Expression of microRNA-155 precursor in peripheral blood mononuclear cells from Hepatitis C patients after antiviral treatment

Comprehensive profiling and characterization of cellular microRNAs in response to coxsackievirus A10 infection in bronchial epithelial cells

Coxsackievirus A10 (CV-A10), the causative agent of hand, foot, and mouth disease (HFMD), caused a series of outbreaks in recent years and often leads to neurological impairment, but a clear understanding of the disease pathogenesis and host response remains elusive. Cellular microRNAs (miRNAs), a large family of non-coding RNA molecules, have been reported to be key regulators in viral pathogenesis and virus-host interactions. However, the role of host cellular miRNAs defensing against CV-A10 infection is still obscure. To address this issue, we systematically analyzed miRNA expression profiles in CV-A10-infected 16HBE cells by high-throughput sequencing methods in this study. It allowed us to successfully identify 312 and 278 miRNAs with differential expression at 12 h and 24 h post-CV-A10 infection, respectively. Among these, 4 miRNAs and their target genes were analyzed by RT-qPCR, which confirmed the sequencing data. Gene target prediction and enrichment analysis revealed that the predicted targets of these miRNAs were significantly enriched in numerous cellular processes, especially in regulation of basic physical process, host immune response and neurological impairment. And the integrated network was built to further indicate the regulatory roles of miRNAs in host-CV-A10 interactions. Consequently, our findings could provide a beneficial basis for further studies on the regulatory roles of miRNAs relevant to the host immune responses and neuropathogenesis caused by CV-A10 infection.

Dairy consumption and hepatocellular carcinoma risk

This review provides epidemiological and translational evidence for milk and dairy intake as critical risk factors in the pathogenesis of hepatocellular carcinoma (HCC). Large epidemiological studies in the United States and Europe identified total dairy, milk and butter intake with the exception of yogurt as independent risk factors of HCC. Enhanced activity of mechanistic target of rapamycin complex 1 (mTORC1) is a hallmark of HCC promoted by hepatitis B virus (HBV) and hepatitis C virus (HCV). mTORC1 is also activated by milk protein-induced synthesis of hepatic insulin-like growth factor 1 (IGF-1) and branched-chain amino acids (BCAAs), abundant constituents of milk proteins. Over the last decades, annual milk protein-derived BCAA intake increased 3 to 5 times in Western countries. In synergy with HBV- and HCV-induced secretion of hepatocyte-derived exosomes enriched in microRNA-21 (miR-21) and miR-155, exosomes of pasteurized milk as well deliver these oncogenic miRs to the human liver. Thus, milk exosomes operate in a comparable fashion to HBV- or HCV- induced exosomes. Milk-derived miRs synergistically enhance IGF-1-AKT-mTORC1 signaling and promote mTORC1-dependent translation, a meaningful mechanism during the postnatal growth phase, but a long-term adverse effect promoting the development of HCC. Both, dietary BCAA abundance combined with oncogenic milk exosome exposure persistently overstimulate hepatic mTORC1. Chronic alcohol consumption as well as type 2 diabetes mellitus (T2DM), two HCC-related conditions, increase BCAA plasma levels. In HCC, mTORC1 is further hyperactivated due to RAB1 mutations as well as impaired hepatic BCAA catabolism, a metabolic hallmark of T2DM. The potential HCC-preventive effect of yogurt may be caused by lactobacilli-mediated degradation of BCAAs, inhibition of branched-chain α-ketoacid dehydrogenase kinase via production of intestinal medium-chain fatty acids as well as degradation of milk exosomes including their oncogenic miRs. A restriction of total animal protein intake realized by a vegetable-based diet is recommended for the prevention of HCC.

Pegylated interferon-α inhibits the proliferation of hepatocellular carcinoma cells by downregulating miR-155

INTRODUCTION AND AIMS

Interferon-α (IFN) has shown potential benefits in patients with hepatocellular carcinoma (HCC), and these effects may be mediated by inhibiting cancer cell proliferation. However, the detailed mechanisms underlying the anti-proliferative effects of IFN remain obscure. In this study, we evaluate the role of the novel oncogenic microRNA (miRNA) miR-155 in the anti-proliferative effects of pegylated interferon-α (PEG-IFN) on HCC cells.

METHODS

The effects of PEG-IFN on HepG2 cell proliferation, migration and invasion were determined using the MTT assay, flow cytometry analysis and the Transwell assay, respectively. Reverse transcription quantitative polymerase chain reaction was used to analyze miR-155 expression. The levels of proteins involved in Wnt/β-catenin signal transduction were determined by western blot analysis and immunofluorescence staining. Mimics of miR-155 were transfected into HepG2 cells to assess the role of miR-155 in the PEG-IFN-induced anti-proliferative effect.

RESULTS

PEG-IFN significantly inhibited the proliferation, migration and invasion of HepG2 cells in a dose-dependent manner by inhibiting cell cycle progression. In parallel with reduced cell proliferation, migration and invasion, miR-155 was efficiently downregulated by PEG-IFN in a dose-dependent manner. Moreover, the transfection of miR-155 decreased the inhibitory effect of PEG-IFN on HepG2cell proliferation, migration and invasion, as well as the downregulation of proteins in the Wnt/β-catenin pathway.

CONCLUSIONS

The anti-proliferative effects of PEG-IFN on HCC are at least partially attributable to the downregulation of miR-155.

miR-155 effectively induces apoptosis in K562 Philadelphia positive cell line through upregulation of p27kip1

Introduction: Chronic myelogenous leukemia (CML) is a myeloproliferative disorder caused by the Philadelphia chromosome translocation, at (9; 22), which results in BCR-ABL fusion tyrosine kinase oncoprotein. This fusion induces down-regulation of miR-155. Upregulation of miR-155 can influence cell fate via the effect on p27kip1 and apoptosis. The aim of this study was to induce apoptosis in K562 CML cell line by overexpression of miR-155.

Methods: The K562 cell line was transfected with pLenti-III-pre mir155-GFP constructs through electroporation. Then, overexpression of miR-155 as well as the expression level of p27kip1 and c-Myc was analyzed by quantitative PCR (qPCR). The level of p27 (Kip1) protein expression was measured by Western blot and the Annexin V method was carried out to investigate apoptosis.

Results: Flow cytometric analysis results of K562 cells transfected with pLenti-III-pre mir155-GFP construct showed a significant increase in cell apoptosis. Gene expression and protein level of p27kip1 were upregulated. However, there was no change in c-Myc expression profile.

Conclusion: miR-155 could be a promising approach to aid in the treatment of CML. However, further studies are required in this respect.

The impact of chronic hepatitis C infection on cholesterol metabolism in PBMCs is associated with microRNA-146a expression

Chronic hepatitis C (CHC) infection is known to induce important changes in host cholesterol metabolism. MicroRNAs (miRNAs) regulate the expression of many genes and, in consequence, control various processes, including human metabolism and response to viral infection. Recently, the alteration of the immune-associated miR-146a, which is abundantly present in peripheral blood mononuclear cells (PBMCs), was found in some viral infections. The study aimed to analyse the influence of hepatitis C virus (HCV) infection on miR-146a expression in PBMCs in vivo and in vitro, as well as to assess the possible impact of miR-146a alteration on the intracellular cholesterol level in PBMCs. Blood samples collected from 42 healthy donors and 72 CHC patients were the source of materials. HCV RNA, intracellular cholesterol level and miR-146a expression were determined in PBMCs, as well as HCV genotype and interferon (IFN)α concentration in sera. The influence of miR-146a inhibition on cholesterol expression in PBMCs was analysed in vitro after transient cell transfections with mirVana™ anti-miR-146a Inhibitor. Our data demonstrated an alteration of miR-146a and intracellular cholesterol expression in PBMCs and of IFNα concentration in sera of genotype 1, HCV-infected patients compared to the healthy donors. Also, in cultured PBMCs, miR-146a expression and intracellular cholesterol level were significantly decreased in CHC patients compared to the healthy donors. In vitro blockage of miR-146a expression in PBMCs of CHC patients greatly impaired intracellular cholesterol expression. In these conditions, miR-146a expression was positively correlated with the intracellular cholesterol level. These results suggest that genotype 1 HCV infection may alter miR-146a expression in PBMCs and, consequently, contribute to the observed dysregulation of cholesterol synthesis.

HCV-induced miR146a controls SOCS1/STAT3 and cytokine expression in monocytes to promote regulatory T-cell development

Host innate and adaptive immune responses must be tightly regulated by an intricate balance between positive and negative signals to ensure their appropriate onset and termination while fighting pathogens and avoiding autoimmunity; persistent pathogens may usurp these regulatory machineries to dampen host immune responses for their persistence in vivo. Here, we demonstrate that miR146a is up-regulated in monocytes from hepatitis C virus (HCV)-infected individuals compared to control subjects. Interestingly, miR146a expression in monocytes without HCV infection increased, whereas its level in monocytes with HCV infection decreased, following Toll-like receptor (TLR) stimulation. This miR146a induction by HCV infection and differential response to TLR stimulation were recapitulated in vitro in monocytes co-cultured with hepatocytes with or without HCV infection. Importantly, inhibition of miR146a in monocytes from HCV-infected patients led to a decrease in IL-23, IL-10 and TGF-β expressions through the induction of suppressor of cytokine signalling 1 (SOCS1) and the inhibition of signal transducer and activator transcription 3 (STAT3), and this subsequently resulted in a decrease in regulatory T cells (Tregs) accumulated during HCV infection. These results suggest that miR146a may regulate SOCS1/STAT3 and cytokine signalling in monocytes, directing T-cell differentiation and balancing immune clearance and immune injury during chronic viral infection.

Role of microRNAs in inflammation-associated liver cancer

Liver cancer, primarily hepatocellular carcinoma (HCC), is a major cause of cancer-related death worldwide. HCC is a suitable model of inflammation-induced cancer because more than 90% of HCC cases are caused by liver damage and chronic inflammation. Several inflammatory response pathways, such as NF-κB and JAK/STAT3 signaling pathways, play roles in the crosstalk between inflammation and HCC. MicroRNAs (miRNAs) are evolutionarily conserved, short endogenous, non-coding single-stranded RNAs that are involved in various biological and pathological processes by regulating gene expression and protein translation. Evidence showed that miRNAs play a pivotal role in hepatitis virus infection and serve as promoters or inhibitors of inflammatory response. Aberrant miRNA was observed during liver inflammation and HCC. Many dysregulated miRNAs modulate the initiation and progression of inflammation-induced HCC. This review summarizes the role and functions of miRNAs in inflammation-associated HCC, as well as the designed therapeutics targeting miRNAs to treat liver inflammation and HCC.

Clinical significance of intragraft miR-122 and -155 expression after liver transplantation

AIM

Recurrent hepatitis C (RHC) and acute cellular rejection (AR) remain critical problems following liver transplantation (LT) in hepatitis C virus (HCV) positive recipients because of the similar clinical features. Discrimination between these conditions can be problematic, and adjunctive biomarkers would be useful to discriminate these processes. The aim of our study was to investigate the possibility of the intragraft miR-122 and -155 expression as new biomarkers after LT.

METHODS

A total of 29 HCV positive recipients were enrolled in this study. Intragraft expressions of miR-122 and -155 were studied between RHC predominant (n = 17) and AR predominant cases (n = 12) using quantitative reverse transcription polymerase chain reaction. Furthermore, we investigated the correlations between these expression levels and clinical serum parameters.

RESULTS

Intragraft miR-122 expression had a good correlation with serum alkaline phosphatase (P = 0.02), but it was not correlated with the serum HCV viral load. The expression levels of miR-122 in the AR group were significantly higher than those in the RHC group (P = 0.0006) and, inversely, the expression levels of miR-155 in the AR group were significantly lower than those in the RHC group (P = 0.01).

CONCLUSION

Our study emphasizes a useful pattern of miR-122 and -155 as ancillary markers to discriminate AR predominant cases from RHC in HCV positive patients after LT.

An update on the role of miRNA-155 in pathogenic microbial infections

MicroRNAs (miRNAs) are evolutionarily conserved and naturally abundant molecules of single-stranded, non-coding RNA from ∼17 to 25 nucleotides long. MiRNAs act at post-transcriptional level either to suppress gene translation or to induce mRNA degradation, according to the degree of complementarity with their target sequences. MiR-155 is a typical representative of the miRNA family that plays a crucial role in cell differentiation and organism development. A number of studies have shown that miR-155 can not only regulate cell proliferation, apoptosis and lymphoma progression, but also plays an important part in various other physiological and pathological processes. For instance, it is involved in hematopoietic cell differentiation, cardiovascular disease, inflammation and immune responses. In recent years, the role of miR-155 in infectious diseases has attracted considerable attention. This review will highlight the participation of miR-155 in the responses to infections caused by different pathogens.

Expression signature of microRNA-155 in hepatitis C virus genotype 4 infection

Hepatits C virus (HCV) genotype 4 (GT4) shows low treatment response rates and discrepancies when compared to other genotypes. However, the reason underlying these discrepancies remains unclear due to the limited number of studies on GT4. microRNA-155 (miR-155) is a noteworthy example of a discrepancy in GT4, as it was found to be upregulated in genotypes 1, 2 and 3 HCV infection, but downregulated in GT4-HCV-infected peripheral blood mononuclear cells (PBMCs). The present study aimed to investigate the expression of miR-155 in PBMCs, serum and liver tissues of GT4-HCV-infected patients. miR-155 expression was assessed using reverse transcription-quantitative polymerase chain reaction in GT4-HCV-infected PBMCs, serum and liver tissues, as well as GT2- and GT4-infected Huh7 cells, and compared to the healthy controls. There was no difference in miR-155 expression observed between naïve GT4-HCV patients and healthy controls in the PBMCs and serum. In HCV-infected liver tissues, however, a significant downregulation was observed. The unique miR-155 expression pattern during GT4 infection was confirmed in the infected Huh7 cell lines when compared to GT2 infection. Clinical data showed a positive correlation between liver transaminases and serum miR-155 expression. In addition, serum miR-155 expression was significantly lower in naïve non-responders (NRs) than naïve sustained virological responders (SVRs), and in post-treatment NRs compared to post-treatment SVRs. In conclusion, miR-155 was not only proven to be a genotype-specific microRNA that is not induced during GT4-HCV infection, but also a good prognostic factor and predictor of response to treatment enabling a non-invasive differentiation between NRs and SVRs during GT4-HCV infection.

MicroRNA and hepatitis C virus--challenges in investigation and translation: a review of the literature

Investigations into the role of microRNA (miRNA) in hepatitis C virus (HCV) infection, disease pathogenesis and host immune and treatment response have potential to produce innovations in diagnosis, prognosis and therapy. However, investigational challenges remain in generating clinically useful and reproducible results. We review the literature with a primary emphasis on methods and technologies used to construct our current understanding of miRNA and HCV disease. A second emphasis is to understand potential clinical research applications and provide clarification of previous study results. Many miRNA have key roles in viral and immunopathogenesis of HCV infection across multiple tissue compartments. Controversy exists among published studies regarding relative measurements, temporal changes and biological significance of specific miRNA and HCV infection. To reconcile diverging data, additional research into optimal sample processing, in vitro models, techniques for microarray differential expression of miRNAs, practices for sample result normalization, and effect of HCV genotype variation on expression are all necessary. Microarray and miRNA isolation techniques should be selected based on ability to generate reproducible results in the sample type of interest. More direct comparisons of efficacy and reliability of various multiplex microarrays and an improved consensus around miRNA normalization and quantitation are necessary so that data can be compared across studies.

MicroRNA-27a modulates HCV infection in differentiated hepatocyte-like cells from adipose tissue-derived mesenchymal stem cells

Background and Aims

Despite the discovery of hepatitis C virus (HCV) entry factor, the mechanism by which it is regulated by miRNAs remains unclear. Adipose tissue-derived human mesenchymal stem cells (AT-hMSCs) have been widely used for differentiated hepatocyte-like cells (DHCs). Here, we established an in vitro HCV infection model using DHCs from AT-hMSCs and identified miRNAs that modulate HCV infectivity.

Methods

AT-hMSCs were differentiated into DHCs using the conditional media, and evaluated for hepatocyte characteristics using RT-PCR, immunocytochemistry, periodic acid-Schiff staining, and a urea synthesis assay. The expression of HCV candidate receptors was also verified using immunocytochemistry. The levels of candidate miRNAs targeting HCV receptors were then determined by relative quantitative RT-PCR (rqRT-PCR). Finally, DHCs were infected using HCVcc and serum from HCV-infected patients, and infectivity of the virus was measured by rqRT-PCR and transmission electron microscopy (TEM).

Results

The expected changes in morphology, function and hepatic gene expression were observed during hepatic differentiation. Moreover, the expression of candidate HCV entry factors and miR-27a were altered during hepatic differentiation. The infection and replication of HCV occurred efficiently in DHCs treated with HCVcc or infected with serum from HCV-infected patients. In addition, HCV infectivity was suppressed in miR-27a-transfected DHCs, due to the inhibition of LDLR expression by miR-27a.

Conclusions

Our results demonstrate that AT-hMSCs are a good source of DHCs, which are suitable for in vitro cultivation of HCV. Furthermore, these results suggest that miR-27a modulates HCV infectivity by regulating LDLR expression.

MicroRNA-155 and microRNA-196b: promising biomarkers in hepatitis C virus infection?

MicroRNAs (miRNAs) are a class of small, evolutionarily conserved, noncoding RNA that regulate several important cellular processes. The versatility of these molecules allowed the accurate predictions that they would also affect the replication and life cycle of HCV. In this review, emphasis has been given to two selected miRNAs: miR-155 and miR-196b. Recent data indicate that miR-155 is overexpressed in HCV-infected patients, inducing an inflammatory state, and promoting virus replication and persistence even after the completion of antiviral treatment. It is also associated with the increased proliferation and inhibited apoptosis of hepatocytes, which promotes the growth of liver tumors. In contrast, miR-196b is reported as a factor inhibiting HCV replication with cytoprotective, anti-inflammatory, and antioxidant properties. Growing evidence suggests that these molecules could be used as potential prognostic and predictive factors and their antagonists or mimics as a promising therapeutic approach in HCV-infected patients.

MicroRNAs in liver disease

Small, noncoding microRNAs (miRNAs) regulate diverse biological functions in the liver and increasing evidence suggests that they have a role in liver pathology. This Review summarizes advances in the field of miRNAs in liver diseases, inflammation and cirrhosis. MicroRNA-122, the most abundant miRNA in hepatocytes, has well-defined roles in HCV replication, and data indicate that it also serves as a viable therapeutic target. The role of miR-122 is also emerging in other liver diseases. Ample evidence exists for the important regulatory potential of other miRNAs in conditions associated with liver inflammation related to alcohol use, the metabolic syndrome or autoimmune processes. In addition, a broad array of miRNAs have been associated with the development of liver fibrosis both in animal models and human studies. The significance of the function and cellular distribution of miRNAs in the liver and the potential of miRNAs as a means of communication between cells and organs is discussed as well as the emerging utility of circulating miRNAs as biomarkers of different forms of liver damage and as early markers of disease and progression in hepatocellular carcinoma. Importantly, miRNA modulation in the liver represents a new therapeutic approach in the treatment armamentarium of hepatologists in the future.

microRNAs in liver disease: from diagnostics to therapeutics

There is a need to identify effective biomarkers for diagnosis, prognosis and prediction of treatment efficacy for many liver diseases such as hepatocellular cancer, and chronic viral hepatitis. The identification of disease-specific alterations in microRNA expression and the ability to detect microRNAs in the circulation provide the basis for identifying novel clinically effective treatments and biomarkers. Knowledge regarding miRNA in human liver disease may eventually lead to serum or tissue biomarkers with clinical utility. A selection of relevant studies is reviewed. There are major challenges that need to be addressed prior to clinical application such as the need for careful validation of diagnostic miRNA candidates in well described clinical cohorts, and technical issues such as quantitation and standardization of assays. The rapid progress in therapeutic interventions using miRNA based strategies for chronic hepatitis C and hepatocellular cancer provides optimism for novel approaches that will build on the existing and emerging knowledge regarding miRNA in liver diseases.

MicroRNA expression profiling in HCV-infected human hepatoma cells identifies potential anti-viral targets induced by interferon-α

Objective

Increasing evidence suggests that miRNAs have a profound impact on host defense to Hepatitis C virus (HCV) infection and clinical outcome of standard HCV therapy. In this study, we investigated modulation of miRNA expression in Huh7.5 hepatoma cells by HCV infection and in vitro interferon-αtreatment.

Methods

MiRNA expression profiling was determined using Human miRNA TaqMan® Arrays followed by rigorous pairwise statistical analysis. MiRNA inhibitors assessed the functional effects of miRNAs on HCV replication. Computational analysis predicted anti-correlated mRNA targets and their involvement in host cellular pathways. Quantitative RTPCR confirmed the expression of predicted miRNA-mRNA correlated pairs in HCV-infected Huh7.5 cells with and without interferon-α.

Results

Seven miRNAs (miR-30b, miR-30c, miR-130a, miR-192, miR-301, miR-324-5p, and miR-565) were down-regulated in HCV-infected Huh7.5 cells (p<0.05) and subsequently up-regulated following interferon-α treatment (p<0.01). The miR-30(a-d) cluster and miR-130a/301 and their putative mRNA targets were predicted to be associated with cellular pathways that involve Hepatitis C virus entry, propagation and host response to viral infection.

Conclusions

HCV differentially modulates miRNAs to facilitate entry and early establishment of infection in vitro. Interferon-α appears to neutralize the effect of HCV replication on miRNA regulation thus providing a potential mechanism of action in eradicating HCV from hepatocytes.

microRNAs in liver disease: from diagnostics to therapeutics

There is a need to identify effective biomarkers for diagnosis, prognosis and prediction of treatment efficacy for many liver diseases such as hepatocellular cancer, and chronic viral hepatitis. The identification of disease-specific alterations in microRNA expression and the ability to detect microRNAs in the circulation provide the basis for identifying novel clinically effective treatments and biomarkers. Knowledge regarding miRNA in human liver disease may eventually lead to serum or tissue biomarkers with clinical utility. A selection of relevant studies is reviewed. There are major challenges that need to be addressed prior to clinical application such as the need for careful validation of diagnostic miRNA candidates in well described clinical cohorts, and technical issues such as quantitation and standardization of assays. The rapid progress in therapeutic interventions using miRNA based strategies for chronic hepatitis C and hepatocellular cancer provides optimism for novel approaches that will build on the existing and emerging knowledge regarding miRNA in liver diseases.

Increased microRNA-155 expression in the serum and peripheral monocytes in chronic HCV infection

Background

Hepatitis C Virus (HCV), a single stranded RNA virus, affects millions of people worldwide and leads to chronic infection characterized by chronic inflammation in the liver and in peripheral immune cells. Chronic liver inflammation leads to progressive liver damage. MicroRNAs (miRNA) regulate inflammation (miR-155, -146a and -125b) as well as hepatocyte function (miR-122).

Methods

Here we hypothesized that microRNAs are dysregulated in chronic HCV infection. We examined miRNAs in the circulation and in peripheral monocytes of patients with chronic HCV infection to evaluate if specific miRNA expression correlated with HCV infection.

Results

We found that monocytes from chronic HCV infected treatment-naïve (cHCV) but not treatment responder patients showed increased expression of miR-155, a positive regulator of TNFα, and had increased TNFα production compared to monocytes of normal controls. After LPS stimulation, miR-155 levels were higher in monocytes from cHCV patients compared to controls. MiR-125b, which has negative regulatory effects on inflammation, was decreased in cHCV monocytes compared to controls. Stimulation of normal monocytes with TLR4 and TLR8 ligands or HCV core, NS3 and NS5 recombinant proteins induced a robust increase in both miR-155 expression and TNFα production identifying potential mechanisms for in vivo induction of miR-155. Furthermore, we found increased serum miR-155 levels in HCV patients compared to controls. Serum miR-125b and miR-146a levels were also increased in HCV patients. Serum levels of miR-122 were elevated in cHCV patients and correlated with increased ALT and AST levels and serum miR-155 levels.

Conclusion

In conclusion, our novel data demonstrate that miR-155, a positive regulator of inflammation, is upregulated both in monocytes and in the serum of patients with chronic HCV infection. Our study suggests that HCV core, NS3, and NS5 proteins or TLR4 and TLR8 ligands can mediate increased miR-155 and TNFα production in chronic HCV infection. The positive correlation between serum miR-155 and miR-122 increase in cHCV may be an indicator of inflammation-induced hepatocyte damage.

Repressed induction of interferon-related microRNAs miR-146a and miR-155 in peripheral blood mononuclear cells infected with HCV genotype 4

MicroRNAs regulate the expression of many genes and subsequently control various cellular processes, such as the immune response to viral infections mediated by type I interferon (IFN). In this study, the expression pattern of two interferon-related microRNAs, miR-146a and miR-155, was examined in healthy and HCV-genotype-4-infected peripheral blood mononuclear cells (PBMCs) using qRT-PCR. In contrast to other viral infections, the expression pattern was similar in both healthy and infected PBMCs. This could be attributed to attenuation of IFN pathway by HCV, which was assessed by investigating the expression of MxA, an interferon-stimulated gene, that showed lower expression in HCV-infected PBMCs. To determine the site of interference of HCV in the IFN pathway, expression of both microRNAs was examined following stimulation of PBMCs with IFN-α2a, an activator of the JAK/STAT pathway as well as with imiquimod, a toll-like receptor-7 (TLR-7) agonist that promotes interferon release. IFN stimulation induced the expression of miR-146a and miR-155 in HCV-infected and healthy PBMCs. Stimulation with imiquimod led to a down-regulation of both microRNAs in infected PBMCs, while it increased their expression in healthy PBMCs, indicating that HCV might interfere with miR-146a and miR-155 expression at sites upstream of interferon release, specifically in the TLR-7 pathway. The pattern of expression of both miR-146a and miR-155 was very similar with a strong positive correlation, but showed no correlation to the patients' clinical or histopathological parameters or response to treatment. In conclusion, HCV infection might repress the induction of miR-146a and miR-155 by interfering with TLR-7 signaling.

The role of microRNAs in human liver cancers

Hepatocellular carcinoma (HCC) is a primary malignancy of the liver of global importance. Recent studies of the expression and role of microRNA (miRNA) in HCC are providing new insights into disease pathogenesis. In addition, therapeutic efforts targeting specific miRNAs are being evaluated in animal models of HCC. The potential of miRNAs as biomarkers of disease or prognostic markers is being explored. Herein, we review studies of miRNA expression in human HCC, and discuss recent advances in knowledge about the involvement and role of selected miRNAs in disease pathogenesis, as biomarkers, or as therapeutic targets for HCC.