Host-derived apolipoproteins play comparable roles with viral secretory proteins Erns and NS1 in the infectious particle formation of Flaviviridae

Abstract

Amphipathic α-helices of exchangeable apolipoproteins have shown to play crucial roles in the formation of infectious hepatitis C virus (HCV) particles through the interaction with viral particles. Among the Flaviviridae members, pestivirus and flavivirus possess a viral structural protein Erns or a non-structural protein 1 (NS1) as secretory glycoproteins, respectively, while Hepacivirus including HCV has no secretory glycoprotein. In case of pestivirus replication, the C-terminal long amphipathic α-helices of Erns are important for anchoring to viral membrane. Here we show that host-derived apolipoproteins play functional roles similar to those of virally encoded Erns and NS1 in the formation of infectious particles. We examined whether Erns and NS1 could compensate for the role of apolipoproteins in particle formation of HCV in apolipoprotein B (ApoB) and ApoE double-knockout Huh7 (BE-KO), and non-hepatic 293T cells. We found that exogenous expression of either Erns or NS1 rescued infectious particle formation of HCV in the BE-KO and 293T cells. In addition, expression of apolipoproteins or NS1 partially rescued the production of infectious pestivirus particles in cells upon electroporation with an Erns-deleted non-infectious RNA. As with exchangeable apolipoproteins, the C-terminal amphipathic α-helices of Erns play the functional roles in the formation of infectious HCV or pestivirus particles. These results strongly suggest that the host- and virus-derived secretory glycoproteins have overlapping roles in the viral life cycle of Flaviviridae, especially in the maturation of infectious particles, while Erns and NS1 also participate in replication complex formation and viral entry, respectively. Considering the abundant hepatic expression and liver-specific propagation of these apolipoproteins, HCV might have evolved to utilize them in the formation of infectious particles through deletion of a secretory viral glycoprotein gene.

CEACAM1 Is Associated With the Suppression of Natural Killer Cell Function in Patients With Chronic Hepatitis C

“…We generated CEACAM1 knockout (KO) Huh7.5.1 cells using the CRISPR/Cas9 system according to previously described methods . We confirmed CEACAM1 deficiency in monoclonal cells by flow cytometry and enzyme‐linked immunosorbent assay (ELISA).…”

Tick-Borne Viruses

“…Family Flaviviridae consists of four genera, Flavivirus , Hepacivirus , Pegivirus , and Pestivirus (Fukuhara et al 2017 ). The genomes of Flaviviridae viruses commonly contain a single-strand positive RNA encoding a polyprotein which will be cleaved into 2–4 structural proteins and 7–9 non-structural proteins (Chambers et al 1990 ).…”

Roles of secretory glycoproteins in particle formation of Flaviviridae viruses

“…In addition, we showed that NS1 participates in the formation of HCV and CSFV particles but not in the replication of viral RNA. 49 Collectively, these data suggest that NS1 plays a dual role in the formation of replication complexes and infectious particles via different mechanisms.…”

“…By contrast, Akey et al showed that NS1 mutants which are unable to generate replication complexes are nonetheless capable of remodeling the membranes of liposomes. In addition, we showed that NS1 participates in the formation of HCV and CSFV particles but not in the replication of viral RNA . Collectively, these data suggest that NS1 plays a dual role in the formation of replication complexes and infectious particles via different mechanisms.…”

“…However, the functional role of the hexametric form of NS1 in the viral life cycle is not yet fully understood. Recently, we reported the comparable roles of host‐ and virus‐derived secretory glycoproteins in the formation of infectious Flaviviridae virus particles (Figure ). Because HCV does not encode genes for secretory proteins, such as E rns and NS1, it has been suggested that host factors, for example exchangeable apolipoproteins or CAMP, are able to compensate for the lack of viral secretory proteins in the life cycle of HCV.…”