Importantly, enforced expression of Mcl-1 prevented HBx-triggered cell apoptosis; conversely, specific knockdown of Mcl-1 exacerbated HBx-induced apoptosis upon exposure to oxidative stress. 1476-4598-10-43-S1.JPEG (608K) GUID:?0F709D0D-398A-4F36-8073-9531BB0162F7 Abstract Background Oxidative stress has been implicated in the pathogenesis of a wide spectrum of human diseases, including Hepatitis B virus (HBV)-related liver disease. Hepatitis B virus X protein (HBx) is a key regulator of HBV that exerts pleiotropic activity on cellular functions. Recent studies showed that HBx alters mitochondrial membrane potential, thereby sensitizing cells to pro-apoptotic signals. However, it remains largely unknown whether susceptibility of hepatocytes could be disturbed by HBx under oxidative stress conditions. The purpose of this study is to determine the apoptotic susceptibility of HBx-expressing hepatocytes upon exposure to pro-oxidant stimuli em in vitro /em and em in vivo /em and explore its underlying mechanism. Results Although expression of HBx itself did not activate apoptotic signaling, it significantly enhanced oxidative stress-induced cell death both em in vitro /em and em in vivo /em . Interestingly, this phenomenon was associated with a Oxybutynin pronounced reduction of protein levels of Mcl-1, but not other Oxybutynin anti-apoptotic Bcl-2 members. Importantly, enforced expression of Mcl-1 prevented HBx-triggered cell apoptosis; conversely, specific knockdown of Mcl-1 exacerbated HBx-induced apoptosis upon exposure to oxidative stress. Furthermore, inhibition of caspase-3 not only abrogated HBx-triggered apoptotic killing but also blocked HBx-induced Mcl-1 loss. Additionally, expression of HBx and Mcl-1 was found to be inversely correlated in HBV-related hepatocellular carcinogenesis (HCC) tissues. Conclusions Our findings indicate that HBx exerts pro-apoptotic effect upon exposure to oxidative stress probably through accelerating the loss of Mcl-1 protein via caspase-3 cascade, which may shed a new light on the molecular mechanism of HBV-related hepatocarcinogenesis. Background Chronic Hepatitis B virus (HBV) infection is a major risk factor of human chronic liver disease and is strongly associated with hepatocellular carcinogenesis (HCC). Among the HBV encoding proteins, HBV X protein (HBx) is considered as a critical viral protein that exhibits multifunctional activities in modulating gene transcription, protein degradation, signal transduction, cell proliferation, cell cycle progress, senescence, autophagy and apoptosis [1-4]. Since apoptosis has been implicated as an important mechanism for liver injury [5,6], much effort has been made to understand the role of HBx in the regulation of apoptosis and its contribution to HCC. To date, the reported effects of HBx on apoptosis are controversial. As reported previously, the discrepancy of the role of HBx on cell apoptosis may be due to the different culture conditions and experimental systems used in these Rabbit Polyclonal to PPM1L studies. Nevertheless, majority of these studies demonstrated that HBx can induce cell death or sensitize hepatocytes to a variety of apoptotic signals such as TNF-, TRAIL, vitamin K3, ethanol, Fas, and UV [7-12]. In experimental animals, Oxybutynin HBx transgenic mice also exhibit increased hepatic apoptosis [13]. It is well known that oxidative stress have been implicated in the pathogenesis of inflammatory diseases and cancer [14] and reactive oxygen species (ROS) are continuously generated within chronic inflammation and malignant tumor tissues. In addition, infiltration of activated phagocytic cells in liver disease provides another source of ROS production that promotes oxidative damage to hepatocytes [15]. Recent work showed that HBx expression could alter mitochondrial membrane potential and increase cellular ROS production, thereby sensitizing hepatoma cells to apoptotic stimuli [9,16]. Consistent with these em in vitro /em findings, HBV transgenic mice also display elevated oxidative stress levels in the liver as compared to the nontransgenic control strain [17]. Thus, it is possible that, in HBV-infected liver, HBx protein and oxidative signals generated within the microenvironment may cooperate to increase cellular ROS accumulation up to a deleterious level, thereby resulting in overt liver cell damage. However, relatively little research has addressed the issue of whether susceptibility of hepatocytes upon exposure to oxidative stress could be affected by HBx. The Bcl-2 protein family plays a pivotal role for mitochondrial membrane integrity and apoptosis regulation [18,19]. Among them, Mcl-1 is both structurally and functionally an anti-apoptotic member of the Bcl-2 family. It mainly locates on the outer membrane of mitochondria and is an important regulator of mitochondria-mediated apoptosis by preventing the release of cytochrome c into cytosol [20]. Recently, it has been demonstrated that Mcl-1 plays a key Oxybutynin role in regulation of apoptosis and survival in multiple.