A Transcriptional Regulatory Network containing Nuclear Receptors and Long Noncoding RNAs Controls Basal and Induced Expression of Cytochrome P450s in Liver Cells

Abstract

Cytochrome P450 (P450) enzymes are responsible for biotransformation of xenobiotics, including environmental toxicants and drugs. Expression of P450s can directly affect drug metabolism, resulting in various outcome in either therapeutic efficacy or adverse effects. Nuclear receptors are a class of transcription factors that can regulate expression of P450s at both basal and drug‐induced levels. Some long non‐coding RNAs (lncRNAs) near a transcription factor are found to participate in the regulatory functions of the transcription factors in either promotion or repression manner. The aim of this study is to determine whether there is a transcriptional regulatory network containing nuclear receptors and lncRNAs controlling both basal and drug‐induced expression of P450s in liver cells. Four nuclear receptors, hepatocyte nuclear factor 1a (HNF1a), hepatocyte nuclear factor 4a (HNF4a), pregnane X receptor (PXR), and constitutive androstane receptor (CAR) as well as two lncRNAs, HNF1a‐antisense 1 (HNF1a‐AS1) and HNF4a‐antisense 1 (HNF4a‐AS1) were examined in control of basal and drug‐induced expression of 8 different P450 enzymes. Small interfering RNAs (siRNAs) were applied to knock down the nuclear receptors and lncRNAs in HepaRG cells with or without treatment of phenobarbital or rifampicin. Expression of the nuclear receptors, lncRNAs, and P450s was measured by RT‐PCR and Western blots. Knocking down of HNF1a or HNF4a affected basal expression of numerous P450s as well as CAR and PXR, and also impaired phenobarbital or rifampicin induced expression of several P450s, which may be due to decreased CAR/PXR expression. Moreover, HNF4a knockdown was able to decrease HNF1a expression and showed more potent effect than HNF1a knockdown. Knocking down of CAR or PXR only affected basal and induced expression of their target P450s without affecting expression of HNF1a or HNF4a. These data suggested the existence of a regulatory network in controlling P450 expression in an order through HNF4a to HNF1a to CAP/PXR. Expression of HNF1a‐AS1 and HNF4a‐AS1 is largely dependent on expression of their nearby coding gene HNF1a and HNF4a. Moreover, HNF4a knockdown depleted expression of both lncRNAs, but HNF1a knockdown only depleted HNF1a‐AS1 expression. Knocking down of HNF1a‐AS1 showed a similar regulation trend on the P450s compared to HNF1a or HNF4a knockdown, indicating involvement of this lncRNA in the regulation of P450s. However, knocking down of HNF4a‐AS1 showed an opposite regulation trend compared to HNF1a or HNF4a knockdown, indicating that HNF4a‐AS1 may play an inhibitory role in the HNF4a function. Altogether, out study concludes that there is a transcription regulatory network among the different nuclear receptors and lncRNAs in the regulation of both basal and drug‐induced expression of P450s in liver cells.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.