Objective      To lay the foundation for working out new clinical treatment strategies by studying the effect of host factor FEN1 on HBV replication.       Methods      FEN1 overexpression lentiviral plasmid was constructed with its sequence identified by restriction enzyme digestion and transfected into 293FT cells. FEN1 protein expression was detected by Western blotting. The plasmid was transfected into stable cell lines with HBV replication. The plasmid pLenti6/V5-D-TOPO was modified by lentivirus packaging and non-transfected plasmid cells served as controls. HBsAg in medium supernatant was detecte

d by ELISA. HBV DNA was detected by RT-PCR and Southern blotting

respectively.       Results       The plasmid extracted from positive clones was digested by restriction endonuclease

and a bright band was observed in FEN1 and linear plasmid

respectively. The lentiviral plasmid sequencing showed that the sequence was inserted correctly. Western blot analysis displayed that the FEN1 protein expression level was 2-3 fold higher in transfected  plasmid cells than in non-transfected plasmid cells. FEN1-overexpressed plasmid could transfect stable cell lines with HBV replication. ELISA demonstrated positive HBsAg in medium supernatant with a D

450

value of 1.982±0.032. RT-PCR revealed intracellular viral DNA with an absolutely-quantified copy number of 1.18×10

9

. Southern blot analysis indicated that the HBV replication level was significantly up-regulated.       Conclusion        Structure-specific nuclease FEN1 can significantly promote HBV DNA replication and is thus one of the important regulatory factors for virus replication.