An internal domain of the hepatitis B virus X antigen is necessary for transactivating activity

Ritter, Steven E.; Whitten, Thomas M.; Quets, A T; Schloemer, Robert H.

doi:10.1016/0042-6822(91)90626-m

Cited by 42 publications

(31 citation statements)

References 28 publications

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“…However, deletions of amino acids 2*70 from the X-ORF encoded by ND-5 showed a 77% decrease of X-activity. These results are consistant with those of Ritter et al (1991) who reported that deletions of amino acids 32 to 66 resulted in the loss of almost all pSVCAT reporter activity.…”

Section: Plabelled Sp1 Is Indicated Bysupporting

confidence: 75%

The human hepatitis B virus transactivator X gene product regulates Sp1 mediated transcription of an insulin-like growth factor II promoter 4

Lee

et al. 1998

Oncogene

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Human hepatitis B virus (HBV) is one of the causative agents of hepatocellular carcinoma (HCC). The virus encodes a 17 kDa protein, X, which is known to be a causative agent in the formation of HCC. An insulin-like growth factor-II (IGF-II) is expressed during the formation of HCC. Among the four promoters of the IGF-II gene, promoters 2, 3 and 4 become activated during the formation of HCC. The high frequency of detection of hepatitis B virus X (HBV-X) antigen in liver cells from patients with chronic hepatitis, cirrhosis, and liver cancer suggested that the expressions of HBV-X and IGF-II are associated. Studies were carried out to test the relationship between the HBV-X gene product and the activation of IGF-II promoter 4. We demonstrated that the HBV-X protein increases the endogenous IGF-II expression from promoter 3 and 4 of IGF-II gene. Analysis of the fourth promoter of IGF-II gene showed that the HBV-X gene product positively regulates transcription. Two copies of a motif are responsible for conferring HBV-X regulation on the fourth promoter of IGF-II. These motifs have been identi®ed as Sp1 binding sites. Sp1 binding to IGF-II P4 promoter was identi®ed by gel mobility shift assay using puri®ed Sp1. By using a GAL4-Sp1 fusion protein it was demonstrated that HBV-X positively regulates the Sp1 mediated transcriptional activity of IGF-II in vivo. A protein-anity chromatography experiment showed that HBV-X protein does not bind directly to Sp1, but HBV-X does augment the DNA binding activity of the phosphorylated form of Sp1 in HepG2 cells. Sp1 was phosphorylated by HBV-X and its DNA-binding activity was up-regulated upon HBV-X transfections. Various HBV-X mutant expression vectors were used for the demonstration of speci®c interactions between Sp1 and HBV-X. These results indicate that HBV-X functions as a positive regulator of transcription, and that Sp1 is a direct target for the transcriptional regulation of IGF-II. Increasing the DNA binding ability of the phosphorylated form of Sp1 by HBV-X might be an important mechanism for regulating the IGF-II gene expression and possibly promoting cell division during hepatic carcinogenesis. Our experimental results suggest that expression of HBV-X might induce the expression of IGF-II and the IGF-II might play a role in hepatitis B virus pathogenesis during the formation of HCC.

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Section: Plabelled Sp1 Is Indicated Bysupporting

confidence: 75%

The human hepatitis B virus transactivator X gene product regulates Sp1 mediated transcription of an insulin-like growth factor II promoter 4

Lee

et al. 1998

Oncogene

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“…An NES is located in the center region of HBx (residues 89 -100). The center region of HBx is retained in HCC frequently and is essential for its transactivation (22)(23)(24). This region also is conserved among HBx from different subtypes (Fig.…”

Section: Hepatocellular Carcinoma (Hcc)mentioning

confidence: 99%

Interaction of the Hepatitis B Virus X Protein with the Crm1-dependent Nuclear Export Pathway

Forgues

Marrogi

Spillare

et al. 2001

Journal of Biological Chemistry

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The leucine-rich nuclear export signal (NES) is used to shuttle large cellular proteins from the nucleus to the cytoplasm. The nuclear export receptor Crm1 is essential in this process by recognizing the NES motif. Here, we show that the oncogenic hepatitis B virus (HBV) X protein (HBx) contains a functional NES motif. We found that the predominant cytoplasmic localization of HBx is sensitive to the drug leptomycin B (LMB), which specifically inactivates Crm1. Mutations at the two conserved leucine residues to alanine at the NES motif (L98A,L100A) resulted in a nuclear redistribution of HBx. A recombinant HBx protein binds to Crm1 in vitro. In addition, ectopic expression of HBx sequesters Crm1 in the cytoplasm. Furthermore, HBx activates NFB by inducing its nuclear translocation in a NES-dependent manner. Abnormal cytoplasmic sequestration of Crm1, accompanied by a nuclear localization of NFB, was also observed in hepatocytes from HBV-positive liver samples with chronic active hepatitis. We suggest that Crm1 may play a role in HBx-mediated liver carcinogenesis.

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“…1 and Luber et al, 1991) is not sufficient to completely destroy the transactivating potential directed to the GT(IIC+I) element. Although we have not yet identified the nature of this activity, it is probably not based on the presence of amino-terminally truncated HBs fragments initiating at methionine 79 and 103, since the region upstream of methionine 79 is indispensable for transactivation of RNA polymerase class II-dependent promoters (Ritter et al, 1991;Arii et al, 1992;Kim et al, 1993;Renner et al, 1995). To date, no evidence exists that GT(IIC + I), like RNA polymeras-class III-dependent regulatory elements (Kwee et al, 1992), can be transactivated by HBx fragments 79-154 or 103-154.…”

Section: M~mentioning

confidence: 99%

“…1 ; see also Luber et al, 1991 ;Kwee et al, 1992;Lauer et al, 1992). However, as shown by mutation and deletion analyses, these HBx fragments are unable to activate RNA polymerase IIdependent regulatory elements (Ritter et al, 1991 ;Arii et al, 1992;Kwee et aL, 1992;Kim et aL, 1993;Renner et al, 1995). The reporter plasmids, containing the rabbit flglobin promoter and the fl-globin gene as a reporter gene, are based on pG1 ( Fig.…”

mentioning

confidence: 99%

Differences in the target specificity of the transactivating factors MHBst and HBx of hepatitis B virus

Mühlbauer

Koch

1995

Journal of General Virology

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Experiments with tissue culture cells revealed that carboxy-terminaUy truncated middle surface antigen (MHBs t) and HBx of hepatitis B virus (HBV) are able to act as transcriptional transactivators (Twu & Schloemer, 1987;Wollersheim et al., 1988;Zahm et al., 1988;Caselmann et al., 1990; Kekul6 et al., 1990). The transactivating function of MHBs t and HBx is directed to many known viral and cellular enhancer and promoter elements. Synopsis of epidemiological and molecular studies led to the assumption that, possibly based on their transactivating property, MHBs t and HBx contribute to the onset or development of hepatocellular carcinoma in individuals who, as a consequence of previous infection with HBV, carry chromosomally integrated viral DNA (for reviews see Tiollais et al., 1985;Ganem & Varmus, 1987;Beasley, 1988;Koshy & Meyer, 1992).The molecular mechanism that underlies the transactivating function of MHBs t and HBx is not known. Recent observations suggested that the generation of reactive oxygen intermediates is required for the activation of nuclear factor-(NF) xB by MHBs t and HBx, and that protein kinase C is involved in the stimulation of activator protein-1 (AP-1) by HBx (Meyer et al., 1992; Kekul~ et al., 1993). It has not been directly examined * Author for correspondence. Present address: German Heart Center Munich, Department of Experimental Cardiology, Lothstrasse 11, D-80335 Munich, Germany. Fax +49 891209549.whether MHBs t and HBx have differences in their target specificities. In theory, the existence of at least one enhancer element that can be stimulated only by one but not by the other of the HBV-derived transactivators would indicate the existence of, at least in part, alternate cellular signal transducing pathways for MHBs t and HBx.To address this issue, we directly compared the ability of MHBs t and HBx to perform their transactivating function, using selected, transcription factor-binding sequence elements present in the enhancer of simian virus 40 (SV40) and in the enhancer of the human metallothionein IIA (hMT IIA) gene. Chang liver cells (Chang, 1954) were cotransfected with transactivator plasmid or non-transactivating control plasmid and one of several reporter plasmids. Transactivator plasmids were pMHBs ta°l, encoding MHBs t and pHBV824, encoding HBx. Control plasmids were pMHBs, encoding fulllength MHBs, and pHBV824fs, encoding, in theory, a short amino-terminal fragment of HBx and aminoterminally truncated fragments of HBx initiating at methionine residues 79 and 103 (Fig.

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An internal domain of the hepatitis B virus X antigen is necessary for transactivating activity

Cited by 42 publications

References 28 publications

The human hepatitis B virus transactivator X gene product regulates Sp1 mediated transcription of an insulin-like growth factor II promoter 4

The human hepatitis B virus transactivator X gene product regulates Sp1 mediated transcription of an insulin-like growth factor II promoter 4

Interaction of the Hepatitis B Virus X Protein with the Crm1-dependent Nuclear Export Pathway

Differences in the target specificity of the transactivating factors MHBst and HBx of hepatitis B virus

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