Human hepatitis B virus X protein promotes cell proliferation and inhibits cell apoptosis through interacting with a serine protease Hepsin

Abstract

The X protein of human hepatitis B virus (HBV) acts as an indirect transcriptional transactivator to regulate the expression of many viral and cellular genes as well as playing a critical role in the development of hepatocellular carcinoma. While the biological importance of HBx has been well established, the cellular and molecular bases of its function remain largely undefined. In this study, we isolated a new HBV field strain from a patient with chronic viral infection. The X protein encoded by this virus was used as a bait protein for screening a human liver cDNA library using a yeast two-hybrid system. Several cell proteins were identified as new HBx interacting partners, including a transmembrane serine protease, Hepsin. Direct interaction between HBx and Hepsin proteins was confirmed by in vitro and in vivo co-immunoprecipitation assays. HBx also co-localized with Hepsin in human cells as determined by confocal immunofluorescence microscopy. The interaction between HBx and Hepsin protein appeared to play a role in both promoting cell proliferation and blocking apoptosis in human liver tumor cell and normal liver cell lines. In addition, the complex of HBx and Hepsin promoted the expression of HBeAg in Hep G2.2.1.5 cells indicating that the association of these two proteins stimulated viral replication.

Hepatitis B virus X protein promotes liver cell proliferation via a positive cascade loop involving arachidonic acid metabolism and p-ERK1/2

“…PTX (ng/ml): HBx enhances the proliferation of liver cells by a positive feedback loop involving AA metabolism by COX-2 and 5-LOX, ERK1/2 activation, released AA metabolites and Gi/o proteins. Our conclusions are consistent with previous results in which HBx induced proliferation in cultured cells [27] and another study in which HBx expression induced cell-cycle progression within the milieu of the regenerating liver [28]. The results of our study oppose the conclusions of other studies that showed that transient transfection of HBx induced apoptosis and that HBx inhibited hepatocyte regeneration [29][30][31].…”

“…Many studies have revealed that p-ERK1/2 can be activated by the Gi/o family of GPCRs [25][26][27]. AA metabolite release is a receptor-dependent event, requiring a transducing Gi/o protein to initiate phospholipid hydrolysis and release AA into the cytosol.…”

Hepatitis B virus-related hepatocellular carcinoma: paradigms for viral-related human carcinogenesis

“…HBx has been shown to interact with p53, thereby inactivating several critical (Chun et al, 2003). HBx can also exert antiapoptotic functions independently of p53 via modulation of activities of the serine protease hepsin (Zhang et al, 2005a) and upregulation of survivin (Li et al, 2003). HBx protein may also promote apoptosis dependent on p53 (Chirillo et al, 1997) or by regulating the expressions of Fas/FasL (Terradillos et al, 1998;Shin et al, 1999;Lee et al, 2002;, inactive procaspase-8, cFLICE (Kim and Seong, 2003), Bax/Bcl-2 (Miao et al, 2005), HSP60 (Tanaka et al, 2004), UV-DDB1 (Sitterlin et al, 2000;Bergametti et al, 2002;Leupin et al, 2003) and c-myc gene (Kalra and Kumar, 2004).…”

Hepatitis B virus X protein up-regulates tumor necrosis factor-α expression in cultured mesangial cells via ERKs and NF-κB pathways

“…Methods: The plasmid pCI-neo-X that carries the X gene of hepatitis B virus was transfected into cultured GMCs Previous studies have shown that the HBV X (HBx) gene plays a important role in promoting cell proliferation and blocking apoptosis in human liver normal cells and tumor cells [11][12][13][14] . Given the important role of tumor necrosis factor α (TNF-α), a proinflammatory factor, in the development of various kidney diseases such as hyperproliferation of mesangial cells and renal injury [15][16][17][18] , we hypothesized that HBx might increase TNF-α expression, and therefore, contribute to the development of glomerulonephritis.…”