Fig. 4.

TERT transcription activation was driven by EnhI of integrated HBV. (A) Typical HBV integration event at human TERT promoter consists of a partial TERT promoter fused with HBV genome having a breakpoint at C‐terminal of HBx. (B,C) Mechanism of transcription activation by TERT HBV integration was studied by luciferase reporter assay using plasmids containing different combinations of the TERT promoter sequence (TERTp), HBx coding sequence (HBx), and HBV EnhI mimicking the actual TERT HBV integration events detected (human TERT is transcribed by reverse strand, with positive strand of integrated HBx joining to the reverse strand of TERT upstream/promoter region forming chimeric fusion). All the numbers refer to the genomic location of the forward strand. TERTp^WT and TERTp^short represent wild‐type or partial TERT promoter detected in TERT HBV integration events. As EnhII is located within HBx, it was included in all plasmids B‐J except E. HBx^FL, HBx^‐14aa, HBx^C1, HBx^FLsg1393, and HBx^FLsg1766 represent different lengths of HBx coding sequences with or without specific single‐nucleotide stop‐gain mutation at positions 1,393 and 1,766. EnhI⁺ and EnhI^‐ denote the presence or absence of HBV EnhI. Investigation of the transcriptional activation effects of HBV enhancers and HBx protein in HepG2 cells using luciferase reporter assay. Fl, full length; w.r.t., with regard to; WT, wild type.