GP73 Is Upregulated by Hepatitis C Virus (HCV) Infection and Enhances HCV Secretion

Longbo Hu,Fang Wang,Xia Rong,Wenxia Yao,Tao Peng,Hong Wanjin

doi:10.1371/journal.pone.0090553

Abstract

Hepatitis C virus (HCV) is a major cause of chronic liver disease. However, little is known about the details of its assembly and secretion. Golgi-related proteins have been recently proven to have a key function in HCV secretion. Golgi protein 73 (GP73), a resident Golgi membrane protein, is a potential serum biomarker for the diagnosis of liver diseases and hepatocellular carcinoma. Previous studies have demonstrated the upregulation of GP73 in the liver samples and sera of HCV-infected patients. However, the function and regulatory mechanism of GP73 in HCV infection at the cellular level remain unknown. In this study, we examined the expression level of GP73 in HCV infected cells and its effect on HCV life cycle in cell culture systems. Both the protein expression and mRNA levels of GP73 significantly increased in HCV subgenomic replicon-harboring cells and HCV-infected cells, which imply that GP73 was upregulated by HCV infection. HCV production was significantly enhanced when GP73 was overexpressed, but dramatically inhibited when GP73 was silenced. However, the overexpression and knockdown of GP73 showed no evident effect on the entry, protein translation, RNA replication, and assembly of HCV, which indicates that GP73 enhanced the secretion process. Moreover, the coiled-coil domain of GP73 was required to increase HCV secretion. GP73 increased and interacted with apolipoprotein E, an identified host factor that assists in HCV secretion. These results demonstrate the critical function of GP73 in HCV secretion and provide new insights into the therapeutic design of antiviral strategies.

Highlights

Hepatitis C virus (HCV), which is a major cause of chronic liver diseases, affects approximately 170 million people worldwide
To determine whether Golgi protein 73 (GP73) is augmented by HCV replication in the cell culture system, HCV subgenomic replicon (SGR)-harboring cells were established by transfecting HCV SGR replicon into Huh7 or
Huh7.5.1, followed by the examination of GP73 expression. Both the mRNA and protein expression levels of GP73 were significantly upregulated in HCV SGR-harboring cells and declined when the HCV genome was cleared by treatment of IFN-a (Figures 1A and 1B)

Summary

Introduction

Hepatitis C virus (HCV), which is a major cause of chronic liver diseases, affects approximately 170 million people worldwide. More than 80% of infected patients develop chronic infection and one-third of these patients develop progressive liver injury, fibrosis, cirrhosis and hepatocellular carcinoma (HCC) over a period of 20 to 30 years [1,2,3]. The life cycle of HCV involves attachment and entry, protein translation, RNA replication, assembly and release[6]. HCV pseudoparticles (HCVpp), subgenomic replicon (SGR), and HCV cell culture systems (HCVcc) have been developed in recent years to study the mechanisms underlying the HCV life cycle [7,8,9,10]. Great progress continuously being made, our knowledge of such mechanisms, of virion assembly and secretion, remains highly limited [6]

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Results

Conclusion