Efficient assembly of hepatitis delta virus (HDV) was achieved by cotransfection of Huh7 cells with two plasmids: one to provide expression of the large, middle, and small envelope proteins of hepatitis B virus (HBV), the natural helper of HDV, and another to initiate replication of the HDV RNA genome. HDV released into the media was assayed for HDV RNA and HBV envelope proteins and characterized by rate-zonal sedimentation, immunoaffinity purification, electron microscopy, and the ability to infect primary human hepatocytes. Among the novel findings were that (i) immunostaining for delta antigen 6 days after infection with 300 genome equivalents (GE) per cell showed only 1% of cells as infected, but this was increased to 16% when 5% polyethylene glycol was present during infection; (ii) uninfected cells did not differ from infected cells in terms of albumin accumulation or the presence of E-cadherin at cell junctions; and (iii) sensitive quantitative real-time PCR assays detected HDV replication even when the multiplicity of infection was 0.2 GE/cell. In the future, this HDV assembly and infection system can be further developed to better understand the mechanisms shared by HBV and HDV for attachment and entry into host cells.

Chronic infection with the human hepatitis B virus (HBV) is a global health problem and a main cause of progressive liver diseases. HBV exhibits a narrow host range, replicating primarily in hepatocytes. Both host and hepatocyte specificity presumably involve specific receptor interactions on the target cell; however, direct evidence for this hypothesis is missing. Following the observation that HBV entry is specifically blocked by L-protein-derived preS1-lipopeptides, we visualized specific HBV receptor/ligand complexes on hepatic cells and quantified the turnover kinetics. Using fluorescein isothiocyanate-labeled, myristoylated HBV preS1-peptides we demonstrate (1) the presence of a highly specific HBV receptor on the plasma membrane of HBV-susceptible primary human and tupaia hepatocytes and HepaRG cells but also on hepatocytes from the nonsusceptible species mouse, rat, rabbit and dog; (2) the requirement of a differentiated state of the hepatocyte for specific preS1-binding; (3) the lack of detectable amounts of the receptor on HepG2 and HuH7 cells; (4) a slow receptor turnover at the hepatocyte membrane; and (5) an association of the receptor with actin microfilaments. The presence of the preS1-receptor in primary hepatocytes from some non-HBV-susceptible species indicates that the lack of susceptibility of these cells is owed to a postbinding step. Conclusion: These findings suggest that HBV hepatotropism is mediated by the highly selective expression of a yet unknown receptor* on differentiated hepatocytes, while species specificity of the HBV infection requires selective downstream events, e.g., the presence of host dependency or the absence of host restriction factors. The criteria defined here will allow narrowing down reasonable receptor candidates and provide a binding assay for HBV-receptor expression screens in hepatic cells. (HEPATOLOGY 2013;58:31-42) See Editorial on Page 9 C hronic hepatitis B is a global medical problem caused by the human hepatitis B virus (HBV). About 350 million people are persistently infected and need therapeutic treatment to reduce the risk of developing liver cirrhosis and HCC.1 Since the currently approved medications are mostly noncurative, novel therapeutic strategies are needed.2 HBV, the prototypic member of the hepadnavirus family, is a 42 nm, enveloped, partially doublestranded DNA virus with a restricted host range and an extraordinary tropism to infect the parenchymal liver cells of its host.3 Since HBV properly assembles

Previous studies have attempted to clarify the roles of the pre-S1 and pre-S2 domains of the large envelope protein of hepatitis B virus (HBV) in attachment and entry into susceptible cells. Difficulties arise in that these domains contain regions involved in the nucleocapsid assembly of HBV and overlapping with the coding regions of the viral polymerase and RNA sequences required for reverse transcription. Such difficulties can be circumvented with hepatitis delta virus (HDV), which needs the HBV large envelope protein only for infectivity. Thus, mutated HBV envelope proteins were examined for their effects on HDV infectivity. Changing the C-terminal region of pre-S1 critical for HBV assembly allowed the envelopment of HDV and had no effect on infectivity in primary human hepatocytes. Similarly, a deletion of the 12 amino acids of a putative translocation motif (TLM) in pre-S2 had no effect. Thus, these two regions are not necessary for HDV infectivity and, by inference, are not needed for HBV attachment and entry into susceptible cells.Hepatitis B virus (HBV) is an important human pathogen, causing acute and chronic hepatitis and hepatocellular carcinoma, and yet we have only a very partial understanding of how it uses its envelope proteins to attach and enter susceptible cells (12). Here we point out some important similarities between the major envelope protein of HBV and that of its distant relative, duck hepatitis B virus (DHBV). Also we make use of hepatitis delta virus (HDV), a subviral agent that uses the envelope proteins of HBV, to address two controversial issues regarding the requirements for HBV attachment and entry.The Hepadnaviridae family is divided into two genera, the ortho-and avihepadnaviruses. HBV is the prototype of the orthohepadnaviruses. As represented in Fig. 1A, HBV encodes three envelope proteins, large (L), middle (M), and small (S), that have a common C terminus. Pre-S1 is the N terminus of L, which is unique relative to M. Similarly, pre-S2 is the N terminus of M, which is unique relative to S. DHBV is the prototype of the avihepadnaviruses. It has only two envelope proteins, L and S (12). We used alignment programs to compare the L proteins of representative HBV and DHBV, with results as summarized in Fig. 1B. Amidst many amino acid differences and several deletions in DHBV relative to HBV, some conserved regions were revealed. Some of these conservations might be due to the fact that the open reading frame for L overlaps with that of the viral polymerase (12). However, other conservations might reflect features of L that are needed for virus assembly and/or infectivity. As indicated, HBV and DHBV share three predicted transmembrane domains in S (7). Only HBV has a fourth domain (12). Beyond this, the folding of the hepadnavirus L proteins is complicated by the fact that the pre-S region is considered to exist in two topologies, inside or outside, relative to the host endoplasmic reticulum during assembly and/or to the viral envelope after release (5,12,27). These two conformatio...

Phlorhizin interferes with glucose transport. Glucose depletion triggers suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and cell membrane scrambling. Eryptosis is further triggered by oxidative stress. The present study explored whether phlorhizin influences eryptosis following glucose depletion or oxidative stress. Cell membrane scrambling was estimated from annexin binding, cell volume from forward scatter (FSC), and cytosolic Ca(2+) concentration from Fluo-3 fluorescence. Phlorhizin (10-100 μM) added alone did not modify scrambling, FSC, or Fluo-3 fluorescence. Glucose depletion (48 h) significantly increased Fluo-3 fluorescence, decreased FSC, and increased annexin binding, effects in part significantly blunted by phlorhizin (annexin binding ≥ 10 μM, FSC ≥ 50 μM). Oxidative stress (30 min 0.3 mM tert-butylhydroperoxide) again significantly increased Fluo-3 fluorescence and triggered annexin binding, effects again in part significantly blunted by phlorhizin (Fluo-3 fluorescence ≥ 50 μM, annexin-binding ≥ 10 μM). Phlorhizin did not blunt the cell shrinkage induced by oxidative stress. The present observations disclose a novel effect of phlorhizin, that is, an influence on suicidal erythrocyte death following energy depletion and oxidative stress.

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