In vivo Imaging Analysis of Steroid-Nuclear Receptor Function

Division Of Basic Sciences - Nci

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Abstract

1. In the United States and globally, contaminant exposure in unregulated water sources is a recognized public-health data gap and an obstacle to both risk-management. To address the lack of data on broad contaminant exposures in hydrologically-vulnerable aquifers, rivers, and tap water, samples were collected from multiple sources. We assessed EDCs activity (aryl hydrocarbon [AhR], androgenic [AR], thyroid [Ty], estrogenic [ER], corticosteroid [CS]) with novel mammalian cell-based assays that express nuclear steroid receptors. We quantified receptor activation relative to negative controls and compared activity by season and utility/sample characteristics. Results demonstrate that AR and AhR activities are commonly detected in water supplies, and that bioactivity varies by season and utility/sample characteristics. Screening EDCs with bioassays holds promise for characterizing population exposure to diverse EDCs mixtures. Continued assessment of unmonitored and unregulated private supply TW is needed to model contaminant exposures and human-health risks. 2. A widely regarded model for glucocorticoid receptor (GR) action postulates that dimeric binding to DNA regulates unfavorable metabolic pathways while monomeric receptor binding promotes repressive gene responses related to its anti-inflammatory effects. This model has been built upon the characterization of the GRdim mutant, allegedly incapable of DNA binding and dimerization. Although quantitative live-cell imaging data shows GRdim as mostly dimeric, genomic studies, on the basis of recovery of enriched half-site response elements, suggest monomeric engagement on DNA. We performed genome-wide studies on GRdim and a constitutively monomeric mutant. Results show that GR must form dimers to bind even pre-accessible chromatin and that earlier characterizations of half-response elements do not constitute solid evidence of monomeric action. Results do not support a physiological role for monomeric GR and are consistent with a common mode of receptor binding via higher order structures that drives both the activating and repres