Journal: Journal of Biomedical Science
Article Title: IFI35 suppresses the transcription of hepatitis B virus cccDNA minichromosome via promoting HNF4α proteasomal degradation
doi: 10.1186/s12929-026-01239-w
Figure Lengend Snippet: IFI35 ubiquitinates HNF4a in TRIM21-dependent manner. A Cell lysates were immunoprecipitated using an anti-TRIM21 antibody. B Detection of HBV DNAs by Southern blot from HepG2 and HepG2-TRIM21-KO cells. Expression levels of HNF4α, IFI35 and TRIM21 in HepG2-TRIM21-KO cells compared to parental HepG2 cells (Control) were assessed by Western blot. HBV DNA levels of HepG2 and HepG2-TRIM21-KO cells were quantified in graph (bottom). C Quantification of HNF4α protein levels in HepG2 and HepG2-TRIM21 knockout (KO) cells transfected with increasing amounts of myc-IFI35. HNF4α levels were determined by immunoblotting and quantified relative to the vector control. Data represent mean ± SD from three independent experiments. D Secreted HBeAg and HBsAg levels were measured by ELISA in HepG2 and HepG2-TRIM21-KO cells transfected with increasing amounts of myc-IFI35. Data represent mean ± SD from three independent experiments. E HepG2 or HepG2-TRIM21 knockout cells were transfected with HBV 1.2mer together with increasing amounts of IFI35. Total RNA was analyzed by Northern blotting to detect HBV transcription. F Effect of TRIM21 on IFI35-mediated HNF4α degradation. HepG2 and HepG2-TRIM21-KO cells were transfected with either empty vector or myc-IFI35. After 48 h, cycloheximide (50ug/ml) were treated for the indicated times, and cells were harvested. Expression levels of HNF4α and IFI35 were evaluated through Western blotting. Quantification of HNF4α levels between HepG2 and HepG2-TRIM21-KO cells (bottom). G HepG2 cells and TRIM21 knockout cells were co-transfected with HA-tagged ubiquitin (1 μg) and either vector or IFI35 (2 μg). At 48 h post-transfection, HNF4α was immunoprecipitated and immunoblotted with anti-ubiquitin antibody to assess polyubiquitination. Total levels of HNF4α, IFI35, TRIM21, and HA-tagged ubiquitin in input lysates were also analyzed by immunoblotting. H Schematic diagram of HBV enhancer luciferase reporter constructs. Constructs containing enhancer I (EnhI), enhancer II (EnhII), or both regions were cloned upstream of the luciferase reporter gene. Mutant constructs lacking HNF4α binding sites were generated in EnhI (ΔHNF4α) or EnhII (ΔHNF4α1 and ΔHNF4α1,2) as indicated. I Basal luciferase activity of HBV enhancer reporter constructs. HepG2 cells were transfected with the indicated luciferase reporter plasmids, and luciferase activity was measured. J Comparison of the effect of IFI35 on EnhI-driven transcription with or without the HNF4α binding site. HepG2 cells were co-transfected with the indicated EnhI luciferase reporters and increasing amounts of myc-IFI35. Luciferase activity was measured 48 h post-transfection. Data represent mean ± SD from three independent experiments. K Comparison of the effect of IFI35 on EnhII-driven transcription with or without HNF4α binding sites. HepG2 cells were co-transfected with EnhII luciferase reporters containing wild-type or mutated HNF4α binding sites together with increasing amounts of myc-IFI35. Luciferase activity was measured 48 h post-transfection. Data represent mean ± SD from three independent experiments. The above experiment was independently conducted three times. Data are shown as mean ± SD. The statistical significance of the differences was assessed by the Student t test: *, P < 0.05; **, P < 0.01, ***, P < 0.001
Article Snippet: The following antibodies were used: IFI35 (sc-100769, Santa Cruz), HNF4α (H-171, Santa Cruz), HNF1α (Η-140, Santa Cruz), HNF3β (RY-7, Santa Cruz), core protein (B0586, Dako, Carpinteria, CA), TRIM21 (sc-25351, Santa Cruz), β-actin (A5441, Sigma) and GFP (sc-9996, Santa Cruz).
Techniques: Immunoprecipitation, Southern Blot, Expressing, Control, Western Blot, Knock-Out, Transfection, Plasmid Preparation, Enzyme-linked Immunosorbent Assay, Northern Blot, Ubiquitin Proteomics, Luciferase, Construct, Clone Assay, Mutagenesis, Binding Assay, Generated, Activity Assay, Comparison