Integration of Region X of Hepatitis B Virus Genome in Human Primary Hepatocellular Carcinomas Propagated in Nude Mice

Abstract

SUMMARYTissues of human primary hepatocellular carcinoma (PHC) from six patients infected with hepatitis B virus (HBV) were propagated in nude mice, as well as a strain of hepatitis B surface antigen-positive PHC (PLC/PRF/5). Integration of viral DNA into chromosomal DNA of tumour cells was evaluated by the capacity to hybridize with radiolabelled DNA probes, each representing fundamental parts of the HBV genome, that is S and C genes and regions pre-S and X. All PHC cells possessed region X integrated in their chromosomes. However, integration of the S gene, C gene and region pre-S was found in only six of the seven PHCs. Based on these findings, the integration of region X seems to be most closely associated with carcinogenesis in HBV infection.Epidemiological surveys (Szmuness, 1978;Beasley et al., 1981) indicate a close correlation between infection with hepatitis B virus (HBV) and the incidence of primary hepatocellular carcinoma (PHC). Moreover, DNA sequences of HBV (HBV-DNA) are integrated into genomic DNA of most patients with PHC seropositive for hepatitis B surface antigen (HBsAg), and also in an HBsAg-positive hepatoma cell line (Brechot et al

The hepatitis B virus X-gene product trans-activates both RNA polymerase II and III promoters.

“…Alternatively, it has been suggested that production of novel class III transcripts may play a role during transformation of rodent cells by SV40 or by chemical carcinogens (Singh et al, 1985;Carey et al, 1986), as well as during active proliferation (Edwards et al, 1985). HBV infected tissues are generally thought to be stimulated to divide, and many HCC tumors derived from infected livers contain integrated copies of at least part of the X-gene (Shaul et al, 1984;Miyaki et al, 1986;Nagaya et al, 1987). Thus, it is tempting to speculate that activation of certain class III genes might be involved in proliferation of infected cells or perhaps carcinogenesis by HBV.…”

“…There is also evidence that the X-gene is expressed during at least some stage of HBV infection, since many individuals produce antibodies to the X-protein (Kay et al, 1985;Moriarity et al, 1985;Elfassi et al, 1986;Meyers et al, 1986;Persing et al, 1986). At least part of the X-ORF is retained in many tumors (Shaul et al, 1984;Miyaki et al, 1986;Nagaya et al, 1987), and in one example, trans-activation ability was maintained (Wollersheim et al, 1988).…”

Expression of hepatitis B virus X protein in HBV-infected human livers and hepatocellular carcinomas

“…78,80,81 In this study, we observed a close statistical correlation between expression of HBx and existence of HBsAg in HCC-bearing liver, which may reflect the frequent preservation of the X gene together with the PreS2/S1 region during the integration of HBV DNA into cellular genomic DNA and the following rearrangements. [65][66][67][68] However, their distribution patterns were differ- ent. Our results demonstrated that the expression of HBx, among the three HBV antigens examined, was preferentially maintained through the multistage process from foci and nodules of altered hepatocytes, for which a preneoplastic nature has been demonstrated, 54,57 to HCC.…”

“…[65][66][67][68] HBx variants expressed from the chromosomally integrated mutants may also contribute to different HBx distribution patterns and expression levels, particularly in the neoplastic lesions. Combined use of several antibodies recognizing different epitopes, as in this study, should greatly increase the possibility to detect HBx in the tissue.…”

“…Expression of the X gene in HBV-infected livers has been inferred from the preferential conservation of the X sequence within integrated HBV DNA in HCC and cirrhotic livers with HBV infection, [65][66][67][68] the frequent occurrence of X sequence components containing RNA in HCC specimens, 33,34 the emergence of circulating antibodies, [35][36][37][38][39][40][41][42] and the demonstration of a frequent cellular immune response 43 specific to HBx. The detection of HBx has, however, proved to be very difficult, and the reported data are contradictory.…”