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1,25-Dihydroxyvitamin D Promotes Negative Feedback Regulation of Toll-Like Receptor Signaling via Targeting MicroRNA-155-SOCS1 in Macrophages

ABSTRACT: The negative feedback mechanism is essential to maintain effective immunity and tissue homeostasis. 1,25-dihydroxyvitamin D (1,25(OH)2D3) modulates innate immune response, but the mechanism remains poorly understood. Here we report that vitamin D receptor (VDR) signaling attenuates Toll-like receptor-mediated inflammation by enhancing the negative feedback inhibition. VDR inactivation leads to a hyperinflammatory response in mice and macrophage cultures when challenged with lipopolysaccharide (LPS) due to miR-155 overproduction that excessively suppresses SOCS1, a key regulator that enhances the negative feedback loop. Deletion of miR-155 attenuates vitamin D suppression of LPS-induced inflammation, confirming that 1,25(OH)2D3 stimulates SOCS1 by down-regulating miR-155. 1,25(OH)2D3 down-regulates bic transcription by inhibiting NF-kappaB activation, which is mediated by a kappaB cis-DNA element located within the first intron of the bic gene. Together these data identify a novel regulatory mechanism for vitamin D to control innate immunity.

ORGANISM(S): Mus musculus Rattus norvegicus Human gammaherpesvirus 8 JC polyomavirus Betapolyomavirus macacae Human immunodeficiency virus 1 Murid gammaherpesvirus 4 Homo sapiens Human betaherpesvirus 5 Betapolyomavirus hominis Human alphaherpesvirus 1 human gammaherpesvirus 4 Murid betaherpesvirus 1

PROVIDER: GSE43300 | GEO | 2013/01/05

SECONDARY ACCESSION(S): PRJNA185321

REPOSITORIES: GEO

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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.

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1,25-Dihydroxyvitamin D Promotes Negative Feedback Regulation of Toll-Like Receptor Signaling via Targeting MicroRNA-155-SOCS1 in Macrophages

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