THE HEPATITIS B VIRUS HBX PROTEIN LOCALIZES TO MITOCHONDRIA IN PRIMARY RAT HEPATOCYTES AND MODULATES MITOCHONDRIAL MEMBRANE POTENTIAL

Graduate Program in Molecular and Cellular Biology and Genetics, and Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA 19102

^* To whom correspondence should be addressed. Email: michael.bouchard{at}drexelmed.edu.

	Abstract

Over 350 million people are chronically infected with the hepatitis B virus (HBV), and a significant number of chronically-infected individuals develop primary liver cancer. HBV encodes seven viral proteins, including the nonstructural X (HBx) protein. The results of studies in immortalized or transformed cells and in HBx-transgenic mice demonstrated that HBx can interact with mitochondria. However, no studies in normal hepatocytes have characterized the precise mitochondrial localization of HBx or the effect of HBx on mitochondrial physiology. We have used cultured primary rat hepatocytes as a model system to characterize the mitochondrial localization of HBx and the effect of HBx expression on mitochondrial physiology. We now show that a fraction of HBx co-localizes with density-gradient-purified mitochondria and associates with the outer mitochondrial membrane. We also demonstrate that HBx regulates mitochondrial membrane potential in hepatocytes and that this function of HBx varies depending on the status of NF-B activity. In primary rat hepatocytes, HBx activation of NF-B prevented mitochondrial membrane depolarization; however, when NF-B activity was inhibited, HBx induced membrane depolarization through modulation of the mitochondrial permeability transition pore. Collectively, these results define potential pathways through which HBx may act in order to modulate mitochondrial physiology, thereby altering many cellular activities, and ultimately contributing to the development of HBV-associated liver cancer.