Thus, the results of this previous report suggest that SMs synthesized by SGMS1 can be easily incorporated into membranous replication complexes. As for SGMS2, we found that HCV infection significantly increased the expression of SGMS2, although the relationship between SGMS2 and HCV replication was hardly seen in this study. The relationship between SGMS2 and HCV propagation, thus, biological activity is an issue that should be elucidated in future studies. We also demonstrated in this study that reduction of SM molecular species by NA808, a hepatotropic SPT inhibitor with little immunosuppressive activity, inhibits HCV replication in humanized chimeric mice regardless of viral genotype (Figure 4). Notably, treatment with NA808 (5 mg/kg) restored SM and ceramide levels in the liver to the levels observed in uninfected chimeric mice (Figure 5).

Apparently, a slight reduction in SM had a significant influence on HCV, indicating that SM plays an important role in the HCV life cycle. SM is required for many viral processes in host-pathogen interactions [29]�C[31]. For instance, viral envelopes of human immunodeficiency virus type 1 (HIV-1) and herpes simplex virus (HSV) are enriched with SM, which is necessary for efficient virus infectivity [32], [33]. With regard to HCV, in addition to efficient virus infectivity [34], SM is present in the raft domain, which serves as a site of virus replication, together with other sphingolipids and cholesterol [6]. Moreover, SM is a component of VLDL whose assembly component and pathway is required for HCV morphogenesis and secretion [34], [35].

The above-mentioned observations suggest that SM plays a multifaceted role in the HCV life cycle; therefore, SM is likely to be a good therapeutic target. HCV is thought to replicate in a specialized compartment characterized as a DRM (designated as the membranous replication complex) [6]. SM, cholesterol, and phosphatidylinositol (PI) are thought to be the lipids that make up the membranous replication complex. With regard to PI, several siRNA screening have recently identified type III phosphatidylinositol 4-kinases (PI4K) as crucial host factors for HCV replication [36]�C[39]. In HCV replicon containing cells, PI4P distribution is altered and enriched in the membranous replication complex by PI4KIII�� synthesis. Although the ability of PI to influence membrane bending and regulate intracellular processes (e.

g. vesicle fusion, budding, and sorting) has been reported, the role of PI4P in the formation of the membranous replication complex remains to be elucidated. SM and cholesterol organize the solid membrane characterized as the DRM, where HCV replicates [6]. In fact, we and other Anacetrapib groups demonstrated that reduction of SM and cholesterol suppressed HCV replication [7], [9], [12], [40]. We performed the immunofluorescent analysis using lysenin. However, lysenin did not co-localize with NS4B protein.