Oxygenation and miR138-5 p act as rheostats in APOBEC3B-mediated Hepatitis B Virus control

Hepatitis B virus (HBV) remains a major health problem with 257 million people chronically infected. Current treatments can control the infection but does not allow its complete eradication leading to relapses upon withdrawn or resistance development. These relapses are due to the persistence of the covalently closed circular DNA (cccDNA), which is not efficiently targeted by those treatments. Agonization of the lymphotoxin β receptor (LTβR) with BS1 was shown to induce APOBEC3B (A3B), which induces DNA damage into cccDNA, which eventually leads to its degradation (Lucifora et al., 2014). Here, we analysed the underlying regulation mechanisms of A3B in the context of HBV-infection.

We show that A3B induction depends on NF-κB pathway signalling, as NIK knock-down and IKKβ inhibition, strongly impair the induction of A3B, reverting the antiviral effect of LTβR-activation. In addition, a latency in A3B induction is observed between 36h to 72h of BS1 treatment, before a strong induction after 4 days onwards. We identified the micro RNA 138 – 5 p (miR-138-5 p) to be implicated in the regulation of A3B. Transfection of dHepaRG cells with the miR-138-p prevents the induction of A3B by BS1, and HBV inhibition. Interestingly, even without the presence of BS1, miR-138-5 p transduction increases HBV replication, highlighting a basal expression of A3B in HBV infected cells. Finally, in livers of HBV infected patients, hypoxic areas are associated with an increased level of HBV- replication and a decreased expression of A3B. In vitro, A3B expression is reduced during hypoxia through a HIF1α dependant mechanism. This leads to impaired A3B dependent cccDNA purging under hypoxia upon BS1 treatment. Removing HIF1a from the system allows again A3B upregulation and antiviral effects.

Altogether, we have characterised the mechanisms of APOBEC3B regulation in hepatocytes through NF-κB and miR-138-5 p. We have also highlighted a fine regulation between HBV infection, APOBEC3B expression and hypoxia, explaining the persistence of HBV even during inflammation and LTβR-stimulation.