Additionally, OA treatment of Cul1 knockdown cells resulted in the formation of phosphorylated

PTTG1 forms (Supporting Fig. 5). We then analyzed the effect of HBx expression on PTTG1 accumulation in Cul1-silenced cells. In both Chang liver and p34x cells, PTTG1 expression levels were increased after Cul1 silencing (Fig. 7). As above, Dox-induced HBx increased PTTG1 levels in p34X control siRNA-treated cells (Fig. BMS-907351 mw 7, lane 7 versus lane 5). Interestingly, PTTG1 accumulation after Cul1 silencing was not further enhanced by HBx (Fig. 7, lane 8 versus lane 6), suggesting that the stabilization of PTTG1 by HBx was Cul1-dependent, not being likely that other ubiquitin ligase was involved. Given Navitoclax purchase that HBx expression mimicked the effects

of Cul-1 knockdown on PTTG1, it can be hypothesized that HBx interferes Cul1-asscociated functions. Overall, these data strongly suggest that HBx promotes the disruption of the PTTG1/SCF association and prevents its ubiquitination and subsequent degradation by the proteasome (Fig. 8). HBV-associated carcinogenesis is a multifactorial process. Liver inflammation results in hepatocellular death and regeneration processes that lead to the accumulation of critical mutations in the host genome. In addition, the regulatory protein HBx has been involved in hepatocarcinogenesis by altering cellular processes. In the present study, we have demonstrated that PTTG1 expression levels increase in HBx-immunoreactive cells as chronic hepatitis B progresses to cirrhosis and HCC. Furthermore, PTTG1 expression increases as HBx transgenic mouse livers progress through hyperplasia to HCC. In addition, PTTG1 accumulates in human and mouse HBx-expressing cell lines and in HBV replicon-containing cells, but not in cells harboring an HBx-defective genome construct. Together, these data strongly suggest that PTTG1 medchemexpress accumulation is, at least partially, an HBx-mediated effect. Several viruses, including HBV, have the ability to stimulate the cell cycle progression in order to facilitate their own

replication. In doing so, viruses generally disrupt the normal cell cycle checkpoints and in turn extend proliferative signals to host cells to establish a carcinogenic environment.29 HBx has been demonstrated to suppress serum dependence for cell cycle activation.30 Furthermore, HBx has been shown to promote transit through G1 in G0-arrested cells and to alter G1-to-S and G2-to-M progression.17, 22 However, in Chang liver p34X cells, the cell cycle profile was unaffected after HBx induction.24 In addition, it is known that HBx transcriptionally induces the expression of viral and cellular genes.2 However, our data strongly suggest that HBx-promoted PTTG1 protein accumulation is not strictly dependent on cell cycle modifications or transcriptional up-regulation. Through interactions with host factors, HBx alters different cellular processes implicated in the development of HCC.