The impact of integrated hepatitis B virus DNA on oncogenesis and antiviral therapy

Abstract

The global burden of hepatitis B virus (HBV) infection remains high, with chronic hepatitis B (CHB) patients facing a significantly increased risk of developing cirrhosis and hepatocellular carcinoma (HCC). The ultimate objective of antiviral therapy is to achieve a sterilizing cure for HBV. This necessitates the elimination of intrahepatic covalently closed circular DNA (cccDNA) and the complete eradication of integrated HBV DNA. This review aims to summarize the oncogenetic role of HBV integration and the significance of clearing HBV integration in sterilizing cure. It specifically focuses on the molecular mechanisms through which HBV integration leads to HCC, including modulation of the expression of proto-oncogenes and tumor suppressor genes, induction of chromosomal instability, and expression of truncated mutant HBV proteins. The review also highlights the impact of antiviral therapy in reducing HBV integration and preventing HBV-related HCC. Additionally, the review offers insights into future objectives for the treatment of CHB. Current strategies for HBV DNA integration inhibition and elimination include mainly antiviral therapies, RNA interference and gene editing technologies. Overall, HBV integration deserves further investigation and can potentially serve as a biomarker for CHB and HBV-related HCC.

Keywords: Antiviral therapy; Hepatitis B virus; Hepatocellular carcinoma; Virus DNA integration.

Fig. 1

The structure of HBV DNA genome and HBV life cycle. (A)The schematic diagram of Dane particle. (B)The circular schematic diagram of genotype C HBV genome. (C) After HBV Dane particles entering hepatocytes, uncoating takes place and genome is released. RcDNA is repaired to form cccDNA which is transcribed to pgRNA and 3.5Kb/3.5Kb/2.4Kb/2.1Kb/0.7Kb transcripts, HBV RNA transcripts are translated into proteins such as HBeAg, Core protein and HBx protein. Polymerase binds to the pgRNA with the recruitment of Core protein to assemble nucleocapsid and package pgRNA, pgRNA serves as the template to reverse transcription synthesize the HBV minus(-)-strand DNA. Polymerase translocates accurately to synthesize the HBV plus(+) strand DNA. Polymerase translocates mistakenly results the synthesis of dslDNA and the integration of dslDNA into the host genome

Fig. 2

Schematic diagram about synthesis of dslDNA and HBV DNA integration. (A) ε stem-loop structure forms and P protein primes at the ε stem-loop structure to form P-ε ribonucleoprotein (RNP) complex. The terminal protein (TP) domain of the P protein binds with the first deoxyribonucleotide in ε stem-loop structure near the 5’cap of pgRNA. After the first four(TGAA) or three (GAA) nucleotides of the new minus(-) strand DNA generated in ε stem-loop structure, the DNA oligo then transferred to DR1 at the 3’end of pgRNA with TP and the synthesis of minus(-) strand starts.(B) pgRNA is degraded by RNase H domain of P protein while the minus(-) strand is synthesizing. (C) The DNA oligomer binds to the direct repeat 2 (DR2) region of the newly synthesized minus(-) strand DNA to guide the synthesis of plus(+) strand DNA, forming a partially circular rcDNA (90–95%). (D) The RNA primer directly initiated in situ without binding to the DR2 region (5–10%), dslDNA will be generated. (E) Inflammation and oxidative stress induce host genomic DNA double-stranded breaking, which provides breakpoints for integration through NHEJ or MMEJ

Fig. 3

Schematic diagram of HBV DNA integration from chronic HBV infection to hepatocellular carcinoma. (A) Initially HBV DNA randomly integrates into host genome. (B) The infected hepatocytes are eliminated by host immune response. Infected hepatocytes with favorable integrations survive and clonally expand. (C) Hepatocytes with integrations expand. When integration happens near/into HCC-related genes, HCC initiating cells may occur. (D) HCC initiating cells expand and HCC cells with carcinogenetic integrations appear. (E) HCC cells with carcinogenetic integrations expand leading to the development of HCC