Morphologic and molecular observation ofhepatitis B virus pre-S mutant proteins-induced endoplasmic reticulum (ER) stress

• Main Authors: Chien-Fu chen, 陳健福
• Other Authors: Ih-Jen Su
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/48090995007512561038

碩士 === 國立成功大學 === 分子醫學研究所 === 92 === 　　Hepatitis B virus (HBV), one of the hepadnavirus family, contains a partially double-stranded DNA genome of 3.2 kb. Individuals infected by HBV potentially become chronic carriers that are at a high risk for the development of hepatocellular carcinoma (HCC). HBV encodes three envelope proteins that named large, middle, and small surface protein. Many naturally occurring HBV mutants in sera or liver tissue of patients with chronic hepatitis B have been identified. Previously, two types of HBV pre-S mutant were identified; one contains a deletion in the pre-S1 region and the other contains a deletion in pre-S2 region. Both pre-S1 ad pre-S2 mutant surface proteins are localized in the endoplasmic reticulum (ER) with distinct distribution patterns. This study is designed to investigate the ER stress induction of specific hepatitis B virus pre-S mutant proteins in the cytoplasm. First, we used immunohistochemical staining and GFP fusion protein to monitor the localizations of pre-S mutant proteins in Huh7 cells, and pre-S mutant proteins showed a blot-like distribution pattern. Transmission electron microscope was used to monitor morphological change of ER induced by the accumulation of HBV mutant surface proteins. The expression of pre-S1 and pre-S2 mutant proteins in Huh7 cells resulted in ER proliferation and subsequently ER enlargement which looked like inclusion bodies. ER accumulations of these mutant proteins also activate ER stress signals in Huh7 cells by which ER stress marker GRP78 and GRP94 were significantly upregulated, while other chaperones and ER proteins such as Hsp60, Hsp70, Hsp90, Erp72 and Erp57 remained unchanged. Pre-S mutant proteins induced ER stress also lead to increase cytoplasmic Ca2+ concentration, but did not cause cell death. The ER accumulation effect seems to restrict to the pre-S mutant proteins without any effects on the protein trafficking of other cellular proteins. In fact, we have observed the enhanced expression of MHC class I on the surface of cells with pre-S mutant proteins. In combination of our results, pre-S mutant proteins indeed accumulate in ER, result in ER enlargement, and induce ER stress. These mutant proteins induce ER stress which leads to the release of Ca2+ from the ER and the subsequent production of reactive oxygen intermediates. In conclusion, the clinical observation of ER changes in mutant surface protein-containing hepatocytes in cirrhotic livers could be associated with different biologic functions of pre-S mutant proteins.