Molecular Mechanism Of Hepatitis B Virus X Protein Inducing Human Immunodeficiency Virus Long Terminal Repeat Driven Transcription

HIV (Human Immunodeficiency Virus) isthe major pathogen of AIDS (acquired immunodeficiency syndrome), which lots of people over the world are suffering from. According to the report from WHO (Vtorld Health Organization), in2007, there were33millions HIV carries, and2millions died from AIDS. HBV (hepatitis B virus) is member of Hepadnaviridae characterized by hepatocyte tropism and DNA genome Over2billion individuals are infected by HBV, of which about350million are chronically infected. Due to HIV and HBV world widely spread and share the route of transmission, the prevalence of HIV HBV co-infection is very common.HBx, encoded by the smallest ORF, is one of HBV nonstructural proteins. Dozens of studies have proved that HBx is a multifunctional protein. For example, HBx plays an important role in HBV replication as well as influencing many intracellular events, including signal transduction, cell cycle control and even is associated with hepatocellular carcinoma development. Of HBV encoded proteins, HBx is the only one that can induce HIV transcription. The mechanism of HBx inducing HIV transcription remains unclear, though there are few reports about it. So our research focuses on explori ng this mechanism.Using HBV infectious clone and its HBx deleting mutant, we found HBx plays a key role in HBV replication inducing HIV transcription. We also confirmed that NF-kB pathway was dispensable in HBx inducing HIV transcription. Through competitive inhibition assays, we identified that CREB and C/EBP pathways possibly involved in HBx inducing HIV. V\fe also found CREB1/2or C/EBPβ could cooperate with HBx to inducing LTR driven transcription. Results from ChlP assays clearly indicated that HBx could promote endogenous CREB2and C/EBPβ bind to HIV LTR. We further identified CRE and CREB sites located in-129to-80engaged in HBx inducing LTR transcription.We also investigated the role of co-activator CBP (CREB binding protein) in HBx inducing LTR transcription. Our results show that CBP and HBx could synergistically enhanced LTR driven transcription. And the presence of HBx could enhance the binding of CBP to LTR. Surprisingly, HAT activity deletion did not impair CBPs function, which indicating that HAT activity is dispensable for CBP cooperate with HBx. However, when CREB1/2or C/EBPp proteins were overexpressed, HAT deletion reduced the cooperation between HBx and CBP, though not totally. So we speculate that CBPmay adopt more than one mechanism to regulate transcription.