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MicroRNAs as key regulators of xenobiotic biotransformation and drug response
Jennifer Bolleyn · Joery De Kock ·
Robim Marcelino Rodrigues · Mathieu Vinken · Vera Rogiers · Tamara Vanhaecke
Received: 9 May 2014 / Accepted: 8 July 2014 / Published online: 31 July 2014 ? Springer-Verlag Berlin Heidelberg 2014
Introduction
Before a new pharmaceutical compound enters the market, rigorous preclinical testing has to be carried out to assure its safety and efficacy. Hereto, several features of the can-didate drug need to be investigated, including its toxico-logical properties (Brandon et al. 2003). Biotransforma-tion, predominantly occurring in hepatocytes, may be an initiating event of drug toxicity. Although the primary aim of biotransformation is detoxification by rendering com-pounds more hydrophilic, bioactivation may occur which could trigger toxicity. In general, the process of biotrans-formation is mediated by a network of biotransformation enzymes (BE) including (1) phase I reactions, implying oxidation, reduction or hydrolysis events and (2) phase II or conjugation reactions, in which chemicals and/or phase I metabolites are coupled to endogenous molecules to fur-ther facilitate excretion from the body (Brandon et al. 2003; Wei et al. 2012; Fasinu et al. 2012). Drug transporters (DT) also contribute to this process, since they mediate absorp-tion, distribution and excretion by translocation of the com-pounds either via active or passive mechanisms (Ramboer et al. 2013). The interaction between BE and DT, together with variations in the expression and/or activity levels of these protein-encoding genes, has thus a number of vast consequences for the interindividual variability of drug dis-position and toxicity (Yu 2009).
Over the years, considerable research efforts have been done to elucidate the transcriptional regulation of BE and DT. As such, it is known that the expression of DT and BE genes is controlled by different nuclear receptors (NR) and transcription factors (TF) (Tirona and Kim 2005). A novel layer of complexity has recently been added to this regu-latory network. Indeed, it has been shown that the protein expression levels of BE and DT often do not reflect their
Abstract In the last decade, microRNAs have emerged as key factors that negatively regulate mRNA expression. It has been estimated that more than 50 % of protein-coding genes are under microRNA control and each microRNA is predicted to repress several mRNA targets. In this respect, it is recognized that microRNAs play a vital role in various cellular and molecular processes and that, depending on the biological pathways in which they intervene, distorted expression of microRNAs can have serious consequences. It has recently been shown that specific microRNA species are also correlated with toxic responses induced by xenobi-otics. Since the latter are primarily linked to the extent of detoxification in the liver by phase I and phase II biotrans-formation enzymes and influx and efflux drug transporters, the regulation of the mRNA levels of this particular set of genes through microRNAs is of great importance for the overall toxicological outcome. Consequently, in this paper, an overview of the current knowledge with respect to the complex interplay between microRNAs and the expression of biotransformation enzymes and drug transporters in the liver is provided. Nuclear receptors and transcription fac-tors, known to be involved in the transcriptional regulation of these genes, are also discussed.
Keywords MicroRNA · Transcription factors · Cytochrome P450 enzymes · Drug transporters · Drug metabolism
J. Bolleyn (*) · J. De Kock · R. M. Rodrigues · M. Vinken · V . Rogiers · T. Vanhaecke
Department of Toxicology, Center for Pharmaceutical
Research, Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, 1090 Brussels, Belgium e-mail: jbolleyn@vub.ac.be
respective mRNA levels, supporting the existence of post-transcriptional regulation, such as microRNA (miR)-medi-ated mechanisms (Yu 2009; Zhang and Su 2009). MicroRNAs
MicroRNAs are a family of small (~22 nucleotides long), endogenous, noncoding RNAs that posttranscriptionally regulate gene expression through translational repression or mRNA degradation (Bartel 2004). It has been estimated that more than 50 % of protein-coding genes are under microRNA control and each microRNA is predicted to repress several mRNA targets (Krol et al. 2010). Currently, as much as 2,578 human mature microRNA sequences have been discovered (miRBase version 20, June 2013). Evidence is accumulating that these RNA molecules are involved in the regulation of different key biological func-tions, including organ development, cell differentiation and proliferation, cell death as well as biotransformation of endo- and exogenous substances (Zhang and Su 2009; Bar-tel 2004; Ambros 2004; To et al. 2008; Takagi et al. 2008; Pan et al. 2009b).
Biogenesis of microRNA and mechanism of action
The biogenesis of microRNAs (Fig. 1) is initiated by the transcription of microRNA genes, located in intronic regions of protein-coding genes, or individual transcripts by RNA polymerase II or RNA polymerase III, yielding long primary transcripts (pri-miRNA). These transcripts, forming distinctive hairpin structures, are further processed by the Drosha–DiGeorge syndrome critical region (DGCR) 8 complex into a ~70 nucleotides long precursor hairpin (pre-miRNA) and are exported to the cytoplasm by Expor-tin 5 (Bartel 2004; Krol et al. 2010; Filipowicz et al. 2008). Besides this canonical pathway, pre-miRNA can also be formed by splicing and debranching of introns (miRtron) (Westholm and Lai 2011; Krol et al. 2010). Both pathways proceed by cleavage of the hairpin structures by means of the RNAse III enzyme Dicer, together with transactivation-responsive (TAR) RNA-binding protein (TRBP), to yield ~20bp microRNA duplexes. One strand, i.e., with the low-est thermodynamic stability at the 5′ untranslated region (UTR) end (guide strand), will act as a mature microRNA and will be incorporated into the RNA-induced silencing complex (RISC). The other strand, the so-called passenger strand, is normally degraded, but can also act as a mature microRNA (Krol et al. 2010; Filipowicz et al. 2008). When mature microRNAs pair through a nearly perfect comple-mentarity with their “seed” region, represented by nucleo-tides 2–8, to the complementary target sites in the 3′ UTR of the target mRNA, a RNA interference-like mechanism is triggered, resulting in endonucleolytic mRNA cleavage and degradation. In mammals, microRNA–target mRNA bind-ing predominantly occurs with an imperfect complemen-tarity, initiating translational inhibition (Filipowicz et al. 2008).
Factors influencing microRNA expression
Previous research has shown that several BE and DT are posttranscriptionally regulated by microRNAs (To et al. 2008; Takagi et al. 2008; Pan et al. 2009a). As such, altera-tions in microRNA levels are anticipated to modify the expression of their target BE and DT genes. This may ulti-mately result in a deviated biotransformation and/or trans-port of the xenobiotic under investigation or a concurrent molecule and could lead to increased toxicity due to cel-lular accumulation (Yu 2009). Consequently, knowledge of potential changes in microRNA expression is promis-ing while assessing drug safety and response. Variations in microRNA levels can occur as a result of (1) single nucleo-tide polymorphisms (SNPs) in microRNAs, (2) epigenetic modifications, (3) developmental changes, (4) progress of tissue from a healthy to a diseased state and (5) pharmaco-therapy (Rukov et al. 2014) (Fig. 2).
Single nucleotide polymorphisms
MicroRNA-mediated gene regulation can be affected by the occurrence of SNPs, also known as miRSNPs. These polymorphisms are present at or near microRNA-binding sites of functional genes as well as in genes involved in microRNA biogenesis and in primary, precursor or mature microRNA sequences (Zhang and Dolan 2010; Mishra et al. 2008). These miRSNPs can affect microRNA func-tions either by directly impairing mRNA expression or by influencing microRNA–target interaction. Hence, these miRSNPs may contribute to the interindividual variabil-ity in expression and activity of BE and DT and thus may underlie differences in drug toxicity and efficacy (Rama-moorthy et al. 2012; Zhang and Dolan 2010; Saunders et al. 2007).
Epigenetics
Many genes encoding for BE, DT and NR are known to be under epigenetic control (Baer-Dubowska et al. 2011). Epi-genetics can be defined as all the heritable changes in gene expression that are not associated with alterations in DNA sequences (Iorio et al. 2010). Prototypical epigenetic events include DNA methylation and histone modifications, which both control the accessibility of gene promoters to the tran-scriptional machinery that determines whether a particular gene is transcriptionally active or repressed (Fraczek et al.
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2012). As microRNAs have been shown to play important roles in controlling DNA methylation and histone modifi-cations (Iorio et al. 2010), microRNA-induced changes in the epigenetic machinery will ultimately affect xenobiotic biotransformation. Vice versa, epigenetic mechanisms can also influence microRNA expression. Indeed, studies show that histone deacetylase (HDAC) inhibitors change micro-RNA expression profiles in different cell types. In this context, our group demonstrated that trichostatin A (TSA), an acknowledged HDAC inhibitor, alters microRNA expression in primary rat hepatocyte cultures. In fact, 18 microRNAs were found to be differentially expressed upon exposure to TSA, thereby affecting different biological net-works, including metabolism, genetic and environmental information processing, cellular processing and organis-mal system pathways (Bolleyn et al. 2011). Others reported that 32 microRNAs were differentially expressed in TSA-treated apoptosis-resistant human breast cancer cells (Rho-des et al. 2012). Collectively, these data clearly suggest that microRNAs are part of a multilevel regulatory mechanism that fine-tunes gene expression (Iorio et al. 2010; Baer-Dubowska et al. 2011).
Exon 1Spliceosome
Processing
Splicing
5’
Drosha
DGCR8
Dicer
TRBP
E x p o r t i n
Fig. 1 Biogenesis of microRNA. After transcription of microRNA genes, microRNAs are processed through the canonical pathway or mirtron pathway into pre-miRNA. Both pathways proceed by cleav-age of hairpin structures by means of RNAse III Dicer. MicroRNA–microRNA duplexes are formed, and from this duplex, only the guide strand is loaded into the RISC complex, forming miRISC. This com-
plex will cause translational repression or mRNA cleavage. Abbre-viations : DGCR DiGeorge syndrome critical region, Pre-miRNA precursor microRNA, Pri-microRNA primary microRNA, RISC RNA-induced silencing complex, TRBP transactivation-responsive RNA-binding protein
Development
MicroRNA expression profiles vary during organismal development and are thought to be essential for tissue-specific mRNA expression (Rukov and Shomron 2011). In human adult liver, several microRNAs are abundantly expressed, including miR-1, miR-16, miR-27b, miR-30d, miR-122, miR-126, miR-133, miR-143 and the let-7 fam-ily. While miR-122 is the most highly expressed micro-RNA in adult liver, miR-92a and miR-483 seem to be pref-erentially expressed in fetal liver (Chen 2009). Further, miR-18a, miR-92a, miR-409-3p, miR-451 and miR-483-3p are more expressed at the embryonic stage (7–10 weeks from gestation) of the human liver development compared to the adult organ. During liver maturation, the let-7 family together with other microRNAs such as miR-22, miR-23b, miR-99a, miR-125b and miR-192 become more expressed, suggesting a regulatory role for the differentially expressed microRNAs (Tzur et al. 2009).
Disease
In humans, the microRNA profile of liver substantially changes during the transition from healthy to diseased state (Lu et al. 2005; Rukov and Shomron 2011). Involvement of microRNAs has indeed been demonstrated in several liver pathologies, including nonalcoholic steatohepatitis (NASH), viral hepatitis, polycystic liver disease and hepa-tocellular carcinoma (HCC) (Chen 2009). Cheung and colleagues showed that NASH is associated with changes in the hepatic expression of microRNAs. The potential targets of these differentially expressed microRNAs are known to influence lipid metabolism, cell growth and dif-ferentiation, apoptosis and inflammation, which are all key processes involved in the development and progression of NASH (Cheung et al. 2008). miR-122 was the first micro-RNA species found to facilitate the replication of the hepa-titis C virus (HCV) (Jopling et al. 2005). In this respect, HCV treatment based on miR-122 inhibition by antisense oligonucleotides has been recently tested in clinical trials. In addition, other microRNAs are currently being investi-gated as possible candidates for HCV treatment (Hoffmann et al. 2012). Similarly, miR-15a is actively involved in the progression of polycystic liver disease. Downregula-tion of miR-15a results in an increased expression of cell division cycle Cdc25A, which is accompanied in vitro by increased proliferation and cystogenesis (Lee et al. 2008; Chen 2009). Also, in the last few years, a number of studies showed differentially expressed microRNAs in HCC versus healthy liver tissue (Gramantieri et al. 2008; Gooderham
Promoter Promoter RNA coding region for microRNA RNA coding region for BE and DT
TF NR
Epigenetic modulators miRSNPs
Mature
miRNA
BE/DT
mRNA
BE/DT
protein
Transcription
Transcription Translation
Drug
response
Disease
Xenobiotics
Fig. 2 Interplay between microRNA-mediated posttranscriptional regulation, and influencing factors, of biotransformation-related gene expression and drug response. Abbreviations: BE biotransformation enzymes, DT drug transporters, NR nuclear receptors, SNP single nucleotide polymorphism, TF transcription factors
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and Koufaris 2014). Among these microRNAs, several ones were equally dysregulated in other types of liver cancer, highlighting the fact that microRNAs can potentially act as oncogenes or tumor suppressors (Gramantieri et al. 2008).
Xenobiotics
Acute or chronic exposure to pharmaceuticals or chemi-cals typically modifies microRNA expression profiles (Fukushima et al. 2007; Moffat et al. 2007; Pogribny et al. 2007; Shah et al. 2007; Lizarraga et al. 2012). For instance, Lizarraga et al. could show that benzo[a]pyrene, a geno-toxic carcinogen, alters eight microRNAs in HepG2 cells, affecting apoptotic signaling, cell cycle arrest, DNA dam-age response and DNA damage repair (Lizarraga et al. 2012). When testing the influence of 19 xenobiotics on the expression of ten microRNAs in four different cell systems, Rodrigues and colleagues showed that changes in micro-RNA expression depend on both the drug and cell type investigated (Rodrigues et al. 2011). In addition, the appro-priate exposure time and dose have to be determined as well. As such, it was shown in vivo that microRNA expres-sion in the liver is initially relatively resistant to acute xenobiotic exposures, but the magnitude of the microRNA deregulations increasing progressively overtime (Gooder-ham and Koufaris 2014). Exposure of rats to tamoxifen, a potent rat hepatocarcinogen, leads to substantial changes in the expression of microRNA liver genes (Pogribny et al. 2007). Moreover, aberrant microRNA expression caused by drugs can induce drug resistance (Pogribny et al. 2010). In tumors, this process leads to the rise of a few cells with resistant phenotypes. Eventually, these resistant cells could overgrow the other ones and become the dominant cell type in the tumor. In this respect, Pogribny et al. (2010) showed that miR-7 and miR-345 were significantly downregulated in human cisplatin-resistant breast cancer MCF-7 cells. Hence, changes in microRNA expression profiles may have drastic implications for clinical cancer treatment (Rukov and Shomron 2011; Pogribny et al. 2007, 2010).
Direct posttranscriptional regulation
of biotransformation enzymes and drug
transporters by microRNAs
Biotransformation enzymes
During phase I biotransformation, 75 % of both exog-enous and endogenous compounds are metabolized by cytochrome P450 enzymes (CYPs) via reduction, oxida-tion or hydrolysis, making the molecule more hydrophilic and thus better excretable (Fasinu et al. 2012). Interindivid-ual CYP gene expression is primarily ascribed to genetic polymorphism (Ingelman-Sundberg et al. 1999). However, growing evidence is emerging that the expression levels of CYPs are also under epigenetic and microRNA-mediated posttranscriptional control (Zanger and Schwab 2013). Phase II enzymes catalyze the conjugation of different cosubstrates, such as glutathione (GSH), uridine diphos-phate (UDP)-glucuronic acid, sulfonates, acetyl Co-A, to xenobiotics or their phase I metabolite(s). As such, phase II BE are mainly transferases (Klaassen et al. 2011; Sheehan et al. 2001). An overview of the most important associa-tions reported with respect to the expression of phase I and II BE and microRNAs is provided here. A more extensive summary can be found in Table 1.
Cytochrome P450 enzymes
CYP1A1 CYP1A1 catalyzes the hydroxylation of several polycyclic aromatic hydrocarbons (Zanger and Schwab 2013; Baer-Dubowska et al. 2011). Using lymphoblastoid cell lines, it was found that mRNA expression of CYP1A1 positively correlates with miR-18b and miR-20b levels. In addition, other members of the phase I BE family, including aldehyde dehydrogenase 2 and flavin-containing monooxy-genase 4, also appear to be linked to the same microRNAs, indicating their important regulatory role in phase I biotrans-formation (Wang et al. 2009; Glubb and Innocenti 2011). Recently, an extensive study was performed by Rieger et al. comparing microRNA levels to protein and activity pheno-types for the ten most important drug metabolizing CYPs. A cohort of 92 human liver samples showed that the protein/ activity levels of CYP1A1 are negatively correlated with miR-130a, miR-132, miR-142-3p, miR-200a/b, miR-21, miR-27a, miR-31 and miR-34a. However, a possible link between miR-18b and miR-20b and CYP1A1 mRNA and protein levels in human liver samples was not found (Rieger et al. 2013). Yet, generalization of results obtained in differ-ent cell types must be done with caution since these discrep-ant results once more show that different microRNA profiles are present in different cell types. In addition, miR-20b was not among the selected microRNAs in the Rieger study. CYP1B1 CYP1B1, known to govern the extra-hepatic metabolism of several procarcinogens and promutagens, was the first phase I biotransformation enzyme discovered to be regulated by microRNAs (Yokoi and Nakajima 2013; Yu 2009; Klaassen et al. 2011). In particular, CYP1B1 is regulated by miR-27b, as evidenced by an increase of the protein level and enzymatic activity of endogenous CYP1B1 in cultured human breast cancer cells upon addi-tion of antisense miR-27b (Tsuchiya et al. 2006). In rela-tion to breast cancer, abnormal CYP1B1 expression caused by lower miR-27b levels leads to an increased conversion of estradiol to 4-hydroxy estradiol. The latter has a toxic
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T a b l e 1 O v e r v i e w o f d i r e c t a n d i n d i r e c t r e g u l a t i o n o f b i o t r a n s f o r m a t i o n e n z y m e s a n d t h e i r r e s p e c t i v e t r a n s c r i p t i o n f a c t o r s o r n u c l e a r r e c e p t o r s b y m i c r o R N A
D i r e c t I n d i r e c t m i R N A R N A l e v e l
P r o t e i n l e v e l A c t i v i t y l e v e l
B i o t r a n s f o r m a t i o n e n z y m e s
P h a s e I
C y t o c h r o m e P 450
e n z y m e s (C Y P )
C Y P 1A 1m i R -130a
?
?N D R i e g e r e t a l . (2013)
m i R -132
?
?N D R i e g e r e t a l . (2013)
m i R -142-3p
?
?N D R i e g e r e t a l . (2013)
m i R -143
?
?N D R i e g e r e t a l . (2013)
m i R -146a
?
?N D R i e g e r e t a l . (2013)
m i R -148a
+
+N D R i e g e r e t a l . (2013)
m i R -150
?
?N D R i e g e r e t a l . (2013)
m i R -185
?
N D
R i e g e r e t a l . (2013)
m i R -18b
+
N D
W a n g e t a l . (2009)
m i R -19a /b
+
N D
R i e g e r e t a l . (2013)
m i R -200a /b
?
?
N D
R i e g e r e t a l . (2013)
m i R -200c
?
N D
R i e g e r e t a l . (2013)
m i R -20b
+
N D
W a n g e t a l . (2009)
m i R -21
?
?
N D
R i e g e r e t a l . (2013)
m i R -214
?
?
N D
R i e g e r e t a l . (2013)
m i R -221
?
?
N D
R i e g e r e t a l . (2013)
m i R -27a
?
?
N D
R i e g e r e t a l . (2013)
m i R -29a
?
N D
R i e g e r e t a l . (2013)
m i R -31
?
?
N D
R i e g e r e t a l . (2013)
m i R -34a
?
?
N D
R i e g e r e t a l . (2013)
m i R -539
?
?
N D
R i e g e r e t a l . (2013)
m i R -9
?
N D
R i e g e r e t a l . (2013)
C Y P 1A 2m i R -101
+
R i e g e r e t a l . (2013)
m i R -122
+
R i e g e r e t a l . (2013)
m i R -130a
?
?
R i e g e r e t a l . (2013)
m i R -132
?
?
R i e g e r e t a l . (2013)
m i R -142-3p
?
?
R i e g e r e t a l . (2013)
m i R -148a
+
+
R i e g e r e t a l . (2013)
m i R -150
?
?
R i e g e r e t a l . (2013)
m i R -200a
??
R i e g e r e t a l . (2013)
m i R -200b
?
R i e g e r e t a l . (2013)
m i R -204
+
R i e g e r e t a l . (2013)
m i R -21
?
?
R i e g e r e t a l . (2013)
m i R -214
?
?
R i e g e r e t a l . (2013)
m i R -221
?
?
R i e g e r e t a l . (2013)
m i R -24
?
?
R i e g e r e t a l . (2013)
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Arch Toxicol (2015) 89:1523–1541
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T a b l e 1 c o n t i n u e d
D i r e c t
I n d i r e c t m i R N A R N A l e v e l P r o t e i n l e v e l A c t i v i t y l e v e l
m i R -27a
??R i e g e r e t a l . (2013)
m i R -31
??R i e g e r e t a l . (2013)
m i R -34a
??R i e g e r e t a l . (2013)
C Y P 1B 1
m i R -27b ??T s u c h i y a e t a l . (2006)
C Y P 2A 6l e t -7g
?R i e g e r e t a l . (2013)
m i R -106b
??R i e g e r e t a l . (2013)
m i R -130a
??R i e g e r e t a l . (2013)
m i R -130b
??R i e g e r e t a l . (2013)
m i R -132
??
R i e g e r e t a l . (2013)
m i R -142-3p
??
R i e g e r e t a l . (2013)
m i R -146a
??
R i e g e r e t a l . (2013)
m i R -150
?
R i e g e r e t a l . (2013)
m i R -185
???
R i e g e r e t a l . (2013)
m i R -200b
?
R i e g e r e t a l . (2013)
m i R -200c
?
?
R i e g e r e t a l . (2013)
m i R -204
+
R i e g e r e t a l . (2013)
m i R -21
?
??
R i e g e r e t a l . (2013)
m i R -22
?
R i e g e r e t a l . (2013)
m i R -221
?
?
R i e g e r e t a l . (2013)
m i R -223
?
R i e g e r e t a l . (2013)
m i R -27a
?
R i e g e r e t a l . (2013)
m i R -34a
??
R i e g e r e t a l . (2013)
C Y P 2B 6
m i R -18b
?
R i e g e r e t a l . (2013)
m i R -455-3p ?
R i e g e r e t a l . (2013)
C Y P 2C 8l e t -7c
+
R i e g e r e t a l . (2013)
m i R -101
+
R i e g e r e t a l . (2013)
m i R -103
?
N D
Z h a n g e t a l . (2012)
m i R -107
?N D
Z h a n g e t a l . (2012)
m i R -133a
+
R i e g e r e t a l . (2013)
m i R -142-3p
?
??
R i e g e r e t a l . (2013)
m i R -148a
+
+
R i e g e r e t a l . (2013)
m i R -204
+
R i e g e r e t a l . (2013)
m i R -21
?
?
R i e g e r e t a l . (2013)
m i R -223
?
R i e g e r e t a l . (2013)
m i R -27a
?
R i e g e r e t a l . (2013)
m i R -539
?
R i e g e r e t a l . (2013)
C Y P 2C 9l e t -7b
?+
R i e g e r e t a l . (2013)
1 3
T a b l e 1 c o n t i n u e d
D i r e c t
I n d i r e c t m i R N A R N A l e v e l P r o t e i n l e v e l A c t i v i t y l e v e l
l e t -7c
+R i e g e r e t a l . (2l e t -7d
?R i e g e r e t a l . (2l e t -7f
+R i e g e r e t a l . (2m i R -106a /b
?R i e g e r e t a l . (2m i R -122
?R i e g e r e t a l . (2m i R -146a
?R i e g e r e t a l . (2m i R -148a
+R i e g e r e t a l . (2m i R -16
?R i e g e r e t a l . (2m i R -17
?R i e g e r e t a l . (2m i R -185
?R i e g e r e t a l . (2m i R -18a /b
?R i e g e r e t a l . (2m i R -19a /b
?R i e g e r e t a l . (2m i R -214
?R i e g e r e t a l . (2m i R -221
?R i e g e r e t a l . (2m i R -223
?R i e g e r e t a l . (2m i R -24
?R i e g e r e t a l . (2m i R -27a
?R i e g e r e t a l . (2m i R -28-3p
?R i e g e r e t a l . (2m i R -28-5p
?R i e g e r e t a l . (2m i R -29a
?
R i e g e r e t a l . (2m i R -455-5p
+
R i e g e r e t a l . (2m i R -539
?
R i e g e r e t a l . (2C Y P 2C 19
m i R -106b
?
R i e g e r e t a l . (2m i R -130a /b
?
?
?
R i e g e r e t a l . (2m i R -132
?
?
?
R i e g e r e t a l . (2m i R -142-3p
?
?
?
R i e g e r e t a l . (2m i R -143
?
R i e g e r e t a l . (2m i R -146a
?
R i e g e r e t a l . (2m i R -150
?
?
?
R i e g e r e t a l . (2m i R -185
??
?
R i e g e r e t a l . (2m i R -19a /b
+
+
R i e g e r e t a l . (2m i R -200a
?
?
?
R i e g e r e t a l . (2m i R -200b
?
R i e g e r e t a l . (2m i R -21
?
??
R i e g e r e t a l . (2m i R -214
?
R i e g e r e t a l . (2m i R -22
?
??
R i e g e r e t a l . (2m i R -221
?R i e g e r e t a l . (2
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T a b l e 1 c o n t i n u e d
D i r e c t
I n d i r e c t m i R N A R N A l e v e l P r o t e i n l e v e l A c t i v i t y l e v e l
m i R -27a
???R i e g e r e t a l . (2m i R -31
???R i e g e r e t a l . (2m i R -34a
???R i e g e r e t a l . (2m i R -539
?R i e g e r e t a l . (2C Y P 2D 6l e t -7b
?R i e g e r e t a l . (2l e t -7c
?R i e g e r e t a l . (2l e t -7d
??R i e g e r e t a l . (2l e t -7f
?R i e g e r e t a l . (2l e t -7g
?
R i e g e r e t a l . (2m i R -106b
?
R i e g e r e t a l . (2m i R -10a
?
R i e g e r e t a l . (2m i R -130a
?
R i e g e r e t a l . (2m i R -142-3p
?
?
R i e g e r e t a l . (2m i R -143
?
R i e g e r e t a l . (2m i R -148b
?
R i e g e r e t a l . (2m i R -152
?
R i e g e r e t a l . (2m i R -16
?
R i e g e r e t a l . (2m i R -185
?
R i e g e r e t a l . (2m i R -18b
?
R i e g e r e t a l . (2m i R -200a
?
?
R i e g e r e t a l . (2m i R -200b
??
R i e g e r e t a l . (2m i R -204
?
R i e g e r e t a l . (2m i R -21
?
?
R i e g e r e t a l . (2m i R -214
?
R i e g e r e t a l . (2m i R -221
?
R i e g e r e t a l . (2m i R -223
?
?
R i e g e r e t a l . (2m i R -24
?
R i e g e r e t a l . (2m i R -26a
?
R i e g e r e t a l . (2m i R -27a
?
?
R i e g e r e t a l . (2m i R -27b
?
R i e g e r e t a l . (2m i R -28-3p
?
R i e g e r e t a l . (2m i R -28-5p
?
R i e g e r e t a l . (2m i R -29a
?
R i e g e r e t a l . (2m i R -31
+
R i e g e r e t a l . (2m i R -34a
?
R i e g e r e t a l . (2m i R -455-3p
?
R i e g e r e t a l . (2m i R -455-5p
?
R i e g e r e t a l . (2m i R -539
?
R i e g e r e t a l . (2
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T a b l e 1 c o n t i n u e d
D i r e c t
I n d i r e c t m i R N A R N A l e v e l P r o t e i n l e v e l A c t i v i t y l e v e l
C Y P 2E 1l e t -7a
?R i e g e r e t a l . (2013)
l e t -7b
?R i e g e r e t a l . (2013)
l e t -7c
?R i e g e r e t a l . (2013)
l e t -7d
?R i e g e r e t a l . (2013)
l e t -7e
?R i e g e r e t a l . (2013)
l e t -7f
?R i e g e r e t a l . (2013)
l e t -7g
?R i e g e r e t a l . (2013)
m i R -106b
?R i e g e r e t a l . (2013)
m i R -10a
?R i e g e r e t a l . (2013)
m i R -125b
?
R i e g e r e t a l . (2013)
m i R -130a
??
R i e g e r e t a l . (2013)
m i R -132
??
R i e g e r e t a l . (2013)
m i R -133a
?
R i e g e r e t a l . (2013)
m i R -142-3p
?
R i e g e r e t a l . (2013)
m i R -143
?
R i e g e r e t a l . (2013)
m i R -146a
?
R i e g e r e t a l . (2013)
m i R -148b
?
R i e g e r e t a l . (2013)
m i R -150
?
R i e g e r e t a l . (2013)
m i R -152
?
R i e g e r e t a l . (2013)
m i R -18b
+
R i e g e r e t a l . (2013)
m i R -200a
??
R i e g e r e t a l . (2013)
m i R -200b /c
?
R i e g e r e t a l . (2013)
m i R -21
?
?
R i e g e r e t a l . (2013)
m i R -214
?
?
?
R i e g e r e t a l . (2013)
m i R -221
??
R i e g e r e t a l . (2013)
m i R -24
?
R i e g e r e t a l . (2013)
m i R -26a /b
?
R i e g e r e t a l . (2013)
m i R -27a
??
?
R i e g e r e t a l . (2013)
m i R -29a
?
R i e g e r e t a l . (2013)
m i R -31
?
?
R i e g e r e t a l . (2013)
m i R -323-3p
?
R i e g e r e t a l . (2013)
m i R -378
??
?
M o h r i e t a l . (2010)
m i R -34a
?
R i e g e r e t a l . (2013)
m i R -455-3p
?
R i e g e r e t a l . (2013)
m i R -455-5p
?
R i e g e r e t a l . (2013)
m i R -539
?
R i e g e r e t a l . (2013)
m i R -9
?
R i e g e r e t a l . (2013)
C Y P 3A 4m i R -101
+
R i e g e r e t a l . (2013)
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T a b l e 1 c o n t i n u e d
D i r e c t
I n d i r e c t m i R N A R N A l e v e l P r o t e i n l e v e l A c t i v i t y l e v e l
m i R -142-3p
??R i e g e r e t a l . (2013)
m i R -148a
++R i e g e r e t a l . (2013)
m i R -200a
??R i e g e r e t a l . (2013)
m i R -204
+R i e g e r e t a l . (2013)
m i R -221
??R i e g e r e t a l . (2013)
m i R -223
?R i e g e r e t a l . (2013)
m i R -27a
?R i e g e r e t a l . (2013)
m i R -27b
??N D P a n e t a l . (2009a )
m i R -34a
???
R i e g e r e t a l . (2013)
m i R -9
+
R i e g e r e t a l . (2013)
m m u -m i R -298
??
N D
P a n e t a l . (2009a )
C Y P 24A 1
m i R -125b ??
K o m a g a t a e t a l . (2009)
O t h e r s
A L D H 2m i R -18b +N D
W a n g e t a l . (2009)
m i R -20b
+N D
W a n g e t a l . (2009)
F M O 4
m i R -18b ?N D
W a n g e t a l . (2009)
m i R -20b
?N D
W a n g e t a l . (2009)
P h a s e I I
G l u t a t h i o n e S -t r a n s f e r a s e (G S T )
G S T P 1m i R -192+N D
W a n g e t a l . (2009)
m i R -194
+N D
W a n g e t a l . (2009)
D r u g t r a n s p o r t e r s U p t a k e
S o l u t e c a r r i e r s (S L C )
S L C 29A 1m i R -221?
N D
W a n g e t a l . (2009)
P h a s e 0
S L C 47A 1
m i R -181a ?
N D
W a n g e t a l . (2009)
m i R -181b
?
N D
W a n g e t a l . (2009)
m i R -213
?
N D
W a n g e t a l . (2009)
E f fl u x
A B C t r a n s p o r t e r s A B C B 1m i R -27a
+
+
+
Z h u e t a l . (2008)
P h a s e I I I
m i R -451
++
+
K o v a l c h u k e t a l . (2008), Z h u e t a l . (2008)
A B C B 4
m i R -363
+
N D
W a n g e t a l . (2009)
A B C G 2
m i R -520h
?
N D
L i a o e t a l . (2008)
m i R -519c
?
N D
T o e t a l . (2008)
m i R -328
?
?
N D
P a n e t a l . (2009b )
M R P 1m i R -326
??
N D
L i a n g e t a l . (2010)
m i R -345
?
N D
P o g r i b n y e t a l . (2010)
m i R -7
?
N D
P o g r i b n y e t a l . (2010)
T r a n s c r i p t i o n f a c t o r s
L i v e r -e n r i c h e d t r a n s c r i p -t i o n f a c t o r s
(L E T F )
H e p a t o c y t e n u c l e a r f a c t o r s H N F 4α
C Y P 7A 1, C Y P 8B 1, C Y P 27A 1, P X R , T T R , A p o B , α1-A T m i R -34a
?
N A
T a k a g i e t a l . (2010), R a m a m o o r t h y e t a l . (2012), W a n g a n d B u r k e (2013)
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T a b l e 1 c o n t i n u e d
D i r e c t
I n d i r e c t m i R N A R N A l e v e l P r o t e i n l e v e l A c t i v i t y l e v e l
C Y P 7A 1, C Y P 8B 1, C Y P 27A 1
m i R -24??N A T a k a g i e t a l . (2010)
P X R , T T R , A p o B , α1-A T
m i R -449a ?N A
R a m a m o o r t h y e t a l .
(2012), W a n g a n d B u r k e (2013)
T T R , A p o B , α1-A T
m i R -34c -5p ?N A
W a n g a n d B u r k e (2013)
N u c l e a r r e c e p -t o r s
P e r o x i s o m e p r o l i f e r a t o r -a c t i v a t e d r e c e p t o r s P P A R α
m i R -21?N A K i d a e t a l . (2011)
m i R -27b
?N A
K i d a e t a l . (2011)
P P A R γ
m i R -27a ??N A
K i m e t a l . (2010)
m i R -27b ?N A
K a r b i e n e r e t a l . (2009), J e n n e w e i n e t a l . (2010)
m i R -130
?
N A
L e e e t a l . (2010)
R e t i n o i d X r e c e p t o r
R X R αm i R -27a ??
N A
J i e t a l . (2009)
m i R -27b
??
N A
J i e t a l . (2009)
P r e g n a n e X r e c e p t o r
P X R m i R -148a ?
N A T a k a g i e t a l . (2008)V i t a m i n D r e c e p t o r
V D R m i R -125b ?
N A
M o h r i e t a l . (2009)
C Y P 3A 4
m i R -27b b ??N A P a n e t a l . (2009a )
C Y P 3A 4
m m u -m i R -298?
?
N A
P a n e t a l . (2009a )
E s t r o g e n r e c e p t o r s
E r αm i R -206?
?
N A
A d a m s e t a l . (2007)
m i R -22?
?
N A
X i o n g e t a l . (2010), P a n d e y a n d P i c a r d (2009)
m i R -211
?
?
N A
Z h a o e t a l . (2008)
m i R -222
?
?
N A
Z h a o e t a l . (2008)
G l u c o c o r t i c o i d r e c e p t o r G R
m i R -18
?
N A
V r e u g d e n h i l e t a l . (2008)
m i R -124a
?
N A
V r e u g d e n h i l e t a l . (2008)
N D n o t d e t e r m i n e d , N A n o t a p p l i c a b l e
E m p t y fi e l d : n o o r n o s i g n i fi c a n t c o r r e l a t i o n w a s f o u n d
+: p o s i t i v e c o r r e l a t i o n
?: n e g a t i v e c o r r e l a t i o n
a
C o n t r a d i c t o r y r e s u l t s w e r e r e p o r t e d b y W e i e t a l . (2013) a n d R i e g e r e t a l . (2013)
b
C o n t r a d i c t o r y r e s u l t s w e r e r e p o r t e d b y R i e g e r e t a l . (2013)
effect and appears to play a role in tumorigenesis, and has therefore been suggested to be involved in the development of estrogen-dependent carcinogenesis (Yokoi and Nakajima 2013; Tsuchiya et al. 2004; Baer-Dubowska et al. 2011). CYP2C8 CYP2C8 is responsible for the detoxification of an array of xenobiotic compounds in human liver, including taxol, cerivastatin, amiodarone, amodiaquine, troglitazone, rosiglitazone and verapamil (Zhang et al. 2012). In a panel of 31 human liver samples, miR-103 and miR-107 were inversely correlated with CYP2C8 protein expression, sug-gesting a negative regulation of CYP2C8 by miR-103/107 (Zhang et al. 2012). In addition, it was shown by Rieger et al. that let-7c, miR-101, miR133a, miR-142-3p, miR-148a, miR-204, miR-21, miR-223, miR-27a and miR-539 are also involved in the regulation of CYP2C8 (Rieger et al. 2013).
CYP2E1 CYP2E1 preferentially metabolizes low molecu-lar weight molecules, including ethanol, drugs (paraceta-mol, chlorzoxazone), organic solvents (acetone) and nar-cotics (halothane) (Klaassen et al. 2011; Mohri et al. 2010; Zanger and Schwab 2013). In silico analysis revealed a pos-sible binding region for miR-378 present in the 3′ UTR of CYP2E1 mRNA. In vitro follow-up studies using human embryonic kidney cells showed that both the CYP2E1 pro-tein level and corresponding activity were decreased upon transfection with precursor miR-378. To verify this mode of action in vivo, a panel of human livers was investigated for their CYP2E1 protein and mRNA expression together with the miR-378 expression. In this study, miR-378 lev-els appeared to be inversely correlated with CYP2E1 pro-tein and the protein/mRNA ratio (Mohri et al. 2010). Also, the expression of miR-130a, miR-132, miR-148b, miR-21, miR-214, miR-221 and miR-27a was negatively correlated with the mRNA/activity levels of CYP2E1 (Rieger et al. 2013).
CYP3A4 CYP3A4 is indispensable for the biotransfor-mation of the majority of therapeutic drugs (Zanger and Schwab 2013). Pan and colleagues revealed in two differ-ent cancer cell lines that the CYP3A4 protein expression is directly targeted by miR-27b and mmu-miR-298. Since a decrease in the CYP3A4 mRNA levels is accompanied by a downregulation of CYP3A4 protein production, involve-ment of mRNA degradation is proposed as the driving mechanism (Pan et al. 2009a). In contrast, to these in vitro studies, Rieger and colleagues were not able to detect a cor-relation between miR-27b and CYP3A4 in healthy human liver samples. This may demonstrate a difference in micro-RNA-mediated regulation of CYP expression in vitro versus in vivo, but also in cancerous versus normal tissues (Rieger et al. 2013).CYP24A1 CYP24A1, also known as vitamin D3 hydroxy-lase, inactivates calcitrol, being a biological active metabolite of vitamin D3 with a determinating role in calcium homeo-stasis and displaying antitumor activity. CYP24A1 has been reported as an oncogene and may contribute to tumor aggres-siveness by abrogating local anticancer effects of calcitrol (King et al. 2010). Calcitrol binds to the vitamin D receptor (VDR) to perform its function. Both CYP24A1 and VDR are believed to be posttranscriptionally regulated by miR-125b, as a recognition element for miR-125b has been identified in the 3′ UTR region of their mRNAs (Mohri et al. 2009; Koma-gata et al. 2009). Because CYP24A1 itself is a transcriptional target of VDR, miR-125b can regulate in a direct and/or indi-rect way the expression of CYP24A1 (Komagata et al. 2009). Glutathione S-transferase
GSTP1 GSTP1 is a cytosolic GST that catalyzes the con-jugation of electrophilic substrates to GSH (Sheehan et al. 2001). The expression levels of GSTP1 parallel those of miR-192 and miR-194, pointing to a potential role of both microRNAs in the control of its production (Wang et al. 2009).
Drug transporters
DT are a family of proteins that facilitate the transport of chemical substances in and out the cells by means of pas-sive and active mechanisms. Depending on the direction of this transport, uptake and efflux transporters can be dis-tinguished (Klaassen and Aleksunes 2010). Uptake trans-porters are responsible for the uptake of both endogenous and exogenous molecules, prior to their biotransformation. They belong to the superfamily of solute carrier (SLC) proteins and act as facilitating transporters or secondary active transporters (Klaassen and Aleksunes 2010; Ram-boer et al. 2013). Efflux transporters, convey xenobiotics or their metabolites, outside of the cell. They are primary active transporters and are called the adenosine triphos-phate (ATP) binding cassette (ABC) transporters, because they contain ATP-binding domains with ATPase activity to provide energy for translocating substrates across mem-branes, most often against concentration gradients (Klaas-sen and Aleksunes 2010). Elevated expression levels of one or more ABC transporters have been associated with mul-tidrug resistance, which is defined by the ability of tumor cells to resist several unrelated drugs after exposure to a single chemotherapeutic agent (Liang et al. 2010).
Solute carrier superfamily
SLC29A1 The SLC29A1 gene encodes for equilibrative nucleoside transporter 1 (ENT1), a cellular transporter
1 3
required for nucleoside transport together with the uptake of cytotoxic nucleosides used in chemotherapy. Using in silico techniques, it was found that SLC29A1 correlates with miR-221 expression (Wang et al. 2009; Glubb and Innocenti 2011).
SLC47A1 The SLC47 family, also known as the multidrug and toxin extrusion (MATE) family, is a recently discovered group of SLC transporters. Unlike the other members of the SLC family, SLC47 possesses efflux transporter prop-erties and takes part in the efflux of organic cations (Ram-boer et al. 2013). Pairwise correlation coefficient analysis showed a correlation between miR-181a, miR-181b and miR-213 and SLC47A1 expression (Glubb and Innocenti 2011; Wang et al. 2009; Baer-Dubowska et al. 2011).
ABC superfamily
P-glycoprotein P-glycoprotein (Pgp/MDR1/ABCB1), a member of the multidrug resistance (MDR) proteins, is responsible for the efflux of a wide repertoire of xenobiotics including anticancer drugs, antibiotics and antiviral agents (Ramboer et al. 2013; Chan et al. 2004). Zhu et al. showed that the expression of Pgp is activated by miR-27a and miR-451. The multidrug-resistant cancer cell lines A2780DX5 and KB-V1 showed a higher expression of both miR-27a and miR-451 compared to the parental lines. In the pres-ence of miR-27a and miR-451 antagomirs, downregula-tion of both Pgp and MDR1 mRNA levels was noticed in A2780DX5 cells (Zhu et al. 2008). Kovalchuk et al. also unveiled the involvement of miR-451 in controlling the expression of the MDR1 gene in MCF-7 breast cancer cells. Moreover, upregulation of miR-451 in doxorubicin-resistant MCF-7 cells increased the sensitivity of the cells to doxo-rubicin, indicating that correction of an altered microRNA expression could serve as a possible therapeutic strategy to overcome multidrug resistance (Kovalchuk et al. 2008). Multidrug resistance protein 3 Multidrug resistance pro-tein 3 (MDR3/ABCB4) is produced in the liver and guides the canalicular translocation of phospholipids and some cytotoxic drugs (Chan et al. 2004; Ramboer et al. 2013). Data mining performed by Wang et al. could associate miR-363 levels to the mRNA expression of ABCB4, which encodes MDR3 (Wang et al. 2009; Baer-Dubowska et al. 2011).
Breast cancer resistance protein Breast cancer resistance protein (Bcrp/ABCG2), a member of the ABCG subfamily, has an important function in the excretion of hydrophobic xenobi-otics and conjugated, usually sulfated, metabolites (Ramboer et al. 2013). Overexpression of ABCG2 is also involved in the mechanism of multidrug resistance (To et al. 2008). Several studies indicated a role for microRNAs in the regulation of ABCG2 expression. Liao et al. were the first to prompt a possi-ble correlation between microRNA and ABCG expression lev-els. In particular, it was found that co-transfection of pre-miR-520h together with a pMIR-Luc-ABCG2 plasmid reduced luciferase activity significantly, indicating that ABCG2 is a target of hsa-miR-520h (Y u 2009; Liao et al. 2008). Subse-quently, To and colleagues showed that ABCG2 is a target of hsa-miR-519c in S1 parental colon cancer. The repression of protein production was, however, linked to the length of the 3′UTR region. As such, the microRNA could not bind to the 3′UTR region of ABCG2 in resistant S1MI80 cells as a conse-quence of a shorter 3′ UTR region (To et al. 2008; Y u 2009). Furthermore, miR-328 and ABCG2 protein levels were shown to be inversely linked to drug-resistant and parental MCF-7 cells. Transfection of miR-328 resulted in a downregulation of the ABCG2 protein expression in MCF-7/MX100 cells, fol-lowing a dramatic increase of the sensitivity of the cells to the anticancer drug mitoxantrone (Pan et al. 2009b; Y u 2009). Multidrug resistance-associated protein 1 Multidrug resistance-associated protein 1 (MRP1) is responsible for the translocation of GSH-, UDP- and sulfate-conjugated and sulfate-unconjugated organic anions (Ramboer et al. 2013). Liang and colleagues compared the microRNA expression levels of the VP-16-resistant MDR cell line, i.e., MCF-7/VP, with its parent cell line MCF-7. They found that MCF-7/ VP overexpressed MRP1 mRNA and protein and showed a lower expression of miR-326 compared to the level found in MCF-7 cells. Furthermore, overexpression of miR-326 in MCF-7/VP downregulated MRP1 mRNA and protein expression and sensitized these cells to VP-16 and doxoru-bicin, indicating the involvement of microRNA in multid-rug resistance via MRP1 expression (Liang et al. 2010). In addition, miR-345 and miR-7 were demonstrated to target MRP1 expression when comparing the breast cancer parent cell line MCF-7 with its cisplatin-resistant variant (MCF-7/CDDP). In fact, transfection of MCF-7/CDDP cells with miR-345 and miR-7 resulted in a significant decrease of MRP1 cellular levels and an increased sensitivity of MCF-7/CDDP to cisplatin (Pogribny et al. 2010).
Indirect influence of microRNAs on xenobiotic biotransformation via posttranscriptional regulation
of nuclear transcription factors and receptors
TF are trans-acting DNA-binding proteins, which can bind to a cis-acting DNA sequence in the regulatory elements of a gene (Schrem et al. 2002). TF enable selective gene expression and regulation. In combination with other pro-teins, coactivating or corepressing, they form a multiprotein complex that drives mRNA synthesis (Schrem et al. 2002).
1 3
MicroRNAs also participate in this transcriptional con-trol in at least two different motifs. First, microRNAs and TF can accomplish a coordinated repression, reinforcing each other’s activity. This process is called coherent feed-forward. When microRNA and TF carry out an opposing activity (incoherent feedforward), a more uniform expres-sion is ensured, which helps to maintain protein homeosta-sis (Tsang et al. 2007; Gurtan and Sharp 2013).
Liver-enriched transcription factors (LETF)
The family of liver-enriched TF (LETF) consists of the hepatocyte nuclear factors (HNF) families HNF1, HNF3, HNF4, HNF6, the CCAAT/enhancer binding protein (c/EBP) and D-binding protein. These TF cooperate to maintain liver-specific gene transcription (Schrem et al. 2002; Duncan 1998).
Hepatocyte nuclear factor 4 α
HNF4α, a member of the nuclear hormone receptor super-family, is considered to be a master regulator of the overall TF network in the liver (Wang and Burke 2013). HNF4αcan transactivate the expression of several target genes, including CYPs, UDP-glucuronosyltransferases (UGTs), sulfotransferases and drug transporters either via direct binding or by regulation of nuclear receptors (NR), includ-ing the pregnane X receptor (PXR) and the constitutive androstane receptor (CaR). This intricate network of tran-scriptional regulation underscores the great influence of HNF4α on drug metabolism and disposition (Ramamoor-thy et al. 2012).
Takagi et al. (2010) found that the expression of HNF4αis controlled through translational repression and mRNA degradation, via miR-34a and miR-24, respectively. Over-expression of these microRNAs in HepG2 cells resulted in a downregulation of some bile acid synthesizing enzymes (CYP7A1 and CYP8B1) and the cholesterol-metaboliz-ing enzyme CYP27A1, reflecting the downregulation of HNF4α (Takagi et al. 2010). Ramamoorthy et al. further showed that, next to miR-34a, miR-449a is also able to downregulate HNF4α protein and mRNA levels and of its target gene PXR in HepG2 cells (Ramamoorthy et al. 2012). In addition, miR-34a-, miR-34c-5p- and miR-449a-induced repression of HNF4α protein expression also leads to a reduced HNF4α binding to its target genes tran-sthyretin, apolipoprotein B and α1-antitrypsin (Wang and Burke 2013).
Nuclear receptors
NR are ligand-activated TF that regulate the expression of target genes by binding to cis-acting DNA sequences. NR can either activate or repress target genes by directly bind-ing to DNA response elements as homo- or heterodimers or through binding to other classes of DNA-bound TF. NR are classified based on their binding to different ligands. The estrogen receptor (ER), androgen receptor (AR), proges-terone receptor (PR) and glucocorticoid receptor (GR) are regulated by endocrine ligands. “Adopted” orphan recep-tors, such as peroxisome proliferator-activated receptors (PPARs) and liver X receptor (LXR), however, have both natural and synthetic ligands (Yang and Wang 2011). Pregnane X receptor (PXR)
PXR is an important regulator of drug metabolism in the liver and small intestine (Yang and Wang 2011). PXR is activated by several endogenous and exogenous chemi-cals, including antibiotics, antimycotics and steroids, to bind to DNA response elements in the regulatory regions of CYP3A genes and a number of other genes involved in the metabolism and elimination of xenobiotics (Kliewer et al. 2002). Takagi showed that miR-148 directly regulates PXR protein expression, but not the expression of CYP3A4, in human liver. Yet, the inducible and/or constitutive levels of CYP3A4 could be modulated via miR-148-mediated regu-lation of PXR (Takagi et al. 2008). However, in other stud-ies, no correlation between hsa-miR-148 and the expres-sion of PXR or CYP3A4 in human liver samples could be demonstrated at both the protein and mRNA level (Wei et al. 2013; Rieger et al. 2013).
Vitamin D receptor
Vitamin D receptor (VDR) is a nuclear steroid hormone receptor that exerts its function via binding to the vitamin D responsive element in the regulatory region of target genes, such as CYP3A4 (Mohri et al. 2009; Wang et al. 2008). Pan and colleagues showed that miR-27b and mmu-miR-298 are able to indirectly regulate CYP3A4 via VDR, in addition to the direct regulation of CYP3A4 through binding to its 3′UTR region (Pan et al. 2009a). Furthermore, Mohri et al. (2009) identified another potential recognition element for miR-125b in the 3′ UTR region of human VDR mRNA. As VDR is regulated posttranscriptionally by miR-125b, the latter could indirectly influence the expression of genes under VDR control, including CYP3A4 (Mohri et al. 2009). Estrogen receptor α
ERs are a group of ligand-activated NR which are trig-gered by estrogen (Xiong et al. 2010). CYP1B1 catalyzes the conversion of estradiol into 4-hydroxy estradiol and the metabolic activation of procarcinogens and promutagens (Yokoi and Nakajima 2011). CYP1B1 is regulated by ERα,
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which is under microRNA control. miR-206 can repress endogenous ERα mRNA and protein expression in MCF-7 cells and T47D breast cancer cells (Adams et al. 2007). miR-22 (Xiong et al. 2010; Pandey and Picard 2009) and miR-211/222 (Zhao et al. 2008) have also been added to the list of possible ERα protein regulators.
Glucocorticoid receptor
Cortisol, as well as other glucocorticoids, binds to the GR, which plays a vital role in development, metabolism and immune responses (Klaassen et al. 2011). GR is involved in the regulation of several BE and NR genes, including CYP2B6, CYP2C9, CYP3A4, PXR and CaR (Nakajima and Yokoi 2011). Both miR-18 and miR-124a were reported to regulate GR protein levels in the brain (Vreugdenhil et al. 2008), but microRNA-dependent regulation of GR has not yet been linked to xenobiotic biotransformation. Peroxisome proliferator-activated receptors
PPARs are ligand-activated TF of the nuclear hormone receptor superfamily. PPARs are divided into three sub-types: α, β/δ and γ. They play a major role in fatty acid metabolism and energy homeostasis. In association with a coactivator complex, PPARs function as heterodimers that bind to a DNA sequence present in the promoter of target genes leading to their transactivation or transrepression (Tyagi et al. 2011).
Research performed by Kida and colleagues indicates that microRNAs are involved in the regulation of lipid-metabolizing enzymes. miR-21 and miR-27b were found to regulate the protein expression of PPARα in Huh7 cells. However, no effect was seen on PPARα mRNA levels, sug-gesting translational repression (Kida et al. 2011). miR-27a, miR-27b and miR-130 were also shown to be involved in PPARγ expression, another subtype of the PPAR fam-ily (Karbiener et al. 2009; Jennewein et al. 2010; Kim et al. 2010; Lee et al. 2011; Peng et al. 2014). Furthermore, reti-noid x receptor α, the heterodimeric partner of PPARγ, was identified as a target of miR-27a and miR-27b in rat-derived hepatic stellate cells, indicating a potential new role of both microRNAs in the regulation of fat metabo-lism and cell proliferation (Ji et al. 2009). Overall, it seems that miR-27 regulates a large variety of lipid-metabolizing enzymes such as CYP4A11, UGT1A9, UGT2B4 and acyl-CoA-synthase through PPAR (Yokoi and Nakajima 2013). Concluding remarks
There is accumulating evidence that microRNAs con-trol the expression of several BE and DT genes at the posttranscriptional level and consequently play an impor-tant role in the process of drug metabolism and disposi-tion (Table 1). Regulation can occur either through direct interaction with the BE and DT mRNAs, or in an indi-rect way by targeting NR and TF mRNAs that are neces-sary for the transcription of the BE and DT genes. Hence, modifications in microRNA profiles may cause an altered expression of BE and DT, which may result in a deviat-ing xenobiotic metabolism and/or transport. In turn, this may affect the biological activity of the compound under consideration, including its potential toxicity. The discovery that microRNAs play a pivotal role in drug response and safety has given rise to the emerging new field of “microRNA pharmacogenomics,” in which micro-RNA and polymorphisms affecting microRNA function are studied in order to predict drug behavior. For exam-ple, a SNP located in the binding site of miR-24 in the 3′UTR region of human dihydrofolate reductase gene leads to overexpression of this gene and methotrexate resist-ance (Mishra et al. 2007). Recently, it was shown that a microRNA-binding site polymorphism in SLC19A1 can influence methotrexate concentration in Chinese children with acute lymphoblastic leukemia (Wang et al. 2014). At present, we are only just beginning to understand the impact of microRNAs on the expression of genes involved in drug metabolism and disposition, and it is anticipated that much more data will become available in the com-ing years. It must, however, be emphasized that up till now, the majority of studies were performed on can-cer cell lines that already display an altered microRNA profile. Because of chemoresistance, cancer cell lines frequently fail to identify the microRNA target genes involved which can distort the results. Therefore, further investigations should focus more on microRNA profil-ing in noncancerous cells. In addition, it should be noted that discrepant results can also be obtained when studying microRNA expression in vitro. Indeed, the in vivo situa-tion is affected by numerous factors and potential effects caused by microRNA may be masked. However, it should also be noted that the in vivo situation has limitations due to the fact that administered drugs can have an effect on the microRNA profile. At last, whenever a possible link between microRNA and BE or DT is identified, its actual influence on drug metabolism should be further explored. Indeed, it is important to measure the enzyme activities involved using well-known reference drugs in the pres-ence or absence of the identified microRNA(s). In actual studies, this is often neglected. In conclusion, unanswer-able linking microRNA expression to particular genes involved in drug response and toxicity remains very dif-ficult. Future research will undoubtedly provide more insights and shed further light on the intricate interplay between microRNAs and drug metabolism.
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Acknowledgments This work is financially supported by grants from the Fund for Scientific Research (FWO), Vlaanderen, Belgium, the Research Council (OZR) of the Vrije Universiteit Brussel, Bel-gium and The Johns Hopkins Centre for Alternatives to Animal Test-ing (CAAT), Baltimore, USA.
Conflict of interest The authors report no declarations of interest. References
Adams BD, Furneaux H, White BA (2007) The micro-ribonucleic acid (miRNA) miR-206 targets the human estrogen receptor-alpha (ERalpha) and represses ERalpha messenger RNA and protein expression in breast cancer cell lines. Mol Endocrinol 21:1132–1147
Ambros V (2004) The functions of animal microRNAs. Nature 431:350–355
Baer-Dubowska W, Majchrzak-Celin′ska A, Cichocki M (2011) Phar-mocoepigenetics: a new approach to predicting individual drug responses and targeting new drugs. Pharmacol Rep 63:293–304 Bartel DP (2004) MicroRNAs: genomics, biogenesis, mechanism, and function. Cell 116:281–297
Bolleyn J, Fraczek J, Vinken M, Lizarraga D, Gaj S, van Delft JHM, Rogiers V, Vanhaecke T (2011) Effect of Trichostatin A on miRNA expression in cultures of primary rat hepatocytes. Toxi-col In Vitro 25:1173–1182
Brandon EFA, Raap CD, Meijerman I, Beijnen JH, Schellens JHM (2003) An update on in vitro test methods in human hepatic drug biotransformation research: pros and cons. Toxicol Appl Pharma-col 189:233–246
Chan LMS, Lowes S, Hirst BH (2004) The ABCs of drug transport in intestine and liver: efflux proteins limiting drug absorption and bioavailability. Eur J Pharm Sci 21:25–51
Chen XM (2009) MicroRNA signatures in liver diseases. World J Gastroenterol 15:1665–1672
Cheung O, Puri P, Eicken C, Contos MJ, Mirshahi F, Maher JW, Kel-lum JM, Min H, Luketic V A, Sanyal AJ (2008) Nonalcoholic ste-atohepatitis is associated with altered hepatic MicroRNA expres-sion. Hepatology 48:1810–1820
Duncan SA (1998) Regulation of a transcription factor network required for differentiation and metabolism. Science 281:692–695 Fasinu P, Bouic P, Rosenkranz B (2012) Liver-based in vitro tech-nologies for drug biotransformation studies—a review. Curr Drug Metab 13:215–224
Filipowicz W, Bhattacharyya SN, Sonenberg N (2008) Mechanisms of post-transcriptional regulation by microRNAs are the answers in sight? Nat Rev Genet 9:102–114
Fraczek JE, Vinken M, Tourwé D, Vanhaecke T, Rogiers V (2012) Synergetic effects of DNA demethylation and histone deacety-lase inhibition in primary rat hepatocytes. Invest New Drugs 30:1715–1724
Fukushima T, Hamada Y, Yamada H, Horii I (2007) Changes of micro-RNA expression in rat liver treated by acetaminophen or carbon tetrachloride-regulating role of micro-RNA for RNA expression.
J Toxicol Sci 32:401–409
Glubb DM, Innocenti F (2011) Mechanisms of genetic regulation in gene expression: examples from drug metabolizing enzymes and transporters. Wiley Interdiscip Rev Syst Biol Med 3:299–313 Gooderham N, Koufaris C (2014) Using microRNA profiles to pre-dict and evaluate hepatic carcinogenic potential. Toxicol Lett 228:127–132
Gramantieri L, Fornari F, Callegari E, Sabbioni S, Lanza G, Croce CM, Bolondi L, Negrini M (2008) MicroRNA involvement in hepatocellular carcinoma. J Cell Mol Med 12:2189–2204Gurtan AM, Sharp PA (2013) The role of miRNAs in regulating gene expression networks. J Mol Biol 425:3582–3600
Hoffmann T, Duverlie G, Bengrine A (2012) MicroRNAs and hepati-tis C virus: toward the end of miR-122 supremacy. Virol J 9:1–8 Ingelman-Sundberg M, Oscarson M, McLellan RA (1999) Polymor-phic human cytochrome P450 enzymes: an opportunity for indi-vidualized drug treatment. Trends Pharmacol Sci 20:1092–1102 Iorio MV, Piovan C, Croce CM (2010) Interplay between microRNAs and the epigenetic machinery: an intricate network. Biochim Bio-phys Acta 1799:694–701
Jennewein C, von Knethen A, Schmid T, Brüne B (2010) MicroRNA-27b contributes to lipopolysaccharide-mediated peroxisome pro-liferator-activated receptor gamma (PPARgamma) mRNA desta-bilization. J Biol Chem 285:11846–11853
Ji J, Zhang J, Huang G, Qian J, Wang X, Mei S (2009) Over-expressed microRNA-27a and 27b influence fat accumulation and cell pro-liferation during rat hepatic stellate cell activation. FEBS Lett 583:759–766
Jopling CL, Yi M, Lancaster AM, Lemon SM, Sarnow P (2005) Mod-ulation of hepatitis C virus RNA abundance by a liver-specific MicroRNA. Science 309:1577–1581
Karbiener M, Fischer C, Nowitsch S, Opriessnig P, Papak C, Ailhaud G, Dani C, Amri EZ, Scheideler M (2009) microRNA miR-27b impairs human adipocyte differentiation and targets PPAR-gamma. Biochem Biophys Res Commun 390:247–251
Kida K, Kajima MKN, Mohri TK, Oda YK, Kagi ST, Kami TKF, Koi TY (2011) PPARα is regulated by miR-21 and miR-27b in human liver. Pharm Res 28:2467–2476
Kim SY, Kim AY, Lee HW, Son YH, Lee GY, Lee JW, Lee YS, Kim JB (2010) miR-27a is a negative regulator of adipocyte differenti-ation via suppressing PPARgamma expression. Biochem Biophys Res Commun 392:323–328
King A, Beer D, Christensen P, Simpson R, Ramnath N (2010) The vitamin D/CYP24A1 story in cancer. Anticancer Agents Med Chem 10:213–224
Klaassen CD, Aleksunes LM (2010) Xenobiotic, bile acid, and cho-lesterol transporters: function and regulation. Pharmacol Rev 62:1–96
Klaassen CD, Lu H, Cui JY (2011) Epigenetic regulation of drug pro-cessing genes. Toxicol Mech Methods 21:312–324
Kliewer SA, Goodwin B, Willson T (2002) The nuclear pregnane X receptor: a key regulator of xenobiotic metabolism. Endocr Rev 23:687–702
Komagata S, Nakajima M, Takagi S, Mohri T, Taniya T, Yokoi T (2009) Human CYP24 catalyzing the inactivation of calcitriol is post-transcriptionally regulated by miR-125b. Mol Pharmacol 76:702–709
Kovalchuk O, Filkowski J, Meservy J, Ilnytskyy Y, Tryndyak VP, Chekhun VF, Pogribny IP (2008) Involvement of microRNA-451 in resistance of the MCF-7 breast cancer cells to chemotherapeu-tic drug doxorubicin. Mol Cancer Ther 7:2152–2159
Krol J, Loedige I, Filipowicz W (2010) The widespread regulation of microRNA biogenesis, function and decay. Nat Rev Genet 11:597–610
Lee SO, Masyuk T, Splinter P, Banales JM, Masyuk A, Stroope A, LaRusso N (2008) MicroRNA15a modulates expression of the cell-cycle regulator Cdc25A and affects hepatic cystogen-esis in a rat model of polycystic kidney disease. J Clin Invest 118:3714–3724
Lee EK, Lee MJ, Abdelmohsen K, Kim W, Kim MM, Srikantan S, Martindale JL, Hutchison ER, Kim HH, Marasa BS, Selimyan R, Egan JM, Smith SR, Fried SK, Gorospe M (2011) miR-130 suppresses adipogenesis by inhibiting peroxisome proliferator-activated receptor expression. Mol Cell Biol 31:626–638
Liang Z, Wu H, Xia J, Li Y, Zhang Y, Huang K, Wagar N, Yoon Y, Cho HT, Scala S, Shim H (2010) Involvement of miR-326 in
1 3
chemotherapy resistance of breast cancer through modulating expression of multidrug resistance-associated protein 1. Biochem Pharmacol 79:817–824
Liao R, Sun J, Zhang L, Lou G, Chen M, Zhou D, Chen Z, Zhang S (2008) MicroRNAs play a role in the development of human hematopoietic stem cells. J Cell Biochem 104:805–817 Lizarraga D, Gaj S, Brauers KJ, Timmermans L, Kleinjans JC, van Delft JHM (2012) Benzo[a]pyrene-induced changes in micro-RNA-mRNA networks. Chem Res Toxicol 25:838–849
Lu J, Getz G, Miska EA, Alvarez-Saavedra E, Lamb J, Peck D, Sweet-Cordero A, Ebert BL, Mak RH, Ferrando AA, Downing JR, Jacks T, Horvitz HR, Golub TR (2005) MicroRNA expres-sion profiles classify human cancers. Nature 435:834–838 Mishra PJ, Humeniuk R, Longo-Sorbello GSA, Banerjee D, Bertino JR (2007) A miR-24 microRNA binding-site polymorphism in dihydrofolate reductase gene leads to methotrexate resistance.
Proc Natl Acad Sci 104:13513–13518
Mishra PJ, Mishra PJ, Banerjee D, Bertino JR (2008) MiRSNPs or MiR-polymorphisms, new players in microRNA mediated regu-lation of the cell: introducing microRNA pharmacogenomics.
Cell Cycle 7:853–858
Moffat ID, Boutros PC, Celius T, Lindén J, Pohjanvirta R, Okey AB (2007) microRNAs in adult rodent liver are refractory to dioxin treatment. Toxicol Sci 99:470–487
Mohri T, Nakajima M, Takagi S, Komagata S, Yokoi T (2009) MicroRNA regulates human vitamin D receptor. Int J Cancer 125:1328–1333
Mohri T, Nakajima M, Fukami T, Takamiya M, Aoki Y, Yokoi T (2010) Human CYP2E1 is regulated by miR-378. Biochem Phar-macol 79:1045–1052
Nakajima M, Yokoi T (2011) MicroRNAs from biology to future pharmacotherapy: regulation of cytochrome P450s and nuclear receptors. Pharmacol Ther 131:330–337
Pan YZ, Gao W, Yu AM (2009a) MicroRNAs regulate CYP3A4 expression via direct and indirect targeting. Drug Metab Dispos 37:2112–2117
Pan YZ, Morris ME, Yu AM (2009b) MicroRNA-328 negatively regulates the expression of breast cancer resistance pro-tein (BCRP/ABCG2) in human cancer cells. Mol Pharmacol 75:1374–1379
Pandey DP, Picard D (2009) miR-22 inhibits estrogen signaling by directly targeting the estrogen receptor alpha mRNA. Mol Cell Biol 29:3783–3790
Peng Y, Yu S, Li H, Xiang H, Peng J, Jiang S (2014) MicroR-NAs: emerging roles in adipogenesis and obesity. Cell Signal 26:1888–1896
Pogribny IP, Tryndyak VP, Boyko A, Rodriguez-Juarez R, Beland FA, Kovalchuk O (2007) Induction of microRNAome deregu-lation in rat liver by long-term tamoxifen exposure. Mutat Res 619:30–37
Pogribny IP, Filkowski JN, Tryndyak VP, Golubov A, Shpyleva SI, Kovalchuk O (2010) Alterations of microRNAs and their targets are associated with acquired resistance of MCF-7 breast cancer cells to cisplatin. Int J Cancer 127:1785–1794
Ramamoorthy A, Li L, Gaedigk A, Bradford LD, Benson EA, Flock-hart DA, Skaar TC (2012) In silico and in vitro identification of microRNAs that regulate hepatic nuclear factor 4α expression.
Drug Metab Dispos 40:726–733
Ramboer E, Vanhaecke T, Rogiers V, Vinken M (2013) Primary hepat-ocyte cultures as prominent in vitro tools to study hepatic drug transporters. Drug Metab Rev 45:196–217
Rhodes LV, Nitschke AM, Segar HC, Martin EC, Driver JL, Elliott S, Nam SY, Li M, Nephew KP, Burow ME, Collins-Burow BM (2012) The histone deacetylase inhibitor trichostatin A alters microRNA expression profiles in apoptosis-resistant breast can-cer cells. Oncol Rep 27:10–16Rieger JK, Klein K, Winter S, Zanger UM (2013) Expression vari-ability of absorption, distribution, metabolism, excretion-related microRNAs in human liver: influence of nongenetic factors and association with gene expression. Drug Metab Dispos 41:1752–1762
Rodrigues AC, Li X, Radecki L, Pan YZ, Winter JC, Huang M, Yu AM (2011) MicroRNA expression is differentially altered by xenobiotic drugs in different human cell lines. Biopharm Drug Dispos 32:355–367
Rukov JL, Shomron N (2011) MicroRNA pharmacogenomics: post-transcriptional regulation of drug response. Trends Mol Med 17:412–423
Rukov JL, Wilentzik R, Jaffe I, Vinther J, Shomron N (2014) Phar-maco-miR: linking microRNAs and drug effects. Brief Bioinform 15:648–659
Saunders MA, Liang H, Li WH (2007) Human polymorphism at microRNAs and microRNA target sites. Proc Natl Acad Sci USA 104:3300–3305
Schrem H, Klempnauer J, Borlak J (2002) Liver-enriched transcrip-tion factors in liver function and development. Part I: the hepato-cyte nuclear factor network and liver-specific gene expression.
Pharmacol Rev 54:129–158
Shah YM, Morimura K, Yang Q, Tanabe T, Takagi M, Gonzalez FJ (2007) Peroxisome proliferator-activated receptor alpha regulates
a microRNA-mediated signaling cascade responsible for hepato-
cellular proliferation. Mol Cell Biol 27:4238–4247
Sheehan D, Meade G, Foley VM, Dowd CA (2001) Structure, func-tion and evolution of glutathione transferases: implications for classification of non-mammalian members of an ancient enzyme superfamily. Biochem J 360:1–16
Takagi S, Nakajima M, Mohri T, Yokoi T (2008) Post-transcrip-tional regulation of human pregnane X receptor by micro-RNA affects the expression of cytochrome P450 3A4. J Biol Chem 283:9674–9680
Takagi S, Nakajima M, Kida K, Yamaura Y, Fukami T, Yokoi T (2010) MicroRNAs regulate human hepatocyte nuclear factor 4 alpha modulating the expression of metabolic enzymes and cell cycle. J Biol Chem 285:4415–4422
Tirona RG, Kim RB (2005) Nuclear receptors and drug disposition gene regulation. J Pharm Sci 94:1169–1186
To KKW, Zhan Z, Litman T, Bates SE (2008) Regulation of ABCG2 expression at the 3′ untranslated region of its mRNA through modulation of transcript stability and protein translation by a putative microRNA in the S1 colon cancer cell line. Mol Cell Biol 28:5147–5161
Tsang J, Zhu J, Oudenaarden A V (2007) MicroRNA-mediated feed-back and feedforward loops are recurrent network motifs in mammals. Mol Cell 26:753–767
Tsuchiya Y, Nakajima M, Kyo S, Kanaya T, Inoue M, Yokoi T (2004) Human CYP1B1 is regulated by estradiol via estrogen receptor.
Cancer Res 64:3119–3125
Tsuchiya Y, Nakajima M, Takagi S, Taniya T, Yokoi T (2006) Micro-RNA regulates the expression of human cytochrome P450 1B1.
Cancer Res 66:9090–9098
Tyagi S, Gupta P, Saini AS, Kaushal C, Sharma S (2011) The peroxi-some proliferator-activated receptor: a family of nuclear receptors role in various diseases. J Adv Pharm Technol Res 2:236–240 Tzur G, Israel A, Levy A, Benjamin H, Meiri E, Shufaro Y, Meir K, Khvalevsky E, Spector Y, Rojansky N, Bentwich Z, Reubinoff BE, Galun E, Chua G (2009) Comprehensive gene and micro-RNA expression profiling reveals a role for microRNAs in human liver development. PLoS One 4:e7511
Vreugdenhil E, Verissimo CSL, Mariman R, Kamphorst JT, Bar-bosa JS, Zweers T, Champagne DL, Schouten T, Meijer OC, Ron de Kloet E, Fitzsimons CP (2008) MicroRNA 18 and 124a down-regulate the glucocorticoid receptor: implications
1 3
for glucocorticoid responsiveness in the brain. Endocrinology 150:2220–2228
Wang Z, Burke PA (2013) The role of microRNAs in hepatocyte nuclear factor-4alpha expression and transactivation. Biochim Biophys Acta 1829:436–442
Wang K, Chen S, Xie W, Wan YJY (2008) Retinoids induce cytochrome P450 3A4 through RXR/VDR-mediated pathway.
Biochem Pharmacol 75:2204–2213
Wang L, Oberg AL, Asmann YW, Sicotte H, McDonnell SK, Riska SM, Liu W, Steer CJ, Subramanian S, Cunningham JM, Cerhan JR, Thibodeau SN, Zhang B (2009) Genome-wide transcriptional profiling reveals microRNA-correlated genes and biological pro-cesses in human lymphoblastoid cell lines. PLoS One 4:e5878 Wang SM, Sun LL, Zeng WX, Wu WS, Zhang GL (2014) Effects of
a microRNA binding site polymorphism in SLC19A1 on metho-
trexate concentrations in Chinese children with acute lympho-blastic leukemia. Med Oncol 31:62
Wei R, Yang F, Urban TJ, Li L, Chalasani N, Flockhart DA, Liu W (2012) Impact of the interaction between 3′-UTR SNPs and microRNA on the expression of human xenobiotic metabolism enzyme and transporter genes. Front Genet 3:248
Wei Z, Chen M, Zhang Y, Wang X, Jiang S, Wang Y, Wu X, Qin S, He L, Zhang L, Xing Q, Wallace GR (2013) No correlation of hsa-miR-148a with expression of PXR or CYP3A4 in human livers from Chinese Han population. PLoS One 8:e59141
Westholm JO, Lai EC (2011) Mirtrons microRNA biogenesis via splicing. Biochimie 93:1897–1904
Xiong J, Yu D, Wei N, Fu H, Cai T, Huang Y, Wu C, Zheng X, Du Q, Lin D, Liang Z (2010) An estrogen receptor alpha suppressor, microRNA-22, is downregulated in estrogen receptor alpha-posi-tive human breast cancer cell lines and clinical samples. FEBS J 277:1684–1694Yang Z, Wang L (2011) Regulation of microRNA expression and function by nuclear receptor signaling. Cell Biosci 1:31
Yokoi T, Nakajima M (2011) Toxicological implications of modula-tion of gene expression by microRNAs. Toxicol Sci 123:1–14 Yokoi T, Nakajima M (2013) microRNAs as mediators of drug toxic-ity. Annu Rev Pharmacol Toxicol 53:377–400
Yu AM (2009) Role of microRNAs in the regulation of drug metabolism and disposition. Expert Opin Drug Metab Toxicol 5:1513–1528
Zanger UM, Schwab M (2013) Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation. Pharmacol Ther 138:103–141 Zhang W, Dolan ME (2010) The emerging role of microRNAs in drug responses. Curr Opin Mol Ther 12:695–702
Zhang R, Su B (2009) Small but influential the role of microRNAs on gene regulatory network and 3′ UTR evolution. J Genet Genom-ics 36:1–6
Zhang SY, Surapureddi S, Coulter S, Ferguson SS, Goldstein JA (2012) Human CYP2C8 is post-transcriptionally regulated by microRNAs 103 and 107 in human liver. Mol Pharmacol 82:529–540
Zhao JJ, Lin J, Yang H, Kong W, He L, Ma X, Coppola D, Cheng JQ (2008) MicroRNA-221/222 negatively regulates estrogen recep-tor alpha and is associated with tamoxifen resistance in breast cancer. J Biol Chem 283:31079–31086
Zhu H, Wu H, Liu X, Evans BR, Medina DJ, Liu CG, Yang JM (2008) Role of MicroRNA miR-27a and miR-451 in the regulation of MDR 1/P-glycoprotein expression in human cancer cells. Bio-chem Pharmacol 76:582–588
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