Surveying type i nuclear receptor activation by environmental toxins

The National Institute of Environmental Health Sciences awarded Ohio University $404,163 on August 7, 2026, under the Environmental Health program (CFDA 93.113) to survey Type I nuclear receptor activation by environmental toxins, specifically endocrine-disrupting chemicals and nanoplastics.

Ohio University will develop and deploy the FLASH-ER assay, a fluorescence-based laboratory method employing bipartite tetracysteine display and biarsenical profluorophore technology to monitor ligand-mediated structural transitions in estrogen receptor ligand-binding domains. The assay tracks how environmental toxins bind to Type I nuclear receptors—including estrogen, androgen, and progesterone receptors—that normally regulate metabolism, development, reproduction, and cell proliferation. The research aims to understand aberrant interactions between endocrine-disrupting chemicals, nanoplastics, and these receptors, which can lead to neurodegeneration, inflammation, autoimmunity, and cancer. The project builds on prior FLASH-ER work examining estrogenic ligands and selective estrogen receptor modulators, and will extend to study ligand-independent transitions in constitutively active estrogen receptor mutants associated with endocrine-resistant breast cancers.

Performance occurs in Athens, Ohio. The period of performance runs from August 7, 2026, through August 6, 2028. This is a project grant, the assistance type supporting research by named principal investigators at eligible institutions.

Abstract

Endocrine-disrupting chemicals (edcs) and nanoplastics (NPS) are environmental toxins that interfere with the normal function of the endocrine system by binding to type i nuclear receptors (NR), a family of ligand-mediated transcription factors that act as key regulators of metabolism, development, reproduction, and cell proliferation. Members of the type i NR family, including estrogen receptors (ER), androgen receptors (AR), and progesterone receptors (PR), are activated through the binding of endogenous steroid hormones and exert their biological effects by controlling the expression of steroid-responsive genes in the nucleus. Unfortunately, many edcs and NPS compete for ligand-binding domains (lbds) of type i NRS by mimicking the size and structure of natural steroid hormones. If left untreated, such aberrant interactions often lead to debilitating physiological disorders, including neurodegeneration, inflammation, autoimmunity and cancer. Broadly speaking, the lbds of type i NRS undergo moderate structural changes upon ligand binding that involves transition of a dynamic c-terminal helix (H12) from an extended (inactive) state to a well-folded (active) state. Our laboratory has developed a novel, in vitro assay that uses a convenient fluorescence-based readout to survey ligand-mediated H12 transitions within the ER-LBD. The assay, termed 'flash-ER', employs bipartite tetracysteine display coupled with the biarsenical profluorophore flash-EDT2 to monitor H12 transitions as a function of fluorescence intensity. Using flash-ER, we have successfully monitored ligand-dependent structural changes of H12 in ER-lbds bound to various estrogenic ligands and selective estrogen receptor modulators, and tracked ligand-independent H12 transitions in constitutively active ER mutants expressed in endocrine-resistant breast cancers. We now seek to utilize the flash-ER assay to directly study how edcs and NPS affect ligand-mediated H12 transitions within type i NRS. In specific aim 1 of this proposal, our work will focus on applying the flash-ER assay to monitor H12 transitions within ERS that have been exposed to edcs or NPS. This will be accomplished by treating wild-type or mutant ERS with discrete edcs or NPS at concentrations that reflect real-world exposure levels and monitoring H12 transitions as they relate to ligand binding. Notably, such studies will allow US to directly determine how edcs and NPS affect active-state (or inactive-state) H12 transitions within the ER. In specific aim 2, we expand the utility of the flash-ER assay by commuting the technique to other type i NR lbds. Here, we will use site-directed mutagenesis to generate tetracysteine-tagged AR-lbds and PR-lbds that will recapitulate an optimized flash- binding motif upon interaction with ligand. Correlative 'flash-AR' and 'flash-PR' assays will then be used to determine how endogenous steroids and environmental toxins, including epcs and NPS, affect active-state H12 transitions within each receptor subtype. Collectively, results obtained from the work outlined in this proposal will determine the molecular mechanisms that drive ligand-mediated activation of type i NRS and will facilitate the development of lead compounds to treat endocrine disorders that arise from exposure to environmental toxins.