Original Article Hepatitis B virus surface antigen interacts with acid alpha-glucosidase and alters glycogen metabolism Jui-Hsiang Hung, 1 * Chiao-Wen Yan, 2 * Ih-Jen Su, 3 Hui-Ching Wang, 3 Huan-Yao Lei, 4 Wan-Chi Lin, 2 Wen-Tsan Chang, 1,2 Wenya Huang, 5 Te-Jung Lu 6 and Ming-Derg Lai 2,7 1 Department of Biotechnology, Chia Nan University of Pharmacy and Science, 3 Division of Clinical Research, National Health Research Institute, 7 Center for Gene Regulation and Signal Transduction Research, College of Medicine, National Cheng Kung University, 2 Department of Biochemistry and Molecular Biology, 4 Department of Microbiology & Immunology, 5 Department of Medical Technology, College of Medicine and 6 Department of Medical Technology, Chung-Hwa College of Medical Technology, Tainan, Taiwan Aim: Hepatitis B virus (HBV) infection is highly correlated with hepatocellular carcinoma. Previous studies have re- ported that expression of hepatitis B virus pre-S2 mutant surface antigen is related to hepatoma development. An aber- rant carbohydrate metabolism is a hallmark of malignant transformation. Methods: We performed yeast two-hybrid screening with HBV pre-S2-del large surface protein (pre-S2D) by using human liver cDNA library, and identified the acid alpha- glucosidase (acid a-glucosidase) as the novel cellular interact- ing protein of pre-S2D. The association of pre-S2D with the acid a-glucosidase was confirmed by confocal immunofluo- rescence and co-immunoprecipitation assay. Further, the acid a-glucosidase activity and glycogen content were analyzed in ML-1 cells expressing pre-S2D. Results: The interaction between HBV large surface protein and acid a-glucosidase was demonstrated with co-immunoprecipitation in vitro and in vivo, and the binding was mediated through c-terminal region 889-952 amino acid of acid a-glucosidase. On the other hand, HBV large surface protein interacted with acid a-glucosidase through N-terminal region 1–157 amino acid of HBV large surface protein. Expression of HBV large surface protein enhanced acid a-glucosidase activity and resulted in decrease of cellular glycogen. Conclusion: Our result demonstrates that HBV large surface protein interacts with acid a-glucosidase which plays an important role in glycogen balance. Together, these data suggest a novel pathway by which HBV large surface protein affects carbohydrate metabolism. Key words: acid alpha-glucosidase, carbohydrate metabolism, glycogen, hepatitis B virus large surface protein, hepatocellular carcinoma INTRODUCTION A N ABERRANT ENERGY metabolism is one of the most consistent features of the malignant neoplas- tic phenotype. 1,2 Tumor cells display characteristic alter- nation of the carbohydrate metabolism that represent one of the earliest discernible events of tumorigenesis. 3 Glycogen is one of the main stores of carbohydrates, and the glycogen content in the cell is tightly controlled through the balance of glycogen-synthesizing enzymes and glycogen-degrading enzymes. In liver cancer, the metabolic switch is one of the first detectable alterna- tions, in which slowly growing glycogenotic cells are converted to highly proliferation basophilic cells. This step is accompanied by a rapid depletion of the intrac- ellular glycogen stores resulting from the changes of acid a-glucosidase activity. 4 Hepatocellular carcinoma (HCC) is a common malig- nancy affecting some one million people around the world annually. 5 Hepatocellular neoplasms regularly develop from preneoplasic foci of altered hepatocytes, irrespective of whether they are caused by virus, chemicals, radiation, or transgenic oncogenes. HBV is considered to be a major etiological factor in the devel- opment of HCC. Chronic hepatitis B virus (HBV) Correspondence: Dr Ming-Derg Lai, Department of Biochemistry, College of Medicine, National Cheng Kung University, Tainan, Taiwan. Email: a1211207@mail.ncku.edu.tw *Both authors contributed equally to this work. Received 20 July 2009; revision 21 January 2010; accepted 26 January 2010. Hepatology Research 2010; 40: 633–640 doi: 10.1111/j.1872-034X.2010.00645.x © 2010 The Japan Society of Hepatology 633