Identification and functional analysis of a novel human CYP2E1 far upstream enhancer

Study on Cytochrome P450 Metabolic Profile of Paclitaxel on Rats using QTOF-MS

BACKGROUND

Paclitaxel (PTX) is a key drug used for chemotherapy for various cancers. The hydroxylation metabolites of paclitaxel are different between humans and rats. Currently, there is little information available on the metabolic profiles of CYP450 enzymes in rats.

OBJECTIVE

This study evaluated the dynamic metabolic profiles of PTX and its metabolites in rats and in vitro.

METHODS

Ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) and LC-MS/MS were applied to qualitative and quantitative analysis of PTX and its metabolites in rats, liver microsomes and recombinant enzyme CYP3A1/3A2. Ten specific inhibitors [NF (CYP1A1), FFL (CYP1A2), MOP (CYP2A6), OND (CYP2B6), QCT (CYP2C8), SFP (CYP2C9), NKT (CYP2C19), QND (CYP2D6), MPZ (CYP2E1) and KTZ (CYP3A4)] were used to identify the metabolic pathway in vitro.

RESULTS

Four main hydroxylated metabolites of PTX were identified. Among them, 3'-p-OH PTX and 2-OH PTX were monohydroxylated metabolites identified in rats and liver microsome samples, and 6α-2-di-OH PTX and 6α-5"-di-OH PTX were dihydroxylated metabolites identified in rats. CYP3A recombinant enzyme studies showed that the CYP3A1/3A2 in rat liver microsomes was mainly responsible for metabolizing PTX into 3'-p- OH-PTX and 2-OH-PTX. However, 6α-OH PTX was not detected in rat plasma and liver microsome samples.

CONCLUSION

The results indicated that the CYP3A1/3A2 enzyme, metabolizing PTX into 3'-p-OH-PTX and 2- OH-PTX, is responsible for the metabolic of PTX in rats. The CYP2C8 metabolite 6α-OH PTX in humans was not detected in rat plasma in this study, which might account for the interspecies metabolic differences between rats and humans. This study will provide evidence for drug-drug interaction research in rats.

A dual inhibition: microRNA-552 suppresses both transcription and translation of cytochrome P450 2E1

MicroRNAs (miRNAs) can direct post-transcriptional or transcriptional gene silencing. Here, we report that miR-552 is in the nucleus and cytosol and inhibits human cytochrome P450 (CYP) 2E1 expression at both transcriptional and post-transcriptional levels. MiR-552 via its non-seed sequence forms hybrids with a loop hairpin of the cruciform structure in CYP2E1 promoter region to inhibit SMARCE1 and RNA polymerase II binding to the promoter and CYP2E1 transcription. Expressing SMARCE1 reverses the inhibitory effects of miR-552 on CYP2E1 mRNA expression. MiR-552 with mutations in non-seed region losses its transcriptional, but retains its post-transcriptional repression to CYP2E1. In contrast, mutation in miR-552 seed sequence suppresses its inhibitory effects on CYP2E1 expression at protein, but not at mRNA, levels. Our results suggest that miR-552 is a miRNA with a dual inhibitory ability at transcriptional and post-transcriptional levels leading to an effective inhibition.

Pharmacogene regulatory elements: from discovery to applications

Regulatory elements play an important role in the variability of individual responses to drug treatment. This has been established through studies on three classes of elements that regulate RNA and protein abundance: promoters, enhancers and microRNAs. Each of these elements, and genetic variants within them, are being characterized at an exponential pace by next-generation sequencing (NGS) technologies. In this review, we outline examples of how each class of element affects drug response via regulation of drug targets, transporters and enzymes. We also discuss the impact of NGS technologies such as chromatin immunoprecipitation sequencing (ChIP-Seq) and RNA sequencing (RNA-Seq), and the ramifications of new techniques such as high-throughput chromosome capture (Hi-C), chromatin interaction analysis by paired-end tag sequencing (ChIA-PET) and massively parallel reporter assays (MPRA). NGS approaches are generating data faster than they can be analyzed, and new methods will be required to prioritize laboratory results before they are ready for the clinic. However, there is no doubt that these approaches will bring about a systems-level understanding of the interplay between genetic variants and drug response. An understanding of the importance of regulatory variants in pharmacogenomics will facilitate the identification of responders versus non-responders, the prevention of adverse effects and the optimization of therapies for individual patients.

Pharmacogenetics and individualized therapy in children: immunosuppressants, antidepressants, anticancer and anti-inflammatory drugs

Pharmacogenetic polymorphisms that change the amino acid sequences in coding regions only account for part of the interindividual differences in disease susceptibility and drug response. Additional pharmacogenomic and epigenetic factors are also involved. In children, pharmacogenetic studies are limited, although it has been clear for many years that the interactions between developmental patterns of drug-metabolizing enzymes and transporters have a major impact on dose exposure with age-specific dosage requirements. This article will analyze the factors affecting variability in drug response in children and focus on the pharmacogenetic polymorphisms of immunosuppressants, antidepressants, anticancer and anti-inflammatory drugs. Additional pharmacogenetic and epigenetic studies should be performed to allow the individualization of therapy in children.

Polyinosinic-polycytidylic acid suppresses acetaminophen-induced hepatotoxicity independent of type I interferons and toll-like receptor 3

Viral infections are often linked to altered drug metabolism in patients; however, the underlying molecular mechanisms remain unclear. Here we describe a mechanism by which activation of antiviral responses by the synthetic double-stranded RNA ligand, polyinosinic-polycytidylic acid (polyI:C), leads to decreased acetaminophen (APAP) metabolism and hepatotoxicity. PolyI:C administration down-regulates expression of retinoic X receptor-α (RXRα) as well as its heterodimeric partner pregnane X receptor (PXR) in mice. This down-regulation results in suppression of downstream cytochrome P450 enzymes involved in conversion of APAP to its toxic metabolite. Although the effects of polyI:C on drug metabolism are often attributed to interferon production, we report that polyI:C can decrease APAP metabolism in the absence of the type I interferon receptor. Furthermore, we demonstrate that polyI:C can attenuate APAP metabolism through both its membrane-bound receptor, Toll-like receptor 3 (TLR3), as well as cytoplasmic receptors.

CONCLUSION

This is the first study to illustrate that in vivo administration of polyI:C affects drug metabolism independent of type I interferon production or in the absence of TLR3 through crosstalk between nuclear receptors and antiviral responses.

IL-4-mediated transcriptional regulation of human CYP2E1 by two independent signaling pathways

Cytochrome P450 2E1 (CYP2E1), the alcohol-inducible member of the cytochrome P450 super family, plays an important role in both physiological and pathophysiological processes. The present study focused on the induction of human CYP2E1 transcription by the anti-inflammatory cytokine interleukin-4 (IL-4) in human hepatoma B16A2 cells and revealed that this regulation is mediated by two independent pathways. RNA interference and overexpression of STAT6, indicated that the JAK-STAT signaling pathway is involved in IL-4-dependent induction and mutagenesis revealed the presence of a STAT6 binding site in CYP2E1 proximal promoter region (-583/-574-bp). However, inhibition of the JAK-STAT6 pathway using JAK1 siRNA constructs could only partially inhibit the induction of CYP2E1 promoter constructs indicating the presence of a second IL-4 responsive element. Indeed by using a series of truncated CYP2E1 promoter constructs a second more distal IL-4 responsive element (-1604/-1428-bp) was identified, which was further shown to involve the activation of IRS1/2. This induction was dependent on the transcription factor NFATc1 as IL-4-induced CYP2E1 expression was altered by silencing or overexpressing NFATc1. A NFATc1 binding site was identified in the second distal IL-4 responsive element (-1551/-1545-bp) by chromatin immunoprecipitation (ChIP) analysis. Finally simultaneous siRNA-mediated down-regulation of both STAT6 and NFATc1 or mutation of both STAT6 and NFATc1 binding sites abolished the IL-4-dependent transcriptional induction of CYP2E1, demonstrating that both pathways are required for maximal activation. In conclusion, the present study indicates that the induction of CYP2E1 transcription by IL-4 is mediated through two independent parallel pathways, involving JAK-STAT6 and IRS1/2 and NFATc1.

Tissue- and expression level-specific chromatin looping at maize b1 epialleles

This work examines the involvement of chromatin looping in the transcriptional regulation of two epialleles of the maize (Zea mays) b1 gene, B-I and B'. These two epialleles are tissue-specifically regulated and are involved in paramutation. B-I and B' are expressed at high and low levels, respectively. A hepta-repeat approximately 100 kb upstream of the transcription start site (TSS) is required for both paramutation and high b1 expression. Using chromosome conformation capture, we show that the hepta-repeat physically interacts with the TSS region in a tissue- and expression level-specific manner. Multiple repeats are required to stabilize this interaction. High b1 expression is mediated by a multiloop structure; besides the hepta-repeat, other sequence regions physically interact with the TSS as well, and these interactions are epiallele- and expression level-specific. Formaldehyde-assisted isolation of regulatory elements uncovered multiple interacting regions as potentially regulatory.

Differential regulation of human hepatic flavin containing monooxygenase 3 (FMO3) by CCAAT/enhancer-binding protein beta (C/EBPbeta) liver inhibitory and liver activating proteins

Flavin-containing monooxygenase 3 (FMO3) is important for oxidative xenobiotic metabolism, but regulation of the FMO3 gene remains poorly understood. FMO3 is not expressed in HepG2 cells, a commonly employed model for hepatic gene regulation studies. Transcription factor transient expression and treatment with histone deacetylase or DNA methylase inhibitors identified decreased hepatic nuclear factor (HNF) 4alpha levels and DNA hypermethylation as mechanisms suppressing HepG2 FMO3 expression. The absence of major deficiencies in transcriptional machinery suggested that within limits, the HepG2 model is suitable for the study of FMO3 regulation. DNA-protein binding studies with HepG2 cell and hepatic tissue nuclear protein extracts and reporter construct transient expression experiments were performed to characterize FMO3 sequences from position -494 to -439 (domain I), previously demonstrated to significantly impact promoter function. Although both HNF3beta and CCAAT enhancer-binding protein (C/EBP) were observed to specifically interact with this element using HepG2 cell nuclear proteins, only C/EBP DNA-protein interactions were observed using adult liver nuclear proteins. No specific DNA/protein interactions were observed using fetal liver nuclear proteins. Mutation of a putative HNF3beta element had no effect on FMO3 promoter activity, while mutagenesis of a distinct, but overlapping C/EBP element resulted in a 55% reduction in activity. Furthermore, promoter activity was regulated as a function of defined C/EBPbeta liver activating protein:liver inhibitory protein ratios through this same element. Chromatin immunoprecipitation demonstrated C/EBPbeta binding to the FMO3 domain I element in intact cells and adult liver tissue. These results are consistent with C/EBPbeta being important for regulating hepatic FMO3 expression.