RNA Editing Modulates Human Hepatic Aryl Hydrocarbon Receptor Expression by Creating MicroRNA Recognition Sequence

Abstract

Adenosine to inosine (A-to-I) RNA editing is the most frequent type of post-transcriptional nucleotide conversion in humans, and it is catalyzed by adenosine deaminase acting on RNA (ADAR) enzymes. In this study we investigated the effect of RNA editing on human aryl hydrocarbon receptor (AhR) expression because the AhR transcript potentially forms double-stranded structures, which are targets of ADAR enzymes. In human hepatocellular carcinoma-derived Huh-7 cells, the ADAR1 knockdown reduced the RNA editing levels in the 3-untranslated region (3-UTR) of the AhR transcript and increased the AhR protein levels. The ADAR1 knockdown enhanced the ligand-mediated induction of CYP1A1, a gene downstream of AhR. We investigated the possibility that A-to-I RNA editing creates miRNA targeting sites in the AhR mRNA and found that the miR-378-dependent down-regulation of AhR was abolished by ADAR1 knockdown. These results indicated that the ADAR1-mediated down-regulation of AhR could be attributed to the creation of a miR-378 recognition site in the AhR 3-UTR. The interindividual differences in the RNA editing levels within the AhR 3-UTR in a panel of 32 human liver samples were relatively small, whereas the differences in ADAR1 expression were large (220-fold). In the human liver samples a significant inverse association was observed between the miR-378 and AhR protein levels, suggesting that the RNA-editingdependent down-regulation of AhR by miR-378 contributes to the variability in the constitutive hepatic expression of AhR. In conclusion, this study uncovered for the first time that A-to-I RNA editing modulates the potency of xenobiotic metabolism in the human liver.

ADAR1 attenuates allogeneic graft rejection by suppressing miR‐21 biogenesis in macrophages and promoting M2 polarization

“…An increasing number of mammalian genes have been found to undergo deamination by ADAR1 (21). Deamination by editing the pre-mRNAs that encode subunits of ionotropic glutamate receptors is one well-studied example (22)(23)(24).…”

Deciphering miRNAs’ Action through miRNA Editing

“…For example, loss of edited sites in the 3 -UTR of phosphatase and actin regulator 4 gene (PHACTR4) due to downregulation of ADAR1 prevented the binding of miR-196a-3p, resulting in higher protein levels of PHACTR4 [66]. As well, ADAR1 knockdown in the hepatic cell line Huh-7 correlated with upregulation of human aryl hydrocarbon receptor (AhR) due to loss of miR-378 target site on its 3 -UTR [74]. Finally, APOBEC1 knockout in mice led to 238 C-to-U substitutions on the 3 -UTRs of several genes, modifying the pattern of miRNAs susceptible to modulate their expressions [56].…”

Adenosine deaminase acting on RNA (ADAR1), a suppressor of double-stranded RNA–triggered innate immune responses

“…Editing of the pri-miR-151 impairs cleavage by Dicer-TAR RNA-binding protein complex (80). Editing within the seed sequence of miR-376 by ADAR2 alters targeting and subsequent silencing (81), whereas ADAR1 creates an miR-378 recognition site in the 3Ј-UTR of the human aryl hydrocarbon receptor transcript (82). Furthermore, comprehensive analyses of miRNAseq datasets of human cancer tissues identified multiple editing sites in miRs and their 3Ј-UTR targets (83,84).…”