Abstract
We recently reported that the PPIase Par14 and Par17 encoded by PIN4 upregulate HBV replication in an HBx-dependent manner by binding to conserved arginine–proline (RP) motifs of HBx. HBV core protein (HBc) has a conserved 133RP134 motif; therefore, we investigated whether Par14/Par17 bind to HBc and/or core particles. Native agarose gel electrophoresis (NAGE) and immunoblotting and co-immunoprecipitation were used. Chromatin immunoprecipitation from HBV-infected HepG2-hNTCP-C9 cells was performed. NAGE and immunoblotting revealed that Par14/Par17 bound to core particles and co-immunoprecipitation revealed that Par14/Par17 interacted with core particle assembly-defective, and dimer-positive HBc-Y132A. Thus, core particles and HBc interact with Par14/Par17. Par14/Par17 interacted with the HBc 133RP134 motif possibly via substrate-binding E46/D74 and E71/D99 motifs. Although Par14/Par17 dissociated from core particles upon heat treatment, they were detected in 0.2 N NaOH-treated opened-up core particles, demonstrating that Par14/Par17 bind outside and inside core particles. Furthermore, these interactions enhanced the stabilities of HBc and core particles. Like HBc-Y132A, HBc-R133D and HBc-R133E were core particle assembly-defective and dimer-positive, demonstrating that a negatively charged residue at position 133 cannot be tolerated for particle assembly. Although positively charged R133 is solely important for Par14/17 interactions, the 133RP134 motif is important for efficient HBV replication. Chromatin immunoprecipitation from HBV-infected cells revealed that the S19 and E46/D74 residues of Par14 and S44 and E71/D99 residues of Par17 were involved in recruitment of 133RP134 motif-containing HBc into cccDNA. Our results demonstrate that interactions of HBc, Par14/Par17, and cccDNA in the nucleus and core particle–Par14/Par17 interactions in the cytoplasm are important for HBV replication.
Highlights
hepatitis B virus (HBV) is a prototype virus in the Hepadnaviridae family with a partially double-stranded, relaxed-circular (RC) DNA genome that shows exclusive tropism for hepatocytes (Seeger and Mason, 2015) HBV infection causes acute hepatitis, which can lead to chronic hepatitis B, liver fibrosis, cirrhosis, and hepatocellular carcinoma (Seeger and Mason, 2015)
In addition to HBx–parvulin 14 (Par14)/parvulin 17 (Par17)–closed circular DNA (cccDNA) interactions in the nucleus and HBx–Par14/Par17 interactions in the cytoplasm and mitochondria (Saeed et al, 2019), we demonstrate that interactions of HBV core protein (HBc), Par14/Par17, and cccDNA in the nucleus and core particle–Par14/Par17 interactions in the cytoplasm can enhance HBV replication through increased transcriptional activity, increased core particle assembly and/ or stability, and increased HBV DNA synthesis
Par14/Par17 interact with two RP motifs of HBx to enhance HBx stability and promote HBV replication (Saeed et al, 2019), PPIase NIMA-interacting 1 (Pin1) interacts with phosphorylated SP motifs of HBx to facilitate HBx transactivation and hepatocarcinogenesis progression (Pang et al, 2007), and Pin1 binds to HBc via specific phosphorylated Thr160-Pro and Ser162-Pro motifs and stabilizes HBc in a phosphorylationdependent manner for efficient HBV propagation (Nishi et al, 2020)
Summary
HBV is a prototype virus in the Hepadnaviridae family with a partially double-stranded, relaxed-circular (RC) DNA genome that shows exclusive tropism for hepatocytes (Seeger and Mason, 2015) HBV infection causes acute hepatitis, which can lead to chronic hepatitis B, liver fibrosis, cirrhosis, and hepatocellular carcinoma (Seeger and Mason, 2015). The episomal cccDNA contains four overlapping open reading frames, which transcribe 3.5 kb pregenomic RNA (pgRNA) encoding HBc (core) and polymerase proteins, 2.4 and 2.1 kb S mRNAs producing large, middle, and small surface (HBs) proteins, and 0.7 kb X mRNA encoding HBx protein (Ganem, 2001; Hu and Seeger, 2015; Seeger and Mason, 2015)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
