Hepatitis C virus (HCV) infection is associated with lipoproteins,
and apolipoprotein E (apoE) plays an essential role in
infectious HCV particles. Although the role of apoE in HCV
infection is well known, its role in the replication of HCV
remains unclear. The aims of this study were to determine
the role of apoE in the RNA replication of major HCV genotypes
1b and 2a, and to determine whether this role is HCVgenotype-
dependent using HCV genotype 1b replicon cells
and HCV genotype 2a producing (HP) cells. HCV infection
was blocked in Huh7.5 cells treated with low-density lipoproteins,
very low-density lipoproteins, or apoE3. An apoE3-
specific monoclonal antibody also efficiently neutralized HCV
infectivity, and HCV infection was dramatically suppressed
by the knockdown of apoE expression with an apoE-specific
small interfering RNA, suggesting a requirement for apoE
in infectious HCV particles. HCV RNA replication was not
affected in HP cells treated with each apoE isoform or transfected
with apoE-specific siRNAs. However, the knockdown
of apoE expression suppressed RNA replication of HCV
genotype 1b. The siRNA-mediated knockdown of apoE,
apoA1, and apoB expression also suppressed the RNA replication
of HCV genotype 1b, but not that of HCV genotype
2a. Taken together, these findings indicate that apoE
plays an important role in HCV genotype 2a infection and
in HCV genotype 1b RNA replication, but not in the replication
of HCV genotype 2a. These results provide important
information for the future development of HCV-genotypespecific
anti-HCV agents.
Viral infection causes stress to the endoplasmic reticulum (ER). The response to endoplasmic reticulum stress, known as the unfolded protein response (UPR), is designed to eliminate misfolded proteins and allow the cell to recover. The role of hepatitis C virus (HCV) non-structural protein NS4B, a component of the HCV replicons that induce UPR, is incompletely understood. We demonstrate that HCV NS4B could induce activating transcription factor (ATF6) and inositol-requiring enzyme 1 (IRE1), to favor the HCV subreplicon and HCV viral replication. HCV NS4B activated the IRE1 pathway, as indicated by splicing of X box-binding protein (Xbp-1) mRNA. However, transcriptional activation of the XBP-1 target gene, EDEM (ER degradation-enhancing a-mannosidase-like protein, a protein degradation factor), was inhibited. These results imply that NS4B might induce UPR through ATF6 and IRE1-XBP1 pathways, but might also modify the outcome to benefit HCV or HCV subreplicon replication.