Abstract:Background and Aims:
Murine hepatic cells cannot support hepatitis B virus (HBV) infection even with supplemental expression of viral receptor, human sodium taurocholate cotransporting polypeptide (hNTCP). However, the specific restricted step remains elusive. In this study, we aimed to dissect HBV infection process in murine hepatic cells.
Approach and Results:
Cells expressing hNTCP were inoculated with HBV or hepatitis delta virus (HDV). HBV pregenomic RNA (pgRNA), covalently closed circular DNA (cccDNA),… Show more
“…Going further, Zhao et al3 found that some rcDNA did reach the murine nucleus, but disappeared over time without cccDNA production (Figure 1B). Their most striking observation, however, was the nearly complete nuclease resistance of cytoplasmic NC‐borne rcDNA in murine cells, whereas in human cells a substantial fraction of this rcDNA was nuclease sensitive.…”
Section: Introductionmentioning
confidence: 82%
“…huNTCP enables HBV entry into murine cells (not explicitly shown), but usually not cccDNA formation. Experiments by Zhao et al [3] to identify the critical step(s) are indicated by white boxes with blue lettering. Artificial delivery of HBV plasmid vectors or cccDNA (not shown) generated all expected RNAs, proteins, and progeny NCs, ruling out transcriptional issues.…”
Section: Introductionmentioning
confidence: 99%
“…Despite these complexities, the studies by Zhao et al3 and Wei et al4 demonstrate the principal ability of murine cells to repair rcDNA into cccDNA, such that further research can fully focus on deciphering the mechanisms of intracellular HBV NC transport, disassembly, and genome uncoating in human versus murine hepatic cells.…”
“…Going further, Zhao et al3 found that some rcDNA did reach the murine nucleus, but disappeared over time without cccDNA production (Figure 1B). Their most striking observation, however, was the nearly complete nuclease resistance of cytoplasmic NC‐borne rcDNA in murine cells, whereas in human cells a substantial fraction of this rcDNA was nuclease sensitive.…”
Section: Introductionmentioning
confidence: 82%
“…huNTCP enables HBV entry into murine cells (not explicitly shown), but usually not cccDNA formation. Experiments by Zhao et al [3] to identify the critical step(s) are indicated by white boxes with blue lettering. Artificial delivery of HBV plasmid vectors or cccDNA (not shown) generated all expected RNAs, proteins, and progeny NCs, ruling out transcriptional issues.…”
Section: Introductionmentioning
confidence: 99%
“…Despite these complexities, the studies by Zhao et al3 and Wei et al4 demonstrate the principal ability of murine cells to repair rcDNA into cccDNA, such that further research can fully focus on deciphering the mechanisms of intracellular HBV NC transport, disassembly, and genome uncoating in human versus murine hepatic cells.…”
“…Furthermore, the ability to support HBV cccDNA formation in AML12 cells could be correlated with enhanced destabilization (uncoating) of mature HBV nucleocapsids [ 17 ]. Similarly, some evidence has been presented recently suggesting that the failure to support nucleocapsid uncoating by mouse hepatocytes may also contribute to the inability of mouse hepatocytes to support cccDNA formation during HBV infection after huNTCP expression [ 78 ]. Consistent with the expectation that the DNA repair reactions involved in rcDNA to cccDNA conversion, per se, are highly conserved during evolution, mouse, and even yeast, DNA repair factors can support cccDNA formation from rcDNA mimics [ 78 , 79 , 80 ].…”
Section: The Role Of Hbc In Specifying Hbv Host Tropismmentioning
confidence: 99%
“…Similarly, some evidence has been presented recently suggesting that the failure to support nucleocapsid uncoating by mouse hepatocytes may also contribute to the inability of mouse hepatocytes to support cccDNA formation during HBV infection after huNTCP expression [ 78 ]. Consistent with the expectation that the DNA repair reactions involved in rcDNA to cccDNA conversion, per se, are highly conserved during evolution, mouse, and even yeast, DNA repair factors can support cccDNA formation from rcDNA mimics [ 78 , 79 , 80 ]. Therefore, overcoming the failure of nucleocapsid disassembly in mouse hepatocytes should help to establish a mouse model that can support HBV cccDNA formation and infection.…”
Section: The Role Of Hbc In Specifying Hbv Host Tropismmentioning
Hepatitis B virus (HBV) relies on the core protein (HBc) to establish productive infection, as defined by the formation of the covalently closed circularized DNA (cccDNA), as well as to carry out almost every step of the lifecycle following cccDNA formation. Multiple copies of HBc form an icosahedral capsid shell that encapsidates the viral pregenomic RNA (pgRNA) and facilitates the reverse transcription of pgRNA to a relaxed circular DNA (rcDNA) within the capsid. During infection, the complete HBV virion, which contains an outer envelope layer in addition to the internal nucleocapsid containing rcDNA, enters human hepatocytes via endocytosis and traffics through the endosomal compartments and the cytosol to deliver its rcDNA to the nucleus to produce cccDNA. In addition, progeny rcDNA, newly formed in cytoplasmic nucleocapsids, is also delivered to the nucleus in the same cell to form more cccDNA in a process called intracellular cccDNA amplification or recycling. Here, we focus on recent evidence demonstrating differential effects of HBc in affecting cccDNA formation during de novo infection vs. recycling, obtained using HBc mutations and small molecule inhibitors. These results implicate a critical role of HBc in determining HBV trafficking during infection, as well as in nucleocapsid disassembly (uncoating) to release rcDNA, events essential for cccDNA formation. HBc likely functions in these processes via interactions with host factors, which contributes critically to HBV host tropism. A better understanding of the roles of HBc in HBV entry, cccDNA formation, and host species tropism should accelerate ongoing efforts to target HBc and cccDNA for the development of an HBV cure and facilitate the establishment of convenient animal models for both basic research and drug development.
Heterogeneous nuclear protein U (HNRNPU) plays a pivotal role in innate immunity by facilitating chromatin opening to activate immune genes during host defense against viral infection. However, the mechanism by which HNRNPU is involved in Hepatitis B virus (HBV) transcription regulation through mediating antiviral immunity remains unknown. Our study revealed a significant decrease in HNRNPU levels during HBV transcription, which depends on HBx‐DDB1‐mediated degradation. Overexpression of HNRNPU suppressed HBV transcription, while its knockdown effectively promoted viral transcription, indicating HNRNPU as a novel host restriction factor for HBV transcription. Mechanistically, HNRNPU inhibits HBV transcription by activating innate immunity through primarily the positive regulation of the interferon‐stimulating factor 2′‐5′‐oligoadenylate synthetase 3, which mediates an ribonuclease L‐dependent mechanism to enhance innate immune responses. This study offers new insights into the host immune regulation of HBV transcription and proposes potential targets for therapeutic intervention against HBV infection.
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