Mechanisms Controlling Sensitivity and Resistance to Dioxin-like Compounds: Role of AIP - Project Summary/Abstract
The aryl hydrocarbon receptor (AHR) plays an essential role in the mechanisms of toxicity of numerous
chemical contaminants, including chlorinated dioxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD),
some polychlorinated biphenyls (PCBs), and polynuclear aromatic hydrocarbons (PAHs). There is inter-
individual variation in sensitivity to effects of these compounds, but the mechanisms are poorly understood.
Variation in the human AHR sequence does not fully explain individual differences in response to AHR ligands,
suggesting that other components of the AHR pathway are involved in controlling sensitivity. Recent genome-
level research in fish populations with evolved resistance to PCBs, TCDD, and PAHs has identified the AHR-
interacting protein (AIP) as a candidate resistance gene. AIP is an AHR chaperone that influences the
stability and nuclear translocation of AHR, but its exact role is poorly defined. In humans, mutations in AIP
predispose patients to familial isolated pituitary adenomas (FIPA), evidence that AIP sequence variation has
functional consequences. Whether AIP variation alters the susceptibility to effects of AHR agonists in vivo is
not known. The goal of this basic research is to elucidate the role of AIP and its sequence variants in
controlling sensitivity to diverse AHR agonists, including environmental contaminants as well as natural AHR
ligands. The central hypothesis is that variation at the AIP locus affects the interaction between AIP and AHR,
leading to altered sensitivity to chemicals that cause toxicity and altered gene expression through the AHR.
This hypothesis will be tested using complementary studies involving zebrafish (Danio rerio) in vivo and human
cells in vitro. In Aim 1, AIP-null zebrafish generated using CRISPR-Cas9 genome-editing will be used to
determine the role of AIP in controlling the sensitivity to developmental toxicity and altered gene expression
caused by diverse AHR agonists in vivo. In Aim 2, the human liver cell line HepaRG will be used to investigate
the molecular mechanisms by which AIP and its variants, including mutations associated with FIPA, affect AHR
function. In Aim 3, targeted knock-in of AIP SNPs into zebrafish will be used to determine how variation in the
AIP protein affects the sensitivity to diverse AHR ligands in vivo. The proposed research represents a unique
opportunity to use insights from environmental exposures in wild fish populations along with mechanistic
studies in human cells and engineered zebrafish embryos to understand fundamental mechanisms underlying
individual differences in susceptibility to chemicals that act through the AHR. The studies address goals of the
NIEHS 2018-2023 Strategic Plan, including basic research on molecular pathways involved in mediating
effects of environmental exposures, research on developmental processes, and understanding mechanisms
underlying individual susceptibility.
