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dimerization, AHR/ARNT leads to Increase, slincR expression
Key Event Relationship Overview
AOPs Referencing Relationship
|AOP Name||Adjacency||Weight of Evidence||Quantitative Understanding||Point of Contact||Author Status||OECD Status|
|Aryl hydrocarbon receptor activation leading to early life stage mortality via sox9 repression induced impeded craniofacial development||adjacent||Moderate||Moderate||Prarthana Shankar (send email)||Under development: Not open for comment. Do not cite|
|Aryl hydrocarbon receptor activation leading to early life stage mortality via sox9 repression induced cardiovascular toxicity||adjacent||Moderate||Moderate||Prarthana Shankar (send email)||Under development: Not open for comment. Do not cite|
Life Stage Applicability
Key Event Relationship Description
Dimerization of Ahr/ARNT take place when the ligand-activated Ahr translocates to the nucleus from the cytoplasm.
The Ahr/ARNT heterodimer can recognize aryl hydrocarbon response elements (AHREs), also known as xenobiotic response elements (XREs) or dioxin response elements (DREs), in the promoter region of downstream genes to regulate gene expression (Schmidt and Bradfield 1996). The target genes can either increase or decrease in their expression.
slincR expression significantly increases when zebrafish are exposed to TCDD, and the slincR promoter includes the core AHRE (5’-T/GCGTG-3’) in multiple locations (Garcia et al., 2017), suggesting that slincR is a direct downstream target of the Ahr/ARNT heterodimer.
Evidence Collection Strategy
Evidence gathered for this KER is primarily from two main studies, (Garcia et al., 2017) and (Garcia et al., 2018), that discovered and described slincR in zebrafish.
Evidence Supporting this KER
Eight putative AHREs have been identified in the slincR promoter of the zebrafish gene (Garcia et al., 2017).
The potential orthologs of slincR in the mouse and human genomes also have conserved AHREs (Garcia et al., 2018).
Empirical evidence and essentiality of KEup for KEdown to occur
Expression of slincR is significantly increased when zebrafish are exposed to TCDD (Garcia et al., 2017). TCDD is a strong Ahr activating ligand that causes the dimerization of Ahr and ARNT, and ARNT1 in zebrafish has been shown to be required for TCDD-induced toxicity (Prasch et al., 2006).
When AHR2-null zebrafish generated using CRISPR-Cas9 are exposed to TCDD, slincR expression at 48 hours post fertilization (hpf) is significantly lower than wildtype zebrafish exposed to TCDD (Garcia et al., 2017).
slincR expression is significantly induced upon exposure to several polycyclic aromatic hydrocarbons (PAHs), many of whom are Ahr activating chemicals (Garcia et al., 2018). The PAHs that induce slincR expression are retene, benzo[j]fluoranthene, benzo[k]fluoranthene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, and benzo[b]fluoranthene.
TCDD-exposed embryonic mouse urogenital tissue samples showed significant increase in expression of the mouse slincR ortholog (2610035D17Rik) compared to the vehicle control, DMSO (Garcia et al., 2018).
Uncertainties and Inconsistencies
Certain PAHs, such as fluoranthene, phenanthrene, and 9-methylanthracene that significantly induce cyp1a greater than log2FC = 2, indicating that Ahr has been activated, do not induce slincR expression in zebrafish (Garcia et al., 2018).
Known modulating factors
Quantitative Understanding of the Linkage
- A TCDD dose-response experiment was conducted measuring gene expression changes of slincR and cyp1a (biomarker for Ahr activation) in 48 hpf zebrafish. While cyp1a expression was always higher than slincR, the expression of the two genes increased in parallel, with significant slincR expression being identified at and above 0.0625 ng/mL TCDD exposure concentration (Garcia et al., 2018).
slincR expression increases in parallel with cyp1a when zebrafish are also exposed individually to several PAHs. Data come from a study that created a gene co-expression network and found that cyp1a and slincR expression were highly correlated with each other across multiple PAH treatments (Shankar et al., 2021).
Known Feedforward/Feedback loops influencing this KER
Domain of Applicability
Ahr activation (and thus, the dimerization of Ahr/ARNT) resulting in significant slincR induction of expression has only been investigated in zebrafish and mice (Garcia et al., 2017; Garcia et al., 2018).
Garcia GR, Goodale BC, Wiley MW, La Du JK, Hendrix DA, Tanguay RL. 2017. In vivo characterization of an ahr-dependent long noncoding rna required for proper sox9b expression. Mol Pharmacol. 91(6):609-619.
Garcia GR, Shankar P, Dunham CL, Garcia A, La Du JK, Truong L, Tilton SC, Tanguay RL. 2018. Signaling events downstream of ahr activation that contribute to toxic responses: The functional role of an ahr-dependent long noncoding rna (slincr) using the zebrafish model. Environ Health Perspect. 126(11):117002.
Prasch AL, Tanguay RL, Mehta V, Heideman W, Peterson RE. 2006. Identification of zebrafish arnt1 homologs: 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity in the developing zebrafish requires arnt1. Mol Pharmacol. 69(3):776-787.
Schmidt JV, Bradfield CA. 1996. Ah receptor signaling pathways. Annu Rev Cell Dev Biol. 12:55-89.
Shankar P, McClure RS, Waters KM, Tanguay RL. 2021. Gene co-expression network analysis in zebrafish reveals chemical class specific modules. BMC Genomics. 22(1):658.