TY  - GEN
A1  - Riedl, Tobias
CY  - Heidelberg
TI  - Deciphering the molecular regulation of the antiviral deaminase APOBEC3B
N2  - Although effective vaccines against the hepatitis B virus (HBV) are available, it remains a major global health burden. The World Health Organisation estimates that nearly 300 million people are infected with HBV as of 2019 and chronic carriers, suffering from chronic hepatitis B (CHB) are at high risk of developing end-stage liver disease, such as liver cirrhosis and liver cancer. HBV has a complicated life cycle with 2 main steps: (I) the establishment of the viral genome - the covalently closed circular DNA (cccDNA) - in the nucleus of infected hepatocytes, which is highly stable and used as the template for all viral RNAs, and (II) a reverse transcription step, which produces a replicative intermediate - the relaxed circular DNA (rcDNA) - from the pre-genomic RNA (pgRNA). In the clinic, CHB patients are often treated with nucleotide and nucleoside analogues (NAs), which efficiently block the reverse transcription and prevent spread of the virus. While these treatments can prevent the progression of the liver disease, they cannot cure the infection. Therefore, the development of resistance against NAs or being non-compliant to the treatment can result in a relapse of the infection. The research group of Prof. Mathias Heikenwälder and colleagues were the first to show that the agonisation of the lymphotoxin beta receptor (LT?R) on the surface of hepatocytes with an antibody (named BS1) leads to the degradation of the cccDNA. Importantly, they presented evidence that the infection did not rebound after withdrawal of the LT?R agonist, which is the case for the treatment with NAs. The degradation of the cccDNA was dependent of the induction of the apolipoproteins B mRNA editing catalytic polypeptide-like 3B (APOBEC3B), an antiviral enzyme with cytidine deaminase activity, which efficiently edited cytosines to uracils within the cccDNA, eventually leading to the degradation of the cccDNA. These findings represented a potential novel treatment option for CHB patients, allowing for a cure of the disease by directly targeting the viral genome and degrading it, therefore preventing viral rebound.

Aim 1: Deciphering transcriptional and post-transcriptional control of APOBEC3B In this scientific context, I investigated key factors involved in the regulation of APOBEC3B on the transcriptional and post-transcriptional level. I used HBV infected and non-infected differentiated HepaRG (dHepaRG), treated or not with the LT?R agonist BS1. Further, CRISPR-Cas9-induced knock-out cell lines of dHepaRG, small interfering RNA, and micro RNA (miRNA) transfections into dHepaRG as well as kinase inhibitors were used to shed light on key molecular mechanisms involved in APOBEC3B regulation. The data of this PhD thesis indicate that APOBEC3B induction is mediated by the nuclear factor kappa B (NF-?B), and that mainly the non-canonical NF-?B signalling, through RelB/p52 dimers, plays an important role in APOBEC3B induction. Furthermore, the miRNA hsa-miR-138-5p is a post-transcriptional repressor of APOBEC3B. Interference with NF-?B signalling and aberrant expression of hsa-miR-138-5p reduced inducibility of APOBEC3B by LT?R activation and prevented strong anti-cccDNA effects of the treatment. I published these results as a co-first author in Journal of Hepatology Reports in August 2021 (DOI: 10.1016/j.jhepr.2021.100354).

Aim 2: Hypoxia reduces antiviral effects of LT?R activation and offers a niche for HBV to avoid immune responses Next, I deciphered how oxygen levels, sensed on a cellular level inter alia by hypoxia induced factor 1 alpha (HIF1?), affect APOBEC3B expression and anti-cccDNA effects of LT?R activation. To this end, I also used HBV infected and non-infected dHepaRG, treated or not with the LT?R agonist BS1. Transgenic dHepaRG cell lines, transfection of siRNAs, and pharmacological inhibition of proline hydroxylases (i.e. proteins involved in the destabilisation of HIF1?) were also used. In addition, I analysed histological stainings of liver sections of CHB patients. I identified HIF1? as a restriction factor for APOBEC3B induction by LT?R activation. RelB protein levels were reduced under high HIF1? protein levels, preventing efficient APOBEC3B induction and subsequent anti-cccDNA effects. My data indicated that liver areas presenting high levels of HIF1? can offer a reservoir for HBV in vivo, in which the virus can avoid immune-mediated clearance. I published these results as a co-first author in Hepatology in April 2021 (DOI: 10.1002/hep.31902).
AV  - public
ID  - heidok31753
Y1  - 2022///
KW  - Hepatitis B Virus
KW  -  NF-kappaB
KW  -  HIF1alpha
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/31753/
ER  -