Impaired HBsAg release and antiproliferative/antioxidant cell regulation by HBeAg-negative patient isolates reflects an evolutionary process

Abstract

Background: The hepatitis B e antigen (HBeAg)-negative infection Phase 3 is characterized by no or minimal signs of hepatic inflammation and the absence of hepatic fibrosis. However, underlying molecular mechanisms leading to this benign phenotype are poorly understood.

Methods: Genotype A, B and D HBeAg-negative patient isolates with precore mutation G1896A from Phase 3 were analysed in comparison with respective HBeAg-positive rescue mutant and HBeAg-positive wild-type reference genomes regarding differences in viral replication, morphogenesis, infectivity and impact on NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE)-dependent gene expression and cellular kinome.

Results: In comparison with reference genomes, the patient isolates are characterized by a lower intra- and extracellular hepatitis B surface antigen (HBsAg)-amount, and HBsAg-retention in the endoplasmic reticulum. Rescue of HBeAg expression increased HBsAg-amount but not its release. Expression of the isolated genomes is associated with a higher Nrf2/ARE-dependent gene expression as compared to reference genomes independent of HBeAg expression. Kinome analyses revealed a decreased activity of receptors involved in regulation of proliferative pathways for all patient isolates compared to the reference genomes. No specific conserved mutations could be found between all genomes from Phase 3.

Conclusions: HBeAg-negative genomes from Phase 3 exhibit distinct molecular characteristics leading to lower HBsAg synthesis and release, enhanced oxidative stress protection and decreased activity of key kinases, triggering an antiproliferative stage, which might contribute to the lower probability of hepatocellular carcinoma. The observed differences cannot be associated with loss of HBeAg or specific mutations common to all analysed isolates, indicating the phenotype of Phase 3 derived genomes to be the result of a multifactorial process likely reflecting a conserved natural selection process.

Keywords: HBsAg composition; chronic HBV; mutational analyses; viral genotype.