The human hepatitis B virus (HBV) is a hepatotropic virus that replicates through an RNA intermediate referred to as the pregenome. The promoter that directs the synthesis of the pregenome and several other transcripts with heterogeneous 5' ends is of particular interest because ofits role in regulating key functions during the viral life cycle. We have examined the liver-specific characteristics of this promoter by DNA-protein interactions and by demonstrating the in vivo function of the promoter using the luciferase reporter gene expression system. The DNA-protein interactions in this region appear to be almost entirely liver-specific. Among these, a liver-specific nuclear factor, CCAAT/enhancer binding protein, binds to at least five sites on this promoter. Transient cotransfection experiments using CCAAT/enhancer binding protein expression vectors and the core promoter in the context of either the native hepatitis B virus genome or the luciferase reporter gene demonstrate that CCAAT/enhancer binding protein at low concentration modestly activates expression from the core promoter but represses at high concentration.The human hepatitis B virus (HBV) causes acute and chronic hepatitis, and the infection has been associated with hepatocellular carcinoma (1). There are four genes encoded by the viral genome: SipreS, Cle, Pol, and X (1). The transcription of these genes is controlled by at least four promoters (1-7). Additionally, an enhancer element has been identified in the HBV genome (8, 9). The core or pregenomic promoter regulates synthesis ofthe 3.6-kilobase (kb) RNAs that include mRNAs for several viral proteins (core, e, and pol) and the pregenomic RNA. Transcriptional regulation of these viral macromolecules makes this promoter a key element of the viral life cycle. The core promoter exhibits enhancerdependence for efficient liver-specific activity (6,(9)(10)(11)(12).In this study, we have used a series of restriction fragments and deletion mutations to define the boundaries of the HBV core/pregenomic promoter by using the firefly luciferase reporter gene (13). Furthermore, DNase I protection analysis was employed to identify nucleotide sequences that are binding sites for trans-acting cellular factors. This analysis revealed at least seven regions of DNA-protein interactions, most of which appear to be liver-specific. We show here that the CCAAT/enhancer binding protein (C/EBP), a liverspecific factor, binds to at least five sites in the promoter region. C/EBP was first purified from rat liver and shown to bind to several viral and cellular promoters/enhancers (14)(15)(16)(17)(18).To assess the role of C/EBP in the core promoter function, cotransfection experiments were carried out with a C/EBP expression vector and the core promoter linked to a reporter gene or in the context ofHBV genome. These studies indicate that C/EBP, at low concentrations, can function as a modest trans-activator of the core promoter. Increasing concentrations of C/EBP, however, resulted in trans-repression of the core ...

No abstract

No abstract

(23) and is not expressed on normal human hepatocytes (24). Although aberrant expression of HLA-DR on hepatocytes observed during HBV infection has been suggested to be due to cytokines produced by the adjacent inflammatory cells (24, 25), it is not known whether HBV itself is involved in the induction process. This study demonstrates that transfection of cultured human hepatoma cell lines with genomic HBV sequences can induce HLA-DR expression in vitro in the absence of inflammation. We further show here that the X gene product of HBV alone is capable of inducing transcription of the HLA-DR gene.

Intercellular adhesion molecule 1 (ICAM-1), a counter-receptor for lymphocyte function-associated antigen 1 on T cells, is critically important to a wide variety of adhesion-dependent leukocyte functons, including antigen presentation and target cell lysis.