Hepatitis C virus production by human hepatocytes dependent on assembly and secretion of very low-density lipoproteins

Abstract

Hepatitis C virus (HCV) and triglyceride-rich very low-density lipoproteins (VLDLs) both are secreted uniquely by hepatocytes and circulate in blood in a complex. Here, we isolated from human hepatoma cells the membrane vesicles in which HCV replicates. These vesicles, which contain the HCV replication complex, are highly enriched in proteins required for VLDL assembly, including apolipoprotein B (apoB), apoE, and microsomal triglyceride transfer protein. In hepatoma cells that constitutively produce infectious HCV, HCV production is reduced by two agents that block VLDL assembly: an inhibitor of microsomal triglyceride transfer protein and siRNA directed against apoB. These results provide a possible explanation for the restriction of HCV production to the liver and suggest new cellular targets for treatment of HCV infection.apolipoprotein B ͉ microsomal triglyceride transfer protein

Hepatitis c virus and host cell lipids: An intimate connection

“…RNAi-mediated knockdown of ApoB and ApoE as well as pharmacological inhibition of microsomal triglyceride transfer protein (MTP), an enzyme crucial for ApoB maturation and VLDL secretion, have been proven effective in inhibiting HCV production in Huh7 cells, suggesting that secretion of HCV relies on the VLDL pathway. 83,[158][159][160][161][162] These results raise the question of how VLDL is formed and what the link is to HCV assembly. In hepatocytes, free fatty acids are converted to triacylglycerols (TGs) and incorporated into three different structures: the cytoplasmic lipid droplets (here simply referred to as lipid droplets; LDs); ApoB-containing precursors of VLDL (pre-VLDL particles or VLDL2); and luminal ApoBfree lipid droplets (luLDs).…”

“…24,82 Finally, newly assembled viral particles are presumably released in a VLDL-dependent manner (see section 7). 83 The envelope proteins E1 and E2 are highly glycosylated type I transmembrane (TM) proteins with an N-terminal ectodomain and a C-terminal hydrophobic membrane anchor. 29,30 By analogy to the related flaviviruses, it is assumed that E1 and E2 initially form heterodimers, but might rearrange into trimeric complexes required for entry.…”

Entry and replication of recombinant hepatitis C viruses in cell culture

“…It seems that HCV can hijack this function for its own assembly as it circulates in patient serum in association with lipoproteins [22,23]. Moreover, host factors crucial for production of VLDL like apolipoprotein E, apolipoprotein B and microsomal triglyceride transfer protein have been found to be important for production and release of infectious HCV particles [24][25][26][27][28][29]. The association of HCV with lipoproteins influences cell entry with the involvement of several lipoprotein (LDL receptor) [30,31] and lipid receptors (Scavenger receptor class B type I, SR-BI; Niemann-Pick C1-like 1 cholesterol uptake receptor, NPC1L1) [32,33].…”

Hepatitis C virus and proprotein convertase subtilisin/kexin type 9: a detrimental interaction to increase viral infectivity and disrupt lipid metabolism

“…HCV secretion was reduced significantly by silencing apoB mRNA 44. HCV production was reduced also by blocking VLDL assembly through knocking‐down or inhibition of MTP 45, 46. However, these observations were not always confirmed 47, 48, probably because of differences in VLDL synthesis capacity between different cell culture systems.…”