| Summary: | 碩士 === 國立臺灣大學 === 藥理學研究所 === 83 === Hepatitis B virus(HBV), which has a partially double-stranded
3.2 kb DNA molecule as its genome, it can encode four unspliced
transcripts of 3.5, 2.4, 2.1 and 0.7 kb and at least three spliced transcripts. Among spliced transcripts, the 2.2 kb doubly-spliced RNA (dsp RNA) has been shown to be present abundantly both in HBV-infected human liver tissues and HBV DNA-transfected hepatoma cells.
Since the dsp RNA was commonly found in many HBV-infected human liver tissues, we believe that it may play certain roles in the process of HBV infection. To study whether the dsp RNA has any regulatory function in gene expression, we tested the effect of dsp RNA on the transcription of c-fos promoter. We found that dsp RNA can repress human c-fos promoter and AP-1 transcriptional activity in both CV-1P and HepG2 cells.In addition to the c-fos promoter, we also found that the dsp RNA product can selectively repress a variety of cellular and viral promoters.
Since the dsp RNA product can repress a broad-range of cellular promoters, we figured that it may have a profound effect on cell growth. We found that cotransfection of the dsp RNA-expression plasmid gave much fewer neomycin-resistant colonies than cotransfection of the control plasmid did. This result clearly indicated that overexpression of the dsp RNA was either toxic to cells or able to inhibit cell growth. We also showed that cells which express dsp RNA constitutively grew much slower than the parental cells, indicating the dsp RNA product, at an appropriate concentration, can repress cell growth.
It is generally believe that liver cell injury by HBV infection is the result of an immune response to viral replication and that the HBV-specific immune response mediated by cytotoxic T lymphocytes would be required for hepatocyte toxicity. Here we showed that overexpression of the dsp RNA was toxic to the hepatoma cells, providing the first evidence that HBV-encoded products may directly involve in the pathogenesis of the virus.
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