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Gene targeting by the vitamin D response element binding protein reveals a role for vitamin D in osteoblast mTOR signaling.

ABSTRACT: Transcriptional regulation by hormonal 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] involves occupancy of vitamin D response elements (VDREs) by the VDRE binding protein (VDRE-BP) or 1,25(OH)(2)D(3)-bound vitamin D receptor (VDR). This relationship is disrupted by elevated VDRE-BP, causing a form of hereditary vitamin D-resistant rickets (HVDRR). DNA array analysis showed that of 114 genes regulated by 1,25(OH)(2)D(3) in control cells, almost all (113) were rendered insensitive to the hormone in VDRE-BP-overexpressing HVDRR cells. Among these was the gene for DNA-damage-inducible transcript 4 (DDIT4), an inhibitor of mammalian target of rapamycin (mTOR) signaling. Chromatin immunoprecipitation PCR using 1,25(OH)(2)D(3)-treated osteoblasts confirmed that VDR and VDRE-BP compete for binding to the DDIT4 gene promoter. Expression of DDIT4 mRNA in these cells was induced (1.6-6 fold) by 1,25(OH)(2)D(3) (10-100 nM), and Western blot and flow cytometry analysis showed that this response involved suppression of phosphorylated S6K1(T389) (a downstream target of mTOR) similar to rapamycin treatment. siRNA knockdown of DDIT4 completely abrogated antiproliferative responses to 1,25(OH)(2)D(3), whereas overexpression of VDRE-BP exerted a dominant-negative effect on transcription of 1,25(OH)(2)D(3)-target genes. DDIT4, an inhibitor of mTOR signaling, is a direct target for 1,25(OH)(2)D(3) and VDRE-BP, and functions to suppress cell proliferation in response to vitamin D.

SUBMITTER: Lisse TS

PROVIDER: S-EPMC3042839 | biostudies-other | 2011 Mar

REPOSITORIES: biostudies-other

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Gene targeting by the vitamin D response element binding protein reveals a role for vitamin D in osteoblast mTOR signaling.

Lisse Thomas S TS Liu Ting T Irmler Martin M Beckers Johannes J Chen Hong H Adams John S JS Hewison Martin M

FASEB journal : official publication of the Federation of American Societies for Experimental Biology 20101201 3

Transcriptional regulation by hormonal 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] involves occupancy of vitamin D response elements (VDREs) by the VDRE binding protein (VDRE-BP) or 1,25(OH)(2)D(3)-bound vitamin D receptor (VDR). This relationship is disrupted by elevated VDRE-BP, causing a form of hereditary vitamin D-resistant rickets (HVDRR). DNA array analysis showed that of 114 genes regulated by 1,25(OH)(2)D(3) in control cells, almost all (113) were rendered insensitive to the hormone in ...[more]

PMID: 21123297

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Project description:Heterogeneous nuclear ribonucleoprotein (hnRNP) C1/C2 plays a pivotal role in vitamin D receptor (VDR) signaling by acting as a vitamin D response element (VDRE)-binding protein (VDRE-BP). Transcriptional regulation by active 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) involves occupancy of VDRE by VDRE-BP or 1,25(OH)2D3 bound-VDR. This relationship is disrupted by over-expression of VDRE-BP and can cause a form of human hereditary vitamin D-resistant rickets (HVDRR). DNA array analyses using B-cells from an HVDRR patient and matched control defined a sub-cluster of genes where 1,25(OH)2D3-regulated transcription was abrogated by over-expression of VDRE-BP. Amongst these, the DNA-damage-inducible transcript 4 (DDIT4), an inhibitor of mammalian target of rapamycin (mTOR) signaling, was also induced by 1,25(OH)2D3 in human osteoblasts. Chromatin immunoprecipitation using 1,25(OH)2D3-treated osteoblasts confirmed that liganded VDR and VDRE-BP compete for binding to the proximal promoter of the DDIT4 gene in a similar fashion to other known 1,25(OH)2D3-target genes. Treatment of osteoblasts with 1,25(OH)2D3 induced DDIT4 expression and suppressed phosphorylated S6K1T389 protein (a downstream target of mTOR). The functional importance of this for 1,25(OH)2D3 responses in osteoblasts was underlined by the fact that siRNA knockdown of DDIT4 expression suppressed antiproliferative and cell growth responses to 1,25(OH)2D3. These data confirm that VDRE-BP is required for normal 1,25(OH)2D3-mediated transcription and cell function in osteoblasts. Conversely over-expression of VDRE-BP exerts a dominant-negative effect on transcription of 1,25(OH)2D3-target genes. Characterization of VDRE-BP action in 1,25(OH)2D3-treated osteoblasts highlights an entirely novel role for vitamin D as a regulator of mTOR – a known ‘master regulator’ of cell function. We performed gene expression microarray analysis in HVDRR EBV-transformed B-cells and control cells in the presence or absence of vitamin D.

Project description:Opinion statementNeuroendocrine tumors (NETs) are a heterogeneous group of malignancies characterized by variable but most often indolent biologic behavior. Well-differentiated NETs can be broadly classified as either carcinoid or pancreatic NET. Although they have similar characteristics on routine histologic evaluation, the 2 tumor subtypes have different biology and respond differently to treatment, with most therapeutic agents demonstrating higher response rates in pancreatic NETs compared with carcinoid. Until recently, systemic treatment options for patients with advanced NETs were limited. However, improvements in our understanding of signaling pathways involved in the pathogenesis, growth, and spread of NETs have translated into an expansion of treatment options. Aberrant signaling through the mechanistic pathway of rapamycin (mTOR) pathway has been implicated in neuroendocrine tumorigenesis. Additionally, altered expression of mTOR pathway components has been observed in NETs and has been associated with clinical outcomes. Targeting the mTOR pathway has emerged as an effective treatment strategy in the management of advanced NETs. In a randomized, placebo-controlled study of patients with advanced pancreatic NET, treatment with the mTOR inhibitor everolimus was associated with improved progression-free survival (PFS). Largely based upon these data, everolimus has been approved in the United States and Europe for the treatment of patients with advanced pancreatic NET. The activity of everolimus remains under investigation in patients with carcinoid tumors. In a randomized study of patients with advanced carcinoid tumors associated with carcinoid syndrome, the addition of everolimus to octreotide was associated with improved PFS compared with octreotide. However, the results did not meet the prespecified level of statistical significance based on central review of radiographic imaging. Results from a randomized study examining the efficacy of everolimus in patients with nonfunctional gastrointestinal and lung NETs are awaited. In addition, further investigation is needed to determine whether primary tumor site or other clinical and molecular factors can impact response to mTOR inhibition. Although everolimus can slow tumor progression, significant tumor reduction is rarely obtained. Targeting multiple signaling pathways is a treatment strategy that may provide better tumor control and overcome resistance mechanisms involved with targeting a single pathway. Results of ongoing and future studies will provide important information regarding the added benefit of combining mTOR inhibitors with other targeted agents, such as VEGF pathway inhibitors, and cytotoxic chemotherapy in the treatment of advanced NETs.

Dataset Information

Gene targeting by the vitamin D response element binding protein reveals a role for vitamin D in osteoblast mTOR signaling.

Publications

Gene targeting by the vitamin D response element binding protein reveals a role for vitamin D in osteoblast mTOR signaling.

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