Hepatitis B virus enhancer 1 activates preS1 and preS2 promoters of integrated HBV DNA impairing HBsAg secretion

Background & Aims

The expression of HBsAg from integrated HBV DNA limits the achievement of functional cure for chronic hepatitis B. Thus, characterising the unique expression and secretion of HBsAg derived from integrated HBV DNA is of clinical significance.

Methods

A total of 563 treatment-naive patients and 62 functionally cured patients were enrolled, and HBsAg and HBcAg immunohistochemistry of their liver biopsy tissues was conducted followed by semi-quantitative analysis. Then, based on stratified analysis of HBeAg-positive and -negative patients, long-read RNA sequencing analysis, as well as an in vitro HBV integration model, we explored the HBsAg secretion characteristics of integrated HBV DNA and underlying mechanisms.

Results

In contrast to the significantly lower serum HBsAg levels, no significant decrease of intrahepatic HBsAg protein was observed in HBeAg-negative patients, as compared with HBeAg-positive patients. The results of long-read RNA sequencing of liver tissues from patients with chronic HBV infection and in vitro studies using integrated HBV DNA mimicking dslDNA plasmid revealed that, the lower HBsAg secretion efficiency seen in HBeAg-negative patients might be attributed to an increased proportion of preS1 mRNA derived from integrated HBV DNA instead of covalently closed circular DNA. The latter resulted in an increased L-HBsAg proportion and impaired HBsAg secretion. Enhancer 1 (EnhI) in integrated HBV DNA could retarget preS1 (SP1) and preS2 (SP2) promoters to disrupt their transcriptional activity balance.

Conclusions

The secretion of HBsAg originating from integrated HBV DNA was impaired. Mechanistically, functional deficiency of core promoter leads to retargeting of EnhI and thus uneven activation of the SP1 over the SP2 promoter, resulting in an increase in the proportion of L-HBsAg.

Impact and implications

Integrated hepatitis B virus (HBV) DNA can serve as an important reservoir for HBV surface antigen (HBsAg) expression, and this limits the achievement of a functional cure. This study revealed that secretion efficiency is lower for HBsAg derived from integrated HBV DNA than HBsAg derived from covalently closed circular DNA, as determined by the unique sequence features of integrated HBV DNA. This study can broaden our understanding of the role of HBV integration and shed new light on antiviral strategies to facilitate a functional cure. We believe our results are of great general interest to a broad audience, including patients and patient organisations, the medical community, academia, the life science industry and the public.