Repression of hepatitis B virus X gene expression by hammerhead ribozymes

The X protein (HBx) of human hepatitis B virus (HBV) is a transcriptional activator protein. The HBx protein plays an important role in viral replication in HBV infected cells and the liver diseases including hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Therefore, the repression of HBx gene expression by hammerhead ribozymes may be a good way to inhibit HBV replication and cure HBV-related liver diseases. We designed two hammerhead ribozymes, RzA and RzB, to cleave target sites at nucleotides 114 and 309 in the HBx open reading frame (ORF), respectively. In vitro, RzA and RzB cleaved HBx RNAs at their target sites up to 52 and 75%, respectively; however, the disabled ribozymes (dRzs) which have mutations in the catalytic site did not cleave the target RNAs at all. When each of the ribozymes were cotransfected into HepG2 cells with HBx expression plasmid, RzA and RzB reduced the level of HBx mRNA to 40 and 57%, respectively. The transactivation activity of HBx protein was also reduced dramatically by the ribozymes. These results suggest that the hammerhead ribozymes, RzA and RzB, can be used for the gene therapy of liver diseases caused by HBV.

The GC box and TATA transcription control elements in the P38 promoter of the minute virus of mice are necessary and sufficient for transactivation by the nonstructural protein NS1

To further define the transcriptional regulation of the P38 promoter in the minute virus of mice (MVM) genome, we constructed a series of internal deletion and linker scanning mutations. The mutant P38 constructs were assayed for transcriptional activity in vitro by primer extension analysis with nuclear extracts from murine A92L fibroblasts. Mutations which disrupted the GC box and TATA box severely reduced transcription in vitro. DNase I footprinting analysis confirmed that the murine transcription factor Sp1 bound to the GC box; however, no factors were observed interacting with a putative transcriptional activation regulatory element, termed the TAR element. The linker scanning mutations were analyzed in vivo by using a chloramphenicol acetyltransferase expression assay system, in both the presence and absence of constructs expressing the viral nonstructural protein, NS1. The ability of NS1 to transactivate the P38 promoter (up to 1,000-fold) depended entirely on the presence of intact GC and TATA box sequences. Disruption of the TAR element by either linker insertion mutations or an internal deletion did not inhibit transactivation of the P38 promoter. These results suggest that NS1 transactivates the P38 promoter indirectly by interacting with one or more components of the P38 core-transcription complex.

Transcriptional analysis of minute virus of mice P4 promoter mutants

A series of 5' deletion, internal deletion, and linker-scanning mutants of the minute virus of mice P4 promoter were constructed and analyzed for transcriptional activity in nuclear extracts of mouse A92L fibroblasts. A GC box and a TATA box essential for in vitro transcription from the P4 promoter were localized between nucleotides 150 and 180 (-55 to -25 relative to the primary RNA start site). Although this region also exhibited homologies to other transcriptional control elements, the simian virus 40 enhancer, and the adenovirus E1A enhancer, only the GC box and TATA box appear functional. These two motifs also play an essential role in vivo, although additional upstream sequences (between -139 and -55) are required for optimal transcription. DNase I footprinting, competitive gel retardation assays, and UV-photocrosslinking were used to identify Sp1-like proteins of 95 and 120 kilodaltons in A92L extracts that interact with the GC box of the minute virus of mice P4 promoter.

Impaired interleukin-2 receptor expression on lymphocytes from patients with chronic active hepatitis type B

To evaluate cell mediated immunopathogenic mechanisms in chronic hepatitis B virus (HBV) infection, we investigated the changes of T4/T8 ratios from the peripheral blood, the percentages of IL-2 receptor expression after stimulation of mitogens (Con A, PHA) and a specific antigen (Hepatitis type B surface antigen, HBs), and the proliferative response mediated by IL-2 receptors after rIL-2 stimulation on mixed mononuclear cell. These experiments were performed comparatively in 5 groups which consisted of serologically negative normal subjects, chronic HBV carriers, patients with chronic active hepatitis (CAH) type B, patients with acute hepatitis (AH) type B, and the antibody positive healthy subjects. There were significant decreases of T4/T8 ratios in chronic HBV carriers, in patients with CAH type B, and in patients with AH type B, compared with negative normal controls. There were no significant differences between patients with CAH type B and the HBs negative normal controls in the percentage of IL-2 receptor positive cells after in-vitro HBs-stimulation and the proliferative response assessed by the incorporation of 3H-thymidine, whereas in patients with AH type B there were significant increases in both. Thus, in addition to a relatively decreased T4/T8 ratio, the impairment of IL-2 receptor expression on the lymphocytes after HBs-stimulation caused a defective response of cellular proliferation, and this might be one of the leading immunopathogenic roles in chronic HBV infection.