The C Terminus of the Hepatitis B Virus e Antigen Precursor Is Required for a Tunicamycin-sensitive Step That Promotes Efficient Secretion of the Antigen

Abstract

The Hepatitis B virus encodes the secreted e antigen (HBe) whose function in the viral life cycle is unknown. HBe derives from a 25-kDa precursor that is directed to the secretory pathway. After cleavage of the signal sequence, the resulting 22-kDa protein (P22) is processed in a post-endoplasmic reticulum compartment to mature HBe by removal of the 34-amino acid C-terminal domain. The efficiency of HBe secretion is specifically decreased in cells grown in the presence of tunicamycin, an inhibitor of N-glycosylation. Inasmuch as HBe precursor is not N-glycosylated, our data suggest that a cellular tunicamycin-sensitive protein increases the intracellular transport through the HBe secretory pathway. The study of the secretion of HBe derived from C-terminal-truncated precursors demonstrates that the tunicamycin-sensitive secretion absolutely requires a part of the C-terminal region that is removed to form mature HBe, indicating that the cellular tunicamycinsensitive protein increases the efficiency of the intracellular transport of P22. We have also shown that the Escherichia coli ␤-galactosidase can be secreted when fused to the HBe precursor signal sequence and that the P22 C-terminal domain renders the secretion of this reporter protein also tunicamycin-sensitive.

Therapeutic potential of furin inhibitors for the chronic infection of hepatitis B virus

“…The underlying mechanism by which the normal HBeAg precursor can enter the cytosol, unlike the HBeAg precursor induced by furin inhibitors which apparently cannot remains unclear. One reason for this may be that the precursor that is present prior to furin proteolysis may have already bound a tunicamycin‐sensitive glycoprotein on the inboard membrane of the endoplasmic reticulum . The glycoprotein may serve as a vehicle to transport the HBeAg precursor protein from the endoplasmic reticulum to the trans ‐Golgi network and finally to the cell surface if not proteolyzed by furin.…”

Hepatitis B core antigen is a potent inductor of interleukin‐18 in peripheral blood mononuclear cells of healthy controls and patients with hepatitis B infection

“…Interestingly, the 10 preC aa prevent capsid forming by a single cysteine present at position À7 [Schodel et al, 1993]. The resulting P22 luminal protein (aa À10 to 183), enters the secretory pathway to be finally processed to the mature 17-kDa HBeAg by removal of 34 aa (aa 149-183) from its carboxy end [Messageot et al, 1998;Diepolder et al, 1999]. Thus, mature HBeAg (aa À10 to 149) shares 4 aa at its carboxy end with the argininerich domain of HBcAg (aa 146-183).…”

Proteolytic Processing of the Hepatitis B Virus e Antigen Precursor

“…One hypothesis derives directly from our previously reported data (10,24). We have shown that the P22 C-terminal domain plays an important role during the intracellular transport of P22 through the secretory pathway, because a sequence located between amino acids 144 and 165 is required for an efficient HBeAg secretion via an interaction with a cellular tunicamycin-sensitive protein named TSP (24). Consequently, it could be envisaged that TSP would interact with a precursor of the HBeAg shorter than P22, like P20, which ends at Arg 167 .…”

“…A possible explanation could be the nonaccessibility of some putative cleavage sites to the protease that could either be caused by to the folding of P22 or to the presence of cellular proteins that interact with its C-terminal domain. We have previously reported two such proteins which interact specifically with the C-terminal domain of P22 (12,24).…”