Hepatitis B Virus HBx Protein Mediates the Degradation of Host Restriction Factors through the Cullin 4 DDB1 E3 Ubiquitin Ligase Complex

Authors

Marissa M Minor
F Blaine Hollinger
Adrienne L McNees
Sung Yun Jung
Antrix Jain
Joseph M Hyser
Karl-Dimiter Bissig
Betty L Slagle

Publication Date

3-30-2020

Journal

Cells

DOI

10.3390/cells9040834

PMID

32235678

PMCID

PMC7226812

PubMedCentral® Posted Date

3-30-2020

PubMedCentral® Full Text Version

Post-Print

Published Open-Access

yes

Keywords

DNA-Binding Proteins, HEK293 Cells, Hep G2 Cells, Hepatitis B virus, Host-Pathogen Interactions, Humans, Liver, Models, Biological, Multiprotein Complexes, Protein Binding, Trans-Activators, Viral Regulatory and Accessory Proteins, Virus Replication, hepatitis B virus, HBx, damaged DNA binding protein 1, cullin 4 RING E3 ligase, SMC6, DDB1 cullin accessory factor

Abstract

The hepatitis B virus (HBV) regulatory HBx protein is required for infection, and its binding to cellular damaged DNA binding protein 1 (DDB1) is critical for this function. DDB1 is an adaptor protein for the cullin 4A Really Interesting New Gene (RING) E3 ubiquitin ligase (CRL4) complex and functions by binding cellular DDB1 cullin associated factor (DCAF) receptor proteins that recruit substrates for ubiquitination and degradation. We compared the proteins found in the CRL4 complex immunoprecipitated from uninfected versus HBV-infected hepatocytes from human liver chimeric mice for insight into mechanisms by which HBV and the cell interact within the CRL4 complex. Consistent with its role as a viral DCAF, HBx was found in the HBV CRL4 complexes. In tissue culture transfection experiments, we showed that HBx expression led to decreased levels of known restriction factor structural maintenance of chromosomes protein 6 (SMC6) and putative restriction factors stromal interaction molecule 1 (STIM1, zinc finger E-box binding homeobox 2 (ZEB2), and proteasome activator subunit 4 (PSME4). Moreover, silencing of these proteins led to increased HBV replication in the HepG2-sodium taurocholate cotransporting polypeptide (NTCP) infection model. We also identified cellular DCAF receptors in CRL4 complexes from humanized mice. Increasing amounts of HBx did not reveal competitive DCAF binding to cullin4 (CUL4)-DDB1 in plasmid-transfected cells. Our results suggest a model in which HBx benefits virus replication by directly or indirectly degrading multiple cellular restriction factors.