Characterization of Quinoline Yellow Dyes As Transient Aryl Hydrocarbon Receptor Agonists.

The aryl hydrocarbon receptor (AHR) and estrogen receptor alpha (ERα) are two ligand activated transcription factors that are targeted by a wide range of anthropogenic compounds. Crosstalk between both receptors is well established but little understood. We previously developed a dual color luciferase assay (i.

Chemical activation of estrogen and aryl hydrocarbon receptor signaling pathways and their interaction in toxicology and metabolism.

Estrogen receptors (ERs) and the arylhydrocarbon receptor (AHR) are ligand-activated transcription factors that regulate the expression of genes involved in many physiological processes. With both receptors binding a broad range of natural and anthropogenic ligands, they are molecular targets for many substances, raising concerns for possible health effects. Areas covered: This review shall give a brief overview on the physiological functions of both receptors including their underlying molecular mechanisms.

Differential cellular metabolite alterations in HaCaT cells caused by exposure to the aryl hydrocarbon receptor-binding polycyclic aromatic hydrocarbons chrysene, benzo[]pyrene and dibenzo[]pyrene.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the human environment. Since they are present in crude oilfractions used for the production of rubber and plastics, consumers may come into direct dermal contacts with these compounds (e.g.

A Novel Dual-Color Luciferase Reporter Assay for Simultaneous Detection of Estrogen and Aryl Hydrocarbon Receptor Activation.

Consumers are exposed to a plethora of anthropogenic and natural substances that can act as agonists or antagonists for various transcription factors. Depending on the exposure and potency, such interactions can potentially lead to adverse health effects, particularly for substances with multiple molecular targets. The early detection of such interactions is thus of high toxicological interest.

Combination of Metabolomics with Cellular Assays Reveals New Biomarkers and Mechanistic Insights on Xenoestrogenic Exposures in MCF-7 Cells.

The disruptive potential of xenoestrogens like bisphenol A (BPA) lies in their 17β-estradiol (E2)-like binding to estrogen receptors (ERs) followed by concomitant modulation of ER target gene expression. Unsurprisingly, most endocrine testing systems focus on the quantification of canonical transcripts or ER-sensitive reporters. However, only little information is available about the corresponding metabolomic changes in vitro.

Estrogenic Activity of Mineral Oil Aromatic Hydrocarbons Used in Printing Inks.

The majority of printing inks are based on mineral oils (MOs) which contain complex mixtures of saturated and aromatic hydrocarbons. Consumer exposure to these oils occurs either through direct skin contacts or, more frequently, as a result of MO migration into the contents of food packaging that was made from recycled newspaper. Despite this ubiquitous and frequent exposure little is known about the potential toxicological effects, particularly with regard to the aromatic MO fractions.

G protein-coupled receptor 30 ligand G-1 increases aryl hydrocarbon receptor signalling by inhibition of tubulin assembly and cell cycle arrest in human MCF-7 cells.

Regulatory crosstalk between the aryl hydrocarbon receptor (AHR) and oestrogen receptor α (ERα) is well established. Apart from the nuclear receptors ERα and ERβ, oestrogen signalling further involves an unrelated G protein-coupled receptor termed GPR30. In order to investigate potential regulatory crosstalk, this study investigated the influence of G-1 as one of the few GPR30-specific ligands on the AHR regulon in MCF-7 cells.

Identification of lipidomic biomarkers for coexposure to subtoxic doses of benzo[a]pyrene and cadmium: the toxicological cascade biomarker approach.

The search for model bioassay systems indicating activation of different toxicological signaling pathways is one of the paramount goals of modern toxicology. Especially coexposure scenarios need to be investigated with respect to synergistic and interdependent effects for the activation of toxicological signaling pathways. The present study introduces an experimental in vitro model system for nontoxic and low-dose coexposures of human mammary carcinoma MCF-7 cells against polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (BP) and heavy metals such as cadmium.

Inhibition of melanocortin-4 receptor dimerization by substitutions in intracellular loop 2.

Obesity is one of the most challenging global health problems. One key player in energy homeostasis is the melanocortin-4 receptor (MC4R), which is a family A G-protein-coupled receptor (GPCR). It has recently been shown that MC4R has the capacity to form homo- or heterodimers.

Effects of triclocarban on the transcription of estrogen, androgen and aryl hydrocarbon receptor responsive genes in human breast cancer cells.

Triclocarban (TCC) is an antimicrobial agent that is used in detergents, soaps and other personal hygiene products. Similarly to triclosan the widespread use of TCC has raised concerns about its endocrine potential. In luciferase-based reporter assays TCC has been shown to enhance estrogenic and androgenic activities following cellular coexposure with estrogen or dihydrotestosterone, respectively.

Identification of the translation start site of the human melanocortin 3 receptor.

Background: The melanocortin-3-receptor (MC3R) is a G-protein coupled receptor participating in hypothalamic energy metabolism. So far, it was assumed that the translation of the human MC3R starts at the non-conserved first ATG, however, a second evolutionary conserved ATG is located 37 amino acids downstream. One frequent polymorphism, T6K, is located between these two ATGs.

Mutually opposite signal modulation by hypothalamic heterodimerization of ghrelin and melanocortin-3 receptors.

Interaction and cross-talk of G-protein-coupled receptors (GPCRs) are of considerable interest because an increasing number of examples implicate a profound functional and physiological relevance of homo- or hetero-oligomeric GPCRs. The ghrelin (growth hormone secretagogue receptor (GHSR)) and melanocortin-3 (MC3R) receptors are both known to have orexigenic effects on the hypothalamic control of body weight. Because in vitro studies indicate heterodimerization of GHSR and MC3R, we investigated their functional interplay.

A new phenotype of nongoitrous and nonautoimmune hyperthyroidism caused by a heterozygous thyrotropin receptor mutation in transmembrane helix 6.

Context: Activating mutations in the TSHR gene were found in patients suffering from nonautoimmune hyperthyroidism. In the past, it was assumed that thyroid hyperplasia is due to constitutive activation of the Gs/adenylyl cyclase signaling pathway; however, the physiological role of the Gq/11 pathway in this context remains unclear.

Objective: In this study, we investigated molecular details of the TSHR in a patient with nonautoimmune and nongoitrous hyperthyroidism.

Heterodimerization of hypothalamic G-protein-coupled receptors involved in weight regulation.

Background: Melanocortin 3 and 4 receptors (MC3R and MC4R) are known to play an essential role in hypothalamic weight regulation. In addition to these two G-protein-coupled receptors (GPCRs), a huge number of other GPCRs are expressed in hypothalamic regions, and some of them are involved in weight regulation. So far, homodimerization was shown for a few of these receptors.

A heterozygous mutation in the third transmembrane domain causes a dominant-negative effect on signalling capability of the MC4R.

Background: Heterozygous MC4R mutation is the most frequent cause of monogenic obesity. For most MC4R mutations a gene dosage effect seems to be the underlying mechanism. However, a dominant negative effect of a heterozygous MC4R mutation was recently identified, pointing to an additional mechanism of MC4R inactivation.

Evolutionary aspects in evaluating mutations in the melanocortin 4 receptor.

More than 70 missense mutations have been identified in the human melanocortin 4 receptor (MC4R), and many of them have been associated with obesity. In a number of cases, the causal link between mutations in MC4R and obesity is controversially discussed. Here, we mined evolution as an additional source of structural information that may help to evaluate the functional relevance of naturally occurring variations in MC4R.

N-ethyl-N-nitrosourea-based generation of mouse models for mutant G protein-coupled receptors.

Chemical random mutagenesis techniques with the germ line supermutagen N-ethyl-N-nitrosourea (ENU) have been established to provide comprehensive collections of mouse models, which were then mined and analyzed in phenotype-driven studies. Here, we applied ENU mutagenesis in a high-throughput fashion for a gene-driven identification of new mutations. Selected members of the large superfamily of G protein-coupled receptors (GPCR), melanocortin type 3 (Mc3r) and type 4 (Mc4r) receptors, and the orphan chemoattractant receptor GPR33, were used as model targets to prove the feasibility of this approach.

Prevalence, spectrum, and functional characterization of melanocortin-4 receptor gene mutations in a representative population-based sample and obese adults from Germany.

Context: Autosomal dominant inheritance of mutations in the melanocortin-4 receptor gene (MC4R) is currently regarded as the most relevant genetic cause for extreme obesity and affects 2-4% of extremely obese individuals.

Objective: Our objective was to assess the relevance of MC4R mutations in a German population-based sample.

Design And Setting: We conducted a mutation screen of the MC4R gene by capillary electrophoresis-based single-strand conformation polymorphism analysis and denaturing HPLC.

MC4R oligomerizes independently of extracellular cysteine residues.

The melanocortin 4 receptor (MC4R) plays an essential role in weight regulation. Recently we could show that the MC4R is able to form receptor dimers. In the present study we investigated the role of extracellular cysteine residues and the structure of the third extracellular loop for receptor dimerization.

Extended clinical phenotype, endocrine investigations and functional studies of a loss-of-function mutation A150V in the thyroid hormone specific transporter MCT8.

Objective: Thyroid hormones, besides having other functions, are known to be essential for the development of the human brain. Recently the monocarboxylate transporter 8 (MCT8) was identified as a thyroid hormone transporter which is expressed in different regions of the human brain. Here we describe in detail the clinical and biochemical features in response to thyroid hormone administration of a boy carrying an MCT8 mutation (A150V) in the second transmembrane domain.

Type 2 diabetes and impaired glucose tolerance in European children and adolescents with obesity -- a problem that is no longer restricted to minority groups.

Background: The incidence of childhood obesity and type 2 diabetes is an increasing problem in Europe. We determined the prevalence of impaired glucose regulation in a predominantly Caucasian cohort of 491 children and adolescents with obesity.

Methods: Fasting glucose and insulin levels were determined in all 491 subjects.

Mutationally induced disulfide bond formation within the third extracellular loop causes melanocortin 4 receptor inactivation in patients with obesity.

By screening patients with severe early onset obesity for mutations within the melanocortin 4 receptor (MC4R) gene, we have identified a missense mutation (C271R) that occurs homozygous in two siblings with obesity. In-depth functional characterization of C271R revealed a right-shifted concentration response curve due to lower affinity to natural and synthetic MC4R agonists and a reduced cell surface expression. Cys-271 is located in the third extracellular loop.