Integrated Hepatitis B Virus DNA Research Articles

Evidence of extrachromosomal forms of hepatitis B viral DNA in a bone marrow culture obtained from a patient recently infected with hepatitis B virus.

A cell culture that produces Dane-like particles was initiated from a bone marrow aspirate of an acute hepatitis B patient. By using Southern blot analysis and a recombinant hepatitis B virus (HBV) DNA plasmid probe, extrachromosomal forms of HBV DNA were detected. The two forms of HBV DNA migrate as a closed circular 2.2-kb form and an open circular 3.9-kb form. There was no evidence of HBV DNA integration into the host genome.

Detection of hepatitis B virus DNA in hepatocellular carcinomas in Japan.

Hepatitis B virus (HBV) DNA in hepatocellular carcinoma (HCC) and/or cirrhotic livers of Japanese patients in Japan was investigated by molecular hybridization utilizing a 32P-labeled cloned HBV DNA of adr subtype. Among 24 HCC cases, 9 (37.5%) were positive for serum HBsAg and 10 (41.7%), including 2 cases which were negative for serum HBV markers, were positive for tissue HBsAg in noncancerous portions of the liver. In the latter 10 cases, integrated HBV DNA was detected in HCC. The restriction pattern of integrated viral DNA was different from one case to another. In the noncancerous portion of these 10 HCC cases, free (3/10), random integration (2/10), or clonal integration (1/10) of viral DNA was demonstrated; no hybridization was detected in the remaining 14 HCC cases, either in cancerous or noncancerous portions. Of 6 cases of liver cirrhosis, 2 were positive for serum and histochemical HBsAg; viral DNA was in free state. Viral DNA was not detected in pancreatic tissue in 5 HBsAg-positive cases. The present results are in agreement with previous reports indicating a high frequency of integrated viral DNA in HBV-associated HCC and heterogeneity in the mode of integration. Our results differ in finding no HBV DNA in HCC cases not associated with HBV markers and in finding clonal populations of hepatocytes with integrated HBV DNA less frequently in the noncancerous portion of the liver of HBsAg carriers.

Integration of hepatitis B virus DNA: evidence for integration in the single-stranded gap.

The DNA of hepatitis B virus (HBV) can integrate into the genomes of infected human liver cells and may be related to the development of primary liver carcinoma (PLC). This report describes the analysis of three integrated HBV DNA sequences cloned from DNA of the human PLC cell line PLC/PRF/5. In all these sequences, integration of the viral DNA is at a site that is single-stranded (gap) in the unintegrated HBV DNA. Contrary to some speculations, there are no large terminal redundancies flanking the inserts as found in retroviral proviruses. The viral sequences show no obvious rearrangements in these clones, but integration can be associated with deletions in the viral DNA and also apparently in the host DNA.

Integrated hepatitis B virus DNA sequences specifying the major viral core polypeptide are methylated in PLC/PRF/5 cells.

The methylation of various hepatitis B virus (HBV) DNA sequences was examined using the restriction endonucleases Hpa II and Msp I. HBV DNA from virions (Dane particles) and virus-infected liver tissue was digested with Hpa II or Msp I and fractionated by electrophoresis in agarose gels, and the restriction enzyme cleavage pattern was examined by Southern blot analysis. No methylation of the 5' C-C-G-G 3' recognition sequence was detected in either virion DNA or HBV DNA from infected liver tissue. The tissue culture cell line PLC/PRF/5, derived from a human hepatoma, possesses HBV DNA exclusively integrated at several sites. Digestion of PLC/PRF/5 DNA with Hpa II and Msp I revealed that the integrated HBV DNA sequences were methylated. Further analysis using probes specific for various regions of the HBV genome showed that some of the hepatitis B viral DNA sequences, including those specifying the major surface antigen polypeptide, were methylated infrequently or not at all. In contrast, the viral DNA sequences coding for the major core polypeptide were extensively methylated. Because the surface antigen is expressed in these cells while the core antigen is not, our results suggest that DNA methylation could account for the selective expression of HBV genes in this hepatoma cell line.

Evidence for supercoiled hepatitis B virus DNA in chimpanzee liver and serum dane particles: Possible implications in persistent HBV infection

In chimpanzee hepatitis B virus (HBV) carriers, the mechanism of viral persistence has been examined by analyzing viral DNA molecules in liver and serum. Chimpanzee liver DNA contained two extrachromosomal HBV DNA molecules migrating on hybridization blots at 4.0 kb and 2.3 kb. There was no evidence for integration of HBV DNA into the host genome. The extrachromosomal molecules were distinct from Dane particle DNA and were converted to linear 3.25 kb full-length double-stranded HBV DNA on digestion with Eco RI. Nucleases S1 and Bal 31 converted "2.3 kb" HBV DNA to 3.25 kb via an intermediate of "4.0 kb" apparent length. The HBV DNA molecule that migrated at 2.3 kb represents a supercoiled form I of the HBV genome, and the molecule that migrated at 4.0 kb represents a full-length "nicked," relaxed circular form II. Evidence for supercoiled HBV DNA in serum Dane particles was obtained by production of form II molecules upon digestion with nuclease S1 or Bal 31. It is proposed that most Dane particles represent interfering noninfectious virus containing partially double-stranded DNA circles and that particles containing supercoiled HBV DNA may represent infectious hepatitis B virus.

Integration of hepatitis B virus DNA into the genome of liver cells in chronic liver disease and hepatocellular carcinoma. Studies in percutaneous liver biopsies and post-mortem tissue specimens.

We used recombinant-DNA technology and gel electrophoresis to find hepatitis B virus DNA (HBV-DNA) in liver and tumor tissue from patients with hepatocellular carcinoma and chronic liver disease, and to study the integration of HBV-DNA into the genome of these tissues' cells. In 12 patients with hepatocellular carcinoma who had hepatitis B surface antigen (HBsAg) in their serum, integrated HBV-DNA was identified in the tumors; it was also found in tumors from three of eight patients who were seronegative for HBsAg but positive for antibody to HBsAg. In some cases, integrated HBV-DNA was also present in nontumorous liver tissue that had the same hybridization pattern or one different from that of the tumor. In five carriers of HBsAg who had evidence of the carrier state and chronic liver disease for less than two years, HBV-DNA was present but not integrated in liver tissue. In the two patients who had carried HBsAg for more than eight years, HBV-DNA was integrated into the host genome. These data suggest that integration of HBV-DNA into hepatocytes occurs during the course of persistent HBV infection and precedes development of gross neoplasm.

DETECTION OF HEPATITIS B VIRUS DNA IN LIVER AND SERUM: A DIRECT APPRAISAL OF THE CHRONIC CARRIER STATE

The detection of hepatitis B virus (HBV) DNA in the liver and the serum permits direct study of the interaction between the virus and the liver cell. 40 HBV chronic carriers were studied by the blot technique of Southern to detect HBV DNA, and the results were compared with the serological status and histological status of the patients. It was possible to define two different chronic carrier states. The first is characterised by free viral DNA in the liver, with viral DNA and hepatitis B e antigen (HBeAg) in the serum; integrated HBV DNA is also present, at least in some patients. The second carrier state is characterised by the presence of only integrated HBV DNA sequences in the liver: viral DNA and HBeAg are not present in the serum. In one HBeAg-negative patient, however, free HBV DNA was detected in the liver and HBV DNA was present in the serum. The hybridisation technique appears to be a very sensitive test which could reflect viral multiplication better than HBe Ag radioimmunoassay. Since a needle biopsy sample provides sufficient tissue for the Southern blot technique, it should be useful in understanding chronic hepatitis, the selection of patients for antiviral therapy, and the estimation of its efficiency.

State of hepatitis B virus DNA in hepatocytes of patients with hepatitis B surface antigen-positive and -negative liver diseases.

Using the Southern blot technique and cloned hepatitis B virus (HBV) DNA as a probe, we studied the state of HBV DNA in the liver of 13 patients with hepatocellular carcinoma, 17 patients with chronic hepatitis, and 2 patients with acute hepatitis. The hybridization results were compared with the serological and immunohistological data. Integration of HBV DNA in cellular DNA of the liver from patients with hepatocellular carcinoma was demonstrated. In two patients from which tumorous and nontumorous liver tissue samples were available the integration patterns were different. In one patient with hepatitis B e antigen (HBeAg)-positive early hepatocellular carcinoma, free viral DNA was present in the liver. In some patients with HBeAg-negative chronic hepatitis, without tumor, integration of HBV DNA in cellular DNA was also demonstrated. This suggests that HBV is not the only factor involved in the development of a tumor. In patients with HBeAg-positive chronic hepatitis, free viral DNA was detected in the liver. In the two acute hepatitis patients analyzed, the restriction endonuclease patterns strongly suggested HBV DNA integration. Therefore, viral DNA integration seems to occur early in infection. Whatever the form of the disease, discrete bands were observed, suggesting the existence of limited and specific integration sites in host cellular DNA. The presence of integrated or free DNA sequences has implications for antiviral therapy. In addition, detection of HBV DNA in the liver is another sensitive viral marker that could be useful for diagnostic purposes.

Identification of integrated hepatitis B virus DNA and expression of viral RNA in an HBsAg-producing human hepatocellular carcinoma cell line.

Alexander and co-workers1 have developed a tissue culture cell line (PLC/PRF/5) from a primary hepatocellular carcinoma of a Mozambican male with a positive serum for hepatitis B virus surface antigen (HBsAg). This cell line produces and secretes HBsAg but no other known viral protein1–3. PLC/PRF/5 therefore contains at least part of the hepatitis B virus (HBV) genome in functional form. The 42-nm, spherical Dane particle in human serum is thought to represent the complete infectious agent of HBV4. The core of this particle contains circular double-stranded DNA in which one strand is ‘nicked’ (complete but not covalently closed) and the other strand is incomplete (lacking 15–45% of its sequence complement)4,5. Four proteins have been associated with the HBsAg, core antigen (HBcAg), e antigen and a viral DNA polymerase4. Several groups have now cloned Dane particle DNA in Escherichia coli6–10, and both restriction maps and a complete DNA sequence have been determined. Various studies suggest that there is sequence heterogeneity in Dane particle DNA isolated from patients expressing the same or different viral subtypes, as well as sequence variation in different clones of Dane particle DNA obtained from a given individual10,11. Other studies12,13 have reported HBV DNA sequences in DNA from liver cancer tissue. In none of these cases was viral DNA reported to be integrated into the host cell genome. With the improvement in techniques for characterizing viral DNA molecules, we have begun to analyse HBV genes and their expression in the PLC/PRF/5 cell line by molecular hybridization of cellular DNA and RNA to cloned 32P-labelled plasmid HBV DNA. We now present evidence in PLC/PRF/5 cells for integration of HBV DNA into the host genome and expression of three RNA molecules containing HBV-specific sequences. These findings are consistent with observations in several animal virus models in which integrated viral DNA is found during oncogenic transformation.