Complex genomes utilize insulators and boundary elements to help define spatial and temporal gene expression patterns. We report that a genome-wide B1 SINE (Short Interspersed Nuclear Element) ...retrotransposon (B1-X35S) has potent intrinsic insulator activity in cultured cells and live animals. This insulation is mediated by binding of the transcription factors dioxin receptor (AHR) and SLUG (SNAI2) to consensus elements present in the SINE. Transcription of B1-X35S is required for insulation. While basal insulator activity is maintained by RNA polymerase (Pol) III transcription, AHR-induced insulation involves release of Pol III and engagement of Pol II transcription on the same strand. B1-X35S insulation is also associated with enrichment of heterochromatin marks H3K9me3 and H3K27me3 downstream of B1-X35S, an effect that varies with cell type. B1-X35S binds parylated CTCF and, consistent with a chromatin barrier activity, its positioning between two adjacent genes correlates with their differential expression in mouse tissues. Hence, B1 SINE retrotransposons represent genome-wide insulators activated by transcription factors that respond to developmental, oncogenic, or toxicological stimuli.
Aryl hydrocarbon receptor (AhR) is a transcription factor that belongs to the basic helix-loop-helix PAS (Per-Arnt-Sim homology domain) family known to mediate the toxic and carcinogenic effects of ...xenobiotics. Interestingly, AhR is widely expressed in the central nervous system, but its physiological and pathological roles are still unclear.
To define the role of AhR in stroke, we used middle cerebral artery occlusion in mice and oxygen-glucose deprivation in rat cortical neurons. The results presented here show that the ischemic insult increases total and nuclear AhR levels and AhR transcriptional activity in neurons in vivo and in vitro. We also show that AhR has a causal role in acute ischemic damage because pharmacological or genetic loss-of-function approaches result in neuroprotection. Inhibition of cAMP response element-binding protein-dependent signaling may participate in the deleterious actions of AhR. Finally, we have also found that L-kynurenine, a tryptophan metabolite with AhR agonistic properties, is an endogenous ligand that mediates AhR activation in the brain after middle cerebral artery occlusion.
Our data demonstrate that an L-kynurenine/AhR pathway mediates acute brain damage after stroke and open new possibilities for the diagnosis and treatment of this pathology.
Aging impairs organismal homeostasis leading to multiple pathologies. Yet, the mechanisms and molecular intermediates involved are largely unknown. Here, we report that aged aryl hydrocarbon ...receptor-null mice (
) had exacerbated cellular senescence and more liver progenitor cells. Senescence-associated markers β-galactosidase (SA-β-Gal), p16
and p21
and genes encoding senescence-associated secretory phenotype (SASP) factors TNF and IL1 were overexpressed in aged
livers. Chromatin immunoprecipitation showed that AhR binding to those gene promoters repressed their expression, thus adjusting physiological levels in
livers. MCP-2, MMP12 and FGF secreted by senescent cells were overproduced in aged AhR-null livers. Supporting the relationship between senescence and stemness, liver progenitor cells were overrepresented in
mice, probably contributing to increased hepatocarcinoma burden. These AhR roles are not liver-specific since adult and embryonic AhR-null fibroblasts underwent senescence in culture, overexpressing SA-β-Gal, p16
and p21
. Notably, depletion of senescent cells with the senolytic agent navitoclax restored expression of senescent markers in
fibroblasts, whereas senescence induction by palbociclib induced an AhR-null-like phenotype in
fibroblasts. AhR levels were downregulated by senescence in mouse lungs but restored upon depletion of p16
-expressing senescent cells. Thus, AhR restricts age-induced senescence associated to a differentiated phenotype eventually inducing resistance to liver tumorigenesis.
Skin is in daily contact with potentially harmful molecules from the environment such as cigarette smoke, automobile emissions, industrial soot and groundwater. Pregnane X receptor (PXR) is a ...transcription factor expressed in liver and intestine that is activated by xenobiotic chemicals including drugs and environmental pollutants. Topical application of the tumor initiator 7,12‐dimethylbenz(a)anthracene (DMBA) enhances Pxr, Cyp1a1, Cyp1b1 and Cyp3a11, but not Ahr expression in the skin. Surprisingly, DMBA‐induced Pxr upregulation is largely impaired in Langerin+ cell‐depleted skin, suggesting that DMBA mainly triggers Pxr in Langerin+ cells. Furthermore, PXR deficiency protects from DNA damage in epidermal cells but to a lesser extent than aryl hydrocarbon receptor (AHR) deficiency. Interestingly, skin exposure to low doses of DMBA induces migration of PXR‐deficient but not of wild‐type and AHR‐deficient Langerhans cells (LCs). PXR‐humanized mice show a marked increase in DNA damage to epidermal cells after topical application of DMBA, demonstrating relevance of these findings in human tissue. This is the first report suggesting that carcinogens might trigger PXR in epidermal cells, particularly in LCs, thus leading to DNA damage. Further studies are required to better delineate the role of PXR in cutaneous carcinogenesis.
Hexachlorobenzene (HCB) is a widespread environmental pollutant and a dioxin-like compound that binds weakly to the aryl hydrocarbon receptor (AhR). Because AhR and transforming growth factor β1 ...(TGF-β1) converge to regulate common signaling pathways, alterations in this crosstalk might contribute to developing preneoplastic lesions. The aim of this study was to evaluate HCB action on TGF-β1 and AhR signaling in mouse mammary gland, through AhR+/+ and AhR−/− models. Results showed a differential effect in mouse mammary epithelial cells (NMuMG), depending on the dose: 0.05μM HCB induced cell migration and TGF-β1 signaling, whereas 5μM HCB reduced cell migration, promoted cell cycle arrest and stimulated the dioxin response element (DRE) -dependent pathway. HCB (5μM) enhanced α-smooth muscle actin expression and decreased TGF-β receptor II mRNA levels in immortalized mouse mammary fibroblasts AhR+/+, resembling the phenotype of transformed cells. Accordingly, their conditioned medium was able to enhance NMuMG cell migration. Assays in C57/Bl6 mice showed HCB (3mg/kg body weight) to enhance ductal hyperplasia, cell proliferation, estrogen receptor α nuclear localization, branch density, and the number of terminal end buds in mammary gland from AhR+/+ mice. Primary culture of mammary epithelial cells from AhR+/+ mice showed reduced AhR mRNA levels after HCB exposure (0.05 and 5μM). Interestingly, AhR−/− mice exhibited an increase in ductal hyperplasia and mammary growth in the absence of HCB treatment, thus revealing the importance of AhR in mammary development. Our findings show that environmental HCB concentrations modulate AhR and TGF-β1 signaling, which could contribute to altered mammary branching morphogenesis, likely leading to preneoplastic lesions and retaining terminal end buds.
•0.05μM HCB induces migration and TGF-β1 signaling in mammary epithelial cells NMuMG.•5μM HCB reduces migration, and promotes cell cycle arrest and AhR nuclear pathway in NMuMG.•HCB enhances α-SMA and decreases TGF-β receptor II expression in fibroblasts AhR+/+.•Conditioned medium from fibroblasts AhR+/+ exposed to HCB enhances NMuMG migration.•HCB increases hyperplasia and branching morphogenesis in AhR+/+ mice mammary gland.
Recent advances in long-read sequencing solve inaccuracies in alternative transcript identification of full-length transcripts in short-read RNA-Seq data, which encourages the development of methods ...for isoform-centered functional analysis. Here, we present tappAS, the first framework to enable a comprehensive Functional Iso-Transcriptomics (FIT) analysis, which is effective at revealing the functional impact of context-specific post-transcriptional regulation. tappAS uses isoform-resolved annotation of coding and non-coding functional domains, motifs, and sites, in combination with novel analysis methods to interrogate different aspects of the functional readout of transcript variants and isoform regulation. tappAS software and documentation are available at https://app.tappas.org.
Recent studies have emphasized the role of the dioxin receptor (AhR) in maintaining cell morphology, adhesion, and migration. These novel AhR functions depend on the cell phenotype, and although AhR ...expression maintains mesenchymal fibroblasts migration, it inhibits keratinocytes motility. These observations prompted us to investigate whether AhR modulates the epithelial-to-mesenchymal transition (EMT). For this, we have used primary AhR+/+ and AhR−/− keratinocytes and NMuMG cells engineered to knock down AhR levels (sh-AhR) or to express a constitutively active receptor (CA-AhR). Both AhR−/− keratinocytes and sh-AhR NMuMG cells had increased migration, reduced levels of epithelial markers E-cadherin and β-catenin, and increased expression of mesenchymal markers Snail, Slug/Snai2, vimentin, fibronectin, and α-smooth muscle actin. Consistently, AhR+/+ and CA-AhR NMuMG cells had reduced migration and enhanced expression of epithelial markers. AhR activation by the agonist FICZ (6-formylindolo3,2-bcarbazole) inhibited NMuMG migration, whereas the antagonist α-naphthoflavone induced migration as did AhR knockdown. Exogenous TGFβ exacerbated the promigratory mesenchymal phenotype in both AhR-expressing and AhR-depleted cells, although the effects on the latter were more pronounced. Rescuing AhR expression in sh-AhR cells reduced Snail and Slug/Snai2 levels and cell migration and restored E-cadherin levels. Interference of AhR in human HaCaT cells further supported its role in EMT. Interestingly, co-immunoprecipitation and immunofluorescence assays showed that AhR associates in common protein complexes with E-cadherin and β-catenin, suggesting the implication of AhR in cell-cell adhesion. Thus, basal or TGFβ-induced AhR down-modulation could be relevant in the acquisition of a motile EMT phenotype in both normal and transformed epithelial cells.
Background: The dioxin receptor (AhR) regulates cell migration and has a role in TGFβ activation.
Results: AhR expression inhibits basal and TGFβ-induced epithelial-to-mesenchymal transition (EMT).
Conclusion: AhR has an intrinsic role in EMT and cross talks with TGFβ.
Significance: The involvement of AhR in EMT can help explain its functions in organ homeostasis and tumor progression.
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