Formation of intracellular particles by hepatitis B virus large surface protein

Xu, Zhichang; Bruss, Volker; Yen, T. S. Benedict

doi:10.1128/jvi.71.7.5487-5494.1997

Cited by 65 publications

(34 citation statements)

References 31 publications

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“…A recent study demonstrated that LHBs itself can form 20-nm particles which are retained in a post-rough endoplasmic reticulum compartment, possibly by interacting with calnexin and other regulatory endoplasmic reticulum proteins. 49 Our analyses excluded the possibility that LHBs inhibits the secretion of IL-2 and GM-CSF. The effects of LHBs on the immune response augmenting properties of IL-2 and GM-CSF in vivo, therefore, were not related to the inhibition of their secretion from the cell by LHBs as demonstrated by in vitro transfection experiments.…”

Section: Discussionmentioning

confidence: 96%

Cytokine and hepatitis B virus DNA Co-immunizations enhance cellular and humoral immune responses to the middle but not to the large hepatitis B virus surface antigen in mice

et al. 1998

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Genetic immunization is a potentially useful strategy to prevent or treat hepatitis B virus (HBV) infection. We have previously shown that HBV envelope proteins are highly immunogenic using this technique. The large envelope protein (LHBs), however, induced significantly weaker humoral and cellular immune responses when compared with the middle envelope protein (MHBs). We studied the effect of co-immunizations with cytokine DNA expression constructs encoding for interleukin (IL)-2 and (GM-CSF) on the immunogenicity of LHBs at the B-and T-cell level. Co-immunizations of mice with plasmids encoding for MHBs and IL-2 or GM-CSF increased anti-HBs responses, helper T-cell proliferative activity, and cytotoxic T lymphocyte (CTL) killing. In contrast, co-immunizations of plasmids encoding for LHBs and IL-2 or GM-CSF had no effect on humoral and cellular immune responses. LHBs did not inhibit the production or secretion of IL-2 and GM-CSF. In addition, IL-2, tumor necrosis factor alfa (TNF-␣), and interferon gamma (IFN-␥) had no suppressive effect on HBV envelope protein expression in vitro. Based on these data, MHBs, but not LHBs, genetic immunization can be augmented by IL-2 or GM-CSF cytokines. (HEPATOLOGY 1998;28:202-210.)Hepatitis B virus (HBV) is a noncytopathic, hepatotropic virus infecting more than 350 million individuals worldwide. 1 Hepatitis B is a leading cause of chronic hepatitis, cirrhosis, and hepatocellular carcinoma. 2 The cellular immune response to HBV is thought to be responsible for viral clearance and pathogenesis of liver disease. In acutely infected patients who successfully clear the virus the CD4ϩ and CD8ϩ T-cell response to HBV is vigorous, polyclonal, and multispecific. [3][4][5][6][7][8][9][10] The T cells typically secrete type-1 antiviral cytokines, such as interferon gamma (IFN-␥) and tumor necrosis factor alfa (TNF-␣), upon antigen stimulation. By contrast, in chronically infected patients, the T-cell response is relatively weak and is antigenetically more restricted, except during acute exacerbations of chronic disease or after spontaneous or IFN-␣ induced viral clearance. [11][12][13] The cytokine profile of the intrahepatic HBVspecific T cells is variable in chronically infected individuals. The observation of spontaneous HBV clearance in some chronically infected individuals implies that the suboptimal cellular immune response may be reversible; therefore, strategies designed to boost the HBV-specific T-cell immune response, to alter the balance between the cytopathic and the regulatory components of the response, or to mimic the regulatory functions of the T-cell response in the liver may be able to terminate persistent infection.In this regard, genetic immunization offers the potential advantage of inducing cellular and humoral immune responses against conserved viral epitopes because this approach uses DNA expression plasmids, instead of proteins, for vaccination. This technique involves the transfer of a viral gene into muscle cells and antigen presenting cells by a plasmid vec...

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Section: Discussionmentioning

confidence: 96%

Cytokine and hepatitis B virus DNA Co-immunizations enhance cellular and humoral immune responses to the middle but not to the large hepatitis B virus surface antigen in mice

et al. 1998

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“…These results indicated that both pre-S mutant constructs lead to retention of large S-protein at the ER. Earlier experiments performed by Xu et al 38 demonstrated that the large S-protein colocalizes with calnexin, a luminar protein of the ER that might prevent the large S-protein from secretion. They also showed that the mutated S-proteins are still capable of building globular HBsAg particles.…”

Section: Discussionmentioning

confidence: 99%

The Pre-S region determines the intracellular localization and appearance of hepatitis B virus

et al. 1999

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The functional role of the hepatitis B virus (HBV) pre-S region for assembly and appearance of the virus is not completely understood. In this study, 3 natural-occurring mutants were investigated. Three mutants of the pre-S region-a point mutation in the CCAAT box (MUT1), a 6-bp deletion (MUT2) 3Ј of the CCAAT box, and a 153-bp deletion (MUT3) in the preS2 domain-were cloned alone or in combinations in replication-competent HBV plasmids and transfected in hepatoma cells. The impact on HBV assembly and appearance was studied by Northern Blot, primer extension analysis, immunofluorescence studies, enzyme-linked immunosorbent assay, and electron microscopy. An inversed ratio of pre-S/S mRNA transcripts compared with wild-type (wt) HBV was found when either MUT1 or -2 were included into the plasmid. Intracellular localization with both mutants showed retention of large S-protein in the endoplasmic reticulum and nuclear accumulation of core protein. The extracellular amount of S-protein was reduced with MUT1 and -2 or combinations in which 1 of the mutants was included. However, the extracellular appearance of viral products was comparable with wtHBV. In contrast, MUT3 showed major changes. Virion-like particles had a fried-egg, and filaments a screw-like appearance. The S-promoter mutations MUT1 and MUT2 correlated with viral retention. MUT3 leads to malformed viral particles. Therefore, different regions in the pre-S domain are essential to determine the intracellular localization and extracellular appearance of HBV, and might contribute to the prognosis of chronic HBV infection. (HEPATOLOGY 1999; 30:517-525.)The hepatitis B virus (HBV) is the smallest DNA virus known to be pathogenic for humans. The HBV is a member of the hepadnavirus family, showing a close host tropism. The genome of the HBV consists of a small circular DNA of 3.2 kb in length. Despite its small size, the HBV genome contains 4 open reading frames partly overlapping and generating at least 7 viral gene products. The 4 open reading frames are under the transcriptional control of 4 promoters (preS1, S, C, and X promoter) and 2 enhancer (enhancer I and II) elements. [1][2][3] The envelope gene of the HBV is controlled by 2 different promoters: the pre-S-and the S-promoter, which regulate transcription of a 2.4-and a 2.1-kb mRNA, respectively. The pre-S-promoter is located 5Ј of the first in frame ATG of the large (pre-S1) envelope protein. The S-promoter is found in the coding region of the pre-S gene and is a TATA-less promoter. Mainly, 2 factors control the activity of the Spromoter: Sp 1 and NF-Y. 4-7 NF-Y binds to the so-called CCAAT box and is especially important for the regulation of the S-gene controlling the ratio between the pre-S and S mRNA. 4,8 The 2 mRNAs transcribed from the S-gene code for 3 S-proteins (small, middle, and large) sharing the 226 amino acids at the C-terminus. Translation of the small S-protein starts at the third in-frame ATG of the S-gene, while the other 2 proteins start at the first and second ATG. However, some sub...

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“…16 In a recent study, the L protein alone was found to form intravesicular 20-nm spherical particles identical to the S and M protein particles but retained in intracellular compartments by calnexin. 17 Nevertheless, the so-called ground-glass appearance of the hepatocytes in chronic HBV infection seems to be caused by the intracellular accumulation of L-protein-rich filaments. This intracellular accumulation is seen in patients in late phases of chronic HBV infection, especially at the phase of cirrhosis, when a high level of intracellular expression of HBV surface proteins is associated with a low level of serum HBV surface proteins.…”

Section: Discussionmentioning

confidence: 99%

Ultrastructural analysis of hepatitis B virus in HepG2-transfected cells with special emphasis on subviral filament morphogenesis

Roingeard

Sureau

1998

Hepatology

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The intracellular accumulation of empty hepatitis B virus (HBV) particles of filamentous shape leads to a direct cytopathic effect in so-called ground-glass hepatocytes. The aim of this study was to investigate how these filaments can be structurally formed at the cellular level. By electron microscopy, we reexamined the HBV-producer HepG2T-14 cells, which have been described as producing a substantial amount of empty HBV filaments compared with the other forms of HBV particles. Examination of ultrathin sections of HepG2T14 cells revealed the presence of HBV virions and filaments at the periphery of extremely large intracellular cisternae, probably related to a pre-Golgi compartment. Very long filaments appeared to be formed by a tubular budding of a long portion of the cisterna membrane. This phenomenon may be identical to that observed in the hepatocytes of HBV chronic carriers, in which the inability of the infected cell to export long HBV filamentous particles through the cellular secretion pathway seems to be at the origin of a direct cytopathic effect. (HEPATOLOGY 1998;28: 1128-1133.)Hepatitis B virus (HBV) is an enveloped hepatotropic DNA virus that infects a large number of people worldwide. 1 Its genome is encapsulated with a virus-encoded polymerase in a nucleocapsid surrounded by a host-derived lipid envelope bearing three viral surface proteins. 2 The large (L) protein, containing the preS1, preS2, and S domains, is translated from the first start codon of the surface open reading frame. The middle (M) protein, containing the preS2 and S domain, and the small (S) protein are translated from in-frame start codons further downstream. 2 During synthesis, all three proteins are cotranslationally inserted into the endoplasmic reticulum (ER) as transmembrane proteins that can form disulfide bridges with each other. 3 The S protein traverses the ER membrane at least twice to form a cytosolic loop and a luminal domain. 4 The M protein has a similar topology with the additional N-terminal preS2 domain located in the ER lumen. 5 The L protein can adopt two different transmembrane topologies, allowing the exposure of the N-terminal preS domain at either the luminal or the cytosolic side of the ER membrane. 6 This latter form is essential during HBV morphogenesis to establish a protein-protein interaction between the cytoplasmic core particle and a specific sequence within the preS domain of the L protein. 7,8 One peculiarity of HBV morphogenesis compared with that of other viruses is that the surface proteins not only envelop the nucleocapsid to form a mature virion, they are capable of forming subviral empty spherical or filamentous particles in the absence of nucleocapsid. 2 Although the envelopes of all types of HBV particles contain the M and S proteins, filamentous and virion envelopes are richer in the L protein. 2 It is thought that during morphogenesis, the M and S proteins, in the absence of any other viral proteins, can bud into a post-ER/pre-Golgi compartment to form 20-nm spherical particles that ca...

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Formation of intracellular particles by hepatitis B virus large surface protein

Cited by 65 publications

References 31 publications

Cytokine and hepatitis B virus DNA Co-immunizations enhance cellular and humoral immune responses to the middle but not to the large hepatitis B virus surface antigen in mice

Cytokine and hepatitis B virus DNA Co-immunizations enhance cellular and humoral immune responses to the middle but not to the large hepatitis B virus surface antigen in mice

The Pre-S region determines the intracellular localization and appearance of hepatitis B virus

Ultrastructural analysis of hepatitis B virus in HepG2-transfected cells with special emphasis on subviral filament morphogenesis

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