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Hepatitis B virus X protein interacts with β5 subunit of heterotrimeric guanine nucleotide binding protein

DOI: 10.1186/1743-422x-2-76

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HBV particles were produced in culture medium of HepG2 cells transfected with the mammalian expression vector containing the linear HBV genome, as assessed by commercially available ELISA assay. A cDNA library was made from these cells exposed to HBV. From yeast two hybrid screening with HBX as bait, human guanine nucleotide binding protein β subunit 5L (GNβ5) was isolated from the cDNA library constructed in this study as a new HBX-interacting protein. The HBX-GNβ5 interaction was further supported by mammalian two hybrid assay.The use of a cDNA library constructed from HBV-transfected HepG2 cells has resulted in the isolation of new cellular proteins interacting with HBX.Infection by hepatitis B virus (HBV), an enveloped DNA virus of the hepadnaviridae family, has been closely related to development of hepatocellular carcinoma (HCC). The role of this virus in the series of events leading to the onset of HCC has remained elusive [1]. However, it has been suggested that the smallest protein encoded by the HBV genome, HBX, is involved in the development of HCC [2].Several proteins have been demonstrated to interact with the HBX protein through the use of the Yeast Two Hybrid system. These include the C-terminal portion of a novel human proteasome alpha subunit which possesses a protein sequence of close relationship to that of the 28 kD subunits from other organisms; PSMA7, the α-subunit of the 20S proteasome complex; PSMC1, the subunit of the 19S proteasome regulatory cap complex; XAPC7, a highly conserved proteasome subunit belonging to the α-subunit of the 20S proteasome complex. PSMA7, PSMC1 and XAPC7 were demonstrated to interact with the second Kunitz-type domain of the HBX protein [3-6]. Another two proteins, XAP2 (X-associated protein 2) and XIP (HBX-interacting protein) were found to be negative regulators of HBX. Overexpression of XAP2 abolished the transactivating function of HBX while the specific interaction of XIP to the carboxy terminus of HBX in diffe


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