Analysis of integrated ground squirrel hepatitis virus and flanking host DNA in two hepatocellular carcinomas.

We cloned the integrated ground squirrel hepatitis B virus (GSHV) sequences from two hepatomas showing a single viral insertion. The GSHV inserts shared structural features with integrated DNAs of other hepadnaviruses. Insertional activation of a cellular gene appears unlikely: the integrated GSHV sequences lacked the known viral enhancers and were not expressed in the tumors, and we found no evidence for the presence of a gene at the integration site. Our results, together with those earlier studies, suggest that GSHV does not behave as an extensive insertional mutagen, in sharp contrast with the closely related woodchuck hepatitis virus. GSHV may thus cause carcinogenesis by more indirect mechanisms, as does the human hepatitis B virus.     

Woodchuck Hepatitis Virus Enhancer I and Enhancer II Are Both Involved in N-myc2 Activation in Woodchuck Liver Tumors

Direct activation of the N-myc2 oncogene by insertion of woodchuck hepatitis virus (WHV) DNA is a major oncogenic step in woodchuck hepatocarcinogenesis. We previously reported that WHV enhancer II (We2), which controls expression of the core/pregenome RNA, can also activate the N-myc2 promoter in hepatoma cell lines. To better define the integrated WHV regulatory sequences responsible for N-myc2 promoter activation in woodchuck liver tumors, we analyzed the structure and enhancer activity of a single viral integrant found at the win locus in tumor 2260T1 and mapping approximately 175 kb 3′ of N-myc2. This viral insert was made of 11 concatemerized WHV fragments, 5 of which overlapped with We2 sequences and 1 with WHV sequence homologous to that of hepatitis B virus enhancer I (We1). In transient transfection assays in hepatoma-derived cells, the We2 activator was found to be fully effective only when inserted in close proximity to the N-myc2 promoter whereas the We1 element by itself was apparently devoid of activity. In contrast, the 2260T1 viral insert exhibited a potent enhancer capacity that depended both on multimerized We2 and on We1 sequences. In a survey of different woodchuck hepatomas, both elements were commonly found within integrated viral sequences involved in long-range N-myc2 activation.     

Core antigen and antibody in woodchucks after infection with woodchuck hepatitis virus

The woodchuck hepatitis virus is a naturally occurring hepatitis B-like virus that infects the eastern woodchuck. Direct immunofluorescence staining for woodchuck hepatitis virus core antigen in liver biopsies demonstrated the presence of this antigen in 14 of 17 chronically infected woodchucks, and in 8 of 10 woodchucks undergoing acute infections. Fluorescent localization of woodchuck hepatitis virus core antigen was typically cytoplasmic, and this was confirmed further by electron microscopy. Experimental infection with woodchuck hepatitis virus was achieved in four of four woodchucks inoculated with serum from chronic carrier woodchucks. All infected animals developed a self-limited disease characterized by seroconversion to antibodies against the major viral antigens (core and surface antigens); naturally acquired acute infection demonstrated a similar course. A chimpanzee seronegative for all markers of hepatitis B virus developed a subclinical infection after inoculation with woodchuck hepatitis virus.     

Cloning and structural analysis of integrated woodchuck hepatitis virus sequences from a chronically infected liver

We have isolated and determined the structure of a recombinant clone in lambda phage Charon 30 which contains woodchuck hepatitis virus sequences integrated in woodchuck genomic DNA sequences. This clone, in contrast to previously reported clones (Ogston et al., Cell 29:385-394, 1982), was isolated from a chronically infected liver which never developed hepatocellular carcinoma. Southern blot analysis of viral sequences in the clone in conjunction with electron microscope heteroduplex analysis showed that the integrated viral sequences did not contain internal rearrangements, as have those from hepatomas, but were colinear with the cloned viral genome except for the deletion of approximately 500 base pairs of viral sequences (between positions 1,000 and 1,550 on the viral map). Therefore, the integration was probably a defective genome incapable of supporting viral replication. However, the complete open reading frames coding for the viral X, core, presurface , and surface antigen genes were present, indicating that the viral sequences could code for viral antigens. Southern blot analysis of the normal cellular flanking sequences, using flanking sequence probes from the clone, showed that no detectable rearrangements of cellular DNA (less than 50 base pairs) had occurred at the site of viral integration.     

Woodchuck gamma interferon upregulates major histocompatibility complex class I transcription but is unable to deplete woodchuck hepatitis virus replication intermediates and RNAs in persistently infected woodchuck primary hepatocytes.

Gamma interferon (IFN-gamma) is an important mediator with multiple functions in the host defense against viral infection. IFN-gamma, in concert with tumor necrosis factor alpha (TNF-alpha), leads to a remarkable reduction of intrahepatic replication intermediates and specific mRNAs of hepatitis B virus (HBV) by a noncytolytic mechanism in the transgenic mouse model. Thus, it is rational to evaluate the potential value of IFN-gamma for the treatment of chronic HBV infection. In the present study, we expressed recombinant woodchuck IFN-gamma (wIFN-gamma) in Escherichia coli and mammalian cells. wIFN-gamma protected woodchuck cells against infection of murine encephalomyocarditis virus in a species-specific manner. It upregulated the mRNA level of the woodchuck major histocompatibility complex class I (MHC-I) heavy chain in permanent woodchuck WH12/6 cells and regulated differentially the gene expression. However, the level of the replication intermediates and specific RNAs of woodchuck hepatitis virus (WHV) in persistently WHV-infected primary woodchuck hepatocytes did not change despite a treatment with 1,000 U of wIFN-gamma per ml or with a combination of wIFN-gamma and woodchuck TNF-alpha. Rather, hepatocytes derived from chronic carriers had an elevated level of the MHC-I heavy-chain mRNAs, most probably due to the exposure to inflammatory cytokines in vivo. Treatment with high doses of wIFN-gamma led to an abnormal cell morphology and loss of hepatocytes. Thus, wIFN-gamma regulates the gene expression in woodchuck hepatocytes but could not deplete WHV replication intermediates and mRNAs in persistently infected hepatocytes. The cellular response to wIFN-gamma may be changed in hepatocytes from chronically WHV-infected woodchucks. It should be clarified in the future whether the continuous exposure of hepatocytes to inflammatory cytokines or the presence of viral proteins leads to changes of the cellular response to wIFN-gamma.     

Nucleotide sequence of a cloned woodchuck hepatitis virus genome: comparison with the hepatitis B virus sequence.

The complete nucleotide sequence of a woodchuck hepatitis virus genome cloned in Escherichia coli was determined by the method of Maxam and Gilbert. This sequence was found to be 3,308 nucleotides long. Potential ATG initiator triplets and nonsense codons were identified and used to locate regions with a substantial coding capacity. A striking similarity was observed between the organization of human hepatitis B virus and woodchuck hepatitis virus. Nucleotide sequences of these open regions in the woodchuck virus were compared with corresponding regions present in hepatitis B virus. This allowed the location of four viral genes on the L strand and indicated the absence of protein coded by the S strand. Evolution rates of the various parts of the genome as well as of the four different proteins coded by hepatitis B virus and woodchuck hepatitis virus were compared. These results indicated that: (i) the core protein has evolved slightly less rapidly than the other proteins; and (ii) when a region of DNA codes for two different proteins, there is less freedom for the DNA to evolve and, moreover, one of the proteins can evolve more rapidly than the other. A hairpin structure, very well conserved in the two genomes, was located in the only region devoid of coding function, suggesting the location of the origin of replication of the viral DNA.     

Failure to detect polyalbumin-binding sites on the woodchuck hepatitis virus surface antigen: implications for the pathogenesis of hepatitis B virus in humans.

Binding sites for polymerized albumin on hepatitis B virus components were reported in human hepatitis B virus chronic carriers predominantly with active viral replication (HB e antigen positive). The presence of comparable albumin-binding sites in the woodchuck hepatitis virus (WHV) model was examined on WHV components obtained from woodchucks with active viral replication (DNA polymerase positive). Binding sites for polymerized woodchuck serum albumin were not detected on the intact WHV virion, on 22-nm woodchuck hepatitis surface antigen (WHsAg), or on WHsAg polypeptides. Woodchuck albumin was not detected in purified 22-nm WHsAg, and anti-albumin antibodies were not detected in WHV chronic-carrier woodchucks. Our results in the WHV model argue against a role for viral polyalbumin-binding sites in tissue- and host-specific virus infectivity.     

Serological relationship of woodchuck hepatitis virus to human hepatitis B virus.

Two antigenic systems of the woodchuck hepatitis virus have been identified. The relationship between viral antigens of the woodchuck hepatitis virus and the human hepatitis B virus was determined by using immunoprecipitation, hemagglutination, and immune electron microscopy techniques. Antigens found on the cores of the two viruses were cross-reactive. Lack of cross-reactivity between the surface antigens of the two viruses in immunodiffusion experiments suggested that the major antigenic determinants of the viral surfaces are different; however, results of passive hemagglutination tests indicated that there are common minor determinants. Nucleic acid homology, as measured by liquid hybridization, was found to be 3 to 5% of the viral genomes. The results of this study provide further evidence that woodchuck hepatitis virus is the second member of a new class of viruses represented by human hepatitis B virus. Since virus-infected woodchucks may acquire chronic hepatitis and hepatocellular carcinoma, these antigens and their respective antibodies will be useful markers for following the course of virus infection in investigations of the oncogenic potential of this class of viruses. The nucleocapsid antigen described may be a class-specific antigen of these viruses and, thus, may be useful in discovering new members of the group.     

荧光定量PCR检测土拨鼠肝炎病毒核酸方法的建立

目的建立土拨鼠肝炎病毒（woodchuck hepatitis virus,WHV）核酸的荧光定量PCR（Real-time PCR）检测方法,应用于土拨鼠肝炎病毒模型的研究。方法分别根据土拨鼠肝炎病毒核心抗原（WHcAg）和表面抗原（WHsAg）的DNA序列设计13对扩增引物,从中筛选无非特异性扩增及引物二聚体且灵敏度高的引物,用于土拨鼠血清中WHV DNA的Real-time PCR检测。建立感染土拨鼠肝炎病毒的土拨鼠血清中WHV核酸的Real-timePCR检测方法。结果根据WHsAg基因的5＇端设计的一对引物WHVSF1与WHVSR1,检测灵敏度可达1×101拷贝/μL,病毒拷贝数与Real-time PCR Ct值的标准曲线的R2值为0.997,且电泳未见明显非特异性条带及引物二聚体。结论建立了土拨鼠血清中WHV DNA的Real-time PCR检测方法,该方法为进一步研究土拨鼠肝炎病毒模型奠定了基础。