DHX9 interacts with APOBEC3B and attenuates the anti-HBV effect of APOBEC3B

Abstract

Hepatitis B virus (HBV) is a partially double-stranded DNA virus that replicates by reverse transcription. We previously demonstrated that the host restriction factor-APOBEC3B (A3B) inhibited HBV replication which was dependent on its deaminase activity during reverse transcription. However, the host factors involved in the process of regulating the anti-HBV function of A3B are less known. In this research, to obtain a comprehensive understanding of the interaction networks of A3B, we conducted coimmunoprecipitation and mass spectrometry to identify A3B-interacting proteins in the presence of HBV. By this approach, we determined that DExD/H-box helicase 9 (DHX9) suppressed the anti-HBV effect of A3B, and this suppression was dependent on their interaction. Although DHX9 did not affect the deamination activity of A3B in vitro assay or the viral DNA editing of A3B in HepG2-NTCP cells that support HBV infection, it inhibited the binding of A3B with pgRNA. These data suggest that DHX9 can interact with A3B and attenuate the anti-HBV efficacy of A3B.

The Enigmatic Helicase DHX9 and Its Association With the Hallmarks of Cancer

“…In addition to this, DHX9 has been identified as a cytosolic viral DNA sensor in plasmacytoid dendritic cells, dependent on interaction with MyD88 [ 51 ], as well as a viral dsRNA sensor in myeloid dendritic cells [ 52 ], actions that are required to trigger NF-κB activation and subsequent induction of the antiviral cytokine response. In apparent opposition to these protective actions, DHX9 also facilitates the replication of numerous viruses, including hepatitis B virus (HBV) [ 53 , 54 ], hepatitis C virus [ 55 ], human immunodeficiency virus [ 56 ] and chikungunya virus [ 57 ]. In particular regarding HBV, it has recently been revealed that the HBV protein X promotes upregulated DHX9 expression, while DHX9 facilitates HBV DNA replication dependent on an interaction with Nup98 to stimulate DHX9’s helicase activity [ 53 ].…”

“…In particular regarding HBV, it has recently been revealed that the HBV protein X promotes upregulated DHX9 expression, while DHX9 facilitates HBV DNA replication dependent on an interaction with Nup98 to stimulate DHX9’s helicase activity [ 53 ]. Another recent study also revealed that DHX9 promotes HBV DNA replication via inhibiting the apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3B (A3B), which usually functions to impede HBV DNA replication [ 54 ].…”

“…DHX9 also facilitates HBV replication via Nup98 regulation, and it was shown that cells infected with HBV contained upregulated DHX9 expression, with levels correlating to viral load [ 53 ]. It was then later revealed that DHX9 interacts with A3B in order to negatively regulate anti-HBV function, therefore contributing to HBV viral DNA replication [ 54 ]. Overall, given DHX9’s regulatory role in the life cycle of many viruses used as OVs, DHX9 could be targeted to enhance cancer cells’ response to OVs, thereby widening the applications of targeting DHX9 in cancer therapy to modulate cancer immunotherapy.…”

Differences in HBV Replication, APOBEC3 Family Expression, and Inflammatory Cytokine Levels Between Wild-Type HBV and Pre-core (G1896A) or Basal Core Promoter (A1762T/G1764A) Mutants

“…An intriguing connection of HBx to APOBEC3B was identified by Shen et al (2020) and demonstrated the up-regulation of DHX9 proteins by HBx. In their related study, Chen et al (2020) reported that DHX9 suppresses APOBEC3B and inhibited the anti-HBV effects. Additionally, HBx post-translational suppression of APOBEC3G has been shown within Huh7 cells (Chen et al, 2017).…”

APOBEC3s: history of an antiviral and mutagenic protein family

“…La protéine X diminue également le niveau intracellulaire d'A3G en favorisant son externalisation par la voie exosomale, indépendamment de sa dégradation par le protéasome ou le lysosome [338]. L'hélicase DHX9 (DExH-Box Helicase 9) s'associe à A3B et inhibe son activité restrictive en perturbant la liaison d'A3B à l'ARNpg [339]. De plus, l'ARN long non codant HULC (Hepatocellular carcinoma Up-regulated Long non-Coding RNA), fortement exprimé dans le cas de carcinome hépatocellulaire (HCC), favorise l'expression du miARN-539 qui cible la 3'UTR de l'ARNm d'A3B, entraînant la dégradation de la protéine [340].…”