Measuring Hepatitis C Virus Envelopment by Using a Proteinase K Protection Assay

Development of Virus-Like Particles (VLPs) for Hepatitis C Virus genotype 4: a novel approach for vaccine development in Egypt

BACKGROUND

Egypt has the highest global prevalence of Hepatitis C Virus (HCV) infection, particularly of genotype 4. The development of a prophylactic vaccine remains crucial for HCV eradication, yet no such vaccine currently exists due to the vaccine development challenges. The ability of Virus-Like Particles (VLPs) to mimic the native virus and incorporate neutralizing and conformational epitopes, while effectively engaging both humoral and cellular immune responses, makes them a promising approach to addressing the challenges in HCV vaccine development.

METHODS

Lentiviral-based vectors were constructed and employed to integrate the full-length sequence of Core, E1, E2, and P7 genes of HCV genotype 4 into the genome of Human Embryonic Kidney cells (HEK293T). Upon the expression, HCV structural proteins can oligomerize and self-assemble into VLPs mimicking the structure of HCV native virus. VLPs were purified and characterized for the development of a potential VLPs-based vaccine.

RESULTS

In this study, mammalian cells were successfully engineered to stably express HCV structural proteins and generate non-infectious VLPs for HCV genotype 4. The expression of HCV-integrated genes resulted in a successful production of HCV structural proteins, which oligomerized and self-assembled into two layers enveloped VLPs. Electron microscopy analysis of purified VLPs revealed spherical particles with an average diameter of 60-65 nm, closely resembling mature HCV virions. These results highlighted the potential of these VLPs as a vaccine candidate for HCV genotype 4.

CONCLUSIONS

HCV genotype 4 remains an underexplored target in vaccine development, despite its significant public health burden, especially in Egypt. The successful generation of VLPs for this genotype represents a promising avenue for further vaccine development. The established system provides a robust platform for the production and study of VLP-based vaccines targeting HCV genotype 4.

Y-Box Binding Protein 1 Interacts with Dengue Virus Nucleocapsid and Mediates Viral Assembly

Infection with dengue virus (DENV) induces vast rearrangements of the endoplasmic reticulum, which allows the compartmentalization of viral RNA replication and particle assembly. Both processes occur in concert with viral and cellular proteins. Prior studies from our group suggest that the host RNA-binding protein (RBP) Y-box binding protein 1 (YBX1) is required for a late step in the DENV replication cycle. Here we report that YBX1 interacts with the viral nucleocapsid, distributes to DENV assembly sites and is required for efficient assembly of intracellular infectious virions and their secretion. Genetic ablation of YBX1 decreased the spatial proximity between capsid and envelope, increased the susceptibility of envelope to proteinase K mediated degradation, resulted in the formation of rough empty-looking particles, and decreased the secretion of viral particles. We propose a model wherein YBX1 enables the interaction between the viral nucleocapsid with the structural protein E, which is required for proper assembly of intracellular virus particles and their secretion. IMPORTANCE The global incidence of dengue virus (DENV) infections has steadily increased over the past decades representing an enormous challenge for public health. During infection, DENV viral RNA interacts with numerous host RNA binding proteins (RBPs) that aid viral replication and thus constitute potential molecular targets to curb infection. We recently reported that Y-box-binding protein 1 (YBX1) interacts with DENV RNA and is required at a late step of the replication cycle. Here we describe the molecular mechanism by which YBX1 mediates DENV infection. We show that YBX1 interacts with the viral nucleocapsid, distributes to DENV assembly sites and is required for efficient assembly of intracellular infectious virions. These results provide important insights into DENV assembly, revealing novel functions of host RBPs during viral infection and opening new avenues for antiviral intervention.

Adaptive mutations promote hepatitis C virus assembly by accelerating core translocation to the endoplasmic reticulum

The envelopment of hepatitis C virus (HCV) is believed to occur primarily in the endoplasmic reticulum (ER)-associated membrane, and the translocation of viral Core protein from lipid droplets (LDs) to the ER is essential for the envelopment of viral particles. However, the factors involved are not completely understood. Herein, we identified eight adaptive mutations that enhanced virus spread and infectivity of genotype 1a clone TNcc in hepatoma Huh7 cells through long-term culture adaptation and reverse genetic study. Of eight mutations, I853V in NS2 and C2865F in NS5B were found to be minimal mutation sets that enabled an increase in virus production without apparently affecting RNA replication, thus suggesting its roles in the post-replication stage of the HCV life cycle. Using a protease K protection and confocal microscopy analysis, we demonstrated that C2865F and the combination of I853V/C2865F enhanced virus envelopment by facilitating Core translocation from the LDs to the ER. Buoyant density analysis revealed that I853V/C2865F contributed to the release of virion with a density of ∼1.10 g/ml. Moreover, we demonstrated that NS5B directly interacted with NS2 at the protease domain and that mutations I853V, C2865F, and I853V/C2865F enhanced the interaction. In addition, C2865F also enhanced the interaction between NS5B and Core. In conclusion, this study demonstrated that adaptive mutations in NS2 and NS5B promoted HCV envelopment by accelerating Core translocation from the LDs to the ER and reinforced the interaction between NS2 and NS5B. The findings facilitate our understanding of the assembly of HCV morphogenesis.