Hepatitis C Virus Increases Occludin Expression via the Upregulation of Adipose Differentiation-Related Protein

Abstract

The hepatitis C virus (HCV) life cycle is closely associated with lipid metabolism. In particular, HCV assembly initiates at the surface of lipid droplets. To further understand the role of lipid droplets in HCV life cycle, we assessed the relationship between HCV and the adipose differentiation-related protein (ADRP), a lipid droplet-associated protein. Different steps of HCV life cycle were assessed in HCV-infected human Huh-7 hepatoma cells overexpressing ADRP upon transduction with a lentiviral vector. HCV infection increased ADRP mRNA and protein expression levels by 2- and 1.5-fold, respectively. The overexpression of ADRP led to an increase of (i) the surface of lipid droplets, (ii) the total cellular neutral lipid content (2.5- and 5-fold increase of triglycerides and cholesterol esters, respectively), (iii) the cellular free cholesterol level (5-fold) and (iv) the HCV particle production and infectivity (by 2- and 3.5-fold, respectively). The investigation of different steps of the HCV life cycle indicated that the ADRP overexpression, while not affecting the viral replication, promoted both virion egress and entry (~12-fold), the latter possibly via an increase of its receptor occludin. Moreover, HCV infection induces an increase of both ADRP and occludin expression. In HCV infected cells, the occludin upregulation was fully prevented by the ADRP silencing, suggesting a specific, ADRP-dependent mechanism. Finally, in HCV-infected human livers, occludin and ADRP mRNA expression levels correlated with each other. Alltogether, these findings show that HCV induces ADRP, which in turns appears to confer a favorable environment to viral spread.

Perilipin-2 is critical for efficient lipoprotein and hepatitis C virus particle production

“…Previous publications investigated PLIN2 in HCV infection and had inconsistent findings: knockdown of PLIN2 using siRNAs had either no or variable effects on HCV infection and on LD morphology (Branche et al, 2016;Zhang et al, 2016). In contrast, when overexpressed, PLIN2 enhanced virus infection, by upregulating the expression of the HCV entry factor occludin (OCLN), and increased average LD volumes.…”

“…The most prominent protein on the surface of LDs in hepatocytes and hepatoma cells permissive for HCV is PLIN2 (Brasaemle et al, 1997;Fujimoto et al, 2004). Previous reports on the interaction of PLIN2 with HCV are contradictory (Branche et al, 2016;Zhang et al, 2016). To investigate whether PLIN2 itself or lipid metabolic processes regulated by PLIN2 are required for HCV infection, we generated lentiviral constructs encoding six different shRNAs targeting PLIN2 and a non-targeting control (shNT) to transduce the hepatoma cell line Huh7.5 (Fig.…”

“…Overexpression of PLIN2 in Huh7 cells alters LD morphology (Branche et al, 2016;Zhang et al, 2016). We investigated the impact of PLIN2 depletion on LDs by performing 3D spinning disk confocal microscopy (Fig.…”

“…But core can also displace PLIN2 from the LD surface (Boulant et al, 2008). Regarding HCV replication, overexpression of PLIN2 leads to an increase in HCV replication while its knockdown using siRNAs has inconsistent effects (Branche et al, 2016;Zhang et al, 2016).…”

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

“…Inhibition of the protease subtilisin/kexin-isozyme-1/site 1 protease (SKI1/S1P), which plays a critical role in the activation of sterol regulatory element-binding proteins (SREBPs) controlling cholesterol and fatty-acid biosynthesis and LD composition, impaired HCV assembly [41]. On the other hand, HCV infection induced the expression of the LD-associated adipose differentiationrelated protein (ADRP), which is known to promote virion assembly and secretion [42].…”