Hepatitis B virus regulatory HBx protein binding to DDB1 is required but is not sufficient for maximal HBV replication

Hodgson, Amanda; Hyser, Joseph M.; Keasler, Victor V.; Cang, Yong; Slagle, Betty L.

doi:10.1016/j.virol.2012.01.021

Cited by 73 publications

(70 citation statements)

References 66 publications

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“…An intriguing speculation coming from previous reports that the HBx-DDB1 interaction is critical for viral genome replication (15,16) was that HBx-targeted host factors that restrict viral DNA replication are regulated by the Cul4-DDB1 ubiquitin E3 ligase (12). Contrary to the expectation of that hypothesis, our findings consistently indicated that the DDB1-HBx interaction is largely dispensable for HBx-stimulated viral genome replication.…”

Section: Discussioncontrasting

confidence: 89%

“…In line with this notion, it was reported previously that the DDB1-HBx interaction imparts HBx-induced genetic instability and HBx-induced S-phase progression, potentially contributing to hepatocellular carcinoma development (8,13,14). Moreover, the DDB1-HBx interaction was shown to be essential for the ability of HBx to stimulate viral genome replication in an experiment carried out in HepG2 cells, a hepatoma cell line (15,16).…”

mentioning

confidence: 52%

“…Previous studies reported that the DDB1-HBx interaction is indispensable for HBx-stimulated viral DNA replication (15,16), suggesting that a host restriction factor that limits HBV replication is regulated by the Cul4-DDB1 ubiquitin E3 ligase (Fig. 7).…”

Section: Discussionmentioning

confidence: 91%

“…A P value of Ͻ0.05 was considered statistically significant. interaction is indispensable for HBx-stimulated viral DNA replication (15,16). To corroborate that finding, we sought to examine whether the ability of HBx to bind DDB1 is essential for HBxstimulated viral genome replication.…”

Section: Methodsmentioning

confidence: 95%

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DDB1 Stimulates Viral Transcription of Hepatitis B Virus via HBx-Independent Mechanisms

Kim

Lee

Son

et al. 2016

J Virol

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HBx, a small regulatory protein of hepatitis B virus (HBV), augments viral DNA replication by stimulating viral transcription. Among numerous reported HBx-binding proteins, DDB1 has drawn attention, because DDB1 acts as a substrate receptor of the Cul4-DDB1 ubiquitin E3 ligase. Previous work reported that the DDB1-HBx interaction is indispensable for HBx-stimulated viral DNA replication, suggesting that the Cul4-DDB1 ubiquitin E3 ligase might target cellular restriction factors for ubiquitination and proteasomal degradation. To gain further insight into the DDB1-HBx interaction, we generated HBx mutants deficient for DDB1 binding (i.e., R96A, L98A, and G99A) and examined whether they support HBx-stimulated viral DNA replication. In contrast to data from previous reports, our results showed that the HBx mutants deficient for DDB1 binding supported viral DNA replication to nearly wild-type levels, revealing that the DDB1-HBx interaction is largely dispensable for HBx-stimulated viral DNA replication. Instead, we found that DDB1 directly stimulates viral transcription regardless of HBx expression. Through an HBV infection study, importantly, we demonstrated that DDB1 stimulates viral transcription from covalently closed circular DNA, a physiological template for viral transcription. Overall, we concluded that DDB1 stimulates viral transcription via a mechanism that does not involve an interaction with HBx. IMPORTANCEDDB1 constitutes a cullin-based ubiquitin E3 ligase, where DDB1 serves as an adaptor linking the cullin scaffold to the substrate receptor. Previous findings that the DDB1-binding ability of HBx is essential for HBx-stimulated viral DNA replication led to the hypothesis that HBx could downregulate host restriction factors that limit HBV replication through the cullin ubiquitin E3 ligase that requires the DDB1-HBx interaction. Consistent with this hypothesis, recent work identified Smc5/6 as a host restriction factor that is regulated by the viral cullin ubiquitin E3 ligase. In contrast, here we found that the DDB1-HBx interaction is largely dispensable for HBx-stimulated viral DNA replication. Instead, our results clearly showed that DDB1, regardless of HBx expression, enhances viral transcription. Overall, besides its role in the viral cullin ubiquitin E3 ligase, DDB1 itself stimulates viral transcription via HBx-independent mechanisms. H epatitis B virus (HBV) infection represents a major global public health concern, with over 300 million chronically infected patients worldwide. Chronic HBV infection carries a great risk of developing into severe liver diseases, including cirrhosis and liver cancer, which result in a million deaths annually (1). HBV carries a small (ca. 3.2-kb), relaxed circular (RC), partially double-stranded DNA. Following entry into the host cell, the viral RC DNA traffics to the nucleus, where it is converted into a covalently closed circular DNA (cccDNA), the template for viral transcription (2). Four viral RNAs are transcribed from their respective promoters and serve a...

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Section: Discussioncontrasting

confidence: 89%

mentioning

confidence: 52%

Section: Discussionmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 95%

See 2 more Smart Citations

DDB1 Stimulates Viral Transcription of Hepatitis B Virus via HBx-Independent Mechanisms

Kim

Lee

Son

et al. 2016

J Virol

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“…This is an attractive idea, because DDB1 is a known DNA-binding protein. HBx mutant proteins that do not bind DDB1 are unable to restore HBx-deficient replication in the HBV plasmid replication assay, and the defect occurs at the level of viral transcription (Leupin et al 2005;Hodgson et al 2012).…”

Section: Hbx and Cccdnamentioning

confidence: 99%

Hepatitis B Virus X and Regulation of Viral Gene Expression

Slagle

Bouchard

2016

Cold Spring Harb Perspect Med

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113

117

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The efficient replication of hepatitis B virus (HBV) requires the HBV regulatory hepatitis B virus X (HBx) protein. The exact contributions of HBx are not fully understood, in part because of the limitations of the assays used for its study. When HBV replication is driven from a plasmid DNA, the contribution of HBx is modest. However, there is an absolute requirement for HBx in assays that recapitulate the infectious virus life cycle. There is much evidence that HBx can contribute directly to HBV replication by acting on viral promoters embedded within protein coding sequences. In addition, HBx may also contribute indirectly by modulating cellular pathways to benefit virus replication. Understanding the mechanism(s) of HBx action during virus replication may provide insight into novel ways to disrupt chronic HBV replication.

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