The X Protein of Hepatitis B Virus Coactivates Potent Activation Domains

Haviv, Izhak; Vaizel, D; Shaul, Yosef

doi:10.1128/mcb.15.2.1079

Cited by 88 publications

(90 citation statements)

References 82 publications

(108 reference statements)

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“…HBx fused to LexA or c/EBP DNA-binding domains can transactivate the reporters harboring the responsive ciselements (9,32). HBx co-activates potent activators, including acidic activators such as VP16 and p53 as well as non-acidic activators such as E1a (33). Finally, we showed that HBx can specifically bind to RPB5, a common subunit shared by eukaryotic nuclear RNA polymerase I, II, and III, both in vitro and in vivo.…”

mentioning

confidence: 87%

“…Therefore an obvious question is how the HBx-RPB5-TFIIB trimeric interaction enables promoter selectivity in HBx transactivation. HBx alone does not transactivate the pGal4-CAT reporter but facilitates the activation of Gal4-VP16, suggesting that HBx acts during activated, but not basal transcription (33,63). 3 In this regard, HBx may directly or indirectly communicate with some transcriptional activators (19,20).…”

Section: Hbx Rpb5 and Tfiib May Form A Ternary Complex-mentioning

confidence: 99%

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Hepatitis B Virus X Protein Is a Transcriptional Modulator That Communicates with Transcription Factor IIB and the RNA Polymerase II Subunit 5

Lin

Nomura

Cheong

et al. 1997

Journal of Biological Chemistry

158

174

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Hepatitis B virus X protein (HBx) transactivates viral and cellular genes through a wide variety of cis-elements. However, the mechanism is still obscure. Our finding that HBx directly interacts with RNA polymerase II subunit 5 (RPB5), a common subunit of RNA polymerases, implies that HBx directly modulates the function of RNA polymerase (Cheong, J. H., Yi, M., Lin, Y., and Murakami, S. (1995) EMBO J. 14, 142-150). In this context, we examined the possibility that HBx and RPB5 interact with other general transcription factors. HBx and RPB5 specifically bound to transcription factor IIB (TFIIB) in vitro, both of which were detected by either far-Western blotting or the glutathione S-transferaseresin pull-down assay. Delineation of the binding regions of these three proteins revealed that HBx, RPB5, and TFIIB each has two binding regions for the other two proteins. Co-immunoprecipitation using HepG2 cell lysates that express HBx demonstrated trimeric interaction in vivo. Some HBx substitution mutants, which had severely impaired transacting activity, exhibited reduced binding affinity with either TFIIB or RPB5 in a mutually exclusive manner, suggesting that HBx transactivation requires the interactions of both RPB5 and TFIIB. These results indicated that HBx is a novel virus modulator that facilitates transcriptional initiation by stabilizing the association between RNA polymerase and TFIIB through communication with RPB5 and TFIIB.

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mentioning

confidence: 87%

Section: Hbx Rpb5 and Tfiib May Form A Ternary Complex-mentioning

confidence: 99%

Hepatitis B Virus X Protein Is a Transcriptional Modulator That Communicates with Transcription Factor IIB and the RNA Polymerase II Subunit 5

Lin

Nomura

Cheong

et al. 1997

Journal of Biological Chemistry

158

174

View full text Add to dashboard Cite

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“…Huh7 cells were maintained in Dulbecco's modified Eagle's minimal essential medium as previously described. 8 Cells were seeded at about 60% confluence 4 to 6 hours before transfection, which was carried out by the CaPi method as previously described. 8 Plasmid Constructs.…”

Section: Methodsmentioning

confidence: 99%

Inhibition of Hepatitis B Virus Expression and Replication by Rna Interference

2003

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RNA interference (RNAi) is the process of sequence-specific gene silencing, initiated by double-stranded RNA (dsRNA) that is homologous in sequence to the target gene. Because it has been shown that RNAi can be accomplished in cultured mammalian cells by introducing small interfering RNAs (siRNAs), much effort has been invested in exploiting this phenomenon for experimental and therapeutic means. In this study, we present a series of experiments showing a significant reduction in hepatitis B virus (HBV) transcripts and proteins in cell culture, as well as in the viral replicative forms, induced by siRNA-producing vectors. The antiviral effect is sequence-specific and does not depend on active viral replication. In conclusion, our data suggest that RNAi may provide a powerful therapeutic tool, acting both on replication-competent and on replication-incompetent HBV. (HEPATOLOGY 2003;37:764-770.) H epatitis B virus (HBV) is a 3.2-kb DNA virus, replicating almost exclusively in the liver. 1 Although effective recombinant vaccines are available, HBV infection is still a major global health problem: Each year, acute and chronic HBV infection causes about 1 million deaths. Among the 350 million people with chronic infection, the risk of dying from HBV-related diseases, such as end-stage cirrhosis and hepatocellular carcinoma (HCC) is between 15% to 25%. 2 Since the early 1990s, chronically infected patients have been treated with recombinant interferons that are effective only in limited cases. 3 Recently, nucleoside analogs, which directly affect viral replication by inhibition of its reverse transcriptase activity, were shown to be highly effective in the clearance of HBV-DNA from serum. However, the recurrence of viremia after cessation of therapy and the development of escape mutants with prolonged treatment remain major obstacles in achieving complete cure. Furthermore, nucleoside analogs, such as 3TC-lamivudine, impede viral replication but do not directly promote its eradication. 3 RNA interference (RNAi) is the process whereby double-stranded RNA (dsRNA) induces the sequence-specific degradation of homologous messenger RNA (mRNA). 4 This process is mediated by 21 to 23 nucleotides, called small interfering RNAs (siRNA), cleaved from dsRNA. Although first discovered in Caenorhabditis elegans, 5 it was soon after shown that RNAi can be induced in various mammalian cells by introducing synthetic 21nt siRNAs 6 to obtain strong and specific suppression (knockdown) of gene expression. Recently, a new vector system called pSUPER (suppression of endogenous RNA), which directs the synthesis of siRNAs and persistently suppresses gene expression in mammalian cells, has been developed. 7 To evaluate the anti-HBV therapeutic potential of RNAi, we designed 2 pSUPER vectors, each targeted against a distinct 19nt sequence in the HBV genome. We have analyzed the levels of viral proteins and transcripts, as well as the viral replicative forms, in the presence of the constructed pSU-PER vectors. We show that RNAi is an effic...

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“…Cells were cultured and transfected as previously described (Haviv et al, 1995). About 8 h before transfection, 2610 5 cells were plated per 3.5 cm dish.…”

Section: Luciferase Assaysmentioning

confidence: 99%

HBV integrants of hepatocellular carcinoma cell lines contain an active enhancer

2001

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Hepatitis B virus (HBV) infection is a major risk factor worldwide for the development of hepatocellular carcinoma (HCC). Integrated HBV DNA fragments, often highly rearranged, are frequently detected in HCC. In woodchuck, the viral enhancer plays a central role in hepatocarcinogenesis, but in humans the mechanism of HBV oncogenesis has not been established. In this study we investigated the status of the viral enhancer in two human HCC cell lines, Hep3B and PLC/PRF/5 each containing one or more integrated HBV DNA fragments. Active enhancer was de®ned by virtue of its protein occupancy as determined by genomic in vivo DMS footprinting. In PLC/ PRF/5 cells, the HBV DNA was integrated in a cellular gene at chromosome 11q13, at a locus reported to be ampli®ed in many tumors. We show here that in both cell lines, the integrated HBV DNA fragments contain an active enhancer-I. In particular, the occupation of the two previously de®ned basic enhancer elements, E and EP, was prominent. While in both cell lines the same protein binds to the EP elements, the E element, however, is occupied in a cell-line speci®c manner. In PLC/PRF/5 but not Hep3B, the prominent binding of an unde®ned protein was detected. Our data suggest that this protein is likely to be the fetoprotein transcription factor (FTF). The ®nding that enhancer sequences are conserved and functional in di erent cell lines suggests a selection pressure for their long-term maintenance. We therefore propose that the HBV enhancer-I might play a role in hepatocellular carcinogenesis. Oncogene (2001) 20, 6811 ± 6819.

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The X Protein of Hepatitis B Virus Coactivates Potent Activation Domains

Cited by 88 publications

References 82 publications

Hepatitis B Virus X Protein Is a Transcriptional Modulator That Communicates with Transcription Factor IIB and the RNA Polymerase II Subunit 5

Hepatitis B Virus X Protein Is a Transcriptional Modulator That Communicates with Transcription Factor IIB and the RNA Polymerase II Subunit 5

Inhibition of Hepatitis B Virus Expression and Replication by Rna Interference

HBV integrants of hepatocellular carcinoma cell lines contain an active enhancer

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