Project Summary (2011-2017)

Superfund site xenobiotics and other environmental toxicants are human health hazards whose toxicity is, in part, associated with altered patterns of gene expression. The goal of Ron Evans’, Ph.D., research is to provide molecular mechanisms and models for exposure, focusing on the "classic" xenobiotic receptors (XenRs) PXR and CAR, and their induction of gene networks encoding the Phase I, II and III clearance pathways. Accordingly, to define the chemical space of XenRs in response to environmental toxins, in Aim II the research group is initiating a comparative chemical library screen using high throughput (HT) cell-based luciferase reporter assays. Recently, the researchers determined that the nuclear receptor ERalpha is capable of responding to anticoagulants, antibacterial and anti-inflammatory drugs, thus identifying it as a candidate xenobiotic sensor. Therefore, as part of this Aim, they are including ERalpha in the above XenRs screen. Some of their HT screens include extracts gathered from Superfund sites by the Research Translation Core. Comparative gene expression studies are being conducted in Aim II to establish the overlap of ERalpha dependent gene regulation with known PXR and CAR target genes. The in vivo relevance will be established using a humanized hPXR/hCAR reporter mouse.

In Aim III the research group is determining how XenRs control the xenobiotic response at the genome-wide level. Chromatin immunoprecipitation coupled with massively parallel deep sequencing (ChlPSeq) is being used to identify PXR, CAR and ERalpha cistromes, before and after treatment with high affinity agonists to reveal unique and common (core) xenobiotic networks. The aggregate binding sites will comprise a "xenobiotic cistrome".

Finally, in Aim I, the researchers are describing a new HT screening platform called NHR Transcriptional Promoter Ontology which allows them to explore xenobiotic regulation by all human NHRs (+/- ligands) by screening against a panel of ~300 drug metabolism reporter constructs comprised of P450 and conjugation enzyme and transporter sets. This is a unique opportunity to redefine the molecular basis of NHR-xenobiotic regulation and will provide a new roadmap for future study. They are collaborating with the Research Translation Core and Community Engagement Core to share this work with the UCSD SRP tribal science partners, industry, EPA, and ATSDR.