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Heterogeneous nuclear ribonucleoprotein C1/C2 links transcriptional and splicing actions of 1,25-dihydroxyvitamin D

ABSTRACT: Heterogeneous nuclear ribonucleoprotein C1/C2 (hnRNPC1/C2) functions as an RNA splicing regulator through co-transcriptional association with nascent mRNA. HnRNPC1/C2 can also bind to double-stranded DNA as a vitamin D response element-binding protein (VDRE-BP), thereby regulating transcriptional activity of the vitamin D receptor (VDR) bound to 1,25-dihydroxyvitamin D (1,25(OH)2D). In this way hnRNPC1/C2 may act as a coupling factor for 1,25(OH)2D-directed transcription and RNA splicing. Studies using MG63 osteoblastic cells confirmed that 1,25(OH)2D-VDR mediated induction of the gene for the enzyme 24-hydroxylase (CYP24A1), involved CYP24A1-specific chromatin and RNA immunoprecipitation of hnRNPC1/C2. Furthermore, small interfering (siRNA) knockdown of hnRNPC1/C2 in MG63 cells and was associated with dysregulated expression of CYP24A1 and an alternatively spliced form of CYP24A1 (CYP24A1-variant 2). Genome-wide analysis of RNA expression and alternative splicing indicated that dual role of hnRNPC1/C2 in directing 1,25(OH)2D-mediated gene expression is not restricted to the classical VDR-target CYP24A1. Knockdown of hnRNPC1/C2 resulted in 3500 differentially expressed genes (DEG), and treatment with 1,25(OH)2D 324 DEG. A further 87 DEG were only observed in 1,25(OH)2D-treated cells in hnRNPC1/C2 knockdown cells. HnRNPC1/C2 knockdown or 1,25(OH)2D treatment also induced alternative splicing (AS) (5039 and 310 AS events respectively). Combined hnRNPC1/C2 knockdown and 1,25(OH)2D treatment resulted in significant overlap between DEG and AS genes, but this was not observed for 1,25(OH)2D treatment alone. These data indicate that hnRNPC1/C2 can act to couple transcriptional and splicing responses to 1,25(OH)2D by binding to both DNA and RNA. Similar mechanisms may also exist for other members of the hnRNP and steroid receptor family.

ORGANISM(S): Homo sapiens

PROVIDER: GSE63086 | GEO | 2016/12/06

SECONDARY ACCESSION(S): PRJNA266575

REPOSITORIES: GEO

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Project description:We investigated how the biologically active form of vitamin D (1,25(OH)2D3) inhibits the epithelial-to-mesenchymal transition (EMT), a critical step in the development of a migratory phenotype in epithelial tumor cells, as well as migration in general, using osteosarcoma (OS) as a model. We looked at how 1,25(OH)2D3 affected pre- and post-EMT migratory states in non-metastatic MG63 and metastatic LM7 OS cell models. In scratch and Boyden chamber assays, 1,25(OH)2D3 inhibited cell migration and invasion, but LM7 cells responded significantly less than MG63 cells (50 vs 26 percent decrease, respectively). 1,25(OH)2D3 inhibited the expression of EMT-inducing genes (e.g., SNAI2) and extracellular contact regulatory genes in MG63 cells but not in LM7 cells (e.g., CD44, MMP3). In comparison to MG63 cells, LM7 cells had significantly lower baseline VDR transcript levels but higher SNAI2 transcript levels. Furthermore, ATAC-seq analysis revealed that 1,25(OH)2D3 epigenetically repressed SNAI2 in MG63 cells, implying that LM7 cells may be constitutively induced to undergo EMT via VDR de-repression mediated by increased SNAI2 levels. Both cell lines appeared to activate an antioxidative pathway involving SOD2 upregulation and concurrent reactive oxygen species (ROS) reduction (e.g., H2O2). ATAC-seq analysis revealed that 1,25(OH)2D3 does not epigenetically regulate SOD2 in MG63 cells, implying a previously unknown indirect link promoting anti-EMT and anti-metastatic oxidation states in both OS cell lines. We studied the fate and migration of mouse hair follicle stem cell progenitor cells after wounding with or without the Vdr because cutaneous wounding and metastasis involve similar signaling factors that regulate cell migration. Conditional loss of Vdr in epithelial progenitor cells promoted cell migration and wound healing in comparison to control animals, indicating that Vdr signaling inhibits cell migration in general. Our findings show that vitamin D signaling inhibits cell migration both in vivo and in vitro, and that inhibiting reactive oxygen species (ROS) in both pre-EMT and post-EMT OS cells is a possible vitamin D mechanism and therapeutic strategy for preventing the onset and progression of OS. MG63 human osteosarcoma cell line treated with vehicle (ethanol) or 1,25(OH)D (10nM) for 24 and 48 hours.

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:The biological effects of 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) on osteoblast differentiation and function differ significantly depending upon the cellular state of maturation. To explore this phenomenon mechanistically, we examined the impact of 1,25(OH)2D3 on the transcriptomes of both pre-osteoblastic (POBs) and differentiated osteoblastic (OBs) MC3T3-E1 cells, and assessed localization of the vitamin D receptor (VDR) at sites of action on a genome-scale using ChIP-seq analysis. We observed that the 1,25(OH)2D3-induced transcriptomes of POBs and OBs were quantitatively and qualitatively different, supporting not only the altered biology observed but the potential for a change in VDR interaction at the genome as well. This idea was confirmed through discovery that VDR cistromes in POBs and OBs were also strikingly different. Depletion of VDR binding sites in OBs, due in part to reduced VDR expression, was the likely cause of the loss of VDR-target gene interaction. Continued novel regulation by 1,25(OH)2D3, however, suggested that factors in addition to the VDR might also be involved. Accordingly, we show that transcriptomic modifications are also accompanied by changes in genome binding of the master osteoblast regulator RUNX2 and the chromatin remodeler C/EBPβ. Importantly, genome occupancy was also highlighted by the presence of epigenetic enhancer signatures which were selectively changed in response to both differentiation and 1,25(OH)2D3. The impact of VDR, RUNX2, and C/EBPβ on osteoblast differentiation is exemplified by their actions at the Runx2 and Sp7 gene loci. We conclude that each of these mechanisms may contribute to the diverse actions of 1,25(OH)2D3 on differentiating osteoblasts. RNA was isolated and applied to gene expression microarrays in undifferentiated MC3T3-E1 cells as well as post 15 day osteogenic differentiation MC3T3-E1 cells, which were treated for 24 hours with 10-7M 1,25(OH)2D3. For the vehicle matched samples, please refer to study GSE41955. The samples were completed in biological triplicate.

Project description:The biological effects of 1?,25-dihydroxyvitamin D3 (1,25(OH)2D3) on osteoblast differentiation and function differ significantly depending upon the cellular state of maturation. To explore this phenomenon mechanistically, we examined the impact of 1,25(OH)2D3 on the transcriptomes of both pre-osteoblastic (POBs) and differentiated osteoblastic (OBs) MC3T3-E1 cells, and assessed localization of the vitamin D receptor (VDR) at sites of action on a genome-scale using ChIP-seq analysis. We observed that the 1,25(OH)2D3-induced transcriptomes of POBs and OBs were quantitatively and qualitatively different, supporting not only the altered biology observed but the potential for a change in VDR interaction at the genome as well. This idea was confirmed through discovery that VDR cistromes in POBs and OBs were also strikingly different. Depletion of VDR binding sites in OBs, due in part to reduced VDR expression, was the likely cause of the loss of VDR-target gene interaction. Continued novel regulation by 1,25(OH)2D3, however, suggested that factors in addition to the VDR might also be involved. Accordingly, we show that transcriptomic modifications are also accompanied by changes in genome binding of the master osteoblast regulator RUNX2 and the chromatin remodeler C/EBP?. Importantly, genome occupancy was also highlighted by the presence of epigenetic enhancer signatures which were selectively changed in response to both differentiation and 1,25(OH)2D3. The impact of VDR, RUNX2, and C/EBP? on osteoblast differentiation is exemplified by their actions at the Runx2 and Sp7 gene loci. We conclude that each of these mechanisms may contribute to the diverse actions of 1,25(OH)2D3 on differentiating osteoblasts. 4 transcription factors and 5 histone modifications were examined in undifferentiated MC3T3-E1 cells as well as post 15 day osteogenic differentiation MC3T3-E1 cells, which were treated for 3 hours prior to ChIP assay with ethanol vehicle or with 10-7M 1,25(OH)2D3. For the vehicle matched samples for RUNX2, CEBP beta and histones, please refer to study GSE41955. The samples were completed in biological replicate and examined separately.

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Heterogeneous nuclear ribonucleoprotein C1/C2 links transcriptional and splicing actions of 1,25-dihydroxyvitamin D

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