Hepatitis C virus core protein induces apoptosis-like caspase independent cell death

From viruses to cancer: exploring the role of the hepatitis C virus NS3 protein in carcinogenesis

Hepatitis C virus (HCV) chronically infects approximately 170 million people worldwide and is a known etiological agent of hepatocellular carcinoma (HCC). The molecular mechanisms of HCV-mediated carcinogenesis are not fully understood. This review article focuses on the oncogenic potential of NS3, a viral protein with transformative effects on cells, although the precise mechanisms remain elusive. Unlike the more extensively studied Core and NS5A proteins, NS3's roles in cancer development are less defined but critical. Research indicates that NS3 is implicated in several carcinogenic processes such as proliferative signaling, cell death resistance, genomic instability and mutations, invasion and metastasis, tumor-related inflammation, immune evasion, and replicative immortality. Understanding the direct impact of viral proteins such as NS3 on cellular transformation is crucial for elucidating HCV's role in HCC development. Overall, this review sheds light on the molecular mechanisms used by NS3 to contribute to hepatocarcinogenesis, and highlights its significance in the context of HCV-associated HCC, underscoring the need for further investigation into its specific molecular and cellular actions.

Egress of non-enveloped enteric RNA viruses

A long-standing paradigm in virology was that non-enveloped viruses induce cell lysis to release progeny virions. However, emerging evidence indicates that some non-enveloped viruses exit cells without inducing cell lysis, while others engage both lytic and non-lytic egress mechanisms. Enteric viruses are transmitted via the faecal-oral route and are important causes of a wide range of human infections, both gastrointestinal and extra-intestinal. Virus cellular egress, when fully understood, may be a relevant target for antiviral therapies, which could minimize the public health impact of these infections. In this review, we outline lytic and non-lytic cell egress mechanisms of non-enveloped enteric RNA viruses belonging to five families: Picornaviridae, Reoviridae, Caliciviridae, Astroviridae and Hepeviridae. We discuss factors that contribute to egress mechanisms and the relevance of these mechanisms to virion stability, infectivity and transmission. Since most data were obtained in traditional two-dimensional cell cultures, we will further attempt to place them into the context of polarized cultures and in vivo pathogenesis. Throughout the review, we highlight numerous knowledge gaps to stimulate future research into the egress mechanisms of these highly prevalent but largely understudied viruses.

Antibody Development to HCV Alternate Reading Frame Protein in Liver Transplant Candidate and its Computational Analysis

Background::

HCV Alternate Reading Frame Protein (ARFP) is a frameshift product of HCV-core encoding. Here, we characterized specific anti-ARFP antibodies in Liver Transplant Candidate (LTC) and chronic HCV-infected patients.

Methods::

The ARFP gene was cloned and the recombinant protein was purified using Nickel chromatography and confirmed by western blotting. ELISA was developed using recombinant core-1a, core- 1b, ARFP-1a protein, and 99-residue synthetic ARFP 1b peptide. By several Bioinformatics tools, general properties, immunogenic epitopes, and structures of these proteins were obtained.

Results::

The seroprevalence of anti-core and anti-ARFP antibodies was 100% in LTC patients, but only 75.2% and 94.3% of chronic patients had evidence of anti-ARFP and anti-core antibodies, respectively. In-silico results demonstrated physicochemical features, antigen properties and potential interactors that could describe progression toward advanced liver disease.

Conclusion::

As the first report, the prevalence of anti-ARFP antibodies in LTC patients is of the order of 100% and titer of anti-ARFP antibody was significantly higher in LTC patients compared to chronic individuals, suggesting the possible role of ARFP in the progression toward advanced liver disease. In addition, docking analysis determined several interactor proteins such as prefoldin 2, cathepsin B, vitronectin, and angiotensinogen that have an important role in progression to chronic infection and liver disease development.

Spontaneous Elimination of Hepatitis C Virus Infection

Hepatitis C virus (HCV) is the etiological agent of chronic hepatitis C and a major cause of liver cirrhosis and hepatocellular carcinoma. Only a minority of infected individuals can clear the virus spontaneously. The knowledge of the determinants of virus clearance would allow the development of effective methods preventing its further spread and optimizing treatment regimens. Viral factors associated with spontaneous virus clearance in the acute phase of infection, such as HCV genotype, virus heterogeneity, and the impact of viral proteins on the immune system have been characterized. Likewise, host genetic markers, such as the interleukin genotypes, HLA alleles, and factors affecting the T lymphocyte response appear to play an important role. Studies have revealed that natural clearance of HCV infection in the chronic phase is rare and its mechanisms are not well understood. In this review, we present the state-of-the art knowledge on the viral and host factors affecting the spontaneous elimination of HCV infection.

Nucleocapsid proteins: roles beyond viral RNA packaging

Viral nucleocapsid proteins (NCs) enwrap the RNA genomes of viruses to form NC–RNA complexes, which act as a template and are essential for viral replication and transcription. Beyond packaging viral RNA, NCs also play important roles in virus replication, transcription, assembly, and budding by interacting with viral and host cellular proteins. Additionally, NCs can inhibit interferon signaling response and function in cell stress response, such as inducing apoptosis. Finally, NCs can be the target of vaccines, benefiting from their conserved gene sequences. Here, we summarize important findings regarding the additional functions of NCs as much more than structural RNA‐binding proteins, with specific emphasis on (1) their association with the viral life cycle, (2) their association with host cells, and (3) as ideal candidates for vaccine development. WIREs RNA 2016, 7:213–226. doi: 10.1002/wrna.1326

This article is categorized under: 1

RNA Interactions with Proteins and Other Molecules > RNA–Protein Complexes

2

RNA Interactions with Proteins and Other Molecules > Protein–RNA Interactions: Functional Implications

3

Translation > Translation Regulation

Regulation of HepG2 cell apoptosis by hepatitis C virus (HCV) core protein via the sirt1-p53-bax pathway

Hepatitis C virus (HCV) core protein stimulates many signaling pathways related to apoptosis inhibition resulting in hepatocellular carcinoma (HCC). It has been reported that sirt1 is involved in regulating apoptosis; therefore, we investigated the influence of HCV core protein on sirt1 expression and apoptosis in human HepG2 cells. Our study showed that HCV core protein inhibited apoptosis of HepG2 cells as well as caspase-3 expression and activity (P < 0.05). At the same time, sirt1 expression was increased at both the mRNA (P < 0.05) and protein (P < 0.05) levels. Furthermore, apoptosis inhibition was reversed when sirt1 was knocked down (P < 0.05). Our study provides further evidence that the sirt1-p53-Bax signaling pathway plays an important role in regulating the suppression of cell apoptosis induced by HCV core protein.

Hepatitis C virus molecular evolution: Transmission, disease progression and antiviral therapy

Hepatitis C virus (HCV) infection represents an important public health problem worldwide. Reduction of HCV morbidity and mortality is a current challenge owned to several viral and host factors. Virus molecular evolution plays an important role in HCV transmission, disease progression and therapy outcome. The high degree of genetic heterogeneity characteristic of HCV is a key element for the rapid adaptation of the intrahost viral population to different selection pressures (e.g., host immune responses and antiviral therapy). HCV molecular evolution is shaped by different mechanisms including a high mutation rate, genetic bottlenecks, genetic drift, recombination, temporal variations and compartmentalization. These evolutionary processes constantly rearrange the composition of the HCV intrahost population in a staging manner. Remarkable advances in the understanding of the molecular mechanism controlling HCV replication have facilitated the development of a plethora of direct-acting antiviral agents against HCV. As a result, superior sustained viral responses have been attained. The rapidly evolving field of anti-HCV therapy is expected to broad its landscape even further with newer, more potent antivirals, bringing us one step closer to the interferon-free era.

Hepatitis C virus-induced hepatocyte cell death and protection by inhibition of apoptosis

Chronic hepatitis C virus (HCV) infection results in progressive liver fibrosis leading to cirrhosis and liver cancer. The mechanism for this remains unclear but hepatocyte apoptosis is thought to play a major role. Hepatocyte apoptosis in human liver tissue was determined by immunohistochemistry for cytokeratin 18 (M30 CytoDEATH) and cleaved poly(ADP-ribose) polymerase (PARP). In vitro studies were performed with replication-defective recombinant adenoviruses expressing HCV proteins (rAdHCV) to study the effects of HCV on cell death in Huh7 cells, primary mouse hepatocytes (PMoHs) and primary human hepatocytes (PHHs). Cell viability and apoptosis were studied using crystal violet assays and Western blots probed for cleaved caspase-3 and cleaved PARP, with and without treatment with the pan-caspase inhibitor Q-VD-OPh and necrostatin-1. Liver tissue of HCV-infected patients expressed elevated levels of apoptotic markers compared with HCV-negative patients. rAdHCV infection reduced cell viability compared with uninfected controls and cells infected with control virus (rAdGFP). Huh7, PMoHs and PHHs infected with rAdHCV showed significantly increased levels of apoptotic markers compared with uninfected controls and rAdGFP-infected cells. In rAdHCV-infected Huh7, treatment with Q-VD-OPh and necrostatin-1 both improved cell viability. Q-VD-Oph also reduced cleaved PARP in rAdHCV-infected Huh7 and PMoHs. Hepatocyte apoptosis is known to be increased in the livers of HCV-infected patients. HCV promoted cell death in primary and immortalized hepatocytes, and this was inhibited by Q-VD-OPh and necrostatin-1. These findings indicate that HCV-induced cell death occurs by both apoptosis and necroptosis, and provide new insights into the mechanisms of HCV-induced liver injury.

Hepatitis C virus-induced mitochondrial dysfunctions

Chronic hepatitis C is characterized by metabolic disorders and a microenvironment in the liver dominated by oxidative stress, inflammation and regeneration processes that lead in the long term to hepatocellular carcinoma. Many lines of evidence suggest that mitochondrial dysfunctions, including modification of metabolic fluxes, generation and elimination of oxidative stress, Ca²⁺ signaling and apoptosis, play a central role in these processes. However, how these dysfunctions are induced by the virus and whether they play a role in disease progression and neoplastic transformation remains to be determined. Most in vitro studies performed so far have shown that several of the hepatitis C virus (HCV) proteins localize to mitochondria, but the consequences of these interactions on mitochondrial functions remain contradictory, probably due to the use of artificial expression and replication systems. In vivo studies are hampered by the fact that innate and adaptive immune responses will overlay mitochondrial dysfunctions induced directly in the hepatocyte by HCV. Thus, the molecular aspects underlying HCV-induced mitochondrial dysfunctions and their roles in viral replication and the associated pathology need yet to be confirmed in the context of productively replicating virus and physiologically relevant in vitro and in vivo model systems.

Enhanced apoptosis in post-liver transplant hepatitis C: Effects of virus and immunosuppressants

Hepatitis C (HCV)-infected patients have a poorer survival post-liver transplantation compared to patients transplanted for other indications, since HCV recurrence post-transplant is universal and commonly follows an aggressive course. There is increasing evidence that in the non-transplant setting, induction of hepatocyte apoptosis is one of the main mechanisms by which HCV drives liver inflammation and fibrosis, and that HCV proteins directly promote apoptosis. Recent studies have shown that post-liver transplant, there is a link between high levels of HCV replication, enhanced hepatocyte apoptosis and the subsequent development of rapidly progressive liver fibrosis. Although the responsible mechanisms remain unclear, it is likely that immunosuppressive drugs play an important role. It is well known that immunosuppressants impair immune control of HCV, thereby allowing increased viral replication. However there is also evidence that immunosuppressants may directly induce apoptosis and this may be facilitated by the presence of high levels of HCV replication. Thus HCV and immunosuppressants may synergistically interact to further enhance apoptosis and drive more rapid fibrosis. These findings suggest that modulation of apoptosis within the liver either by changing immunosuppressive therapy or the use of apoptosis inhibitors may help prevent fibrosis progression in patients with post-transplant HCV disease.

HCV NS4B induces apoptosis through the mitochondrial death pathway

The hepatitis C virus (HCV) NS4B protein is known to induce the formation of a membranous web that is thought to be the site of viral RNA replication. However, the exact functions of NS4B remain poorly characterized. In this study, we found that NS4B induced apoptosis in 293T cells and Huh7 cells, as confirmed by Hoechst staining, DNA fragmentation, and annexin V/PI assays. Furthermore, protein immunoblot analysis demonstrated that NS4B triggered the cleavage of caspase 3, caspase 7, and poly(ADP-ribose) polymerase (PARP). Further studies revealed that NS4B induced the activation of caspase 9, the reduction of mitochondrial membrane potential and the release of cytochrome c from the mitochondria. However, NS4B expression did not trigger XBP1 mRNA splicing and increase the expression of binding immunoglobulin protein (BiP, or GRP78) and C/EBP homologous protein (CHOP), which serves as the indicators of ER stress. Taken together, our results suggest that HCV NS4B induces apoptosis through the mitochondrial death pathway.

TRAIL dependent fratricidal killing of gp120 primed hepatocytes by HCV core expressing hepatocytes

The mechanism by which HIV and HCV cooperatively accelerate hepatocyte damage is not clearly understood; however, each virus affects the TRAIL: TRAIL-receptor system. We, therefore, questioned whether the independent effects of HCV and HIV combine to synergistically result in TRAIL dependent hepatocyte killing. We describe that Huh7 hepatocytes treated with HIV gp120 results in both increase TRAIL-R2 expression and an acquired sensitivity to TRAIL mediated killing. Moreover HCV infection and HCV core expression alone in Huh7 cells upregulates TRAIL. Co-incubation of HIV gp120 primed hepatocytes with HCV core expressing hepatocytes results in the selective death of the HIV gp120 primed hepatocytes that is selectively blocked by TRAIL-R2-Fc fusion protein. Liver biopsies from HIV mono-infected patients have increased TRAIL-R2; biopsies from HCV infected patients have increased TRAIL, while co-infected liver biopsies have increased PARP cleavage within hepatocytes indicating enhanced apoptosis. These findings suggest a pathogenic model to understand why HIV/HCV co-infection accelerates liver injury.

Innate host response in primary human hepatocytes with hepatitis C virus infection

BACKGROUND AND AIM

The interaction between hepatitis C virus (HCV) and innate antiviral defense systems in primary human hepatocytes is not well understood. The objective of this study is to examine how primary human hepatocytes response to HCV infection.

METHODS

An infectious HCV isolate JFH1 was used to infect isolated primary human hepatocytes. HCV RNA or NS5A protein in the cells was detected by real-time PCR or immunofluorescence staining respectively. Apoptosis was examined with flow cytometry. Mechanisms of HCV-induced IFN-β expression and apoptosis were determined.

RESULTS

Primary human hepatocytes were susceptible to JFH1 virus and released infectious virus. IFN-α inhibited viral RNA replication in the cells. IFN-β and interferon-stimulated genes were induced in the cells during acute infection. HCV infection induced apoptosis of primary human hepatocytes through the TRAIL-mediated pathway. Silencing RIG-I expression in primary human hepatocytes inhibited IFN-β and TRAIL expression and blocked apoptosis of the cells, which facilitated viral RNA replication in the cells. Moreover, HCV NS34A protein inhibited viral induced IFN-β expression in primary human hepatocytes.

CONCLUSION

Innate host response is intact in HCV-infected primary human hepatocytes. RIG-I plays a key role in the induction of IFN and TRAIL by viruses and apoptosis of primary human hepatocytes via activation of the TRAIL-mediated pathway. HCV NS34A protein appears to be capable of disrupting the innate antiviral host responses in primary human hepatocytes. Our study provides a novel mechanism by which primary human hepatocytes respond to natural HCV infection.

Characterization of chronic HCV infection-induced apoptosis

Background

To understand the complex and largely not well-understood apoptotic pathway and immune system evasion mechanisms in hepatitis C virus (HCV)-associated hepatocellular carcinoma (HCC) and HCV associated chronic hepatitis (CH), we studied the expression patterns of a number of pro-apoptotic and anti-apoptotic genes (Fas, FasL, Bcl-2, Bcl-xL and Bak) in HepG2 cell line harboring HCV- genotype-4 replication. For confirmation, we also assessed the expression levels of the same group of genes in clinical samples obtained from 35 HCC and 34 CH patients.

Methods

Viral replication was assessed in the tissue culture medium by RT-PCR, quantitative Real-Time PCR (qRT-PCR); detection of HCV core protein by western blot and inhibition of HCV replication with siRNA. The expression level of Fas, FasL, Bcl-2, Bcl-xL and Bak was assessed by immunohistochemistry and RT-PCR whereas caspases 3, 8 and 9 were assessed by colorimetric assay kits up to 135 days post infection.

Results

There was a consistent increase in apoptotic activity for the first 4 weeks post-CV infection followed by a consistent decrease up to the end of the experiment. The concordance between the changes in the expression levels of Fas, FasL, Bcl-2, Bcl-xL and Bak in vitro and in situ was statistically significant (p < 0.05). Fas was highly expressed at early stages of infection in cell lines and in normal control liver tissues followed by a dramatic reduction post-HCV infection and an increase in the expression level of FasL post HCV infection. The effect of HCV infection on other apoptotic proteins started very early post-infection, suggesting that hepatitis C modulating apoptosis by modulating intracellular pro-apoptotic signals.

Conclusions

Chronic HCV infection differently modulates the apoptotic machinery during the course of infection, where the virus induces apoptosis early in the course of infection, and as the disease progresses apoptosis is modulated. This study could open a new opportunity for understanding the various signaling of apoptosis and in the developing a targeted therapy to inhibit viral persistence and HCC development.

Development of mouse hepatocyte lines permissive for hepatitis C virus (HCV)

The lack of a suitable small animal model for the analysis of hepatitis C virus (HCV) infection has hampered elucidation of the HCV life cycle and the development of both protective and therapeutic strategies against HCV infection. Human and mouse harbor a comparable system for antiviral type I interferon (IFN) induction and amplification, which regulates viral infection and replication. Using hepatocytes from knockout (ko) mice, we determined the critical step of the IFN-inducing/amplification pathways regulating HCV replication in mouse. The results infer that interferon-beta promoter stimulator (IPS-1) or interferon A receptor (IFNAR) were a crucial barrier to HCV replication in mouse hepatocytes. Although both IFNARko and IPS-1ko hepatocytes showed a reduced induction of type I interferons in response to viral infection, only IPS-1-/- cells circumvented cell death from HCV cytopathic effect and significantly improved J6JFH1 replication, suggesting IPS-1 to be a key player regulating HCV replication in mouse hepatocytes. We then established mouse hepatocyte lines lacking IPS-1 or IFNAR through immortalization with SV40T antigen. Expression of human (h)CD81 on these hepatocyte lines rendered both lines HCVcc-permissive. We also found that the chimeric J6JFH1 construct, having the structure region from J6 isolate enhanced HCV replication in mouse hepatocytes rather than the full length original JFH1 construct, a new finding that suggests the possible role of the HCV structural region in HCV replication. This is the first report on the entry and replication of HCV infectious particles in mouse hepatocytes. These mouse hepatocyte lines will facilitate establishing a mouse HCV infection model with multifarious applications.

Mitochondria and viruses

Mitochondria are involved in a variety of cellular metabolic processes, and their functions are regulated by extrinsic and intrinsic stimuli including viruses. Recent studies have shown that mitochondria play a central role in the primary host defense mechanisms against viral infections, and a number of novel viral and mitochondrial proteins are involved in these processes. Some viral proteins localize in mitochondria and interact with mitochondrial proteins to regulate cellular responses. This review summarizes recent findings on the functions and roles of these molecules as well as mitochondrial responses to viral infections.