Molecular studies of hepatitis B virus.

摘要

Hepatitis B virus (HBV) infection is a major cause of disease with over 200 million chronically infected people worldwide. Molecular biology has become a powerful tool in characterizing biochemical structure and functional mechanism of different components of the virus, in studying pathogenic mechanisms of HBV and in developing effective vaccines against the virus. Demonstrated here are examples of applying molecular biology to studying the basic mechanisms of gene regulation of the virus and to developing a new vaccine strategy against the virus.;Molecular biology techniques were also used in a vaccine study. In an effort to develop a new vaccine strategy, two known protective epitopes of surface antigens of HBV (HBsAg) were expressed in immunogenic forms as a hybrid proteins with flagellin of a vaccine strain of Salmonella dublin (SL5928). Such live recombinant bacteria expressing the HBsAg epitopes were able to elicit specific antibody responses in animals immunized either parenterally or orally. This type of oral vaccine, if proven to elicit effective humoral and cellular responses in humans, may provide a new generation of HBV vaccine which is easy to administer, convenient to store and inexpensive to produce. Such properties are essential for wide distribution of an effective HBV vaccine in many developing countries with high prevalence of HBV infection. This may also provide a model for developing new vaccines for other pathogens, especially, enteric pathogens.;The HBV genome encodes several structural genes and a regulatory gene, X gene (hbx gene). Although it has been shown by many studies that the hbx gene encodes a transcriptional transactivator acting on many different target DNA sequences, the biochemical nature of the hbx gene product and its functional mechanism remains unknown. To characterize the hbx gene product and understand its functional mechanism, we expressed the hbx gene as a full-length, discrete protein in E. coli using an inducible T7 system. The purified and renatured hbx protein was shown to be functionally active in a cell-free system in transactivating transcription controlled by the long terminal repeat (LTR) region of human immunodeficiency virus type 1 (HIV-1). The hbx protein was shown to have an intrinsic serine/threonine protein kinase activity which is associated with its ability to induce or enhance certain cellular factors to bind to HIV-1-LTR and possibly thereby to activate transcription regulated by that sequence.