Activation of the Envelope Proteins by a Metalloproteinase Enables Attachment and Entry of the Hepatitis B Virus into T-Lymphocyte

Abstract

Previously, we identified an HBV binding factor (HBV-BF), a 50-kDa serum glycoprotein which interacts with HBV envelope proteins and which is also located in the membrane of normal human hepatocyte (A. Budkowska et al. (1993) J. Virol. 67, 4316). Here we show that HBV-BF is a neutral metalloproteinase which shares substrate specificity and properties with a newly described family of membrane type matrix metalloproteinases. HBV-BF treatment of the HBV resulted in the cleavage of the N-terminal part of the middle HBV envelope protein at the pre-S2(136-141) amino acid sequence VRGLYF/L (containing a single arginine cleavage site). HBV-BF affected the reactivity of the large HBV protein with pre-S1-specific MAbs, probably inducing the conformational change of the pre-S1 domain. The HBV-BF-digested virus remained morphologically intact with unchanged S antigenic determinants. The structural modifications of the viral envelope proteins induced by HBV-BF enabled cell membrane attachment and viral entry into the T-lymphocyte. Both processes were blocked by the metalloproteinase inhibitor 1,10 phenanthroline. Thus, the host-dependent proteolytic activation of the envelope proteins seems to be essential for the HBV entry into the cell. HBV-BF under a membrane bound or a secreted form could be (one of) the molecule(s) responsible for the HBV proteolytic activation.

Hepatitis B virus replication is upregulated in proliferated peripheral blood lymphocytes

“…Furthermore HBV DNA replication was increased with active cell proliferation. Similar observations were reported by Budkowska et al (17), no detectable cccDNA was observed when PBMCs were co-cultured with a HBV binding factor-digested virus that modified the structure of the envelope proteins and enhanced the capacity of HBV to bind and enter into PBMCs. However, the HBV DNA signal did not decline over time in the cell culture (if there is no virus replication in PBMCs, a progressive reduction of HBV products would be expected).…”

“…It is particularly difficult to detect covalently closed circular DNA (cccDNA), which functions as a template for transcription and a marker for HBV replication. Currently, it is unclear whether HBV replicates in PBMCs (12)(13)(14)(15)(16) and whether the virus readily infects PBMCs (17) due to a lack of cccDNA detection methods. Thus, further studies are required to develop more sensitive methods to detect small quantities of viral products in PBMCs, and eventually determine whether HBV infects and replicates in PBMCs.…”

Cellular receptors for viruses: links to tropism and pathogenesis

“…HBV BF is a neutral metalloproteinase which shares substrate specificity with a family of membrane-type matrix metalloproteinases. Treatment of HBV with the metalloproteinase results in cleavage of the N-terminal part of the pre-S2 envelope protein, and probably induces a conformational change in the pre-S1 domain that enables cell membrane attachment and virus entry into T lymphocytes (Budkowska et al , 1997 ). Since an inhibitor of the metalloproteinase blocked both processes, the host-dependent proteolytic activation of the envelope proteins seems to be essential for HBV entry into cells.…”

“…Since an inhibitor of the metalloproteinase blocked both processes, the host-dependent proteolytic activation of the envelope proteins seems to be essential for HBV entry into cells. The tissue tropism of HBV may be determined by this process of envelope activation and not by cellular receptors, which might be expressed ubiquitously (Budkowska et al , 1997 ; Köck et al , 1996 ).…”

Sulphated and Sulphonated Polymers Inhibit the Initial Interaction of Hepatitis B Virus with Hepatocytes

“…Other proteins that have been identified as a putative HBV receptor, include endonexin II (also called annexin V) (Hertogs et al, 1993), apoliprotein H (Mehdi et al, 1994), the transferrin receptor (CD71) (Franco et al, 1992) and a soluble metalloproteinase (Budkowska et al, 1993). The latter cleaves the N-terminal amino-acid sequence (136-141) of preS2, induces the preS1 domain to change conformation and may enable the HBV particle to attach to, and enter, the target cells (Budkowska et al, 1997). It has also been suggested that two of the putative receptors cited above, namely the apolipoprotein H and endonexin II, bind to lipid rather than protein components on the virus (Neurath et al, 1994).…”