroxylase], keeping serum levels of 1alpha,25(OH)2D3 constant. Deficiency of vitamin D and mutations in the genes like VDR (type II genetic rickets) are known to cause rickets like lowered serum calcium, alopecia and impaired bone formation. However, the molecular basis of vitamin D VDR system in the vitamin D action in intact animals remained to be established. In addition, the 1alpha-hydroxylase gene from any species had not yet been cloned, irrespective of its biological significance and putative link to the type I genetic rickets. We generated VDR-deficient mice (VDR KO mice). VDR KO mice grew up normally until weaning, but after weaning they developed abnormality like the type II rickets patients. These results demonstrated indispensability of vitamin D-VDR system in mineral and bone metabolism only in post-weaning life. Using a newly developed cloning system, we cloned the cDNA encoding a novel P450 enzyme, mouse and human 1alpha-hydroxylase. The study in VDR KO mice demonstrated the function of liganded VDR in the negative feed-back regulation of 1alpha,25(OH)2D3 production. Finally, from the analysis of type I rickets patients, we found missense genetic mutations in 1alpha-hydroxylase, leading to the conclusion that this gene is responsible for the type I rickets.

Correlation between 25-hydroxyvitamin D3 1α-hydroxylase gene expression in alveolar macrophages and the activity of sarcoidosis

PURPOSEnTo demonstrate expression of the 25-hydroxyvitamin D3 1 alpha-hydroxylase (1 alpha-hydroxylase) gene in human alveolar macrophages and measure the correlations among the 1 alpha-hydroxylase mRNA level, the activity of sarcoidosis, and calcium metabolism.nnnSUBJECTS AND METHODSnWe examined 7 patients with sarcoidosis and 6 control patients with other pulmonary disorders who underwent bronchoalveolar lavage. Levels of 1 alpha-hydroxylase mRNA were measured by semiquantitative polymerase chain reaction amplification. We measured serum levels of calcium, ionized calcium, parathyroid hormone, calcitriol (1,25-dihydroxyvitamin D3), and 25-hydroxyvitamin D3 to evaluate calcium metabolism. To estimate the activity of sarcoidosis, we measured the cell count, the CD4/CD8 ratio in bronchoalveolar lavage cells, and the serum angiotensin-converting enzyme (ACE) activity.nnnRESULTSnExpression of 1 alpha-hydroxylase was demonstrated in purified human alveolar macrophages. The 1 alpha-hydroxylase mRNA levels in bronchoalveolar lavage cells were fivefold higher in sarcoidosis patients than in control patients (10.8 +/- 3.6 vs. 2.2 +/- 1.4, P <0.003). Among all patients studied, there were significant correlations between the 1 alpha-hydroxylase mRNA level in bronchoalveolar lavage samples and the percentage of alveolar lymphocytes (r = 0.83, P <0.005), the CD4/CD8 ratio (r = 0.77, P <0.02), serum ACE level (r = 0.58, P <0.05), serum ionized calcium level (r = 0.58, P <0.05), and the calcitriol/25-hydroxyvitamin D3 ratio (r = 0.57, P <0.05). In the sarcoidosis patients, a significant correlation was also observed between 1 alpha-hydroxylase mRNA and the percentage of alveolar lymphocytes (r = 0.82, P <0.05).nnnCONCLUSIONnThere is a correlation between 1 alpha-hydroxylase gene expression in alveolar macrophages with the activity of sarcoidosis and its associated disturbances in calcium metabolism.

Molecular Genetics of Vitamin D- Dependent Hereditary Rickets

Vitamin D exerts a wide variety of biological actions. The active form of vitamin D, 1α,25(OH)₂D₃, is biosynthesized from cholesterol. The final, critical step in this biosynthesis is conversion from 25-hydroxyvitamin D₃ to 1α,25(OH)₂D₃ by the enzyme 25-hydroxyvitamin D₃ 1α-hydroxylase(CYP27B1)[1α(OH)ase]. 1α,25(OH)₂D₃ transcriptionally controls the expression of a particular set of target genes mediated through nuclear vitamin D receptor(VDR) acting as a ligand-inducible factor. Two types of vitamin D-dependent hereditary rickets (VDDR) are known to be caused by mutations in the 1α(OH)ase and VDR genes. The 1α(OH)ase gene is responsible for VDDR type I, and VDR for type II. Both of the diseases display an autosomal-recessive trait, but clinical features and response to administrated 1α,25(OH)₂D₃ are distinct. The phenotypes of the gene KO mice deficient of 1α(OH)ase and VDR exhibited the clinical abnormalities observed in the VDDR patients.