Patrick Labonté

PCSK9 Impedes Hepatitis C Virus Infection In Vitro and Modulates Liver CD81 Expression

Human PCSK9 is known to enhance the degradation of membrane‐bound receptors such as the hepatocyte low‐density lipoprotein receptor (LDLR), ApoER2, and very low‐density lipoprotein receptor. Because the LDLR is suspected to be involved in hepatitis C virus (HCV) entry, we also tested whether PCSK9 can affect the levels of CD81, a major HCV receptor. Interestingly, stable expression of PCSK9 or a more active membrane‐bound form of the protein (PCSK9‐ACE2) resulted in a marked reduction in CD81 and LDLR expression. Therefore, we analyzed the antiviral effect of PCSK9 in vitro using the HCV genotype 2a (JFH1) virus. The results clearly demonstrated that cells expressing PCSK9 or PCSK9‐ACE2, but not the ACE2 control protein, were resistant to HCV infection. Furthermore, addition of purified soluble PCSK9 to cell culture supernatant impeded HCV infection in a dose‐dependent manner. As expected, HuH7 cells expressing PCSK9‐ACE2 were also resistant to infection by HCV pseudoparticles. In addition, we showed that CD81 cell surface expression is modulated by PCSK9 in an LDLR‐independent manner. Finally, in the liver of single Pcsk9 and double (Pcsk9 + Ldlr) knockout mice, both LDLR and/or CD81 protein expression levels were significantly reduced, but not those of transferrin and scavenger receptor class B type 1. Conclusion: Our results demonstrate an antiviral effect of the circulating liver PCSK9 on HCV in cells and show that PCSK9 down‐regulates the level of mouse liver CD81 expression in vivo. Therefore, we propose that the plasma level and/or activity of PCSK9 may modulate HCV infectivity in humans. (HEPATOLOGY 2009.)

Autophagy protein ATG5 interacts transiently with the hepatitis C virus RNA polymerase (NS5B) early during infection

Abstract Autophagy is an important cellular process by which ATG5 initiates the formation of double membrane vesicles (DMVs). Upon infection, DMVs have been shown to harbor the replicase complex of positive-strand RNA viruses such as MHV, poliovirus, and equine arteritis virus. Recently, it has been shown that autophagy proteins are proviral factors that favor initiation of hepatitis C virus (HCV) infection. Here, we identified ATG5 as an interacting protein for the HCV NS5B. ATG5/NS5B interaction was confirmed by co-IP and metabolic labeling studies. Furthermore, ATG5 protein colocalizes with NS4B, a constituent of the membranous web. Importantly, immunofluorescence staining demonstrated a strong colocalization of ATG5 and NS5B within perinuclear regions of infected cells at 2days postinfection. However, colocalization was completely lacking at 5DPI, suggesting that HCV utilizes ATG5 as a proviral factor during the onset of viral infection. Finally, inhibition of autophagy through ATG5 silencing blocks HCV replication.

Use of FDA approved therapeutics with hNTCP metabolic inhibitory properties to impair the HDV lifecycle.

Worldwide there are approximately 240million individuals chronically infected with the hepatitis B virus (HBV), including 15-20million coinfected with the hepatitis delta virus (HDV). Treatments available today are not fully efficient and often associated to important side effects and development of drug resistance. Targeting the HBV/HDV entry step using preS1-specific lipopeptides appears as a promising strategy to block viral entry for both HBV and HDV (Gripon et al., 2005; Petersen et al., 2008). Recently, the human Sodium Taurocholate Cotransporting Polypeptide (hNTCP) has been identified as a functional, preS1-specific receptor for HBV and HDV. This groundbreaking discovery has opened a very promising avenue for the treatment of chronic HBV and HDV infections. Here we investigated the ability of FDA approved therapeutics with documented inhibitory effect on hNTCP cellular function to impair viral entry using a HDV in vitro infection model based on a hNTCP-expressing Huh7 cell line. We demonstrate the potential of three FDA approved molecules, irbesartan, ezetimibe, and ritonavir, to alter HDV infection in vitro.

Membrane fusion-mediated autophagy induction enhances morbillivirus cell-to-cell spread.

ABSTRACT In the context of viral infections, autophagy induction can be beneficial or inhibitory. Within the Paramyxoviridae family, only morbilliviruses have been investigated and are reported to induce autophagy. Here we show that morbilliviruses rapidly induce autophagy and require this induction for efficient cell-to-cell spread. Coexpression of both glycoproteins in cells expressing one of the cellular receptors was required for autophagy induction, and LC3 punctum formation, indicative of autophagy, was mainly observed in syncytia. A similar correlation between syncytium formation and autophagy induction was also observed for other paramyxovirus glycoproteins, suggesting that membrane fusion-mediated autophagy may be common among paramyxoviruses and possibly other enveloped viruses.

Inhibition of tumor growth with doxorubicin in a new orthotopically implanted human hepatocellular carcinoma model.

A number of human xenograft orthotopic models of hepatocellular carcinoma (HCC) have been previously established by growing histologically-intact patient specimens in nude mice. However, the availability of HBV and HCV negative human hepatocellular carcinoma specimens is scarce and the pattern of tumor growth in nude mice varies depending on the tumor type. In the present study, we have established a reproducible xenograft orthotopic model using a human HCC cell line designated HuT7-3 that was derived from two rounds of subcloning of the parental Huh-7 cell line. The tumor growth rate of the HuT7-3 cell line, grown at a primary subcutaneous site, was markedly higher than that of the Huh-7 parental cell line or the human hepatoblastoma Hep-G2 cell line. Furthermore, we have shown that doxorubicin, when administered intravenously, is efficient in inhibiting the development of subcutaneous tumor but leads to the regression of the orthotopic human HCC. Consequently, this novel HCC xenograft orthotopic model can be used for the evaluation of antitumor drugs.

SKI-1/S1P inhibition: a promising surrogate to statins to block hepatitis C virus replication.

Hepatitis C virus (HCV) is often associated with steatosis, cirrhosis and hepatocellular carcinoma (HCC). Statins (HMG-CoAR inhibitors) have been shown to exert an antiviral effect in vitro, principally on replicon harboring cells, but the effect of their use alone in vivo remains controversial. In clinical trials, when used in combination with the standards of care (SOC), they led to an increased proportion of sustained virological responder (SVR). Here we investigated the implication of SKI-1/S1P, a master lipogenic pathways regulator upstream of HMG-CoAR, on different steps of HCV life cycle. We compared the HCV antiviral effect of the most potent SKI-1/S1P small molecule inhibitor (PF-429242) with a set of two statins on different steps of the viral life cycle, and showed that SKI-1/S1P inhibitor blocked HCVcc (strain JFH-1) RNA replication (EC(50)= 5.8 μM) more efficiently than statins. Moreover, we showed that PF-429242 could reduce lipid droplets accumulation in Huh7 cells. Interestingly, PF-429242 dramatically reduced infectious particles production (EC(90)= 4.8 μM). Such inhibition could not be achieved with statins. SKI-1/S1P activity is thus essential for viral production and its inhibition should be considered for antiviral drug development.

The autophagy elongation complex (ATG5-12/16L1) positively regulates HCV replication and is required for wild-type membranous web formation

Hepatitis C virus (HCV) infection induces intracellular membrane rearrangements, thus forming a membranous web (MW) in which HCV replication and assembly occur. The HCV-induced MW is primarily composed of double membrane vesicles (DMVs) transfused by multi-membrane vesicles. The autophagy machinery has been proposed to participate in the formation of such vesicles. However, no clear evidence has been found linking autophagy to the formation of these DMVs. In this study, we evaluated the role of the autophagy elongation complex (ATG5-12/16L1) in HCV replication and MW formation. Using a dominant negative form of ATG12 and an siRNA approach, we demonstrated that the ATG5-12 conjugate, but not LC3-II formation, is crucial for efficient viral replication. Furthermore, purification of HCV MW revealed the presence of ATG5-12 and ATG16L1 along with HCV nonstructural proteins. Interestingly, LC3 was not recruited along with the elongation complex to the site of viral replication. Finally, inhibition of the elongation complex, but not LC3, greatly impaired the formation of the wild-type MW phenotype. To our knowledge, this study provides the first evidence of the involvement of autophagy proteins in the formation of wild-type MWs.

Plasma Membrane Tetraspanin CD81 Complexes with Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) and Low Density Lipoprotein Receptor (LDLR), and Its Levels Are Reduced by PCSK9.

Background: PCSK9 is a modulator of LDLR and the tetraspanin CD81. Results: Although CD81 is targeted for degradation by PCSK9 in an LDLR-independent manner, it can associate with the LDLR. Conclusion: CD81 and LDLR are two independent targets of PCSK9 that bind to each other. Significance: Structure-based mutagenesis of PCSK9 reveals functional interactions of CD81 with LDLR and PCSK9. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an important factor in plasma cholesterol regulation through modulation of low density lipoprotein receptor (LDLR) levels. Naturally occurring mutations can lead to hyper- or hypocholesterolemia in human. Recently, we reported that PCSK9 was also able to modulate CD81 in Huh7 cells. In the present study, several gain-of-function and loss-of-function mutants as well as engineered mutants of PCSK9 were compared for their ability to modulate the cell surface expression of LDLR and CD81. Although PCSK9 gain-of-function D374Y enhanced the degradation both receptors, D374H and D129N seemed to only reduce LDLR levels. In contrast, mutations in the C-terminal hinge-cysteine-histidine-rich domain segment primarily affected the PCSK9-induced CD81 degradation. Furthermore, when C-terminally fused to an ACE2 transmembrane anchor, the secretory N-terminal catalytic or hinge-cysteine-histidine-rich domain domains of PCSK9 were able to reduce CD81 and LDLR levels. These data confirm that PCSK9 reduces CD81 levels via an intracellular pathway as reported for LDLR. Using immunocytochemistry, a proximity ligation assay, and co-immunoprecipitation, we found that the cell surface level of PCSK9 was enhanced upon overexpression of CD81 and that both PCSK9 and LDLR interact with this tetraspanin protein. Interestingly, using CHO-A7 cells lacking LDLR expression, we revealed that LDLR was not required for the degradation of CD81 by PCSK9, but its presence strengthened the PCSK9 effect.

Novel HCV replication mouse model using human hepatocellular carcinoma xenografts.

In the absence of an immunocompetent mouse model for HCV replication, we developed a convenient xenograft mouse model that produces infectious viral particles. For this purpose, HCV-permissive tumors were generated in SCID/beige mice using a tumorigenic population of the human hepatocarcinoma-derived Huh7 cell line. Following infection, HCV RNA increased in the mouse sera and the human tumor by up to 10(5)GE/ml and 10(7)GE/microg of RNA, respectively. Immunohistochemistry analysis revealed that active viral replication had taken place within the tumor. Moreover, virus recovered from infected mice sera was readily infectious in cell culture. Finally, we showed that interferon-alpha and the protease inhibitor BILN-2061 inhibited the cell culture HCVcc strain JFH1 replication in vivo. In conclusion, we developed a simple and inexpensive mouse model that allows the production of infectious HCV particles in vivo. Such a model will be an extremely valuable tool for the characterization of promising drug candidates.

Sequence and expression of the ns2 protein gene of human coronavirus OC43.

The complete nucleotide sequence of the ns2 gene of human coronavirus OC43 (HCV-OC43) was determined. Sequence analysis revealed an open reading frame that could encode a protein of 278 amino acids, with an estimated molecular mass of 32.2 kDa. Six potential phosphorylation sites are present but no sites of N-glycosylation were found. The amino acid sequence of the HCV-OC43 ns2 protein shows 92% identity with that of the Mebus strain of bovine coronavirus (BCV). However, a stretch of nine consecutive amino acids near the C terminus is completely different, causing it to be very hydrophilic, which contrasts with the hydrophobic nature of this region in BCV. As shown by immunofluorescence with a monospecific antiserum, the ns2 protein was expressed in the cytoplasm of HCV-OC43-infected HRT-18 cells.