Characterization of integration patterns and flanking cellular sequences of hepatitis B virus in childhood hepatocellular carcinomas

Abstract

Hepatitis B virus (HBV) DNA integration into host chromosomes is detected in more than 80% of HBV-related hepatocellular carcinomas (HCC), yet its significance in tumor development remains obscure. In this study, we re-examined the integration pattern of HBV in childhood HCC tissues, which has less environmental confounding factors than adult HCC. The HBV junctions and flanking cellular sequences were amplified from five childhood HCC patients by the inverse polymerase chain reaction (IPCR) method using primers located near HBV direct repeats (DR) 1 and 2. The viral junctions in nine of the ten obtained IPCR clones were demonstrated to be located near HBV DR1, and their patterns were classified to type I integrants. Southern blot analyses demonstrate that the cellular junctions derived from two of the five HCC tissues were male specific and contained sequences homologous to human long interspersed DNA elements (LINE-1). HBV integrant of one HCC tissue (1217T) was integrated into a RNA binding motif Y chromosome (RBMY) gene. The expression of RBMY, which is normally found only in male germ cells, was detected in HCC tissue 1217T by RT-PCR but not in the corresponding non-tumor liver tissue. The prevalence of RBMY expression in liver tissues from the tumor and non-tumor parts of ten other HCC children and seven biliary atresia (BA) children was studied by RT-PCR. No RBMY transcripts were detected in the non-tumor parts of HCC patients or the cirrhotic livers of BA children, whereas 30% (three of ten) of HCC tissues specifically expressed RBMY. The results indicate that HBV integration and activation of RBMY gene expression in liver cells may be associated with the development of childhood HCC.

RBMY, a male germ cell-specific RNA-binding protein, activated in human liver cancers and transforms rodent fibroblasts

“…In our previous report, HBV DNA integration at intron 6 of RBMY gene was identified in one childhood HCC tissue (Tsuei et al, 2002). We also found that the expression of RBMY transcripts was detected in the corresponding tumor and three other childhood HCC tissues.…”

The role of hepatitis B virus integrations in the pathogenesis of human hepatocellular carcinoma

“…They found that the cellular junctions derived from two of the five HCC tissues were male specific and contained sequences homologous to human long interspersed DNA elements (LINE-1). In one of the HCCs, designated 1217T, the HBV DNA was integrated into the RNA binding motif Y chromosome (RBMY) gene [97]. Subsequently, they have shown that RBMY, which is normally expressed exclusively in the testis, was expressed in 36% of HCCs from 90 males and in 67% of hepatoblastomas from six boys.…”

“…Ogata et al proposed the hypothesis that integration of HBV DNA into unstable genomic regions may be responsible for generation of additional chromosomal alterations that contribute to the carcinogenic process [93]. In most studies of large numbers of HBV integrations performed thus far, a significant proportion of the integrations occur into repeat regions within the host genome, including long interspersed nuclear element 1 (LINE1) and short interspersed nuclear elements (SINE), for example, Alu sequences [94][95][96][97].…”

Mechanisms of HBV-related hepatocarcinogenesis

“…Besides acting by cis-or trans-activation, HBV insertions have been associated with major genetic alterations within the cell genome, including large deletions, duplications and chromosomal translocations [112][113][114][115][116]. The association of HBV integration with large genomic changes might reflect the abrogation of control mechanisms that safeguard chromosomal integrity [49].…”