GP73 represses host innate immune response to promote virus replication by facilitating MAVS and TRAF6 degradation

Abstract

Hepatitis C virus (HCV) infection is a leading cause of chronic liver diseases and hepatocellular carcinoma (HCC) and Golgi protein 73 (GP73) is a serum biomarker for liver diseases and HCC. However, the mechanism underlying GP73 regulates HCV infection is largely unknown. Here, we revealed that GP73 acts as a novel negative regulator of host innate immunity to facilitate HCV infection. GP73 expression is activated and correlated with interferon-beta (IFN-β) production during HCV infection in patients’ serum, primary human hepatocytes (PHHs) and human hepatoma cells through mitochondrial antiviral signaling protein (MAVS), TNF receptor-associated factor 6 (TRAF6) and mitogen-activated protein kinase kinase/extracellular regulated protein kinase (MEK/ERK) pathway. Detailed studies revealed that HCV infection activates MAVS that in turn recruits TRAF6 via TRAF-interacting-motifs (TIMs), and TRAF6 subsequently directly recruits GP73 to MAVS via coiled-coil domain. After binding with MAVS and TRAF6, GP73 promotes MAVS and TRAF6 degradation through proteasome-dependent pathway. Moreover, GP73 attenuates IFN-β promoter, IFN-stimulated response element (ISRE) and nuclear factor κB (NF-κB) promoter and down-regulates IFN-β, IFN-λ1, interleukin-6 (IL-6) and IFN-stimulated gene 56 (ISG56), leading to the repression of host innate immunity. Finally, knock-down of GP73 down-regulates HCV infection and replication in Huh7-MAVSR cells and primary human hepatocytes (PHHs), but such repression is rescued by GP73m4 (a mutant GP73 resists to GP73-shRNA#4) in Huh7-MAVSR cells, suggesting that GP73 facilitates HCV infection. Taken together, we demonstrated that GP73 acts as a negative regulator of innate immunity to facilitate HCV infection by interacting with MAVS/TRAF6 and promoting MAVS/TRAF6 degradation. This study provides new insights into the mechanism of HCV infection and pathogenesis, and suggests that GP73 is a new potential antiviral target in the prevention and treatment of HCV associated diseases.

A hMTR4‐PDIA3P1‐miR‐125/124‐TRAF6 Regulatory Axis and Its Function in NF kappa B Signaling and Chemoresistance

“…Activation of TRAF6 requires K63‐linked polyubiquitination, and removing the K63‐linked ubiquitin chains from TRAF6 terminates NF‐κB signaling . On the other hand, K48‐linked polyubiquitination‐mediated degradation and miRNA‐mediated suppression are important mechanisms by which the protein level of TRAF6 is regulated . Here, we identified a mechanism of TRAF6 expression regulation that was mediated by noncoding RNA: miR‐125a/b and miR‐124 suppressed the expression of TRAF6, whereas PDIA3P1 enhanced the TRAF6 protein level by acting as a ceRNA to bind miR‐125a/b/miR‐124 and relieve their repression on TRAF6.…”

Induction of OTUD4 by viral infection promotes antiviral responses through deubiquitinating and stabilizing MAVS

“…These include OTUD4, PCBP2, RNF5, Tetherin, NS1 of Duck Tembusu Virus, iRhom2, ECSIT and GP73. 27,29,34,36,[52][53][54] The TM domain of MAVS is also crucial for its oligomerization after viral infection. 11,55 Interestingly, the truncated MAVS(aa361-540) used in this study is sufficient to activate ISRE or NF-κB in reporter assays.…”

Regulation of MAVS Expression and Signaling Function in the Antiviral Innate Immune Response

“…HCV infection upregulates the expression of Golgi protein 73 (GP73), a serum marker of liver disease and hepatocellular carcinoma, and promotes the coiled-coil domain of TRAF6 to recruit GP73 to MAVS. GP73 binding leads to the degradation of MAVS and TRAF6 through a proteasome-dependent pathway, thereby supporting HCV infection (91). HCV infection also upregulates NLRX1 (also known as NOD5/NOD9/NOD26) and induces MAVS K48-linked ubiquitination and degradation via PCBP2.…”