Mechanisms of Hepadnavirus Assembly and Replication

Hepatitis B virus (HBV) is a major cause of chronic viral hepatitis that increases dramatically the risk of liver cancer and other end-stage liver diseases such as cirrhosis. The major obstacle to curing chronic HBV infection is the persistence of the viral nuclear episome, the covalently closed circular (CCC) DNA, which is derived from the relaxed circular (RC) DNA contained within the viral nucleocapsid. Moreover, the inability of mouse hepatocytes to support CCC DNA formation remains a major hurdle in the development of an immuno-competent mouse model for HBV infection. This MERIT Award Extension application builds on, and extends, our current work on the disassembly of viral nucleocapsids (uncoating), which releases the RC DNA into the host cell nucleus, a prerequisite step for nuclear CCC DNA formation but also exposing RC DNA for potential degradation or triggering of host cell DNA sensing and immune responses. The main goal of the Extension is to better understand viral and host control of HBV CCC DNA formation and infection. Four Specific Aims are proposed. Aim 1 will elucidate the deficiencies in mouse hepatocytes for HBV infection. Aim 2 will develop cell-free systems for nucleocapsid uncoating and CCC DNA formation. Aim 3 will define the late HBV entry events controlled by the viral capsid and host factors. Aim 4 will assess the role of DNA sensing in HBV infection. RELEVANCE (See instructions): The hepatitis B virus (HBV) is a global cause of chronic liver diseases, including liver cirrhosis and cancer. We propose to elucidate the mechanisms of, and viral and host factors involved in, the viral trafficking events during infection and the disassembly of HBV nucleocapsid, which are essential but poorly understood steps in viral replication and contribute to the host tropism of HBV. These studies will bring novel insights into HBV infection and nucleocapsid disassembly and facilitate ongoing efforts to develop novel antiviral agents targeted at these processes as well as mouse models of HBV infection.