Y-Box Binding Protein 1 Stabilizes Hepatitis C Virus NS5A via Phosphorylation-Mediated Interaction with NS5A To Regulate Viral Propagation

Abstract

Replication of hepatitis C virus (HCV) is dependent on virus-encoded proteins and numerous cellular factors. DDX3 is a well-HCV is a positive-stranded RNA virus that contains a 9.6-kb genome consisting of a single open reading frame flanked by 5= and 3= nontranslated regions (NTR). An internal ribosome entry site (IRES) in the 5=NTR directs the translation of a polyprotein, which is processed co-and posttranslationally into 10 or more viral proteins (3, 4). HCV infection is sustained by spatiotemporal interplay between viral proteins and a panel of cellular cofactors to coordinate translation of the viral genome, viral RNA replication, and the production of infectious viral particles. However, there is still limited understanding of the molecular mechanisms underlying the coordinated interactions of these events.The nonstructural protein 5A (NS5A) is a phosphoprotein highly variable among genotypes of HCV (5). NS5A is recognized as a key modulator of the HCV life cycle, and the factor has emerged as a new target of drug development (2). NS5A, consisting of three domains (6), is a component of the HCV replication complex (7-10) required for infectious virus production (11-13). Domain I of NS5A is essential for HCV RNA replication (14), while most of domain II is not involved (12). Domain III partici-

RNA helicase DDX3 maintains lipid homeostasis through upregulation of the microsomal triglyceride transfer protein by interacting with HNF4 and SHP

“…All these reports implied a direct correlation between HCV and liver steatosis. Given that DDX3 interacts with HCV core and NS5A 16 17 18 34 and is down-regulated by HCV infection ( Fig. 1a ), HCV infection may interfere with the DDX3-augmented transactivation activity of HNF4 on MTP promoter leading to reduced MTP expression by which, at least in part, HCV infection induces liver steatosis.…”

“…While at the later stage of infection, suppression of MTP expression is beneficial for the “storage” of HCV virus particles in lipid droplets for its latency and persistent infection 61 . Interestingly, DDX3 was identified as a cellular cofactor of HCV infection 32 33 34 62 63 64 . From this point of view, it makes sense that HCV hijack DDX3 to regulate MTP promoter to aid its virus propagation and persistent infection.…”

“…A recent study indicated that DDX3 knockout mice were embryonic lethal 31 . Apart from acting as a multifunctional host cellular factor, DDX3 has been found to be involved in the HCV life cycle 32 33 34 . As noted, DDX3 was initially identified as an HCV core-interacting protein 16 17 18 , moreover, HCV core protein induces steatosis in HCV core-expressing transgenic mice 35 36 .…”

Phosphorylation-Mediated Interaction of Hepatitis C Virus NS5A and the Cellular YB-1 Controls HCV Propagation and the Early Stage of Viral RNA Replication

“…To explore how YB-1 regulates the HCV life cycle, we first examined the interaction between NS5A and YB-1, and our data clearly identify YB-1 as a novel NS5A-interacting protein [23] , and that YB-1 regulates HCV RNA replication. Furthermore, by comparing the effects of knockdown of YB-1, before and after HCV infection, on intracellular HCV RNA levels and the formation of the replication complexes, we presented evidences to indicate that YB-1 is involved in the early stage, but not the steady state, of HCV RNA replication.…”

“…H. Wu Lee, unpublished data and ref. [27] ), and both factors associate with core, NS3, NS5A and the HCV RNA [4,23,[27][28][29][30] , implying that they function as a complex at least in some steps of the HCV life cycle. However, while DDX3 promotes HCV IRES-mediated translation [31,32] , we found that YB-1 moderately inhibits HCV translation early in the Figure 1.…”