A comparative study of human and zebrafish glucocorticoid receptor activities of natural and pharmaceutical steroids

IntroductionThe action of environmental steroids on the human glucocorticoid receptor (hGR) has been pointed out with the risk to impair physiological immune and metabolic processes regulated by this nuclear receptor. However, there is still a lack of mechanistic information regarding their ability to interact with GR in aquatic species.MethodsTo investigate ligand activation differences between hGR and zebrafish GR (zfGR), we tested several natural and synthetic steroids using reporter cell lines expressing hGR or zfGR.Results and discussionAlmost all the glucocorticoids tested (dexamethasone, cortisol, bimedrazol, medrol, cortivazol and fluticasone) are agonists of the two receptors with similar potencies. The dissociated glucocorticoids, RU24782 and RU24858 are agonists of both zfGR and hGR but with a better potency for the latter. On the other hand, the synthetic glucocorticoid forbimenol and the mineralocorticoid aldosterone are agonist on hGR but antagonist on zfGR. The other steroids tested, androgens and progestins, are all antagonists of both GRs with equal or lower potency on zfGR than on hGR. Surprisingly, the lower efficacy and potency on zfGR of aldosterone, forbimenol and the dissociated glucocorticoids is not related to their affinity for the receptors which would suggest that it could be related to less efficacious recruitment of coactivators by zfGR compared to hGR

A Cell Model Suitable for a High-Throughput Screening of Inhibitors of the Wnt/β-Catenin Pathway

A constitutive activation of the Wnt/β-catenin pathway is an initiating event in colon carcinogenesis. We developed colon cancer cells models that highlight the non-selectivity of previously described inhibitors of the Wnt pathway and we propose our model as a suitable screening system for inhibitors of the pathway

Selectivity of natural, synthetic and environmental estrogens for zebrafish estrogen receptors.

International audience: Zebrafish, Danio rerio, is increasingly used as an animal model to study the effects of pharmaceuticals and environmental estrogens. As most of these estrogens have only been tested on human estrogen receptors (ERs), it is necessary to measure their effects on zebrafish ERs. In humans there are two distinct nuclear ERs (hERα and hERβ), whereas the zebrafish genome encodes three ERs, zfERα and two zfERβs (zfERβ1 and zfERβ2). In this study, we established HeLa-based reporter cell lines stably expressing each of the three zfERs. We first reported that estrogens more efficiently activate the zfERs at 28°C as compared to 37°C, thus reflecting the physiological temperature of zebrafish in wildlife. We then showed significant differences in the ability of agonist and antagonist estrogens to modulate activation of the three zfER isotypes in comparison to hERs. Environmental compounds (bisphenol A, alkylphenols, mycoestrogens) which are hER panagonists and hERβ selective agonists displayed greater potency for zfERα as compared to zfERβs. Among hERα selective synthetic agonists, PPT did not activate zfERα while 16α-LE2 was the most zfERα selective compound. Altogether, these results confirm that all hER ligands control in a similar manner the transcriptional activity of zfERs although significant differences in selectivity were observed among subtypes. The zfER subtype selective ligands that we identified thus represent new valuable tools to dissect the physiological roles of the different zfERs. Finally, our work also points out that care has to be taken in transposing the results obtained using the zebrafish as a model for human physiopathology

Functional profiling of bisphenols for nuclear receptors

International audienceBisphenol-A (BPA) is one of the most abundant chemicals produced worldwide. Exposure to BPA has been associated with various physiological dysregulations, involving reproduction, development, metabolism, as well as genesis and progression of hormone-dependent cancers. It has been well published that BPA along with its analogs bind and activate estrogen receptors (ER) α and β, estrogen related receptor (ERR) γ and pregnan X receptor (PXR). BPA has been also characterized as an inhibitor of the androgen (AR) and progesterone (PR) receptor. Thus, the need for safer alternatives to BPA among bisphenols is rising. In this regard, we used reporter cell lines to analyze the effects of 24 bisphenols on the selected nuclear receptors (NRs), known and potential targets of BPA. We showed that bisphenols differently modulated the activities of NRs. ERs, ERRγ and PXR were generally activated by bisphenols, whereas many compounds of this family acted as AR, PR, GR and MR antagonists. On the other hand, some bisphenols such as BPA, BPC and BPE modulated the activity of several NRs, but others lacked the activity of other NRs. Altogether, these data provide the guidelines for development of safer BPA substitutes with reduced hormonal activity

: Vitamine B6 et cancer

International audienceVitamin B6 is well-known for its role as a cofactor in many enzymatic reactions and recently, several epidemiological studies have highlighted the importance of this vitamin as a protective agent against various cancers: elevated vitamin B6 plasma levels were associated with a lower risk of colorectal cancer development, for example. In vivo studies have shown that vitamin B6 decreased cell proliferation and enhanced the immune response. At the cellular level, antioxidant, pro-apoptotic and anti-angiogenic effects have been identified. At the molecular level, vitamin B6 is able to inhibit the transactivation potential of various nuclear receptors. Interestingly, a recent paper has described the conjugation of vitamin B6 to RIP140 (receptor interacting protein of 140 kDa), a protein that acts as a transcriptional corepressor of nuclear receptors. This post-translational modification increases the transcriptional repression of RIP140 and regulates its subcellular localization and its ability to interact with different protein partners. Finally, vitamin B6 is involved in the methyl donor cycle ant thus, some of the antitumor properties of vitamin B6 may involve an indirect effect on the level of DNA or histone methylation. All of these mechanistic and clinical data justify further studies to decipher the mechanism of action of vitamin B6 and its clinical interest in combination with molecules typically used in chemotherapy or hormonal therapy

Reporter cell lines to evaluate the selectivity of chemicals for human and zebrafish estrogen and peroxysome proliferator activated γ receptors

International audienceZebrafish is increasingly used as an animal model to study the effects of environmental nuclear receptors (NRs) ligands. As most of these compounds have only been tested on human NRs, it is necessary to measure their effects on zebrafish NRs. Estrogen receptors (ER) α and β and peroxysome proliferator activated receptor (PPAR) γ are main targets of environmental disrupting compounds (EDCs). In humans there are two distinct nuclear ERs (hERα and hERβ), whereas the zebrafish genome encodes three ERs, zfERα, zfERβ1, and zfERβ2. Only one isoform of PPARγ is expressed in both humans and zebrafish. In this review, we described reporter cell lines that we established to study the interaction of EDCs with human and zebrafish ERs and PPARγ. Using these cell lines, we observed that zfERs are thermo-sensitive while zfPPARγ is not. We also showed significant differences in the ability of environmental and synthetic ligands to modulate activation of zfERs and zfPPARγ in comparison to hERs and hPPARγ. Some environmental estrogens (bisphenol A, mycoestrogens) which are hER panagonists displayed greater potency for zfERα as compared to zfERβs. hERβ selective agonists (8βVE2, DPN, phytoestrogens) also displayed zfERα selectivity. Among hERα selective synthetic agonists, 16α-LE2 was the most zfERα selective compound. Almost all zfPPARγ environmental ligands (halogenated bisphenol A derivatives, phthalates, perfluorinated compounds) displayed similar affinity for human and zebrafish PPARγ while pharmaceutical hPPARγ agonists like thiazolidones are not recognized by zfPPARγ. Altogether, our studies show that all hERs and hPPARγ ligands do not control in a similar manner the transcriptional activity of zfERs and zfPPARγ and point out that care has to be taken in transposing the results obtained using the zebrafish as a model for human physiopathology

Reporter Cell Lines for the Characterization of the Interactions between Human Nuclear Receptors and Endocrine Disruptors

International audienceEndocrine-disrupting chemicals (EDCs) are exogenous substances interfering with hormone biosynthesis, metabolism, or action, and consequently causing disturbances in the endocrine system. Various pathways are activated by EDCs, including interactions with nuclear receptors (NRs), which are primary targets of numerous environmental contaminants. The main NRs targeted by environmental contaminants are the estrogen (ER α, β) and the androgen (AR) receptors. ERs and AR have pleiotropic regulatory roles in a diverse range of tissues, notably in the mammary gland, the uterus, and the prostate. Thus, dysfunctional ERs and AR signaling due to inappropriate exposure to environmental pollutants may lead to hormonal cancers and infertility. The pregnane X receptor (PXR) is also recognized by many environmental molecules. PXR has a protective role of the body through its ability to regulate proteins involved in the metabolism, the conjugation, and the transport of many exogenous and endogenous compounds. However, the permanent activation of this receptor by xenobiotics may lead to premature drug metabolism, the formation, and accumulation of toxic metabolites and defects in hormones homeostasis. The activity of other NRs can also be affected by environmental molecules. Compounds capable of inhibiting or activating the estrogen related (ERRγ), the thyroid hormone (TRα, β), the retinoid X receptors (RXRα, β, γ), and peroxisome proliferator-activated (PPAR α, γ) receptors have been identified and are highly suspected to promote developmental, reproductive, neurological, or metabolic diseases in humans and wildlife. In this review, we provide an overview of reporter cell lines established to characterize the human NR activities of a large panel of EDCs including natural as well as industrial compounds such as pesticides, plasticizers, surfactants, flame retardants, and cosmetics

Synthetic progestins activate human and zebrafish nuclear progesterone receptor in vitro

As compared to (xeno-)estrogens, natural and synthetic ligands of the progesterone receptor (PR) have been scarcely studied on aquatic organisms while the potential risk posed by environmental progestins has been recently pointed out. However, there is still a lack of data to accurately characterize the hazards posed by these compounds. In that respect, the capacity of synthetic progestins to interact with fish nuclear progesterone receptor was poorly investigated. In the present work we aimed at assessing potential endocrine disruption of these compounds towards zebrafish nPR and to compare their effects with that of human nPR to identify possible interspecies differences. Two human cell lines co-expressing either human PR (hPR) or the zebrafish PR (ZfPR) and luciferase gene, namely HELN-hPRB and U2OS-zfPR cells, were developed and characterized using promegestone (R5020) as a reference agonist ligand. R5020 induced luciferase activity in both cell lines in a concentration-dependent manner. These effects were completely blocked by co-exposing the cells with mifepristone (RU486), a potent PR antagonist. A large set of natural and synthetic progestins (25) was screened in the two cell lines. All of the compounds except the natural zebrafish progestin 17α,20β-dihydroxy-4-pregnen-3-one (DHP) activated the hPR. About half of the progestins induced a maximum effect of 100% when compared to R5020 while the other half partially induced luciferase activity. In contrast to cells expressing hPR, progestins behaved very differently with the zfPR since only five of them were active on zfPR. Interestingly, we found that DHP strongly activated zfPR but not hPR. To assess whether some progestins were partial agonists, they were coexposed with R5020. Half of them antagonized the activity induced by R5020 on hPR and are thus partial hPR agonists. All the active progestins on zfPR antagonized R5020 and are therefore partial zfPR agonists. Two new luciferase reporter cell lines were developed and characterized, providing novel information regarding the activity of a large set of progestins on the zfPR. These models allowed us to highlight major interspecies differences. These results support the need to further determine the effects of zfPR agonist progestins on PR-dependent physiological processes in order to characterize the hazards posed by progestins in fish

A Cell Model Suitable for a High-Throughput Screening of Inhibitors of the Wnt/β-Catenin Pathway

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A Comparative Study of Human and Zebrafish Pregnane X Receptor Activities of Pesticides and Steroids Using In Vitro Reporter Gene Assays

International audienceThe nuclear receptor pregnane X receptor (PXR) is a ligand-dependent transcription factor that regulates genes involved in xenobiotic metabolism in mammals. Many studies suggest that PXR may play a similar role in fish. The interaction of human PXR (hPXR) with a variety of structurally diverse endogenous and exogenous chemicals is well described. In contrast, little is known about the zebrafish PXR (zfPXR). In order to compare the effects of these chemicals on the PXR of these two species, we established reporter cell lines expressing either hPXR or zfPXR. Using these cellular models, we tested the hPXR and zfPXR activity of various steroids and pesticides. We provide evidence that steroids were generally stronger activators of zfPXR while pesticides were more potent on hPXR. In addition, some chemicals (econazole nitrate, mifepristone, cypermethrin) showed an antagonist effect on zfPXR, whereas no antagonist chemical has been identified for hPXR. These results confirm significant differences in the ability of chemicals to modulate zfPXR in comparison to hPXR and point out that zfPXR assays should be used instead of hPXR assays for evaluating the potential risks of chemicals on aquatic species