PIWI-interacting RNA-23210 protects against acetaminophen-induced liver injury by targeting HNF1A and HNF4A

Acetaminophen (APAP) overdose is one of the leading causes of acute liver failure in the US and other developed countries, the molecular mechanisms of APAP-induced hepatotoxicity remain speculative. PIWI-interacting RNAs (piRNAs), a novel class of small non-coding RNAs, have been identified as epigenetic regulators of transposon silencing, mRNA deadenylation, and elimination. However, the functional role of piRNAs in APAP-induced liver injury remains unclear. In the current study, the piRNA profiles were constructed in HepaRG cells after APAP exposure, and the roles of piR-23210 in regulating nuclear receptors (NRs) expression, metabolizing enzymes expression, and consequently APAP-induced liver injury were systematically investigated. As a result, 57 upregulated piRNAs were identified after APAP exposure, indicating the stress-response characteristic of piRNA molecules. Subsequent in vitro and in vivo experiments proved that piR-23210 is a novel self-protective molecule that targets HNF1A and HNF4A transcripts by interacting with RNA binding protein Nucleolin (NCL), suppresses downstream CYPs (CYP2E1, CYP3A4, and CYP1A2) expression, and protects against APAP-induced liver injury. In conclusion, our findings provided new mechanistic clues revealing potential protective role of a piRNA against the hepatoxicity of APAP.

Silencing of long non-coding RNA XIST represses gastric cancer progression through blocking NFκB pathway via inhibiting HNF4A-mediated transcription of EPHA1

Gastric cancer (GC) is a common cancer and a leading cause of cancer-related deaths worldwide. Recent studies have supported the important role of long non-coding RNAs (lncRNAs) in GC progression. This study identified functional significance of X inactive specific transcript (XIST) in GC. The expression of XIST and EPHA1 in GC tissues and cells was measured. Then, dual luciferase reporter gene assay, RNA immunoprecipitation (RIP) assay and Chromatin Immunoprecipitation (ChIP) assay were performed to explore the interaction among XIST, EPHA1 and HNF4A. The effects of XIST on GG progression were evaluated by determining expression of proliferation- and invasion-related proteins (Ki67, PCNA, MMP-2, and MMP-9). Further, the functional role of XIST in GC with the involvement of NFκB pathway was also analyzed. Subsequently, the tumor growth in nude mice was evaluated. High expression of XIST and EPHA1 was observed in GC. XIST elevated EPHA1 expression by recruiting HNF4A. In addition, silencing of XIST inhibited GC progression in vitro and in vivo. Overexpressed XIST and EPHA1 yielded a reversed effect on cell proliferation and invasion. SN50 treatment (inhibitor of NFκB pathway) counteracted the promotive effect on GC cell proliferation and invasion mediated by XIST. The present study unveils that XIST increases the enrichment of HNF4A in the promoter region of EPHA1, thus promoting the deterioration of GC.

Andrographolide modulates HNF4α activity imparting on hepatic metabolism

Hepatic nuclear factor 4 alpha (HNF4α) drives the expression of apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTP) and phospholipase A2 G12B (PLA2G12B), governing hepatic very-low-density lipoprotein (VLDL) production and secretion. Andrographolide (AP) is a major constituent isolated from Andrographis paniculata. We found that AP can disrupt the interaction between HNF4α and its coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α). Virtual docking and mutational analysis indicated that arginine 235 of HNF4α is essential for binding to AP. As a consequence of antagonizing the activity of HNF4α, AP suppresses the expression of ApoB, MTP and PLA2G12B and reduces the rate of hepatic VLDL secretion in vivo. AP additionally reduced gluconeogenesis via down-regulating the expression of HNF4α target genes phosphoenolpyruvate carboxykinase (Pepck) and glucose-6-phosphatase (G6pc). Collectively, our results suggest that AP affects liver function via modulating the transcriptional activity of HNF4α.

Repression of hepatocyte nuclear factor 4 alpha by AP-1 underlies dyslipidemia associated with retinoic acid

All-trans retinoic acid (atRA) is used to treat certain cancers and dermatologic diseases. A common adverse effect of atRA is hypercholesterolemia; cytochrome P450 (CYP) 7A repression is suggested as a driver. However, the underlying molecular mechanisms remain unclear. We investigated CYP7A1 expression in the presence of atRA in human hepatocytes and hepatic cell lines. In HepaRG cells, atRA increased cholesterol levels dose-dependently alongside dramatic decreases in CYP7A1 expression. Lentiviral-mediated CYP7A1 overexpression reversed atRA-induced cholesterol accumulation, suggesting that CYP7A1 repression mediated cholesterol accumulation. In CYP7A1 promoter reporter assays and gene-knockdown studies, altered binding of hepatocyte nuclear factor 4 α (HNF4α) to the proximal promoter was essential for atRA-mediated CYP7A1 repression. Pharmacologic inhibition of c-Jun N-terminal kinase (JNK) and ERK pathways attenuated atRA-mediated CYP7A1 repression and cholesterol accumulation. Overexpression of AP-1 (c-Jun/c-Fos), a downstream target of JNK and ERK, repressed CYP7A1 expression. In DNA pull-down and chromatin immunoprecipitation assays, AP-1 exhibited sequence-specific binding to the proximal CYP7A1 promoter region overlapping the HNF4α binding site, and atRA increased AP-1 but decreased HNF4α recruitment to the promoter. Collectively, these results indicate that atRA activates JNK and ERK pathways and the downstream target AP-1 represses HNF4α transactivation of the CYP7A1 promoter, potentially responsible for hypercholesterolemia.

Interleukin-35 stimulates hepatitis B virus transcription and replication by targeting transcription factor HNF4α

Hepatitis B virus (HBV) infection is a major health problem worldwide. Interleukin-35 (IL-35) is a definite immunosuppressive cytokine belonging to the IL-12 family. Nevertheless, the role of IL-35 in HBV replication remains elusive. In this study, we found that the level of HBV DNA replicative intermediates detected by qPCR and Southern blotting analysis was significantly increased by rhIL-35 in a dose-dependent manner. Moreover, HBV 3.5 kb mRNA levels were up-regulated by rhIL-35. The HBV core protein level as well as the HBsAg and HBeAg secretion levels were also increased by rhIL-35. Moreover, a mechanistic study demonstrated that IL-35 promoted HBV replication by enhancing the HBV core promoter activity. Importantly, hepatocyte nuclear factor 4α (HNF4α) was probably the target of IL-35. Mutation of the HNF4α-binding site on HBV core promoter or silencing HNF4α abolished the enhancement of HBV replication induced by IL-35. Finally, rhIL-35 was able to increase HBV replication in HBV transgenic mice. Taken together, our findings demonstrated that IL-35 has a novel role in HBV replication.

Bisphenol A Disrupts HNF4α-Regulated Gene Networks Linking to Prostate Preneoplasia and Immune Disruption in Noble Rats

Exposure of humans to bisphenol A (BPA) is widespread and continuous. The effects of protracted exposure to BPA on the adult prostate have not been studied. We subjected Noble rats to 32 weeks of BPA (low or high dose) or 17β-estradiol (E2) in conjunction with T replenishment. T treatment alone or untreated groups were used as controls. Circulating T levels were maintained within the physiological range in all treatment groups, whereas the levels of free BPA were elevated in the groups treated with T+low BPA (1.06 ± 0.05 ng/mL, P < .05) and T+high BPA (10.37 ± 0.43 ng/mL, P < .01) when compared with those in both controls (0.1 ± 0.05 ng/mL). Prostatic hyperplasia, low-grade prostatic intraepithelial neoplasia (PIN), and marked infiltration of CD4+ and CD8+ T cells into the PIN epithelium (P < .05) were observed in the lateral prostates (LPs) of T+low/high BPA-treated rats. In contrast, only hyperplasia and high-grade PIN, but no aberrant immune responses, were found in the T+E2-treated LPs. Genome-wide transcriptome analysis in LPs identified differential changes between T+BPA vs T+E2 treatment. Expression of multiple genes in the regulatory network controlled by hepatocyte nuclear factor 4α was perturbed by the T+BPA but not by the T+E2 exposure. Collectively these findings suggest that the adult rat prostate, under a physiologically relevant T environment, is susceptible to BPA-induced transcriptomic reprogramming, immune disruption, and aberrant growth dysregulation in a manner distinct from those caused by E2. They are more relevant to our recent report of higher urinary levels BPA found in patients with prostate cancer than those with benign disease.

Impairment of hepatic nuclear factor-4α binding to the Stim1 promoter contributes to high glucose-induced upregulation of STIM1 expression in glomerular mesangial cells

The present study was carried out to investigate if hepatic nuclear factor (HNF)4α contributed to the high glucose-induced increase in stromal interacting molecule (STIM)1 protein abundance in glomerular mesangial cells (MCs). Western blot and immunofluorescence experiments showed HNF4α expression in MCs. Knockdown of HNF4α using a small interfering RNA approach significantly increased mRNA expression levels of both STIM1 and Orai1 and protein expression levels of STIM1 in cultured human MCs. Consistently, overexpression of HNF4α reduced expressed STIM1 protein expression in human embryonic kidney-293 cells. Furthermore, high glucose treatment did not significantly change the abundance of HNF4α protein in MCs but significantly attenuated HNF4α binding activity to the Stim1 promoter. Moreover, knockdown of HNF4α significantly augmented store-operated Ca(2+) entry, which is known to be gated by STIM1 and has recently been found to be antifibrotic in MCs. In agreement with those results, knockdown of HNF4α significantly attenuated the fibrotic response of high glucose. These results suggest that HNF4α negatively regulates STIM1 transcription in MCs. High glucose increases STIM1 expression levels by impairing HNF4α binding activity to the Stim1 promoter, which subsequently releases Stim1 transcription from HNF4α repression. Since the STIM1-gated store-operated Ca(2+) entry pathway in MCs has an antifibrotic effect, inhibition of HNF4α in MCs might be a potential therapeutic option for diabetic kidney disease.

HNF-4α-mediated hepatocyte differentiation is blocked by mutant IDH

Mutant IDH prevents hepatocyte differentiation and promotes tumorigenesis via HNF-4α inhibition.

Hepatocyte nuclear factors 4α and 1α regulate kidney developmental expression of drug-metabolizing enzymes and drug transporters

The transcriptional regulation of drug-metabolizing enzymes and transporters (here collectively referred to as DMEs) in the developing proximal tubule (PT) is not well understood. As in the liver, DME regulation in the PT may be mediated through nuclear receptors, which are thought to "sense" deviations from homeostasis by being activated by ligands, some of which are handled by DMEs, including drug transporters. Systems analysis of transcriptomic data during kidney development predicted a set of upstream transcription factors, including hepatocyte nuclear factor 4α (Hnf4a) and Hnf1a, as well as Nr3c1 (Gr), Nfe2l2 (Nrf2), peroxisome proliferator-activated receptor α (Pparα), and Tp53. Motif analysis of cis-regulatory enhancers further suggested that Hnf4a and Hnf1a are the main transcriptional regulators of DMEs in the PT. Available expression data from tissue-specific Hnf4a knockout tissues revealed that distinct subsets of DMEs were regulated by Hnf4a in a tissue-specific manner. Chromatin immunoprecipitation combined with massively parallel DNA sequencing was performed to characterize the PT-specific binding sites of Hnf4a in rat kidneys at three developmental stages (prenatal, immature, adult), which further supported a major role for Hnf4a in regulating PT gene expression, including DMEs. In ex vivo kidney organ culture, an antagonist of Hnf4a (but not a similar inactive compound) led to predicted changes in DME expression, including among others Fmo1, Cyp2d2, Cyp2d4, Nqo2, as well as organic cation transporters and organic anion transporters Slc22a1 (Oct1), Slc22a2 (Oct2), Slc22a6 (Oat1), Slc22a8 (Oat3), and Slc47a1 (Mate1). Conversely, overexpression of Hnf1a and Hnf4a in primary mouse embryonic fibroblasts, sometimes considered a surrogate for mesenchymal stem cells, induced expression of several of these proximal tubule DMEs, as well as epithelial markers and a PT-enriched brush border marker Ggt1. These cells had organic anion transporter function. Taken together, the data strongly supports a critical role for HNF4a and Hnf1a in the tissue-specific regulation of drug handling and differentiation toward a PT-like cellular identity. We discuss our data in the context of the "remote sensing and signaling hypothesis" (Ahn and Nigam, 2009; Wu et al., 2011).

Two novel cis-elements involved in hepatocyte nuclear factor 4α regulation of acyl-coenzyme A:cholesterol acyltransferase 2 expression

Acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) is important for cholesterol ester synthesis and secretion. A previous study revealed that ACAT2 gene promoter activity was upregulated by hepatocyte nuclear factor 4α (HNF4α) through two sites around -247 and -311 of ACAT2 gene promoter. Here, we identified two novel cis-elements, site I (-1006 to -898) and site II (-38 to -29), which are important for HNF4α effect. In HepG2 cells, mutation of site I decreased ACAT2 gene promoter activity to one-fifth of that of the wild type, while mutation of site II reduced promoter activity to less than one-tenth of that of the wild type. In 293T cells, mutation of these two cis-elements profoundly impaired the HNF4α induction effect. When either of these two elements was inserted into pGL3-promoter, HNF4α induced promoter activity through the inserted element, while mutation of the element impaired HNF4α induction effect. In electrophoretic mobility shift assay and chromatin immunoprecipitation experiment, HNF4α bound to these two elements. Thus, the two cis-elements are important for HNF4α effect on ACAT2 gene transcription. We also showed that HNF4α positively regulates ACAT2 gene expression at mRNA level. Overexpression of HNF4α increased ACAT2 expression, whereas knockdown of HNF4α decreased ACAT2 expression. Peroxisome proliferator-activated receptor gamma coactivator 1α (PCG1α), a coactivator of HNF4α, increased ACAT2 expression, while small heterodimer partner (SHP), a corepressor of HNF4α, decreased ACAT2 expression. These results provide more insights into transcriptional regulation of ACAT2 expression.

HNF4alpha dysfunction as a molecular rational for cyclosporine induced hypertension

Induction of tolerance against grafted organs is achieved by the immunosuppressive agent cyclosporine, a prominent member of the calcineurin inhibitors. Unfortunately, its lifetime use is associated with hypertension and nephrotoxicity. Several mechanism for cyclosporine induced hypertension have been proposed, i.e. activation of the sympathetic nervous system, endothelin-mediated systemic vasoconstriction, impaired vasodilatation secondary to reduction in prostaglandin and nitric oxide, altered cytosolic calcium translocation, and activation of the renin-angiotensin system (RAS). In this regard the molecular basis for undue RAS activation and an increased signaling of the vasoactive oligopeptide angiotensin II (AngII) remain elusive. Notably, angiotensinogen (AGT) is the precursor of AngII and transcriptional regulation of AGT is controlled by the hepatic nuclear factor HNF4alpha. To better understand the molecular events associated with cyclosporine induced hypertension, we investigated the effect of cyclosporine on HNF4alpha expression and activity and searched for novel HNF4alpha target genes among members of the RAS cascade. Using bioinformatic algorithm and EMSA bandshift assays we identified angiotensin II receptor type 1 (AGTR1), angiotensin I converting enzyme (ACE), and angiotensin I converting enzyme 2 (ACE2) as genes targeted by HNF4alpha. Notably, cyclosporine represses HNF4alpha gene and protein expression and its DNA-binding activity at consensus sequences to AGT, AGTR1, ACE, and ACE2. Consequently, the gene expression of AGT, AGTR1, and ACE2 was significantly reduced as evidenced by quantitative real-time RT-PCR. While RAS is composed of a sophisticated interplay between multiple factors we propose a decrease of ACE2 to enforce AngII signaling via AGTR1 to ultimately result in vasoconstriction and hypertension. Taken collectively we demonstrate cyclosporine to repress HNF4alpha activity through calcineurin inhibitor mediated inhibition of nuclear factor of activation of T-cells (NFAT) which in turn represses HNF4alpha that leads to a disturbed balance of RAS.

Germ line transmission and expression of an RNAi cassette in mice generated by a lentiviral vector system

We have used a lentiviral delivery system (LentiLox3.7) to generate transgenic mice harbouring RNA interference (RNAi) against the hepatocyte nuclear factor 4 gamma (HNF4gamma). HNF4gamma is a nuclear receptor with unknown function. Our analyses performed on founder (F(0)) and first generation (F(1)) mice revealed mosaicism in F(0) founders and a low efficiency of transgenesis (6%) in F(1) mice. These data, together with the observation of multiple silenced transgenes, do not favour the use of LentiLox3.7 lentivirus for transgenesis. Despite the low efficiency of transgenesis, we achieved a tissue-dependent knockdown of HNF4gamma expression in some mice.

Underexpressed Coactivators PGC1α AND SRC1 Impair Hepatocyte Nuclear Factor 4α Function and Promote Dedifferentiation in Human Hepatoma Cells

Hepatocyte nuclear factor 4alpha (HNF4alpha) plays critical roles during liver development and in the transcriptional regulation of many hepatic genes in adult liver. Here we have demonstrated that in human hepatoma HepG2 cells, HNF4alpha is expressed at levels as high as in human liver but its activity on target genes is very low or absent. We have discovered that the low expression of key coactivators (PGC1alpha, SRC1, SRC2, and PCAF) might account for the lack of function of HNF4alpha in HepG2 cells. Among them, PGC1alpha and SRC1 are the two most important HNF4alpha coactivators as revealed by reporter assays with an Apo-CIII promoter construct. Moreover, the expression of these two coactivators was found to be down-regulated in all human hepatomas investigated. Overexpression of SRC1 and PGC1alpha by recombinant adenoviruses led to a significant up-regulation of well characterized HNF4alpha-dependent genes (ApoCIII, ApoAV, PEPCK, AldoB, OTC, and CYP7A1) and forced HepG2 cells toward a more differentiated phenotype as demonstrated by increased ureogenic rate. The positive effect of PGC1alpha was seen to be dependent on HNF4alpha. Finally, insulin treatment of human hepatocytes and HepG2 cells caused repression of PGC1alpha and a concomitant down-regulation of ApoCIII, PEPCK, AldoB, and OTC. Altogether, our results suggest that SRC1, and notably PGC1alpha, are key coactivators for the proper function of HNF4alpha in human liver and for an integrative control of multiple hepatic genes involved in metabolism and homeostasis. The down-regulation of key HNF4alpha coactivators could be a determinant factor for the dedifferentiation of human hepatomas.

Inhibition of hepatocyte nuclear factor 4 transcriptional activity by the nuclear factor kappaB pathway

HNF-4 (hepatocyte nuclear factor 4) is a key regulator of liver-specific gene expression in mammals. We have shown previously that the activity of the human APOC3 (apolipoprotein C-III) promoter is positively regulated by the anti-inflammatory cytokine TGFbeta (transforming growth factor beta) and its effectors Smad3 (similar to mothers against decapentaplegic 3) and Smad4 proteins via physical and functional interactions between Smads and HNF-4. We now show that the pro-inflammatory cytokine TNFalpha (tumour necrosis factor alpha) antagonizes TGFbeta for the regulation of APOC3 gene expression in hepatocytes. TNFalpha was a strong inhibitor of the activity of apolipoprotein promoters that harbour HNF-4 binding sites and this inhibition required HNF-4. Using specific inhibitors of TNFalpha-induced signalling pathways, it was shown that inhibition of the APOC3 promoter by TNFalpha involved NF-kappaB (nuclear factor kappaB). Latent membrane protein 1 of the Epstein-Barr virus, which is an established potent activator of NF-kappaB as well as wild-type forms of various NF-kappaB signalling mediators, also inhibited strongly the APOC3 promoter and the transactivation function of HNF-4. TNFalpha had no effect on the stability or the nuclear localization of HNF-4 in HepG2 cells, but inhibited the binding of HNF-4 to the proximal APOC3 HRE (hormone response element). Using the yeast-transactivator-GAL4 system, we showed that both AF-1 and AF-2 (activation functions 1 and 2) of HNF-4 are inhibited by TNFalpha and that this inhibition was abolished by overexpression of different HNF-4 co-activators, including PGC-1 (peroxisome-proliferator-activated-receptor-gamma co-activator 1), CBP [CREB (cAMP-response-element-binding protein) binding protein] and SRC3 (steroid receptor co-activator 3). In summary, our findings indicate that TNFalpha, or other factors that trigger an NF-kappaB response in hepatic cells, inhibit the transcriptional activity of the APOC3 and other HNF-4-dependent promoters and that this inhibition could be accounted for by a decrease in DNA binding and the down-regulation of the transactivation potential of the AF-1 and AF-2 domains of HNF-4.

Transcriptional regulation of the human hepatic lipase (LIPC) gene promoter

Hepatic lipase (HL) plays a key role in the metabolism of plasma lipoproteins, and its level of activity requires tight regulation, given the association of both low and high levels with atherosclerosis and coronary artery disease. However, little is known about the factors responsible for HL expression. Here, we report that the human hepatic lipase gene (LIPC) promoter is regulated by hepatocyte nuclear factor 4alpha (HNF4alpha), peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), apolipoprotein A-I regulatory protein-1 (ARP-1), and hepatocyte nuclear factor 1alpha (HNF1alpha). Reporter analysis showed that HNF4alpha directly regulates the LIPC promoter via two newly identified direct repeat elements, DR1 and DR4. PGC-1alpha is capable of stimulating the HNF4alpha-dependent transactivation of the LIPC promoter. ARP-1 displaces HNF4alpha from the DR1 site and blocks its ability to activate the LIPC promoter. Induction by HNF1alpha requires the HNF1 binding site and upon cotransfection with HNF4alpha leads to an additive effect. In addition, the in vivo relevance of HNF4alpha in LIPC expression is shown by the ability of the HNF4alpha antagonist Medica 16 to repress endogenous LIPC mRNA expression. Furthermore, disruption of Hnf4alpha in mice prevents the expression of HL mRNA in liver. The overall effect these transcription factors have on HL expression will ultimately depend on the interplay between these various factors and their relative intracellular concentrations.

Hepatocyte Nuclear Factor-4α Regulates the Human Apolipoprotein AV Gene: Identification of a Novel Response Element and Involvement in the Control by Peroxisome Proliferator-Activated Receptor-γ Coactivator-1α, AMP-Activated Protein Kinase, and Mitogen-Activated Protein Kinase Pathway

The recently discovered apolipoprotein AV (apoAV) gene has been reported to be a key player in modulating plasma triglyceride levels. Here we identify the hepatocyte nuclear factor-4alpha (HNF-4alpha) as a novel regulator of human apoAV gene. Inhibition of HNF-4alpha expression by small interfering RNA resulted in down-regulation of apoAV. Deletion, mutagenesis, and binding assays revealed that HNF-4alpha directly regulates human apoAV promoter through DR1 [a direct repeat separated by one nucleotide (nt)], and via a novel element for HNF-4alpha consisting of an inverted repeat separated by 8 nt (IR8). In addition, we show that the coactivator peroxisome proliferator-activated receptor-gamma coactivator-1alpha was capable of stimulating the HNF-4alpha-dependent transactivation of apoAV promoter. Furthermore, analyses in human hepatic cells demonstrated that AMP-activated protein kinase (AMPK) and the MAPK signaling pathway regulate human apoAV expression and suggested that this regulation may be mediated, at least in part, by changes in HNF-4alpha. Intriguingly, EMSAs and mice with a liver-specific disruption of the HNF-4alpha gene revealed a species-distinct regulation of apoAV by HNF-4alpha, which resembles that of a subset of HNF-4alpha target genes. Taken together, our data provide new insights into the binding properties and the modulation of HNF-4alpha and underscore the role of HNF-4alpha in regulating triglyceride metabolism.