Search

Abstract: The signaling cascade of the transcription factor vitamin D receptor (VDR) is triggered by its specific ligand 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3). In this study we demonstrate that in THP-1 human monocytic leukemia cells 87.4% of the 1034 most prominent genome-wide VDR binding sites co-localize with loci of open chromatin. At 165 of them 1α,25(OH)2D3 strongly increases chromatin accessibility and has at further 217 sites weaker effects. Interestingly, VDR binding sites in 1α,25(OH)2D3-responsive chromatin regions are far more often composed of direct repeats with 3 intervening nucleotides (DR3s) than those in ligand insensitive regions. DR3-containing VDR sites are enriched in the neighborhood of genes that are involved in controling cellular growth, while non-DR3 VDR binding is often found close to genes related to immunity. At the example of six early VDR target genes we show that the slope of their 1α,25(OH)2D3-induced transcription correlates with the basal chromatin accessibility of their major VDR binding regions. However, the chromatin loci controlling these genes are indistinguishable in their VDR association kinetics. Taken together, ligand responsive chromatin loci represent dynamically regulated contact points of VDR with the genome, from where it controls early 1α,25(OH)2D3 target genes. [Copyright &y& Elsevier]

Abstract: The basic helix-loop-helix protein BHLHE40 functions as a transcriptional repressor and is involved in the control of cellular growth, development and circadian rhythms. By the use of genome-wide data on vitamin D receptor (VDR) location, open chromatin and histone modification backed-up by gene-specific mRNA expression studies we show that the human BHLHE40 gene is dynamically up-regulated by the VDR ligand 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) and down-regulated by the histone deactylase inhibitor trichostatin A. The VDR binding site is located 1.7kb upstream of the transcription start site of the BHLHE40 gene and the chromatin at this genomic site is significantly opened by treatment with 1α,25(OH)2D3. The stair case style fluctuations in the BHLHE40 mRNA accumulation relate to the short half-life of the gene's mRNA of 0.9h. The identification of the widely expressed BHLHE40 gene as a primary VDR target may explain secondary effects of 1α,25(OH)2D3 on BHLHE40 responding genes. This article is part of a Special Issue entitled ‘Vitamin D Workshop’. [Copyright &y& Elsevier]

The placenta regulates the passage of both endogenous and xenobiotic compounds to the fetus during pregnancy. A small number of xenobiotic metabolizing CYP enzymes are constantly expressed in placenta, those include CYP19A1 which mainly converts androgens to estrogens, and CYP1A1 whose substrates include steroid hormones and xenobiotics. We performed an analysis of co-expression of xenobiotic metabolizing enzyme-coding genes and transcription factors in placenta and in 86 other tissues to discern the unique characteristics of the placental transcriptome. Transcription factors (TFs) driving the expression of proteins involved in phase I and II xenobiotic metabolism in the liver were not expressed in the placenta, nor were the bulk of xenobiotic metabolizing hepatic CYP enzymes. In contrast, TFs whose co-expression correlated with CYP1A1, i.e. AHR, PPARG, and CEBPB were highly expressed in placenta. The placenta is a hormonal tissue, and one needs to maintain the tissue-specific focus by removing the hepatic spectacles. [ABSTRACT FROM AUTHOR]

The moisturizing and potentially protective properties of the organic osmolyte betaine (trimethylglycine) have made it an attractive component for skin care products. Its wide use despite the lack of comprehensive studies addressing its specific effects in skin led us to characterize the molecular targets of betaine in keratinocytes and to explore, whether it modifies the effects of acute UVB exposure. Genome-wide expression analysis was performed on organotypic cultures of rat epidermal keratinocytes, treated either with betaine (10 mM), UVB (30 mJ/cm 2 ) or their combination. Results were verified with qRT-PCR, western blotting and immunohistochemistry. Additionally, cell proliferation and differentiation were analyzed. Among the 89 genes influenced by betaine, the differentiation marker keratin 2 showed the highest upregulation, which was also confirmed at protein level. Expression of Egr1 , a transcription factor, and Purkinje cell protein 4, a regulator of Ca 2 + /calmodulin metabolism, also increased, while downregulated genes included several ion-channel components, such as Fxyd2 . Bioinformatics analyses suggest that genes modulated by betaine are involved in DNA replication, might counteract UV-induced processes, and include many targets of transcription factors associated with cell proliferation and differentiation. Our results indicate that betaine controls unique gene expression pathways in keratinocytes, including some involved in differentiation. [ABSTRACT FROM AUTHOR]