Analysis of integrated hepatitis B virus DNA and flanking cellular sequence by inverse polymerase chain reaction

piggyBac transposon mediated transgenesis of the human blood fluke, Schistosoma mansoni

The transposon piggyBac from the genome of the cabbage looper moth Trichoplusia ni has been observed in the laboratory to jump into the genomes of key model and pathogenic eukaryote organisms including mosquitoes, planarians, human and other mammalian cells, and the malaria parasite Plasmodium falciparum. Introduction of exogenous transposons into schistosomes has not been reported but transposon-mediated transgenesis of schistosomes might supersede current methods for functional genomics of this important human pathogen. In the present study we examined whether the piggyBac transposon could deliver reporter transgenes into the genome of Schistosoma mansoni parasites. A piggyBac donor plasmid modified to encode firefly luciferase under control of schistosome gene promoters was introduced along with 7-methylguanosine capped RNAs encoding piggyBac transposase into cultured schistosomula by square wave electroporation. The activity of the helper transposase mRNA was confirmed by Southern hybridization analysis of genomic DNA from the transformed schistosomes, and hybridization signals indicated that the piggyBac transposon had integrated into numerous sites within the parasite chromosomes. piggyBac integrations were recovered by retrotransposon-anchored PCR, revealing characteristic piggyBac TTAA footprints in the vicinity of the endogenous schistosome retrotransposons Boudicca, SR1, and SR2. This is the first report of chromosomal integration of a transgene and somatic transgenesis of this important human pathogen, in this instance accomplished by mobilization of the piggyBac transposon.

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HBV integrants of hepatocellular carcinoma cell lines contain an active enhancer

Hepatitis B virus (HBV) infection is a major risk factor worldwide for the development of hepatocellular carcinoma (HCC). Integrated HBV DNA fragments, often highly rearranged, are frequently detected in HCC. In woodchuck, the viral enhancer plays a central role in hepatocarcinogenesis, but in humans the mechanism of HBV oncogenesis has not been established. In this study we investigated the status of the viral enhancer in two human HCC cell lines, Hep3B and PLC/PRF/5 each containing one or more integrated HBV DNA fragments. Active enhancer was defined by virtue of its protein occupancy as determined by genomic in vivo DMS footprinting. In PLC/PRF/5 cells, the HBV DNA was integrated in a cellular gene at chromosome 11q13, at a locus reported to be amplified in many tumors. We show here that in both cell lines, the integrated HBV DNA fragments contain an active enhancer-I. In particular, the occupation of the two previously defined basic enhancer elements, E and EP, was prominent. While in both cell lines the same protein binds to the EP elements, the E element, however, is occupied in a cell-line specific manner. In PLC/PRF/5 but not Hep3B, the prominent binding of an undefined protein was detected. Our data suggest that this protein is likely to be the fetoprotein transcription factor (FTF). The finding that enhancer sequences are conserved and functional in different cell lines suggests a selection pressure for their long-term maintenance. We therefore propose that the HBV enhancer-I might play a role in hepatocellular carcinogenesis.