Squamous Cell Carcinoma Antigen 1-mediated Binding of Hepatitis B Virus to Hepatocytes Does Not Involve the Hepatic Serpin Clearance System

Abstract

The cellular receptor for hepatitis B virus (HBV)has not yet been identified. A recent candidate is a homologue of squamous cell carcinoma antigen 1 (SCCA1), a serpin. This study confirms that transfection of SCCA1 into mammalian cells (both hepatocyte-derived and of non-hepatocyte origin) results in increased HBV binding. Furthermore, virus bound to transfected cells is protected significantly from degradation by trypsin (75% compared with 30% in untransfected cells). The possibility that HBV enters cells via the hepatic clearance system for serpin-enzyme complexes was investigated by analysis of the reactive site loop of SCCA1. Functional and deletion mutants of SCCA1 were constructed by site-directed mutagenesis and compared with the wild type construct. In no case was virus binding reduced by functional alterations or deletions within the reactive site loop. A possible role for the low density lipoprotein receptor-related protein (LRP) in binding virus was investigated. SCCA1 transfection of Huh7 cells was shown to result in up-regulation of LRP expression, reaching levels observed in total liver. However, the use of receptor-associated protein (RAP), a competitive ligand for LRP, suggests than LRP up-regulation is not responsible for enhanced virus binding to SCCA1-transfected cells.Hepatitis B virus (HBV) 1 is a member of the hepadnavirus family and exhibits extreme host and tissue specificity, being able to infect only humans and higher primates and its replication being limited almost exclusively to hepatocytes. The molecular basis of this hepatotropism remains poorly understood but may be attributable to a combination of factors, including liver-specific transcription factors required by the virus for replication, and liver-specific expression of the host cell receptor utilized during the initial stages of infection (1).The early stages of the HBV life cycle, virus binding and internalization, remain obscure, largely because of the lack of a permissive cell culture system. Many studies have made use of primary hepatocytes, but difficulties in obtaining these cells, and variability between and within batches, hamper the use of primary tissue. Moreover, primary hepatocytes lose susceptibility to HBV infection within days (2).The cellular receptor for HBV has proved elusive. , bears significant sequence homology to a serine proteinase inhibitor (serpin), squamous cell carcinoma antigen 1 (SCCA1). HBV-BP was shown to interact with the pre-S1 domain of the HBV surface protein, which is now widely accepted to be the viral ligand involved in the initial interaction with the cellular receptor (4, 5). Furthermore, transfection of HBV-BP into HepG2 cells resulted in a 2-fold increase in virus binding capacity, whereas Chinese hamster ovary cells transfected with HBV-BP showed a newly acquired susceptibility to virus binding, albeit at low levels. It was reported also that virus particles were internalized to a greater degree in cells expressing HBV-BP. These results have not yet been confirmed.The possibility tha...

SERPINB3 modulates TGF-β expression in chronic liver disease

“…To explore the effect of the RSL of SERPINB3 in the induction of the TGF-b1 gene, previously described deletion loop mutants of SERPINB3, 28 were also used for cell transfection. The following vectors showing lack of inhibition of target proteinases were chosen: Mutant A (deletion of total hinge region of RSL-SERPINB3), Mutant B (deletion of total RSL-SERPINB3), and Mutant C (Mutation of the P14 codon from alanine to arginine) ( Figure 6).…”

Gene therapy of liver tumors with human liver-specific nanoparticles

“…30 The hepatotropic specificity of HBV and consequently also the L nanoparticles, is determined by the interaction of the HBsAg with an elusive cellular receptor, although several candidate receptors or co-receptors have been proposed, including annexin V 31 and squamous cell carcinoma antigen-1 homolog (SCCA-1). 32 L nanoparticles are well tolerated and do not appear to induce serious adverse effects (Table 1, Figure 2). Furthermore, L nanoparticles by themselves have no effect on tumor suppression or progression (Figure 1).…”

Expression of squamous cell carcinoma antigen‐1 in liver enhances the uptake of hepatitis B virus envelope‐derived bio‐nanocapsules in transgenic rats

“…One of these groups first isolated SCCA1 as a ligand of the tetrameric pre‐S1 (21–47) peptide and showed that expression of SCCA1 enhances HBV infection and that recombinant SCCA1 inhibits HBV infection [10]. Another group demonstrated that the SCCA1‐mediated HBV infection does not involve the hepatic serpin clearance system [11]. The in vitro experiments described in the present study (Fig.…”

“…2C: d,e and D). Taken together, these results indicate that SCCA1 is capable of interacting directly with BNC, as well as with HBV [10,11], and that the soluble SCCA1 protein inhibits the attachment of BNC to the surface of hepatic cells, presumably by competing with SCCA1 expressed on the cell surface.…”