JVI: Xia Yuchen's research group revealed that the core protein of hepatitis B virus is not involved in the transcription regulation of cccDNA

Recently, the research group of Professor Xia Yuchen of the State Key Laboratory of Virology/Taikang Life Medicine Center/Institute of Medical Virology, Taikang Medical College (School of Basic Medicine) of Wuhan University was published in the international authoritative journal of virology "J ournal of Virology published a research paper entitled "Hepatitis B virus core protein is not required for cccDNA transcriptional regulation"
。 This study used a series of cell and mouse models to find that the core protein of hepatitis B virus does not participate in the transcriptional regulation of viral microchromosome ccc DNA, which not only further revealed the regulatory mechanism of hepatitis B virus cccDNA microchromosome.
At the same time, it also pointed out the limitations
of drugs that target the core protein of the virus, which are currently of great concern.

Hepatitis B Virus (HBV) infection is a serious global health health problem
.
Globally, nearly 250 million people with chronic hepatitis B have a higher risk of developing cirrhosis and liver cancer
.
There are currently two main drugs for the treatment of chronic hepatitis B: interferon α and nucleoside analogues
.
Although these two classes of drugs can inhibit viral replication to a certain extent and control the disease process, they cannot clear the template of viral replication in infected cells - cccDNA
.

Hepatitis B virus core protein (HBc) is an important structural protein that makes up the viral nucleocapsid, which participates in multiple steps of the viral replication cycle, including viral nucleic acid nuclear transport, pregenomicRNA packaging, viral emergence, etc
.
In addition, there are studies that suggest that H Bc may be involved in cccDNA regulation: HBccan bind to cccDNA On the microchromosome (Bock et al, JMB, 2001) and enriched in the transcriptional regulatory region (Guo et al, Epigenetics, 2011）； Duck hepatitis B virus (DHBV) has significant limited transcription after the absence of HBc (Schultz et al, J Virol, 1999).
）； HBcregulates HBV gene transcription in plasmid transfection systems (Chong et al, Antiviral Res, 2017).

However, H BV virus particles (H BVΔHB) that do not express H Bc are used c) After infecting cells, the transcription of cccDNA was not affected, suggesting that the newly produced HB c after virus infection did not participate in cccDNA regulation (Qi et al, Plos Pathog, 2016; Tu et al, JHEP Rep, 2021）
。 However, since the HbvδHb Cvirus particles themselves canalso bind to c cc DNA for a long time( Lucifora et al, JHEP Rep, 2021), on whether HBc affects cccDNA The transcription of has been controversial
.

In order to avoid the interference of H Bc carried by virus particles to the experiment, Professor Xia Yuchen's research group used HBV that can simulate ccc DNA Circle and in vitro synthesis of cccDNA transfection models, finding that the deletion of H Bc on hepatocyte lines and hepatic primary cells does not affect viral RNA and antigen levels
.
On this basis, the backfilling and overexpression of H Bcdo not affect the transcription
of ccc DNA.
Considering that synthetic c ccDNA molecules may be regulated differently from c ccDNA formed under natural infection conditions, the authors also study H The BV infection system verified the role of H Bc and showed that cccDNA regulation was not affected by HBc Impact
.
The authors further carried out animal experiments on a novel mouse model of HBV cccDNA established in the early stage of the research group (Xu et al, CMGH, 2022), H Bc-deleted c ccDNA and wild-type cccDNA produce viral surface antigen ( HBsAg) level
.
Consistent with the results of cell experiments, the backfilling and overexpression of H B c did not affectviral indicators
such as H B sAg.
Since the transcription of c ccDNA is regulated by a series of histone modifications and transcription factors, the authors used ChIP-seq and other methods to compare the differences in these epigenetic modifications in the absence of H Bc
。 The results showed that HBcdid not affect
the histone modification of the ccc DNA microchromosomes and the binding of transcription factors.
Finally, the authors investigated the effect of
H Bc on ccc DNA transcription by using nucleocapsid inhibitors.
The authors used three nucleocapsid inhibitors (GLS4, BAY41-4109, AT-130 Treat cccDNA transfection and HBV-infected cells
.
ChIP experiments found that nucleocapsid inhibitors reduced HBC bound to ccc DNA, but did not affect H BV RNA and viral antigen levels
.
In summary, HBCis not involved in the transcriptional regulation
of H BV ccc DNA.
For the cure of chronic hepatitis B, new treatments targeting cccDNA are still needed because nucleocapsid inhibitors cannot inhibit the transcription of ccc DNA
.

Master student Zhong Quanquan and doctoral student Wu Chuanjian are the co-first authors of the paper, and Professor Xia Yuchen is the corresponding author
.
This research work was supported by the National Natural Science Foundation of China (81971936), Gilead Asian Liver Disease Research Fund, Hubei Medical Young Top Talents, Hubei Innovative Research Group (2020CFA015), Hubei Provincial Health Commission Innovation Group (WJ2021C002), Zhongnan Hospital of Wuhan University- Funded by the Joint Fund of Clinical Medicine Translation Sharing Platform and other projects.

Full text link:

https://journals.
asm.
org/doi/10.
1128/jvi.
01362-22

Professor Xia Yuchen has been committed to the research of viral hepatitis since returning to China through the Overseas High-level Talent Program in 2018, and has done a series of work on the establishment of experimental models of hepatitis B virus, the mechanism of virus-host interaction and new antiviral treatments, as the corresponding author in the Journal of Hepatology, Hepatology, Cellular and Molecular He has published several papers
in academic journals such as Gastroenterology and Hepatology, Journal of Virology, etc.
The laboratory recruits 1-2 postdoctoral fellows, please contact yuchenxia@whu.
edu.
cn for details