Interferon-Stimulated Gene 15 Conjugation Stimulates Hepatitis B Virus Production Independent of Type I Interferon Signaling Pathway In Vitro

Figure 4

ISGylation is important in ISG15-promoted HBV production. UBE1L knockdown was performed by RNAi to abrogate ISGylation in HepG2.2.15 cells. (a) Knockdown efficiency was determined by real-time PCR showing UBE1L mRNA expression 24 h after 50 nM negative siRNA, 50 nM UBE1L siRNA, or 100 nM UBE1L siRNA treatment. (b) Comparison of protein ISGylation (western blot for ISG15) after UBE1L knockdown and ISG15 overexpression. Molecular mass markers are shown on the left (kDa). (c) Real-time PCR was used to assess the supernatant HBV DNA after UBE1L knockdown and ISG15 overexpression. Control, untreated control; PEI, ISG15 transfection regent polyethyleneimine (PEI) treatment only; ISG15, ISG15 overexpression by transfection with 1.4 μg ISG15 plasmid; UBE1L siRNA+ISG15, 50 nM UBE1L siRNA treatment followed by ISG15 overexpression; Mock+ISG15, siRNA transfection regent treatment followed by ISG15 overexpression; NC+ISG15, 50 nM negative siRNA treatment followed by ISG15 overexpression; IFN, 100 IU/mL IFNα2b treatment. The results are presented as the means ± SD, ; error bars indicate SD. < 0.05; .

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