Inhibition of Hepatitis B Virus Replication by cIAP2 Involves Accelerating the Ubiquitin-Proteasome-Mediated Destruction of Polymerase

Abstract

Cellular inhibitor of apoptosis protein 2 (cIAP2) is a potent suppressor of apoptotic cell death. We have shown previously that cIAP2 is involved in the tumor necrosis factor alpha (TNF-␣)-induced anti-hepatitis B virus (HBV) response; however, the mechanism for this antiviral effect remains unclear. In the present study, we demonstrate that cIAP2 can significantly reduce the levels of HBV DNA replication intermediates but not the total viral RNA or core protein levels. Domain-mapping analysis revealed that the carboxy-terminal domains of cIAP2 were indispensable for this anti-HBV ability and that an E3 ligase-deficient mutant of cIAP2 (termed cIAP2*) completely lost its antiviral activity. We further identified HBV polymerase as the target of cIAP2. Overexpression of cIAP2 but not cIAP2* reduced polymerase protein levels, while cIAP2 knockdown increased polymerase expression. In addition, we observed that cIAP2 promoted the degradation of the viral polymerase through a proteasome-dependent pathway. Further experiments demonstrated that cIAP2 can bind to polymerase and promote its polyubiquitylation. Finally, we found that cIAP2 downregulated the encapsidation of HBV pregenomic RNA. Taken together, these data reveal a novel mechanism for the inhibition of HBV replication by cIAP2 via acceleration of the ubiquitin-proteasome-mediated decay of polymerase and reduction of the encapsidation of HBV pregenomic RNA, making this mechanism a novel strategy for HBV therapy.Infection with hepatitis B virus (HBV) is a public health problem worldwide. It is estimated that at least 10% of the population of tropical Africa and Far East Asia are chronic carriers of the virus (40). Epidemiological studies have estimated that 350 million people are chronic carriers of HBV, with the potential to develop chronic active hepatitis, liver cirrhosis, or hepatocellular carcinoma (HCC) (9). HBV is a small double-stranded DNA virus belonging to the family Hepadnaviridae and replicates primarily in hepatocytes. In the nuclei of hepatocytes, the covalently closed circular DNA (cccDNA) of HBV serves as the transcription template for the viral pregenomic RNA (pgRNA) and subgenomic RNAs. The pgRNA is a multifunctional transcript. This transcript encodes the viral polymerase and core protein while also functioning as the template for HBV reverse transcription. HBV genome replication is initiated upon the recognition and binding of pgRNA by the viral polymerase protein. The complex formed by pgRNA and polymerase is then packaged into nucleocapsids, and in the nucleocapsids, polymerase catalyzes the conversion of pgRNA into single-stranded DNA (ssDNA) and relaxed circular DNA (rcDNA). The mature nucleocapsids are then enveloped and secreted (37).

The ubiquitin-proteasome system is required for the early stages of porcine circovirus type 2 replication

“…For instance, MG132 affects hepatitis E virus replication likely through the inhibition of viral transcription and/or translation without a significant effect on cellular translation (Karpe and Meng, 2012). Wang et al (2011) demonstrated that cellular inhibitor of apoptosis protein 2 (cIAP2) can significantly reduce the levels of hepatitis B virus DNA replication via acceleration of the UPS-mediated decay of the polymerase. In the present study, we examined the effects of the proteasome inhibitors MG132 and lactacystin on PCV2 replication and found that the inhibition of the UPS reduces the number of viral DNA copies at 12 hpi (Fig.…”

Hepatitis B Virus Polymerase Disrupts K63-Linked Ubiquitination of STING To Block Innate Cytosolic DNA-Sensing Pathways

“…The following expression plasmids were generously provided: pIFN-␤-Luc (Rongtuan Lin, McGill University, Canada); pEF-STING and p-55C1B-Luc (Takashi Fujita, Kyoto University, Japan); pFlag-MITA, pcDNA3.1-HA-MITA, pFlag-TRIM32, and pFlag-TRIM56 (Hongbing Shu, Wuhan University, China); and pcDNA3.1-CMV-HBV1.1 (Youhua Xie, Fudan University, China), which contains the wildtype HBV 1.1-mer overlength genomic sequence. pHBV1.3, pFlag-Pol (pcDNA3.1-Flag-Pol and pQCXIP-Flag-Pol), the series of truncated mutants of Pol, pcDNA3.1-Flag-Core, pcDNA3.1-Flag-HBx, pcDNA3.1-Flag-Precore, pcDNA3.1-Flag-HBsAg, pFlag-TBK1, pHA-RIG-I, pCMV-Myc-Pol, and pcDNA3-HA-Ub were described previously (10,(26)(27)(28)(29). pHBV1.3-⌬Pol and pCMV-HBV-⌬Pol, defective in viral polymerase expression, were derived from pHBV1.3 and pcDNA3.1-CMV-HBV1.1, respectively, by introducing a frameshift mutation into the Pol gene after codon 108.…”

“…The supernatants were collected, precleared with protein A/G Plus agarose beads (Santa Cruz) for 30 min, and incubated with anti-Flag or anti-HA antibodies at 4°C. After 2 h, 25 l of a 1:1 slurry of protein A/G Plus agarose beads was added and incubated for additional 2 h. The immunoprecipitates were washed five times with lysis buffer and boiled in 1% (wt/vol) SDS sample buffer, followed by SDS-PAGE and Western blot analysis as described previously (27).…”

The Superimposed Deubiquitination Effect of OTULIN and Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Nsp11 Promotes Multiplication of PRRSV

“…The UPS is involved in the replication of a broad range of viruses (6). Hindering the activity of the cellular ubiquitin proteasome system, the physiological processes of many viruses are blocked, including invasion by the virus (7), nucleic acid synthesis (8)(9)(10)(11), and the release of virus particles (12). On the other hand, virus infection also affects the host's ubiquitin proteasome system (9).…”