A Role for the Host DNA Damage Response in Hepatitis B Virus cccDNA Formation—and Beyond?

Schreiner, Sabrina; Nassal, Michael

doi:10.3390/v9050125

Cited by 85 publications

(86 citation statements)

References 175 publications

(244 reference statements)

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“…It is possible that the induction of the ATR-CHK1 pathway by HBV in these cells was very transient under some conditions or that CHK1 activation was dependent on some yet-to-be defined factors. Interestingly, HBV activation of ATR and CHK1 has been reported previously although the precise mechanisms remains unclear (43)(44)(45). In particular, the viral X protein (HBx) has been suggested to activate the ATR-CHK1 pathway.…”

Section: Discussionmentioning

confidence: 99%

Involvement of Host ATR-CHK1 Pathway in Hepatitis B Virus Covalently Closed Circular DNA Formation

Luo

Luckenbaugh

et al. 2020

mBio

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The covalently closed circular (CCC) DNA of hepatitis B virus (HBV) functions as the only viral transcriptional template capable of producing all viral RNA species and is essential to initiate and sustain viral replication. CCC DNA is converted from a relaxed circular (RC) DNA, in which neither of the two DNA strands is covalently closed. As RC DNA mimics damaged cellular DNA, the host cell DNA damage repair (DDR) system is thought to be responsible for HBV CCC DNA formation. The potential role of two major cellular DDR pathways, the ataxia telangiectasia mutated (ATM) pathway and the ATM and Rad3-related (ATR) pathway, in HBV CCC DNA formation was thus investigated. Inhibition, or expression knockdown, of ATR and its downstream signaling factor CHK1, but not of ATM, decreased CCC DNA formation during de novo HBV infection, as well as intracellular CCC DNA amplification, when RC DNA from extracellular virions and intracellular nucleocapsids, respectively, is converted to CCC DNA. Furthermore, a novel RC DNA processing product with 5′ truncated minus strands was detected when the ATR-CHK1 pathway was inhibited, further indicating that this pathway controls RC DNA processing during its conversion to CCC DNA. These results provide new insights into how host cells recognize and process HBV RC DNA in order to produce CCC DNA and have implications for potential means to block CCC DNA production. IMPORTANCE Hepatitis B virus (HBV) chronically infects hundreds of millions of people and remains a major cause of viral hepatitis, cirrhosis, and liver cancer. HBV persistence is sustained by a viral nuclear episome that directs all viral gene expression needed to support viral replication. The episome is converted from an incomplete DNA precursor in viral particles in an ill-understood process. We report here that the incomplete DNA precursor is recognized by the host cell in a way similar to the sensing of damaged cellular DNA for subsequent repair to form the nuclear episome. Intense efforts are ongoing to develop novel antiviral strategies to eliminate CCC DNA so as to cure chronic HBV infection. Our results here provide novel insights into, and suggest novel ways of perturbing, the process of episome formation. Furthermore, our results inform mechanisms of cellular DNA damage recognition and repair, processes essential for normal cell growth.

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Section: Discussionmentioning

confidence: 99%

Involvement of Host ATR-CHK1 Pathway in Hepatitis B Virus Covalently Closed Circular DNA Formation

Luo

Luckenbaugh

et al. 2020

mBio

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“…Activation of the different DDR pathways appears to play other important roles in the HBV life cycle. The formation of the episomal HBV cccDNA from rcDNA relies on cellular enzymes that are components of a DDR pathway sensing nicked DNA to be repaired [21]. It is very likely that this process also facilitates HBV DNA integration, a process that has an important implication in virus mediated pathogenesis [22].…”

Section: Discussionmentioning

confidence: 99%

A short HBV RNA region induces RNR-R2 expression in non-cycling cells and in primary human hepatocytes

Ricardo-Lax

Broennimann

Adler

et al. 2018

Preprint

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25 Hepatitis B virus infects non-dividing cells in which dNTPs are scarce. HBV replication 26 requires dNTPs. To cope with this constraint the virus induces the DNA damage response 27 (DDR) pathway culminating in RNR-R2 expression and the generation of an active RNR 28 holoenzyme, the key regulator of dNTP levels. Previously we reported that the HBx open 29 reading frame (ORF) triggers this pathway. Unexpectedly however, we report here that 30 the production of HBx protein is not essential. We found that a small region of 125 bases 31 within the HBx transcript is sufficient to induce RNR-R2 expression in growth arrested 32 HepG2 cells and in primary human hepatocytes (PHH). The observed HBx embedded 33 regulatory element is named ERE. We demonstrate that ERE is functional as a positive 34 strand RNA polymerase-II transcript. Remarkably, ERE is sufficient to induce the Chk1-35 E2F1-RNR-R2 DDR pathway, previously reported to be activated by HBV. Furthermore, 36 we found that ERE activates ATR but not ATM in eliciting this DDR pathway in 37 upregulating RNR-R2. These findings demonstrate the multitasking role of HBV 38 transcripts in mediating virus-host cell interaction, a mechanism that explains how such a 39 small genome effectively serves such a pervasive virus. 40 41 Author summary 42 The hepatitis B virus (HBV) infects the human liver and over 250 million people 43 worldwide are chronically infected with HBV and at risk for cirrhosis and liver cancer.44 HBV has a very small DNA genome with only four genes, much fewer than other 45 viruses. For propagation the virus consumes dNTPs, the building blocks of DNA, in 46 much higher amounts than the infected cells provide. To cope with this constraint, the 3 47 virus manipulates the cells to increase the production of dNTPs. We found that the virus 48 activates the cellular response to DNA damage upon which the cells increase the 49 production of dNTPs, but instead of repairing cellular DNA, the virus uses them for 50 production of its own DNA. Usually viruses manipulate host cells with one or more of 51 their unique proteins, however the small HBV genome cannot afford having such a 52 unique gene and protein. Instead, we found that here the virus relies on RNA to 53 manipulate the host cells. Our findings highlight the unprecedented principle of a 54 multitasking viral RNA that is not only designed to be translated into proteins but also 55 harbors an independent role in activating the cellular DNA damage response. 56 57 Introduction 58 Hepatitis B virus (HBV) is a non-cytopathic enveloped virus containing a small circular 59 partially double-stranded DNA genome. Upon entering the cell the genome is converted 60 into a covalently closed circular DNA (cccDNA), the viral transcription template [1]. The 61 HBV genome harbors enhancers and promoters regulating the transcription of a number 62 of positive strand transcripts. The generated RNA species are nuclear exported by a 63 unique mechanism that is not entirely understood but requires a RNA region shared by all 64 t...

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“…Upon fusion with the host membrane, the rcDNA‐containing nucleocapsid is released into the cytoplasm and travels to the nucleus (Figure ). Once inside, rcDNA is converted to a highly stable episomal DNA known as covalently closed circular DNA (cccDNA) via the host DNA repair machinery molecule . cccDNA is the transcriptional template for subsequent virus gene expression and generation of pregenomic RNA (pgRNA) .…”

Section: Hbv Replication Cycle and Therapeutic Targetsmentioning

confidence: 99%

“…Once inside, rcDNA is converted to a highly stable episomal DNA known as covalently closed circular DNA (cccDNA) via the host DNA repair machinery molecule. 4,5 cc-cDNA is the transcriptional template for subsequent virus gene expression and generation of pregenomic RNA (pgRNA). 6 HBV DNA is also found integrated into the host chromosome.…”

Section: Hbv Replication Cycle and Therapeutic Targetsmentioning

confidence: 99%

Towards HBV curative therapies

Schinazi

Ehteshami

Bassit

et al. 2018

Liver International

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Tremendous progress has been made over the last 2 decades to discover and develop approaches to control hepatitis B virus (HBV) infections and to prevent the development of hepatocellular carcinoma using various interferons and small molecules as antiviral agents. However, none of these agents have significant impact on eliminating HBV from infected cells. Currently the emphasis is on silencing or eliminating cccDNA, which could lead to a cure for HBV. Various approaches are being developed including the development of capsid effectors, CRISPR/Cas9, TALENS, siRNA, entry and secretion inhibitors, as well as immunological approaches. It is very likely that a combination of these modalities will need to be employed to successfully eliminate HBV or prevent virus rebound on discontinuation of therapy. In the next 5 years clinical data will emerge which will provide insight on the safety and feasibility of these approaches and if they can be applied to eradicate HBV infections globally. In this review, we summarize current treatments and we highlight and examine recent therapeutic strategies that are currently being evaluated at the preclinical and clinical stage. K E Y W O R D Santiviral agents, cccDNA, HBV cure, immunotherapy

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A Role for the Host DNA Damage Response in Hepatitis B Virus cccDNA Formation—and Beyond?

Cited by 85 publications

References 175 publications

Involvement of Host ATR-CHK1 Pathway in Hepatitis B Virus Covalently Closed Circular DNA Formation

Involvement of Host ATR-CHK1 Pathway in Hepatitis B Virus Covalently Closed Circular DNA Formation

A short HBV RNA region induces RNR-R2 expression in non-cycling cells and in primary human hepatocytes

Towards HBV curative therapies

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