title: trans-activation of viral enhancers by the hepatitis B virus X protein.
abstract: We have used the chloramphenicol acetyltransferase (cat) gene expression system to study the effect of the X protein of hepatitis B virus (HBV) on viral enhancers. Plasmids containing the HBV enhancer and the core gene promoter linked to the cat gene were cotransfected with a plasmid containing the X gene into the human hepatoma cell line PLC/PRF/5. Our results indicate that the transfected X gene caused a trans-activation of the HBV enhancer. If a frameshift mutation or a deletion in the X structural gene was created, this trans-activation function was abolished. This result and the observation that the frameshift mutation did not alter the transcription of X mRNA suggest that the X protein is the trans-activating factor. Using similar techniques, we found that the X protein was also capable of trans-activating the simian virus 40 (SV40) and Rous sarcoma virus enhancers (pSV2cat and pRSVcat) in CV-1 cells. However, trans-activation of the SV40 enhancer by the X protein was not observed in COS-1 cells. By cotransfecting pSV2cat and the X gene with a plasmid containing either the intact SV40 genome, the SV40 genome devoid of the T-antigen (T-ag) gene, or only the T-ag gene, we demonstrated that SV40 T-ag can suppress trans-activation by the X protein. SV40 T-ag did not inhibit expression of the X gene or inactivate the X protein. The most probable mechanism of this inhibition is that T-ag competes with the X protein for a common target.
authors.affiliation: Department of Pathology, Indiana University School of Medicine, Indianapolis 46223.
authors.forename: D F
authors.initials: DF
authors.lastname: Spandau
authors.forename: C H
authors.initials: CH
authors.lastname: Lee
mesh_terms: D000123:Acetyltransferases / Q000235:genetics / Q000378:metabolism; D000957:Antigens, Viral, Tumor; D001358:Avian Sarcoma Viruses / Q000235:genetics; D015500:Chloramphenicol O-Acetyltransferase; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D005796:Genes; D005814:Genes, Viral; D006515:Hepatitis B virus / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D006801:Humans; D010957:Plasmids; D011401:Promoter Regions, Genetic; D013539:Simian virus 40 / Q000235:genetics; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D014764:Viral Proteins / Q000235:genetics* / Q000502:physiology; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D000957:Antigens, Viral, Tumor; D015534:Trans-Activators; D014157:Transcription Factors; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D000123:Acetyltransferases; D015500:Chloramphenicol O-Acetyltransferase