Activation of the Ras/Raf/MEK pathway facilitates hepatitis C virus replication via attenuation of the interferon-JAK-STAT pathway. J Virol. 2012;86:1544-1554. [PMID: 22114332 DOI: 10.1128/jvi.00688-11]

Set7 facilitates hepatitis C virus replication via enzymatic activity-dependent attenuation of the IFN-related pathway

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, usually resulting in persistent infection involving hepatic steatosis, cirrhosis, and hepatocellular carcinoma via escape of the host's immune response. Set7 is a lysine-specific methyltransferase that is involved in gene regulation and virus replication. However, the mechanism underlying the immune evasion between HCV and Set7 is not well understood. In this study, we observed that the expression of Set7 in Huh7.5.1 cells was upregulated by HCV infection, and high levels of Set7 expression were also found in the sera, PBMCs, and liver tissue of HCV patients relative to healthy individuals. Further investigation showed that Set7 enhanced HCV replication in an enzymatic activity-dependent manner. Moreover, our data showed that Set7 decreased the expression of virus-induced IFN and IFN-related effectors, such as dsRNA-activated protein kinase and 2',5'-oligoadenylate synthetase. Further investigation suggested that Set7 suppressed the endogenous IFN expression by reducing the nuclear translocation of IFN regulatory factor 3/7 and the p65 subunit of NF-κB and reduced IFN-induced dsRNA-activated protein kinase and 2',5'-oligoadenylate synthetase via attenuation of the phosphorylation of STAT1 and STAT2. Additionally, IFN receptors, including IFNAR1 and IFNAR2, which are located upstream of the JAK/STAT pathway, were reduced by Set7. Taken together, our results reveal that Set7 facilitates HCV replication through the attenuation of IFN signaling pathways and IFN-related effectors.

Prognostic factors in patients with hepatocellular carcinoma refractory or intolerant to sorafenib

OBJECTIVE

The aim of this study was to identify the prognostic factors in patients with advanced hepatocellular carcinoma (HCC) who are refractory or intolerant to sorafenib and to exclude unsuitable candidates from subsequent therapy.

METHODS

The study cohort consisted of 111 patients who had discontinued sorafenib therapy. Uni- and multivariate analyses were conducted to identify the prognostic factors for survival after discontinuation of sorafenib therapy.

RESULTS

The median age of the patients was 70 years, and 96 of them (86%) were male. The Eastern Cooperative Oncology Group performance status was 0-1 in 94 patients (85%). Forty patients (36%) were classified as Child-Pugh class A and 57 (51%) as Child-Pugh class B. The median survival time after discontinuation of sorafenib therapy was 146 days. Hepatitis C viral antibody negativity, presence of ascites, absence of a history of previous treatment excluding sorafenib, elevated serum total bilirubin level, and elevated serum α-fetoprotein level were identified as the independent unfavorable prognostic factors by multivariate analysis. The median survival time of the patients with 4 or 5 unfavorable prognostic factors was 59 days.

CONCLUSIONS

We should judge the indication of any subsequent therapy carefully in patients with 4 or 5 of the aforementioned factors.

Hepatitis C virus NS3 protein enhances cancer cell invasion by activating matrix metalloproteinase-9 and cyclooxygenase-2 through ERK/p38/NF-κB signal cascade

Hepatitis C virus (HCV) infection causes acute and chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma (HCC). However, the mechanisms by which HCV causes the diseases are largely unknown. Here, we elucidated the effects of HCV on the invasion and migration of hepatoma cells, with the aim to reveal the mechanism by which HCV infection induces HCC. We initially showed that matrix metalloproteinase-9 (MMP-9) was elevated in the sera of HCV-infected patients, and demonstrated that HCV nonstructural protein 3 (NS3) activated MMP-9 transcription through nuclear factor-κB (NF-κB) by stimulating translocation of NF-κB from cytosol to the nucleus to enhance its binding to MMP-9 promoter. In addition, cyclooxygenase-2 (COX-2) and extracellular signal-regulated kinase (ERK1/2)/mitogen-activated protein kinase (p38) pathway were involved in HCV-activated MMP-9 expression. Moreover, NS3 enhanced hepatoma cell invasion and migration through MMP-9 and COX-2. Thus, this study provides new insights into the roles of HCV NS3, MMP-9 and COX-2 in regulating cancer cell invasion.

miR-27a suppresses EV71 replication by directly targeting EGFR

Enterovirus 71 (EV71), a major causative agent of hand, foot, and mouth disease, has broken out several times and was accompanied by neurological disease. microRNAs, a class of small non-coding RNAs that are approximately 20 nucleotides long, play important roles in the regulation of various biological processes, including antiviral defense. However, the roles of miRNAs in EV71 replication and pathogenesis are not well understood. In this study, we found that the expression of miR-27a was significantly decreased in EV71-infected cells. Interestingly, the over-expression of miR-27a could inhibit EV71 replication, as measured by virus titration, qPCR, and Western blotting. We identified EGFR mRNA is a bona fide target of miR-27a by computational analysis and luciferase reporter assays. Furthermore, miR-27a could decrease EGFR expression, as measured by qPCR and Western blotting. Moreover, the inhibition of EGFR expression by miR-27a decreased the phosphorylation of Akt and ERK, which facilitate EV71 replication. These results suggest that miR-27a may have antiviral activity against EV71 by inhibiting EGFR.

Fluoxetine a novel anti-hepatitis C virus agent via ROS-, JNK-, and PPARβ/γ-dependent pathways

More than 20% of chronic hepatitis C (CHC) patients receiving interferon-alpha (IFN-α)-based anti-hepatitis C virus (HCV) therapy experienced significant depression, which was relieved by treatment with fluoxetine. However, whether and how fluoxetine affected directly the anti-HCV therapy remained unclear. Here, we demonstrated that fluoxetine inhibited HCV infection and blocked the production of reactive oxygen species (ROS) and lipid accumulation in Huh7.5 cells. Fluoxetine facilitated the IFN-α-mediated antiviral actions via activations of signal transducer and activator of transcription (STAT)-1 and c-Jun amino-terminal kinases (JNK). Alternatively, fluoxetine elevated peroxisome proliferator-activated receptor (PPAR) response element activity under HCV infection. The inhibitory effects of fluoxetine on HCV infection and lipid accumulation, but not production of ROS, were partially reversed by the PPAR-β, -γ, and JNK antagonists. Furthermore, fluoxetine intervention to the IFN-α-2b regimen facilitated to reduce HCV titer and alanine transaminase level for CHC patients. Therefore, fluoxetine intervention to the IFN-α-2b regimen improved the efficacy of anti-HCV treatment, which might be related to blockades of ROS generation and lipid accumulation and activation of host antiviral JNK/STAT-1 and PPARβ/γ signals.

MicroRNA binding site polymorphisms as biomarkers in cancer management and research

MicroRNAs (miRNAs) are important regulators of eukaryotic gene expression. They have been implicated in a broad range of biological processes, and miRNA-related genetic alterations probably underlie several human diseases. Single nucleotide polymorphisms of transcripts may modulate the posttranscriptional regulation of gene expression by miRNAs and explain interindividual variability in cancer risk and in chemotherapy response. On the basis of recent association studies published in the literature, the present review mainly summarizes the potential role of miRNAs as molecular biomarkers for disease susceptibility, diagnosis, prognosis, and drug-response prediction in tumors. Many clues suggest a role for polymorphisms within the 3' untranslated regions of KRAS rs61764370, SET8 rs16917496, and MDM4 rs4245739 as SNPs in miRNA binding sites highly promising in the biology of human cancer. However, more studies are needed to better characterize the composite spectrum of genetic determinants for future use of markers in risk prediction and clinical management of diseases, heading toward personalized medicine.

Measles virus suppresses RIG-I-like receptor activation in dendritic cells via DC-SIGN-mediated inhibition of PP1 phosphatases

Dendritic cells (DCs) are targets of measles virus (MV) and play central roles in viral dissemination. However, DCs express the RIG-I-like receptors (RLRs) RIG-I and Mda5 that sense MV and induce type I interferon (IFN) production. Given the potency of this antiviral response, RLRs are tightly regulated at various steps, including dephosphorylation by PP1 phosphatases, which induces their activation. We demonstrate that MV suppresses RIG-I and Mda5 by activating the C-type lectin DC-SIGN and inducing signaling that prevents RLR dephosphorylation. MV binding to DC-SIGN leads to activation of the kinase Raf-1, which induces the association of PP1 inhibitor I-1 with GADD34-PP1 holoenzymes, thereby inhibiting phosphatase activity. Consequently, GADD34-PP1 holoenzymes are unable to dephosphorylate RIG-I and Mda5, hence suppressing type I IFN responses and enhancing MV replication. Blocking DC-SIGN signaling allows RLR activation and suppresses MV infection of DCs. Thus, MV subverts DC-SIGN to control RLR activation and escape antiviral responses.

Interaction of L-SIGN with hepatitis C virus envelope protein E2 up-regulates Raf-MEK-ERK pathway

Liver/lymph node-specific intercellular adhesion molecule-3-grabbing integrin (L-SIGN) facilitates hepatitis C virus (HCV) infection through interaction with HCV envelope protein E2. Signaling events triggered by the E2 via L-SIGN are poorly understood. Here, kinase cascades of Raf-MEK-ERK pathway were defined upon the E2 treatment in NIH3T3 cells with stable expression of L-SIGN. The E2 bound to the cells through interaction with L-SIGN and such binding subsequently resulted in phosphorylation and activation of Raf, MEK, and ERK. Blockage of L-SIGN with antibody against L-SIGN reduced the E2-induced phosphorylation of Raf, MEK, and ERK. In the cells infected with cell culture-derived HCV, phosphorylation of these kinases was enhanced by the E2. Up-regulation of Raf-MEK-ERK pathway by HCV E2 via L-SIGN provides new insights into signaling cascade of L-SIGN, and might be a potential target for control and prevention of HCV infection.

Role of hepatitis B virus X protein in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the fifth most common cancer in the world and the third most common cause of cancer-related death. Chronic hepatitis B virus (HBV) infection has been identified as a major risk factor for HCC. Evidence suggests that the HBV X protein (HBx) plays a crucial role in the carcinogenesis of HCC. HBx is a multifunctional regulator that plays a key role in the occurrence, development, invasion and metastasis of cancers. Due to its important roles in the development of HCC, the research on the HBx protein has become a hot topic in recent years. This review describes the latest advances in understanding the role of the HBx protein in hepatocarcinogenesis.

Soluble interleukin-6 receptor-mediated innate immune response to DNA and RNA viruses

The interleukin-6 (IL-6) receptor, which exists as membrane-bound and soluble forms, plays critical roles in the immune response. The soluble IL-6 receptor (sIL6R) has been identified as a potential therapeutic target for preventing coronary heart disease. However, little is known about the role of this receptor during viral infection. In this study, we show that sIL6R, but not IL-6, is induced by viral infection via the cyclooxygenase-2 pathway. Interestingly, sIL6R, but not IL-6, exhibited extensive antiviral activity against DNA and RNA viruses, including hepatitis B virus, influenza virus, human enterovirus 71, and vesicular stomatitis virus. No synergistic effects on antiviral action were observed by combining sIL6R and IL-6. Furthermore, sIL6R mediated antiviral action via the p28 pathway and induced alpha interferon (IFN-α) by promoting the nuclear translocation of IFN regulatory factor 3 (IRF3) and NF-κB, which led to the activation of downstream IFN effectors, including 2',5'-oligoadenylate synthetase (OAS), double-stranded RNA-dependent protein kinase (PKR), and myxovirus resistance protein (Mx). Thus, our results demonstrate that sIL6R, but not IL-6, plays an important role in the host antiviral response.

ERK signaling is triggered by hepatitis C virus E2 protein through DC-SIGN

Dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) is a binding receptor for hepatitis C virus (HCV). Binding of HCV envelope protein E2 to target cells is a prerequisite to DC-SIGN-mediated signaling. Using cell lines with stable or transient expression of DC-SIGN, we investigated effects of soluble HCV E2 protein on ERK pathway. MEK and ERK are activated by the E2 in NIH3T3 cells stably expressing DC-SIGN. Treatment of the cells with antibody to DC-SIGN results in inhibition of the E2 binding as well as the E2-induced MEK and ERK activation. In HEK293T cells transiently expressing DC-SIGN, activation of MEK and ERK is also induced by the E2. Activation of ERK pathway by HCV E2 through DC-SIGN provides useful information for understanding cellular receptor-mediated signaling.

Mammalian phosphatidylinositol 4-kinases as modulators of membrane trafficking and lipid signaling networks

The four mammalian phosphatidylinositol 4-kinases modulate inter-organelle lipid trafficking, phosphoinositide signalling and intracellular vesicle trafficking. In addition to catalytic domains required for the synthesis of PI4P, the phosphatidylinositol 4-kinases also contain isoform-specific structural motifs that mediate interactions with proteins such as AP-3 and the E3 ubiquitin ligase Itch, and such structural differences determine isoform-specific roles in membrane trafficking. Moreover, different permutations of phosphatidylinositol 4-kinase isozymes may be required for a single cellular function such as occurs during distinct stages of GPCR signalling and in Golgi to lysosome trafficking. Phosphatidylinositol 4-kinases have recently been implicated in human disease. Emerging paradigms include increased phosphatidylinositol 4-kinase expression in some cancers, impaired functioning associated with neurological pathologies, the subversion of PI4P trafficking functions in bacterial infection and the activation of lipid kinase activity in viral disease. We discuss how the diverse and sometimes overlapping functions of the phosphatidylinositol 4-kinases present challenges for the design of isoform-specific inhibitors in a therapeutic context.

Recent advances in understanding viral evasion of type I interferon

The type I interferon (IFN) system mediates a wide variety of antiviral effects and represents an important first barrier to virus infection. Consequently, viruses have developed an impressive diversity of tactics to circumvent IFN responses. Evasion strategies can involve preventing initial virus detection, via the disruption of the Toll‐like receptors or the retinoic acid inducible gene I (RIG‐I) ‐like receptors, or by avoiding the initial production of the ligands recognized by these receptors. An alternative approach is to preclude IFN production by disarming or degrading the transcription factors involved in the expression of IFN, such as interferon regulatory factor 3 (IRF3)/IRF7, nuclear factor‐κB (NF‐κB), or ATF‐2/c‐jun, or by inducing a general block on host cell transcription. Viruses also oppose IFN signalling, both by disturbing the type I IFN receptor and by impeding JAK/STAT signal transduction upon IFN receptor engagement. In addition, the global expression of IFN‐stimulated genes (ISGs) can be obstructed via interference with epigenetic signalling, and specific ISGs can also be selectively targeted for inhibition. Finally, some viruses disrupt IFN responses by co‐opting negative regulatory systems, whereas others use antiviral mechanisms to their own advantage. Here, we review recent developments in this field.

Hepatitis C virus-related hepatocellular carcinoma: An insight into molecular mechanisms and therapeutic strategies

Hepatitis C virus (HCV) infects more than 170 million people worldwide, and thereby becomes a series global health challenge. Chronic infection with HCV is considered one of the major causes of end-stage liver disease including cirrhosis and hepatocellular carcinoma. Although the multiple functions of the HCV proteins and their impacts on the modulation of the intracellular signaling transduction processes, the drive of carcinogenesis during the infection with HCV, is thought to result from the interactions of viral proteins with host cell proteins. Thus, the induction of mutator phenotype, in liver, by the expression of HCV proteins provides a key mechanism for the development of HCV-associated hepatocellular carcinoma (HCC). HCC is considered one of the most common malignancies worldwide with increasing incidence during the past decades. In many countries, the trend of HCC is attributed to several liver diseases including HCV infection. However, the development of HCC is very complicated and results mainly from the imbalance between tumor suppressor genes and oncogenes, as well as from the alteration of cellular factors leading to a genomic instability. Besides the poor prognosis of HCC patients, this type of tumor is quite resistance to the available therapies. Thus, understanding the molecular mechanisms, which are implicated in the development of HCC during the course of HCV infection, may help to design a general therapeutic protocol for the treatment and/or the prevention of this malignancy. This review summarizes the current knowledge of the molecular mechanisms, which are involved in the development of HCV-associated HCC and the possible therapeutic strategies.

Porcine circovirus type 2 induces autophagy via the AMPK/ERK/TSC2/mTOR signaling pathway in PK-15 cells

Porcine circovirus type 2 (PCV2) uses autophagy machinery to enhance its replication in PK-15 cells. However, the underlying mechanisms are unknown. By the use of specific inhibitors, RNA interference, and coimmunoprecipitation, we show that PCV2 induces autophagy in PK-15 cells through a pathway involving the kinases AMP-activated protein kinase (AMPK) and extracellular signal-regulated kinase 1/2 (ERK1/2), the tumor suppressor protein TSC2, and the mammalian target of rapamycin (mTOR). AMPK and ERK1/2 positively regulate autophagy through negative control of the mTOR pathway by phosphorylating TSC2 in PCV2-infected PK-15 cells. Thus, PCV2 might induce autophagy via the AMPK/ERK/TSC2/mTOR signaling pathway in the host cells, representing a pivotal mechanism for PCV2 pathogenesis.

Hepatitis C virus activates Bcl-2 and MMP-2 expression through multiple cellular signaling pathways

Hepatitis C virus (HCV) infection is associated with numerous liver diseases and causes serious global health problems, but the mechanisms underlying the pathogenesis of HCV infections remain largely unknown. In this study, we demonstrate that signal transducer and activator of transcription 3 (STAT3), matrix metalloproteinase-2 (MMP-2), and B-cell lymphoma 2 (Bcl-2) are significantly stimulated in HCV-infected patients. We further show that HCV activates STAT3, MMP-2, Bcl-2, extracellular regulated protein kinase (ERK), and c-Jun N-terminal kinase (JNK) in infected Huh7.5.1 cells. Functional screening of HCV proteins revealed that nonstructural protein 4B (NS4B) is responsible for the activation of MMP-2 and Bcl-2 by stimulating STAT3 through repression of the suppressor of cytokine signaling 3 (SOCS3). Our results also demonstrate that multiple signaling cascades, including several members of the protein kinase C (PKC) family, JNK, ERK, and STAT3, play critical roles in the activation of MMP-2 and Bcl-2 mediated by NS4B. Further studies revealed that the C-terminal domain (CTD) of NS4B is sufficient for the activation of STAT3, JNK, ERK, MMP-2, and Bcl-2. We also show that amino acids 227 to 250 of NS4B are essential for regulation of STAT3, JNK, ERK, MMP-2, and Bcl-2, and among them, three residues (237L, 239S, and 245L) are crucial for this regulation. Thus, we reveal a novel mechanism underlying HCV pathogenesis in which multiple intracellular signaling cascades are cooperatively involved in the activation of two important cellular factors, MMP-2 and Bcl-2, in response to HCV infection.

A miR-1231 binding site polymorphism in the 3'UTR of IFNAR1 is associated with hepatocellular carcinoma susceptibility

Hepatocellular carcinoma (HCC) is a common liver malignancy worldwide and genetic factors play important roles in the pathogenesis of HCC. Based on in-silico analysis, a case-control study including 420 HCC patients and 420 healthy controls was conducted to investigate the association between HCC susceptibility with a 4-bp insertion/deletion polymorphism (rs17875871) in the 3'UTR of IFNAR1. Computational modeling suggested that rs17875871 was located in seed region of miR-1231 potential target sequence in IFNAR1 3'UTR. Logistic regression analysis showed that the heterozygote and the 4-bp del/del homozygote genotypes confer significantly higher risks of HCC (adjusted OR=1.35, 95% CI=1.01-1.83, P=0.045; OR=1.84, 95% CI=1.18-2.84, P=0.006, respectively). Stratification analysis revealed that this association was more pronounced in HBsAg positive subgroup. Our findings suggested common genetic changes in IFNAR1 may influence HCC risk, likely through miR-1231-mediated regulation, which is possibly involved in the pathogenesis of HBV related HCC. Further replication studies and functional characterization of rs17875871 were needed to fully clarify the underlined molecular mechanism.