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Query: UMLS:C0338671 (Steroids)
 9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

OK cells are a transformed cell line derived from opossum kidney proximal tubule cells. Prior studies have utilized this cell line to study both positive and negative transcriptional responses to Vitamin D. However, there was a noticeable decrease in sensitivity on the part of these cells to respond to Vitamin D treatment in transfection assays, particularly when assessing transcriptional activity from a heterologous promoter construct that used the chicken parathyroid hormone (cPTH) repressor Vitamin D response element (VDRE). Western blotting revealed the apparently diminished expression of both the Vitamin D receptor (VDR) together with its heterodimeric DNA-binding partner, the retinoid X receptor (RXR), in these cellular extracts. Co-transfection of either a VDR or RXR expression vector alone had little effect on hormone-dependent enhancer transcriptional activity from the human osteocalcin (hOC) reporter construct, or the degree of repression from the cPTH construct. Indeed, significant effects on repressor or enhancer activity were only observed in these cells when expression vectors for both the VDR and RXR were simultaneously introduced into the cells via transfection experiments. Analogous results were obtained irrespective of the identity of RXR isoform; co-transfection of either RXRalpha or RXRbeta expression vectors together with the VDR-produced similar improvements in repressor activity. Titration of Vitamin D hormone under conditions of co-expression of the two receptors indicated that half-maximal responses were comparable for both VDREs and occurred at <1nM concentration. In summary, these results are consistent with prior in vitro studies indicating interaction of the VDR with these VDREs occurs as a heterodimer complex with RXR. The decreased expression of both heterodimer partners observed in these cells could explain the requirement for additional VDR/RXR expression, in particular in order to compensate for the reportedly lower binding affinity of the heterodimer with the repressor cPTH VDRE. The extent of expression of both heterodimer partners, therefore, may act to modulate the available responses to Vitamin D in target cells.
Steroids 2003 Apr
PMID:Heterodimer requirement for gene regulation by Vitamin D in variant OK cells. 1278 91

Osteoblasts are a main target for the steroid 1alpha,25(OH)2-Vitamin D3 (1,25D3), where a major outcome is the modulation of the bone remodeling process. 1,25D3 deficiency leads to clinical disorders such as osteomalacia and osteoporosis, characterized by a state of insufficiently calcified tissue and bone loss, respectively. In the osteoblast nucleus, 1,25D3 modulates gene transcription for the synthesis of bone matrix proteins via the Vitamin D receptor (VDR). At the plasma membrane level, 1,25D3 potentiates ion channel functions, activates signal transduction pathways, and increases cytoplasmic calcium concentrations. So far, no clear physiological significance has been attributed to membrane-initiated 1,25D3 actions in single cells. To investigate if (a) 1,25D3 is a modulatory agent of secretion in osteoblasts and (b) the classical VDR is involved in rapid electrical events in the cell membrane, we studied hormone effects on ion channel activities in relation to exocytosis in osteoblasts isolated from VDR knockout (KO) and wild-type (WT) mice. This paper is a retrospect of the electrophysiological studies done in our laboratory to date. We found that 1,25D3-promoted ion channel responses are coupled to secretion in calvarial osteoblasts, and develop only in the presence of a functional nuclear steroid VDR. This 1,25D3-regulated exocytosis in osteoblasts, which takes place within minutes of hormone application, seems to be the natural complement of genomic actions that evolve at a longer time scale. The absence of both 1,25D3 membrane and nuclear effects in VDR KO osteoblasts may explain bone abnormalities typically found in VDR KO mice.
Steroids 2004 Aug
PMID:Electrical responses to 1alpha,25(OH)2-Vitamin D3 and their physiological significance in osteoblasts. 1528 70

Over the past 20 years much has been learned about the cellular actions of the steroid hormone 1alpha,25(OH)2-Vitamin D3 (1,25D). Perhaps most importantly structure-function studies led to the discovery that different chemical and physical features of 1,25D are preferred to initiate either exonuclear, non-genomic or endonuclear, genomic cellular signaling. It is well documented that both a 1alpha-OH and 25-OH, and a 6-s-trans, bowl-shaped, sterol conformation are absolutely required for efficient gene transcription, while 6-s-cis locked analogs and 1-deoxy, 25(OH)D3 metabolites activate a variety of non-genomic, rapid responses. These results and the observation that S237 (helix-3; H3) and R274 (H5) are the most static residues in the human 1,25D-Vitamin D receptor (VDR) X-ray construct (see B-values in pdb: 1DB1) and form H-bonds with the 1alpha-OH of 1,25D in the X-ray, genomic pocket (G-pocket), provided the basis for the molecular modeling experiments that led to the discovery of a putative VDR alternative ligand binding pocket (A-pocket). The conformational ensemble model generated from the in silico results provides an explanation for how the VDR can function as a receptor propagating both genomic and non-genomic signaling events. In this report the theoretical gating properties controlling ligand access to the A- and G-pockets will be compared and the model will be used to provide a molecular explanation for the confusing structure-function results pertaining to 1,25D, its side-chain metabolite, 23S,25R-1alpha,25(OH)2-D3-26,23-lactone (BS), and its synthetic two side-chain analog, 21-(3'-hydroxy-3'-methylbutyl)-1alpha,25(OH)2-D3 (KH or Gemini). In addition, evidence that the model is consistent with the pH requirement for Vitamin D sterol-VDR crystallization will be presented.
Steroids
PMID:Applications of the Vitamin D sterol-Vitamin D receptor (VDR) conformational ensemble model. 1586 32

Parathyroid hormone-related protein (PTHrP) increases the growth and osteolytic potential of prostate cancer cells, making it important to control PTHrP expression in these cells. We show that 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its non-hypercalcemic analog, EB1089, decrease PTHrP mRNA and cellular protein levels in the androgen-dependent human prostate cancer cell line LNCaP and its androgen-independent derivative, the C4-2 cell line. This effect is mediated via a negative Vitamin D response element (nVDREhPTHrP) within the human PTHrP gene and involves an interaction between nVDREhPTHrP and the Vitamin D receptor (VDR). The retinoid X receptor (RXR) is a frequent heterodimeric partner of the VDR. We show that RXRalpha forms part of the nuclear protein complex that interacts with nVDREhPTHrP along with the VDR in LNCaP and C4-2 cells. We also show that the RXR ligand, 9-cis-retinoic acid, downregulates PTHrP mRNA levels; this decrease is more pronounced in LNCaP than in C4-2 cells. In addition, 9-cis-retinoic acid enhances the 1,25(OH)2D3-mediated downregulation of PTHrP expression in both cell lines; this effect also is more pronounced in LNCaP cells. Proliferation of LNCaP, but not C4-2, cells is decreased by 9-cis-retinoic acid. Promoter activity driven by nVDREhPTHrP cloned upstream of the SV40 promoter and transiently transfected into LNCaP and C4-2 cells is downregulated in response to 1,25(OH)2D3 and EB1089 in both cell lines. Co-treatment with these compounds and 9-cis-retinoic acid further decreases CAT activity in LNCaP, but not C4-2, cells. These results indicate that PTHrP gene expression is regulated by 1,25(OH)2D3 in a cell type-specific manner in prostate cancer cells.
Steroids 2006 Feb
PMID:Prostate cancer cell type-specific involvement of the VDR and RXR in regulation of the human PTHrP gene via a negative VDRE. 1624 70

1,25-Dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] acts on chondrocytes and osteoblasts through traditional nuclear Vitamin D receptor (VDR) mechanisms as well as through rapid actions on plasma membranes that initiate intracellular signaling pathways. We have investigated the mechanisms involved in activation of protein kinase C (PKC) and downstream biological responses that depend on the latter pathway. These studies show that PKC activation depends on presence of a membrane receptor ERp60 and rapid increases in phospholipase A(2) (PLA(2)) activity. Cells that are responsive to 1alpha,25(OH)(2)D(3) express PLA(2) activating protein (PLAA), suggesting a link between ERp60 and PLA(2). Increased PLA(2) results in increased arachidonic acid release and formation of lysophospholipid, which then activates phospholipase C beta (PLCbeta), leading to rapid formation of inositol-trisphosphate (IP3) and diacylglycerol (DAG). PLA(2), PLC, and DAG are all associated with lipid rafts including caveolae in many cells, suggesting that the caveolar environment may be an important mediator of PKC activation by 1alpha,25(OH)(2)D(3). Here, we use the VDR(-/-) mouse costochondral cartilage growth plate to examine the expression of ERp60 and PLAA in vivo in 1alpha,25(OH)(2)D(3)-responsive hypertrophic chondrocytes (growth zone cells) and in resting zone cells that do not respond to this Vitamin D metabolite in vitro. In addition, we determined if intact lipid rafts are required for the response of rat costochondral cartilage growth zone cells to 1alpha,25(OH)(2)D(3). The results show that ERp60 and PLAA are localized to 1alpha,25(OH)(2)D(3)-responsive growth zone cells and metaphyseal osteoblasts, even in VDR(-/-) mice. Disruption of lipid rafts using beta-cyclodextrin blocks the activation of PKC by 1alpha,25(OH)(2)D(3) and reduces the ability of 1alpha,25(OH)(2)D(3) to regulate [(35)S]-sulfate incorporation.
Steroids 2006 Apr
PMID:Plasma membrane requirements for 1alpha,25(OH)2D3 dependent PKC signaling in chondrocytes and osteoblasts. 1632 16

Vitamin D receptor (VDR) agonists supporting human osteoblast (hOB) differentiation in the absence of bone resorption are attractive agents in a bone regenerative setting. One potential candidate fulfilling these roles is 24,25-dihydroxy vitamin D3 (24,25D). Over forty years ago it was reported that supraphysiological levels of 24,25D could stimulate intestinal calcium uptake and aid bone repair without causing bone calcium mobilisation. VDR agonists co-operate with certain growth factors to enhance hOB differentiation but whether 24,25D might act similarly in promoting cellular maturation has not been described. Given our discovery that lysophosphatidic acid (LPA) co-operated with VDR agonists to enhance hOB maturation, we co-treated MG63 hOBs with 24,25D and a phosphatase-resistant LPA analog. In isolation 24,25D inhibited proliferation and stimulated osteocalcin expression. When co-administered with the LPA analog there were synergistic increases in alkaline phosphatase (ALP). These are encouraging findings which may help realise the future application of 24,25D in promoting osseous repair.
Steroids 2014 May
PMID:24,25-Dihydroxyvitamin D3 cooperates with a stable, fluoromethylene LPA receptor agonist to secure human (MG63) osteoblast maturation. 2451 53