Lipoprotein component associated with hepatitis C virus is essential for virus infectivity

Downregulation of adipose triglyceride lipase by EB viral-encoded LMP2A links lipid accumulation to increased migration in nasopharyngeal carcinoma

Epstein–Barr virus (EBV)‐associated nasopharyngeal carcinoma (NPC) is one of the most common human cancers in South‐East Asia exhibiting typical features of lipid accumulation. EBV‐encoded latent membrane protein 2A (LMP2A) is expressed in most NPCs enhancing migration and invasion. We recently showed an increased accumulation of lipid droplets in NPC, compared with normal nasopharyngeal epithelium. It is important to uncover the mechanism behind this lipid metabolic shift to better understand the pathogenesis of NPC and provide potential therapeutic targets. We show that LMP2A increased lipid accumulation in NPC cells. LMP2A could block lipid degradation by downregulating the lipolytic gene adipose triglycerol lipase (ATGL). This is in contrast to lipid accumulation due to enhanced lipid biosynthesis seen in many cancers. Suppression of ATGL resulted in enhanced migration in vitro, and ATGL was found downregulated in NPC biopsies. The reduced expression level of ATGL correlated with poor overall survival in NPC patients. Our findings reveal a new role of LMP2A in lipid metabolism, correlating with NPC patient survival depending on ATGL downregulation.

A serum protein factor mediates maturation and apoB-association of HCV particles in the extracellular milieu

BACKGROUND & AIMS

In the sera of infected patients, hepatitis C virus (HCV) particles display heterogeneous forms with low-buoyant densities (<1.08), underscoring their lipidation via association with apoB-containing lipoproteins, which was proposed to occur during assembly or secretion from infected hepatocytes. However, the mechanisms inducing this association remain poorly-defined and most cell culture grown HCV (HCVcc) particles exhibit higher density (>1.08) and poor/no association with apoB. We aimed to elucidate the mechanisms of lipidation and to produce HCVcc particles resembling those in infected sera.

METHODS

We produced HCVcc particles of Jc1 or H77 strains from Huh-7.5 hepatoma cells cultured in standard conditions (10%-fetal calf serum) vs. in serum-free or human serum conditions before comparing their density profiles to patient-derived virus. We also characterized wild-type and Jc1/H77 hypervariable region 1 (HVR1)-swapped mutant HCVcc particles produced in serum-free media and incubated with different serum types or with purified lipoproteins.

RESULTS

Compared to serum-free or fetal calf serum conditions, production with human serum redistributed most HCVcc infectious particles to low density (<1.08) or very-low density (<1.04) ranges. In addition, short-time incubation with human serum was sufficient to shift HCVcc physical particles to low-density fractions, in time- and dose-dependent manners, which increased their specific infectivity, promoted apoB-association and induced neutralization-resistance. Moreover, compared to Jc1, we detected higher levels of H77 HCVcc infectious particles in very-low-density fractions, which could unambiguously be attributed to strain-specific features of the HVR1 sequence. Finally, all 3 lipoprotein classes, i.e., very-low-density, low-density and high-density lipoproteins, could synergistically induce low-density shift of HCV particles; yet, this required additional non-lipid serum factor(s) that include albumin.

CONCLUSIONS

The association of HCV particles with lipids may occur in the extracellular milieu. The lipidation level depends on serum composition as well as on HVR1-specific properties. These simple culture conditions allow production of infectious HCV particles resembling those of chronically-infected patients.

LAY SUMMARY

Hepatitis C virus (HCV) particles may associate with apoB and acquire neutral lipids after exiting cells, giving them low-buoyant density. The hypervariable region 1 (HVR1) is a majorviral determinant of E2 that controls this process. Besides lipoproteins, specific serum factors including albumin promote extracellular maturation of HCV virions. HCV particle production in vitro, with media of defined serum conditions, enables production of infectious particles resembling those of chronically infected patients.

The Correlation between miR-122 and Lipoprotein Lipase Expression in Chronic Hepatitis C Patients

Chronic HCV infection is strictly associated with host lipid/lipoprotein metabolism disorders. The study aimed to analyze the relationship between viral load, lipid profile, IFNγ, and the expression of miR-122 and LPL in the liver and PBMCs. Sera, PBMCs, and matching liver biopsies from 17 chronic hepatitis C patients were enrolled in this study. Collected data shows that liver (not PBMCs) miR-122 expression is positively correlated with HCV RNA load and IFNγ and reversely with LPL expression in CHC patients. Presented, for the first time, in this study, the reverse correlation of miR-122 and LPL expression in liver; miR-122 and LPL seem to be important factors of CHC infection.

Dual effects of the Nrf2 inhibitor for inhibition of hepatitis C virus and hepatic cancer cells

BACKGROUND

We previously showed that knockdown of nuclear factor E2-related factor 2 (Nrf2) resulted in suppression of hepatitis C virus (HCV) infection. In this study, whether brusatol, an Nrf2 inhibitor, has dual anti-HCV and anticancer effects was explored.

METHODS

The anti-HCV effect of brusatol was investigated by analyzing HCV RNA and proteins in a hepatic cell line persistently-infected with HCV, HPI cells, and by analyzing HCV replication in a replicon-replicating hepatic cell line, OR6 cells. Then, dual anti-HCV and anticancer effects of brusatol and enhancement of the effects by the combination of brusatol with anticancer drugs including sorafenib, which has been reported to have the dual effects, were then investigated.

RESULTS

Brusatol suppressed the persistent HCV infection at both the RNA and protein levels in association with a reduction in Nrf2 protein in the HPI cells. Analysis of the OR6 cells treated with brusatol indicated that brusatol inhibited HCV persistence by inhibiting HCV replication. Combination of brusatol with an anticancer drug not only enhanced the anticancer effect but also, in the case of the combination with sorafenib, strongly suppressed HCV infection.

CONCLUSIONS

Brusatol has dual anti-HCV and anticancer effects and can enhance the comparable effects of sorafenib. There is therefore the potential for combination therapy of brusatol and sorafenib for HCV-related hepatocellular carcinoma.

Innate and Adaptive Immune Responses in Chronic HCV Infection

Hepatitis C virus (HCV) remains a public health problem of global importance, even in the era of potent directly-acting antiviral drugs. In this chapter, I discuss immune responses to acute and chronic HCV infection. The outcome of HCV infection is influenced by viral strategies that limit or delay the initiation of innate antiviral responses. This delay may enable HCV to establish widespread infection long before the host mounts effective T and B cell responses. HCV's genetic agility, resulting from its high rate of replication and its error prone replication mechanism, enables it to evade immune recognition. Adaptive immune responses fail to keep up with changing viral epitopes. Neutralizing antibody epitopes may be hidden by decoy structures, glycans, and lipoproteins. T cell responses fail due to changing epitope sequences and due to exhaustion, a phenomenon that may have evolved to limit immune-mediated pathology. Despite these difficulties, innate and adaptive immune mechanisms do impact HCV replication. Immune-mediated clearance of infection is possible, occurring in 20-50% of people who contract the disease. New developments raise hopes for effective immunological interventions to prevent or treat HCV infection.

The HCV Replicase Complex and Viral RNA Synthesis

Replication of hepatitis C virus (HCV) is tightly linked to membrane alterations designated the membranous web, harboring the viral replicase complex. In this chapter we describe the morphology and 3D architecture of the HCV-induced replication organelles, mainly consisting of double membrane vesicles, which are generated by a concerted action of the nonstructural proteins NS3 to NS5B. Recent studies have furthermore identified a number of host cell proteins and lipids contributing to the biogenesis of the membranous web, which are discussed in this chapter. Viral RNA synthesis is tightly associated with these membrane alterations and mainly driven by the viral RNA dependent RNA polymerase NS5B. We summarize our current knowledge of the structure and function of NS5B, the role of cis-acting replication elements at the termini of the genome in regulating RNA synthesis and the contribution of additional viral and host factors to viral RNA synthesis, which is still ill defined.

Neglected but Important Role of Apolipoprotein E Exchange in Hepatitis C Virus Infection

Hepatitis C virus (HCV) is a major cause of chronic liver disease, infecting approximately 170 million people worldwide. HCV assembly is tightly associated with the lipoprotein pathway. Exchangeable apolipoprotein E (apoE) is incorporated on infectious HCV virions and is important for infectious HCV virion morphogenesis and entry. Moreover, the virion apoE level is positively correlated with its ability to escape E2 antibody neutralization. However, the role of apoE exchange in the HCV life cycle is unclear. In this study, the relationship between apoE expression and cell permissiveness to HCV infection was assessed by infecting apoE knockdown and derived apoE rescue cell lines with HCV. Exchange of apoE between lipoproteins and HCV lipoviral particles (LVPs) was evaluated by immunoprecipitation, infectivity testing, and viral genome quantification. Cell and heparin column binding assays were applied to determine the attachment efficiency of LVPs with different levels of incorporated apoE. The results showed that cell permissiveness for HCV infection was determined by exogenous apoE-associated lipoproteins. Furthermore, apoE exchange did occur between HCV LVPs and lipoproteins, which was important to maintain a high apoE level on LVPs. Lipid-free apoE was capable of enhancing HCV infectivity for apoE knockdown cells but not apoE rescue cells. A higher apoE level on LVPs conferred more efficient LVP attachment to both the cell surface and heparin beads. This study revealed that exogenous apoE-incorporating lipoproteins from uninfected hepatocytes safeguarded the apoE level of LVPs for more efficient attachment during HCV infection.

IMPORTANCE

In this study, a neglected but important role of apoE exchange in HCV LVP infectivity after virus assembly and release was identified. The data indicated that apoE expression level in uninfected cells is important for high permissiveness to HCV infection. Secreted apoE-associated lipoprotein specifically enhances infection of HCV LVPs. apoE exchange between HCV LVP and lipoproteins is important to maintain an adequate apoE level on LVPs for their efficient attachment to cell surface. These data defined for the first time an extracellular role of exchangeable apoE in HCV infection and suggested that exchangeable apolipoproteins reach a natural equilibrium between HCV LVPs and lipoprotein particles, which provides a new perspective to the understanding of the heterogeneity of HCV LVPs in composition.

Roles of Lipoproteins and Apolipoproteins in Particle Formation of Hepatitis C Virus

More than 160 million people worldwide are infected with hepatitis C virus (HCV), and cirrhosis and hepatocellular carcinoma induced by HCV infection are life-threatening diseases. HCV takes advantage of many aspects of lipid metabolism for an efficient propagation in hepatocytes. Due to the morphological and physiological similarities of HCV particles to lipoproteins, lipid-associated HCV particles are named lipoviroparticles. Recent analyses have revealed that exchangeable apolipoproteins directly interact with the viral membrane to generate infectious HCV particles. In this review, we summarize the roles of lipid metabolism in the life cycle of HCV.

Immune control and failure in HCV infection--tipping the balance

Despite the development of potent antiviral drugs, HCV remains a global health problem; global eradication is a long way off. In this review, we discuss the immune response to HCV infection and particularly, the interplay between viral strategies that delay the onset of antiviral responses and host strategies that limit or even eradicate infected cells but also contribute to pathogenesis. Although HCV can disable some cellular virus-sensing machinery, IFN-stimulated antiviral genes are induced in the infected liver. Whereas epitope evolution contributes to escape from T cell-mediated immunity, chronic high antigen load may also blunt the T cell response by activating exhaustion or tolerance mechanisms. The evasive maneuvers of HCV limit sterilizing humoral immunity through rapid evolution of decoy epitopes, epitope masking, stimulation of interfering antibodies, lipid shielding, and cell-to-cell spread. Whereas the majority of HCV infections progress to chronic hepatitis with persistent viremia, at least 20% of patients spontaneously clear the infection. Most of these are protected from reinfection, suggesting that protective immunity to HCV exists and that a prophylactic vaccine may be an achievable goal. It is therefore important that we understand the correlates of protective immunity and mechanisms of viral persistence.

The role of von Willebrand factor as a biomarker of tumor development in hepatitis B virus-associated human hepatocellular carcinoma: a quantitative proteomic based study

Chronic hepatitis B virus (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC), the sixth most common cancer worldwide. To explore potential biomarkers for HCC, iTRAQ coupled with mass spectrometry was used to analyze proteins in plasma from individuals with HBV-associated HCC, nonmalignant cirrhosis, chronic hepatitis B, and healthy individuals. Twenty-one aberrantly expressed proteins were identified from HCC patients as compared with nontumor controls. Overexpression of von Willebrand factor (vWF) was confirmed by Western blotting, and immunohistochemical analysis from liver biopsies and ELISA from plasma samples revealed a correlation between vWF expression and HCC clinicopathologic staging. Furthermore, siRNA-induced vWF silencing reduced HBV replication by over two-fold via the interferon-signaling pathway and impaired the invasion and migration of HCC cells in vitro. These results indicate that vWF can serve as a biomarker, and perhaps an alternative target for therapeutic intervention of HCC progression and HBV viral infection.

BIOLOGICAL SIGNIFICANCE

We report comparative plasma proteome profiles of HBV-associated HCC and nonmalignant chronic liver diseases, including chronic hepatitis B and cirrhosis. The quantification of these datasets showed altered abundance of 21 proteins in HBV-related HCC and provides a reference point for future applied and basic research. In addition, we have demonstrated that the candidate protein vWF is involved in the pathogenesis of HBV infection and replication, and also associated with clinicopathologic staging of HCC patients with HBV infection. Overall these findings provide information on the mechanism of HCC development, which may assist in the development of novel cancer and HBV therapeutic drugs.

The acyclic retinoid Peretinoin inhibits hepatitis C virus replication and infectious virus release in vitro

Clinical studies suggest that the oral acyclic retinoid Peretinoin may reduce the recurrence of hepatocellular carcinoma (HCC) following surgical ablation of primary tumours. Since hepatitis C virus (HCV) infection is a major cause of HCC, we assessed whether Peretinoin and other retinoids have any effect on HCV infection. For this purpose, we measured the effects of several retinoids on the replication of genotype 1a, 1b, and 2a HCV in vitro. Peretinoin inhibited RNA replication for all genotypes and showed the strongest antiviral effect among the retinoids tested. Furthermore, it reduced infectious virus release by 80-90% without affecting virus assembly. These effects could be due to reduced signalling from lipid droplets, triglyceride abundance, and the expression of mature sterol regulatory element-binding protein 1c and fatty acid synthase. These negative effects of Peretinoin on HCV infection may be beneficial in addition to its potential for HCC chemoprevention in HCV-infected patients.

Serum carnitine level and its associated factors in patients with chronic viral hepatitis

ABSTRACT: 

Aim: Serum carnitine level and its associated factors have been evaluated in patients with chronic viral hepatitis. Methods: Patients with confirmed chronic viral hepatitis based on the serological markers and liver biopsy were included. In total, 86 volunteers and 86 patients with chronic viral hepatitis completed the study. Demographic data, type of treatment regimen and nutritional status of the patients were recorded and one blood sample was collected from each patient after an overnight fasting. A double antibody sandwich ELISA kit was used to measure carnitine serum level. Results: Mean ± standard deviation of serum carnitine level in the case and control groups were 34.3 ± 15.3 and 55.7 ± 28.4 μmol/l, respectively (p = 0.001). Regarding carnitine deficiency definition, 64 out of 86 patients (74.4%) and 21 out of 86 (24.5%) healthy individuals suffered from carnitine deficiency (p < 0.001). Carnitine dietary intake was significantly lower (p < 0.001). Compared with patients with chronic hepatitis C infection, a more severe form of carnitine deficiency was detected in patients with chronic hepatitis B infection (18.39 ± 15.68 μmol/l vs 42.30 ± 32.92 μmol/l; p = 0.03). In addition, serum carnitine level (41.1 ± 14.8 μmol/l) was significantly higher in the cirrhotic than noncirrhotic patients (31.60 ± 13.2 μmol/l; p = 0.04). Conclusion: Although the cirrhotic patients had higher serum carnitine level compared with noncirrhotic patients, serum carnitine level in the patients with chronic hepatitis was significantly lower than the healthy individuals. Also compared with the defined cut-off point for normal carnitine serum level, carnitine deficiency was common in Iranian patients with chronic hepatitis.

HIV/hepatitis C virus coinfection ameliorates the atherogenic lipoprotein abnormalities of HIV infection

BACKGROUND

Higher levels of small low-density lipoprotein (LDL) and lower levels of high-density lipoprotein (HDL) subclasses have been associated with increased risk of cardiovascular disease. The extent to which HIV infection and HIV/hepatitis C virus (HCV) coinfection are associated with abnormalities of lipoprotein subclasses is unknown.

METHODS

Lipoprotein subclasses were measured by nuclear magnetic resonance (NMR) spectroscopy in plasma samples from 569 HIV-infected and 5948 control participants in the Fat Redistribution and Metabolic Change in HIV Infection (FRAM), Coronary Artery Risk Development in Young Adults (CARDIA), and Multi-Ethnic Study of Atherosclerosis (MESA) studies. Multivariable regression was used to estimate the association of HIV and HIV/HCV coinfection with lipoprotein measures with adjustment for demographics, lifestyle factors, and waist-to-hip ratio.

RESULTS

Relative to controls, small LDL levels were higher in HIV-monoinfected persons (+381 nmol/l, P <0.0001), with no increase seen in HIV/HCV coinfection (-16.6 nmol/l). Levels of large LDL levels were lower (-196 nmol/l, P <0.0001) and small HDL were higher (+8.2 μmol/l, P < 0.0001) in HIV monoinfection with intermediate values seen in HIV/HCV coinfection. Large HDL levels were higher in HIV/HCV-coinfected persons relative to controls (+1.70 μmol/l, P <0.0001), whereas little difference was seen in HIV-monoinfected persons (+0.33, P = 0.075). Within HIV-infected participants, HCV was associated independently with lower levels of small LDL (-329 nmol/l, P <0.0001) and small HDL (-4.6 μmol/l, P <0.0001), even after adjusting for demographic and traditional cardiovascular risk factors.

CONCLUSION

HIV-monoinfected participants had worse levels of atherogenic LDL lipoprotein subclasses compared with controls. HIV/HCV coinfection attenuates these changes, perhaps by altering hepatic factors affecting lipoprotein production and/or metabolism. The effect of HIV/HCV coinfection on atherosclerosis and the clinical consequences of low small subclasses remain to be determined.

Hepatic triglyceride lipase plays an essential role in changing the lipid metabolism in genotype 1b hepatitis C virus replicon cells and hepatitis C patients

AIM

Recently, several studies have shown the existence of associations between lipoprotein profiles and hepatitis C virus (HCV), although only a limited amount of information is available about the mechanisms underlying the changes in the lipoprotein profiles associated with HCV. In this study, we investigated the association between lipoprotein profile, classified according to the particle size, and lipoprotein metabolism.

METHODS

We used four kinds of cells for this experiment; full-length genome HCV RNA replicon cells (OR6), sub-genomic HCV RNA replicon cells (sO), and OR6c cells and sOc cells, which were the same cell lines treated with interferon-α. The triglyceride (TG) levels in the lipoprotein subclasses of the culture medium were measured by high-performance liquid chromatography. The mRNA expression levels of several molecules associated with lipoprotein metabolism were measured in the OR6, OR6c, sO and sOc cells. To confirm some of the results obtained using the in vitro system, liver biopsy samples obtained from the patients were also examined.

RESULTS

The content of TG in the large low-density lipoprotein (LDL) and medium LDL in the culture medium was increased only in the OR6 cells. The hepatic triglyceride lipase (HTGL) mRNA expression levels were lower in the OR6 cells than in the OR6c cells (P < 0.01). Examination of the HTGL expression levels in the patients' livers revealed a decrease in HTGL expression in the chronic hepatitis C liver as compared with that in the chronic hepatitis B or non-alcoholic steatohepatitis liver (P < 0.01).

CONCLUSION

We showed that HCV inhibits HTGL production in hepatocytes, inducing a change of the lipoprotein profile.

Hepatocyte nuclear factor 4α and downstream secreted phospholipase A2 GXIIB regulate production of infectious hepatitis C virus

Hepatitis C virus (HCV) is a major cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma in humans. The life cycle of HCV is closely associated with the metabolism of lipids, especially very-low-density lipoprotein (VLDL) in hepatocytes. Hepatocyte nuclear factor 4α (HNF4α), the most abundant transcription factor in the liver, regulates the VLDL secretory pathway. However, the effects of HNF4α on the HCV life cycle are unclear. In this study, we investigated the regulatory effects of HNF4α on HCV assembly and secretion. HCV in HNF4α-deficient hepatocytes showed reduced assembly and secretion but unchanged entry and RNA replication. Bezafibrate, a chemical inhibitor of HNF4α, suppressed HCV assembly and secretion. HNF4α downregulation resulted in rearrangement of cytosolic lipid droplets (LDs), as evidenced by the aggregation of large LDs and distorted cytosolic distribution. Phospholipase A2 GXIIB (PLA2GXIIB), an HNF4α-regulated factor involved in VLDL secretion, was found to be crucial in HCV secretion. PLA2GXIIB expression was upregulated in hepatocytes harboring HCV subgenomic replicons or in HCV-infected hepatocytes. This upregulation was transcriptionally controlled in an HNF4α-dependent manner after HCV infection. Furthermore, PLA2GXIIB combined with microsomal triglyceride transfer protein was found to be responsible for the regulation of HNF4α-induced HCV infectivity. These results suggest that HNF4α and its downstream PLA2GXIIB are important factors affecting the late stage of the HCV life cycle and may serve as potential drug targets for the treatment of HCV infection.

Hepatitis C virus-induced cytoplasmic organelles use the nuclear transport machinery to establish an environment conducive to virus replication

Hepatitis C virus (HCV) infection induces formation of a membranous web structure in the host cell cytoplasm where the viral genome replicates and virions assemble. The membranous web is thought to concentrate viral components and hide viral RNA from pattern recognition receptors. We have uncovered a role for nuclear pore complex proteins (Nups) and nuclear transport factors (NTFs) in the membranous web. We show that HCV infection leads to increased levels of cytoplasmic Nups that accumulate at sites enriched for HCV proteins. Moreover, we detected interactions between specific HCV proteins and both Nups and NTFs. We hypothesize that cytoplasmically positioned Nups facilitate formation of the membranous web and contribute to the compartmentalization of viral replication. Accordingly, we show that transport cargo proteins normally targeted to the nucleus are capable of entering regions of the membranous web, and that depletion of specific Nups or Kaps inhibits HCV replication and assembly.

Triglyceride-rich lipoproteins and cytosolic lipid droplets in enterocytes: key players in intestinal physiology and metabolic disorders

During the post-prandial phase, intestinal triglyceride-rich lipoproteins (TRL) i.e. chylomicrons are the main contributors to the serum lipid level, which is linked to coronary artery diseases. Hypertriglyceridemia can originate from decreased clearance or increased production of TRL. During lipid absorption, enterocytes produce and secrete chylomicrons and transiently store lipid droplets (LDs) in the cytosol. The dynamic fluctuation of triglycerides in cytosolic LDs suggests that they contribute to TRL production and may thus control the length and amplitude of the post-prandial hypertriglyceridemia. In this review, we will describe the recent advances in the characterization of enterocytic LDs. The role of LDs in chylomicron production and secretion as well as potential previously unsuspected functions in the metabolism of vitamins, steroids and prostaglandins and in viral infection will also be discussed.

Sigma-1 receptor regulates early steps of viral RNA replication at the onset of hepatitis C virus infection

Hepatitis C virus (HCV) genome replication is thought to occur in a membranous cellular compartment derived from the endoplasmic reticulum (ER). The molecular mechanisms by which these membrane-associated replication complexes are formed during HCV infection are only starting to be unraveled, and both viral and cellular factors contribute to their formation. In this study, we describe the discovery of nonopioid sigma-1 receptor (S1R) as a cellular factor that mediates the early steps of viral RNA replication. S1R is a cholesterol-binding protein that resides in lipid-rich areas of the ER and in mitochondrion-associated ER membranes (MAMs). Several functions have been ascribed to this ER-resident chaperone, many of which are related to Ca(2+) signaling at the MAMs and lipid storage and trafficking. Downregulation of S1R expression by RNA interference (RNAi) in Huh-7 cells leads to a proportional decrease in susceptibility to HCV infection, as shown by reduced HCV RNA accumulation and intra- and extracellular infectivity in single-cycle infection experiments. Similar RNAi studies in persistently infected cells indicate that S1R expression is not rate limiting for persistent HCV RNA replication, as marked reduction in S1R in these cells does not lead to any decrease in HCV RNA or viral protein expression. However, subgenomic replicon transfection experiments indicate that S1R expression is rate limiting for HCV RNA replication without impairing primary translation. Overall, our data indicate that the initial steps of HCV infection are regulated by S1R, a key component of MAMs, suggesting that these structures could serve as platforms for initial RNA replication during HCV infection.

Hepatitis C virus, cholesterol and lipoproteins--impact for the viral life cycle and pathogenesis of liver disease

Hepatitis C virus (HCV) is a leading cause of chronic liver disease, including chronic hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Hepatitis C infection associates with lipid and lipoprotein metabolism disorders such as hepatic steatosis, hypobetalipoproteinemia, and hypocholesterolemia. Furthermore, virus production is dependent on hepatic very-low-density lipoprotein (VLDL) assembly, and circulating virions are physically associated with lipoproteins in complexes termed lipoviral particles. Evidence has indicated several functional roles for the formation of these complexes, including co-opting of lipoprotein receptors for attachment and entry, concealing epitopes to facilitate immune escape, and hijacking host factors for HCV maturation and secretion. Here, we review the evidence surrounding pathogenesis of the hepatitis C infection regarding lipoprotein engagement, cholesterol and triglyceride regulation, and the molecular mechanisms underlying these effects.

Phosphoinositides in the hepatitis C virus life cycle

Eukaryotes possess seven different phosphoinositides (PIPs) that help form the unique signatures of various intracellular membranes. PIPs serve as docking sites for the recruitment of specific proteins to mediate membrane alterations and integrate various signaling cascades. The spatio-temporal regulation of PI kinases and phosphatases generates distinct intracellular hubs of PIP signaling. Hepatitis C virus (HCV), like other plus-strand RNA viruses, promotes the rearrangement of intracellular membranes to assemble viral replication complexes. HCV stimulates enrichment of phosphatidylinositol 4-phosphate (PI4P) pools near endoplasmic reticulum (ER) sites by activating PI4KIIIα, the kinase responsible for generation of ER-specific PI4P pools. Inhibition of PI4KIIIα abrogates HCV replication. PI4P, the most abundant phosphoinositide, predominantly localizes to the Golgi and plays central roles in Golgi secretory functions by recruiting effector proteins involved in transport vesicle generation. The PI4P effector proteins also include the lipid-transfer and structural proteins such as ceramide transfer protein (CERT), oxysterol binding protein (OSBP) and Golgi phosphoprotein 3 (GOLPH3) that help maintain Golgi-membrane composition and structure. Depletion of Golgi-specific PI4P pools by silencing PI4KIIIβ, expression of dominant negative CERT and OSBP mutants, or silencing GOLPH3 perturb HCV secretion. In this review we highlight the role of PIPs and specifically PI4P in the HCV life cycle.

The cell biology of receptor-mediated virus entry

The cell imposes multiple barriers to virus entry. However, viruses exploit fundamental cellular processes to gain entry to cells and deliver their genetic cargo. Virus entry pathways are largely defined by the interactions between virus particles and their receptors at the cell surface. These interactions determine the mechanisms of virus attachment, uptake, intracellular trafficking, and, ultimately, penetration to the cytosol. Elucidating the complex interplay between viruses and their receptors is necessary for a full understanding of how these remarkable agents invade their cellular hosts.