Saskia Trump

An endogenous tumour-promoting ligand of the human aryl hydrocarbon receptor

Activation of the aryl hydrocarbon receptor (AHR) by environmental xenobiotic toxic chemicals, for instance 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin), has been implicated in a variety of cellular processes such as embryogenesis, transformation, tumorigenesis and inflammation. But the identity of an endogenous ligand activating the AHR under physiological conditions in the absence of environmental toxic chemicals is still unknown. Here we identify the tryptophan (Trp) catabolite kynurenine (Kyn) as an endogenous ligand of the human AHR that is constitutively generated by human tumour cells via tryptophan-2,3-dioxygenase (TDO), a liver- and neuron-derived Trp-degrading enzyme not yet implicated in cancer biology. TDO-derived Kyn suppresses antitumour immune responses and promotes tumour-cell survival and motility through the AHR in an autocrine/paracrine fashion. The TDO–AHR pathway is active in human brain tumours and is associated with malignant progression and poor survival. Because Kyn is produced during cancer progression and inflammation in the local microenvironment in amounts sufficient for activating the human AHR, these results provide evidence for a previously unidentified pathophysiological function of the AHR with profound implications for cancer and immune biology.

Transcription Factor AP1 Potentiates Chromatin Accessibility and Glucocorticoid Receptor Binding

Ligand-dependent transcription by the nuclear receptor glucocorticoid receptor (GR) is mediated by interactions with coregulators. The role of these interactions in determining selective binding of GR to regulatory elements remains unclear. Recent findings indicate that a large fraction of genomic GR binding coincides with chromatin that is accessible prior to hormone treatment, suggesting that receptor binding is dictated by proteins that maintain chromatin in an open state. Combining DNaseI accessibility and chromatin immunoprecipitation with high-throughput sequencing, we identify the activator protein 1 (AP1) as a major partner for productive GR-chromatin interactions. AP1 is critical for GR-regulated transcription and recruitment to co-occupied regulatory elements, illustrating an extensive AP1-GR interaction network. Importantly, the maintenance of baseline chromatin accessibility facilitates GR recruitment and is dependent on AP1 binding. We propose a model in which the basal occupancy of transcription factors acts to prime chromatin and direct inducible transcription factors to select regions in the genome.

Kinetic Complexity of the Global Response to Glucocorticoid Receptor Action

We have characterized the kinetic response of gene targets throughout the murine genome to transcriptional modulation by the glucocorticoid receptor (GR). In contrast to a model in which multiple genes are either repressed or activated during the GR response, the vast majority of responsive genes are subject to complex regulation profiles, frequently with alternate activation and repression phases. We also observe that GR binding at response elements does not always correlate with the target gene response profile. Thus, the cellular response to GR stimulation involves a highly orchestrated series of regulatory actions and not simply a binary response to hormone.

Environment-induced epigenetic reprogramming in genomic regulatory elements in smoking mothers and their children

Epigenetic mechanisms have emerged as links between prenatal environmental exposure and disease risk later in life. Here, we studied epigenetic changes associated with maternal smoking at base pair resolution by mapping DNA methylation, histone modifications, and transcription in expectant mothers and their newborn children. We found extensive global differential methylation and carefully evaluated these changes to separate environment associated from genotype‐related DNA methylation changes. Differential methylation is enriched in enhancer elements and targets in particular “commuting” enhancers having multiple, regulatory interactions with distal genes. Longitudinal whole‐genome bisulfite sequencing revealed that DNA methylation changes associated with maternal smoking persist over years of life. Particularly in children prenatal environmental exposure leads to chromatin transitions into a hyperactive state. Combined DNA methylation, histone modification, and gene expression analyses indicate that differential methylation in enhancer regions is more often functionally translated than methylation changes in promoters or non‐regulatory elements. Finally, we show that epigenetic deregulation of a commuting enhancer targeting c‐Jun N‐terminal kinase 2 (JNK2) is linked to impaired lung function in early childhood.

From the exposome to mechanistic understanding of chemical-induced adverse effects

The exposome encompasses an individuals exposure to exogenous chemicals, as well as endogenous chemicals that are produced or altered in response to external stressors. While the exposome concept has been established for human health, its principles can be extended to include broader ecological issues. The assessment of exposure is tightly interlinked with hazard assessment. Here, we explore if mechanistic understanding of the causal links between exposure and adverse effects on human health and the environment can be improved by integrating the exposome approach with the adverse outcome pathway (AOP) concept that structures and organizes the sequence of biological events from an initial molecular interaction of a chemical with a biological target to an adverse outcome. Complementing exposome research with the AOP concept may facilitate a mechanistic understanding of stress-induced adverse effects, examine the relative contributions from various components of the exposome, determine the primary risk drivers in complex mixtures, and promote an integrative assessment of chemical risks for both human and environmental health.

Prenatal maternal stress and wheeze in children: novel insights into epigenetic regulation

Psychological stress during pregnancy increases the risk of childhood wheeze and asthma. However, the transmitting mechanisms remain largely unknown. Since epigenetic alterations have emerged as a link between perturbations in the prenatal environment and an increased disease risk we used whole genome bisulfite sequencing (WGBS) to analyze changes in DNA methylation in mothers and their children related to prenatal psychosocial stress and assessed its role in the development of wheeze in the child. We evaluated genomic regions altered in their methylation level due to maternal stress based of WGBS data of 10 mother-child-pairs. These data were complemented by longitudinal targeted methylation and transcriptional analyses in children from our prospective mother-child cohort LINA for whom maternal stress and wheezing information was available (n = 443). High maternal stress was associated with an increased risk for persistent wheezing in the child until the age of 5. Both mothers and children showed genome-wide alterations in DNA-methylation specifically in enhancer elements. Deregulated neuroendocrine and neurotransmitter receptor interactions were observed in stressed mothers and their children. In children but not in mothers, calcium- and Wnt-signaling required for lung maturation in the prenatal period were epigenetically deregulated and could be linked with wheezing later in children’s life.

T-2 toxin is a cytochrome P450 1A1 inducer and leads to MAPK/p38- but not aryl hydrocarbon receptor-dependent interleukin-8 secretion in the human intestinal epithelial cell line Caco-2.

T-2 toxin (T-2) is a secondary metabolite produced by various mould species of the genus Fusarium and a common contaminant detectable in staple foods of cereal origin. In the present study the impact of this mycotoxin on the inflammatory response of the intestinal epithelial cell line Caco-2 was examined by measuring interleukin (IL)-8 secretion. A T-2 concentration dependent IL-8 up-regulation was detected in IL-1β stimulated and unstimulated Caco-2 cells. To elucidate the possible underlying molecular mechanism of this conditional T-2-provoked IL-8 induction, a possible involvement of the aryl hydrocarbon receptor (AHR) and the mitogen-activated protein kinase (MAPK) pathway was investigated. Like benzo-[a]-pyrene (B[a]P), a well known AHR ligand, T-2 led to cytochrome P450 1A1 (CYP1A1) mRNA expression in Caco-2 cells, which could be inhibited by the AHR antagonist resveratrol. However, resveratrol did not influence T-2-dependent IL-8 induction. Since T-2 did not lead to AHR-translocation in stably GFP-AHR-transfected cells, an AHR dependency of T-2-triggered IL-8 induction could be excluded. But finally, up to a total inhibition of T-2-induced IL-8 was obtained using p38 inhibitors. Therefore, we conclude that p38 MAPK is responsible for mediating the inflammatory properties of the type A trichothecene T-2.

Increased vitamin D levels at birth and in early infancy increase offspring allergy risk—evidence for involvement of epigenetic mechanisms

To the Editor: Although a beneficial effect of vitamin D on health is widely accepted, its role in allergy development has been controversial. Both allergy-preventing and allergy-promoting effects have been reported. Thus, a deeper mechanistic understanding of how vitamin D is related to the regulation of immune reactivity and allergic inflammation is required. Vitamin D was shown to modify gene expression through binding of the vitamin D receptor to vitamin D response elements. However, only 26% of the genes identified as regulated by vitamin D have a vitamin D response element in proximity to their transcription start site (TSS), indicating that additional mechanisms are involved in the transcriptional control by vitamin D. As an additional mechanism, epigenetically mediated transcriptional deregulation through vitamin D–induced changes in DNA methylation was suggested. Here, we studied DNA-methylation pattern on a genomewide scale at base-pair resolution in healthy newborn children with high and low vitamin D levels to elucidate the role of vitamin D in epigenetic programming of an allergy-protective or allergypromoting immune reactivity. Within the LINA (Lifestyle and environmental factors and their Influence on Newborns Allergy risk) mother-child cohort, differential DNA methylation was assessed by using whole genome bisulfite sequencing in 6 cord blood samples comparing 3 children with high to 3 children with low

Maternal phthalate exposure promotes allergic airway inflammation over 2 generations through epigenetic modifications

Background: Prenatal and early postnatal exposures to environmental factors are considered responsible for the increasing prevalence of allergic diseases. Although there is some evidence for allergy‐promoting effects in children because of exposure to plasticizers, such as phthalates, findings of previous studies are inconsistent and lack mechanistic information. Objective: We investigated the effect of maternal phthalate exposure on asthma development in subsequent generations and their underlying mechanisms, including epigenetic alterations. Methods: Phthalate metabolites were measured within the prospective mother‐child cohort Lifestyle and Environmental Factors and Their Influence on Newborns Allergy Risk (LINA) and correlated with asthma development in the children. A murine transgenerational asthma model was used to identify involved pathways. Results: In LINA maternal urinary concentrations of mono‐n‐butyl phthalate, a metabolite of butyl benzyl phthalate (BBP), were associated with an increased asthma risk in the children. Using a murine transgenerational asthma model, we demonstrate a direct effect of BBP on asthma severity in the offspring with a persistently increased airway inflammation up to the F2 generation. This disease‐promoting effect was mediated by BBP‐induced global DNA hypermethylation in CD4+ T cells of the offspring because treatment with a DNA‐demethylating agent alleviated exacerbation of allergic airway inflammation. Thirteen transcriptionally downregulated genes linked to promoter or enhancer hypermethylation were identified. Among these, the GATA‐3 repressor zinc finger protein 1 (Zfpm1) emerged as a potential mediator of the enhanced susceptibility for TH2‐driven allergic asthma. Conclusion: These data provide strong evidence that maternal BBP exposure increases the risk for allergic airway inflammation in the offspring by modulating the expression of genes involved in TH2 differentiation through epigenetic alterations.

Benzo[a]pyrene affects Jurkat T cells in the activated state via the antioxidant response element dependent Nrf2 pathway leading to decreased IL-2 secretion and redirecting glutamine metabolism

There is a clear evidence that environmental pollutants, such as benzo[a]pyrene (B[a]P), can have detrimental effects on the immune system, whereas the underlying mechanisms still remain elusive. Jurkat T cells share many properties with native T lymphocytes and therefore are an appropriate model to analyze the effects of environmental pollutants on T cells and their activation. Since environmental compounds frequently occur at low, not acute toxic concentrations, we analyzed the effects of two subtoxic concentrations, 50nM and 5μM, on non- and activated cells. B[a]P interferes directly with the stimulation process as proven by an altered IL-2 secretion. Furthermore, B[a]P exposure results in significant proteomic changes as shown by DIGE analysis. Pathway analysis revealed an involvement of the AhR independent Nrf2 pathway in the altered processes observed in unstimulated and stimulated cells. A participation of the Nrf2 pathway in the change of IL-2 secretion was confirmed by exposing cells to the Nrf2 activator tBHQ. tBHQ and 5μM B[a]P caused similar alterations of IL-2 secretion and glutamine/glutamate metabolism. Moreover, the proteome changes in unstimulated cells point towards a modified regulation of the cytoskeleton and cellular stress response, which was proven by western blotting. Additionally, there is a strong evidence for alterations in metabolic pathways caused by B[a]P exposure in stimulated cells. Especially the glutamine/glutamate metabolism was indicated by proteome pathway analysis and validated by metabolite measurements. The detrimental effects were slightly enhanced in stimulated cells, suggesting that stimulated cells are more vulnerable to the environmental pollutant model compound B[a]P.