# Molecular Mechanisms of HBV cccDNA Formation

> **NIH NIH R01** · UNIVERSITY OF PITTSBURGH AT PITTSBURGH · 2021 · $382,533

## Abstract

ABSTRACT
Hepatitis B virus (HBV) covalently closed circular (ccc) DNA plays a central role in the establishment of viral
infection and persistence, and is the basis for viral rebound after the cessation of therapy, as well as the
elusiveness of a cure even after extended treatment with current approved medications. HBV cccDNA is
established upon initial infection through conversion of the partially double stranded relaxed circular (rc) DNA
viral genome containing terminal peculiarities, through employment of the host cell’s DNA repair mechanisms
in the nucleus. The cccDNA episome levels are maintained through a replication cycle that involves
retrotranscription of a cccDNA transcript, termed pregenomic RNA, into progeny rcDNA genomes, some of
which are returned to the nucleus for conversion into cccDNA. The conversion of rcDNA into cccDNA requires
the removal of a covalently-linked copy of the polymerase from the 5’ end of one of the DNA strands, and this
“deproteination” step generates a DNA intermediate, the deproteinated rcDNA (DP-rcDNA), as precursor for
cccDNA formation. The rcDNA deproteination is a trigger signal for transportation of HBV nucleocapsid
containing mature viral DNA into nucleus, where the rcDNA to cccDNA conversion takes place. We have
recently mapped the termini of cytoplasmic DP-rcDNA, which demonstrated that the viral polymerase and RNA
primer are completely removed from rcDNA during deproteination, the plus strand DNA is further elongated but
the terminal redundant sequence is maintained on DP-rcDNA. In addition, recent studies by us and others
have identified a handful of host DNA repair factors involved in cccDNA formation. However, there are many
molecular details yet to be elucidated for a better understanding of cccDNA biosynthesis, and the
establishment of immunocompetent small animal model for HBV infection is hampered by the inability of
cccDNA formation in mouse hepatocyte. In this research application, by making use of a battery of molecular
biology, biochemistry, proteomics and genomics technologies, we propose to further elucidate the molecular
mechanisms underlying the biogenesis of DP-rcDNA (Aim 1) and cccDNA (Aim 2), and to define the host
determinant(s) for the failure of cccDNA formation in mouse hepatocyte (Aim 3). Our ultimate goal is to
illustrate a coherent picture of the molecular mechanisms/pathway for HBV cccDNA formation. The
accomplishment of this project will reveal new potential antiviral targets for treatment of hepatitis B and aid the
development of a mouse model fully susceptible to HBV infection.

## Key facts

- **NIH application ID:** 10313040
- **Project number:** 2R01AI110762-06
- **Recipient organization:** UNIVERSITY OF PITTSBURGH AT PITTSBURGH
- **Principal Investigator:** Haitao Guo
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $382,533
- **Award type:** 2
- **Project period:** 2016-03-11 → 2026-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10313040

## Citation

> US National Institutes of Health, RePORTER application 10313040, Molecular Mechanisms of HBV cccDNA Formation (2R01AI110762-06). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10313040. Licensed CC0.

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