Investigation of Hepatitis B virus entry mechanism

Raymond, Chidinma (2022) Investigation of Hepatitis B virus entry mechanism. PhD thesis, University of Nottingham.

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Hepatitis B infection is a global public health challenge that attacks the liver, resulting in severe hepatic and non-hepatic complications, particularly liver cirrhosis and hepatocellular carcinoma. This infection caused by the Hepatitis B virus (HBV) is the cause of the world's most common liver infection and the second leading cause of cancer worldwide. HBV is known to have a complicated replication cycle in which it utilises a reverse transcriptase with proofreading inability. The overlapping nature of the HBV genome, in addition to the proofreading inability of the HBV polymerase, culminates in high mutation rates with pleiotropic effects on both the polymerase and the surface genes. Mutations in the surface gene (HBsAg) have been linked to several clinical implications, such as vaccine escape and failure of HBV diagnostic assays. We hypothesised that the HBsAg variability would go beyond immune escape mutants, potentially extending to its interaction with cell receptors and entry. Therefore, in this study, we have studied the effect of HBsAg mutations on HBsAg interactions with cell receptors and on HBV entry using the pseudotyping system.

The entry of HBV pseudotyped particles into the Huh7 hepatoma cell line transduced to express the NTCP receptor was studied. This study has generated several unusual data particularly focused on the unusual entry phenotype of the clinical isolate BT10D4 and its ability to infect Huh7 cells independent of the NTCP receptor. Sequence analysis of this isolate identified 2 rare amino acid substitutions at positions s69 and s96 that possibly interact with each other and with one or more other amino acid positions to achieve the unusual entry phenotype. Data from this study showed that BT10D4 utilised the HBsAg PreS2-48 amino acids, the epidermal growth factor receptor (EGFR), the clathrin-dependent endocytosis for entry and internalisation. Interestingly, this study showed that unlike the entry into Huh7 cells, BT10D4 could not infect HepG2 hepatoma cells in the absence of NTCP.

In light of the above findings, we propose that the presence of the mutations in BT10D4, which interact with each other, alter the conformation of the HBsAg in such a way that favours its interaction with one or more unknown Huh7 cell receptors. Consequently, future work will explore this hypothesis to provide the much-needed answers about the BT10D4 isolate, the rare amino acid substitutions and its unusual entry phenotype.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Tarr, Alexander
Irving, William
Keywords: Hepatitis B virus
Subjects: Q Science > QR Microbiology > QR180 Immunology
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Life Sciences
Item ID: 68635
Depositing User: Raymond, Chidinma
Date Deposited: 31 Jul 2022 04:41
Last Modified: 31 Jul 2022 04:41

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