TIM22 and TIM29 inhibit HBV replication by up-regulating SRSF1 expression.

Hepatitis B virus (HBV) infection is a serious global health problem. After the viruses infect the human body, the host can respond to the virus infection by coordinating various cellular responses, in which mitochondria play an important role. Evidence has shown that mitochondrial proteins are involved in host antiviral responses. In this study, we found that the overexpression of TIM22 and TIM29, the members of the inner membrane translocase TIM22 complex, significantly reduced the level of intracellular HBV DNA and RNA and secreted HBV surface antigens and E antigen. The effects of TIM22 and TIM29 on HBV replication and transcription is attributed to the reduction of core promoter activity mediated by the increased expression of SRSF1 which acts as a suppressor of HBV replication. This study provides new evidence for the critical role of mitochondria in the resistance of HBV infection and new targets for the development of treatment against HBV infection.

Nicotinamide N-Methyltransferase inhibits HBV replication by suppressing NR5A1 expression invitro.

Chronic hepatitis B virus (HBV) infection can lead to fibrosis, liver cirrhosis, and primary hepatocellular carcinoma. Investigating host factors that regulate HBV replication helps to identify antiviral targets. In the current study, we identified Nicotinamide N-Methyltransferase gene (NNMT) as a novel factor that regulates HBV transcription. NNMT is up-regulated at both the mRNA and protein levels in HepG2.2.15 cells compared to HepG2 cells. Overexpression of NNMT reduces HBV replication in several cell models, while knockdown of NNMT enhances HBV DNA levels. Mechanistically, NNMT suppresses HBV DNA replication by inhibiting HBV RNA transcription. The region required for the inhibitory effect of NNMT was narrowed to nt 1672-1708 in enhancer II by luciferase assays. On the other hand, ChIP assays and EMSA results showed that NNMT does not bind to this region substantially, either directly or indirectly. Next, a collection of hepatic nuclear receptor transcription factors was screened to determine whether they were affected by NNMT overexpression. NR5A1, a positive regulator of HBV replication, decreased significantly after NNMT overexpression. Collectively, the findings of this study shed light on the regulation of HBV transcription.

Establishment of a human cell line with a surface display system for screening and optimizing Na+-taurocholate cotransporting polypeptide-binding peptides.

One of the most desirable targets for HBV medications is the sodium taurocholate cotransporting polypeptide (NTCP), an entry receptor for the hepatitis B virus (HBV). N-myristoylated preS1 2-48 (Myrcludex B or Hepcludex), an NTCP-binding peptide from the large surface protein of HBV, has been developed as the first-in-class entry inhibitor. However, its relatively large molecular weight contributes to increased immunogenicity and antibody production. As a result, it is preferable to look for an NTCP-binding peptide with a smaller size. To do this, we developed a human cell surface display strategy and screened peptides based on preS1-21. PreS1-21 (genotype D) was extended by 7 random amino acids and fused with mCherry and FasL transmembrane domain. The pooled constructs were transfected into HEK293 cells by using the transposon/transposase system to create a library displaying various peptides on the cell surface with red fluorescence. On the other hand, we expressed NTCP protein fused with EGFP on HEK293 and used the membrane lysate containing NTCP-GFP as the bait protein to select peptides with increased NTCP affinity. After 7 cycles of selection, the deep sequencing results revealed that some polypeptides were more than 1,000 times enriched. Further screening of the mostly enriched 10 peptides yields the peptide preS1-21-pep3. Replacing the preS1-21 sequence of preS1-21-pep3 with those from different genotypes demonstrated that the consensus sequence of genotype A-F had the best performance. The peptide (Myr-preS1-21-pep3) was synthesized and tested on the HepG2-NTCP cell model. The results showed that Myr-preS1-21-pep3 is approximately 10 times more potent than the initial peptide Myr-preS1-21 in preventing HBV infection. In conclusion, we developed a new strategy for screening peptides binding to membrane proteins and identified a new NTCP-binding peptide with a much smaller size than Hepcludex.

Identification of STAU1 as a regulator of HBV replication by TurboID-based proximity labeling.

The core promoter (CP) of hepatitis B virus (HBV) is critical for HBV replication by controlling the transcription of pregenomic RNA (pgRNA). Host factors regulating the activity of the CP can be identified by different methods. Biotin-based proximity labeling, a powerful method with the capability to capture weak or dynamic interactions, has not yet been used to map proteins interacting with the CP. Here, we established a strategy, based on the newly evolved promiscuous enzyme TurboID, for interrogating host factors regulating the activity of HBV CP. Using this strategy, we identified STAU1 as an important factor involved in the regulation of HBV CP. Mechanistically, STAU1 indirectly binds to CP mediated by TARDBP, and recruits the SAGA transcription coactivator complex to the CP to upregulate its activity. Moreover, STAU1 binds to HBx and enhances the level of HBx by stabilizing it in a ubiquitin-independent manner.