MAB8419 Sigma-AldrichAnti-Hepatitis B Virus Antibody, X-Protein, a.a. 90-115, clone 227

Six transmembrane protein of prostate 2 (STAMP2) plays a key role in linking inflammatory and diet-derived signals to systemic metabolism. STAMP2 is induced by nutrients/feeding as well as by cytokines such as TNFα, IL-1β, and IL-6. Here, we demonstrated that STAMP2 protein physically interacts with and decreases the stability of hepatitis B virus X protein (HBx), thereby counteracting HBx-induced hepatic lipid accumulation and insulin resistance. STAMP2 suppressed the HBx-mediated transcription of lipogenic and adipogenic genes. Furthermore, STAMP2 prevented HBx-induced degradation of IRS1 protein, which mediates hepatic insulin signaling, as well as restored insulin-mediated inhibition of gluconeogenic enzyme expression, which are gluconeogenic genes. We also demonstrated reciprocal expression of HBx and STAMP2 in HBx transgenic mice. These results suggest that hepatic STAMP2 antagonizes HBx-mediated hepatocyte dysfunction, thereby protecting hepatocytes from HBV gene expression.

Chronic hepatitis B is a disease of the liver that can progress to cirrhosis and liver cancer. The hepatitis B virus X (HBx) protein of hepatitis B virus is a multifunctional regulator that induces endoplasmic reticulum (ER) stress by previously unknown mechanism. ER stress plays a critical role in inflammatory induction and cyclooxygenase-2 (COX2) is an important mediator of this inflammation. Here, we demonstrate the molecular mechanisms of HBx on induction of ER stress and COX2 expression. In addition, HBx protein reduced expression of enzymes, which are involved in mitochondrial β-oxidation of fatty acids, and the mitochondrial inner membrane potential. The reduction of intracellular ATP levels by HBx induced the unfolded protein response and COX2 expression through the eIF2α-ATF4 pathway. We confirmed that ATF4 binding to the COX2 promoter plays a critical role in the HBx-mediated COX2 induction. These results suggest that HBV infection contributes hepatic inflammatory induction through cell organelles dysfunction including ER and mitochondria.

Metastasis-associated protein 1 (MTA1), a master chromatin modifier, has been shown to regulate cancer progression and is widely upregulated in human cancer, including hepatitis B virus-associated hepatocellular carcinomas (HCCs). Here we provide evidence that hepatitis B virus transactivator protein HBx stimulates the expression of MTA1 but not of MTA2 or MTA3. The underlying mechanism of HBx stimulation of MTA1 involves HBx targeting of transcription factor nuclear factor (NF)-kappaB and the recruitment of HBx/p65 complex to the NF-kappaB consensus motif on the relaxed MTA1 gene chromatin. We also discovered that MTA1 depletion in HBx-expressing cells severely impairs the ability of HBx to stimulate NF-kappaB signaling and the expression of target proinflammatory molecules. Furthermore, the presence of HBx in HBx-infected HCCs correlated well with increased MTA1 and NF-kappaB-p65. Collectively, these findings revealed a previously unrecognized integral role of MTA1 in HBx stimulation of NF-kappaB signaling and consequently, the expression of NF-kappaB targets gene products with functions in inflammation and tumorigenesis.

Hepatitis B virus (HBV) is a major cause of chronic liver diseases, and frequently results in hepatitis, cirrhosis, and ultimately hepatocellular carcinoma. The role of HCV in associations with insulin signaling has been elucidated. However, the pathogenesis of HBV-associated insulin signaling remains to be clearly characterized. Therefore, we have attempted to determine the mechanisms underlying the HBV-associated impairment of insulin signaling.The expressions of insulin signaling components were investigated in HBx-transgenic mice, HBx-constitutive expressing cells, and transiently HBx-transfected cells. Protein and gene expression was examined by Western blot, immunohistochemistry, RT-PCR, and promoter assay. Protein-protein interaction was detected by coimmunoprecipitation.HBx induced a reduction in the expression of IRS1, and a potent proteasomal inhibitor blocked the downregulation of IRS1. Additionally, HBx enhanced the expression of SOCS3 and induced IRS1 ubiquitination. Also, C/EBPalpha and STAT3 were involved in the HBx-induced expression of SOCS3. HBx interfered with insulin signaling activation and recovered the insulin-mediated downregulation of gluconeogenic genes.These results provide direct experimental evidences for the contribution of HBx in the impairment of insulin signaling.

BACKGROUND/AIMS: The hepatitis B virus X protein (HBx) has been implicated as a potential trigger of the epigenetic deregulation of some genes, but the underlying mechanisms remain unknown. The aim of this study was to identify underlying mechanisms involved in HBx-mediated epigenetic modification. METHODS: Interactions between HBx and DNA methyltransferase (DNMT) or histone deacetylase-1 (HDAC1) were assessed by co-immunoprecipitation. DNA methylation of gene promoters was detected by bisulfite sequencing, and HBx-mediated protein binding to gene regulatory elements was evaluated by chromatin immunoprecipitation. Target gene transcriptional activity was measured by real-time polymerase chain reaction. RESULTS: HBx can interact directly with DNMT3A and HDAC1. HBx recruited DNMT3A to the regulatory promoters of interleukin-4 receptor and metallothionein-1F and subsequently silenced their transcription via de novo DNA methylation. By contrast, the transcription of CDH6 and IGFBP3 was triggered by HBx through the deprivation of DNMT3A from their promoters. Transcriptional levels of target genes in hepatocellular carcinoma (HCC) specimens were strongly correlated with the occurrence of HBx. CONCLUSIONS: The interaction of HBx and DNMT3A facilitates cellular epigenetic modification (via regional hypermethylation or hypomethylation) at distinct genomic loci, providing an alternative mechanism within HBx-mediated transcriptional regulation, and a profound understanding of hepatitis and HCC pathogenesis.

HBV (hepatitis B virus) is a primary cause of chronic liver disease, which frequently results in hepatitis, cirrhosis and ultimately HCC (hepatocellular carcinoma). Recently, we showed that HBx (HBV protein X) expression induces lipid accumulation in hepatic cells mediated by the induction of SREBP1 (sterol-regulatory-element-binding protein 1), a key regulator of lipogenic genes in the liver. However, the molecular mechanisms by which HBx increases SREBP1 expression and transactivation remain to be clearly elucidated. In the present study, we demonstrated that HBx interacts with LXRalpha (liver X receptor alpha) and enhances the binding of LXRalpha to LXRE (LXR-response element), thereby resulting in the up-regulation of SREBP1 and FAS (fatty acid synthase) in the presence or absence of the LXR agonist T0901317 in the hepatic cells and HBx-transgenic mice. Furthermore, HBx also augments the ability to recruit ASC2 (activating signal co-integrator 2), a transcriptional co-activator that controls liver lipid metabolic pathways, to the LXRE with LXRalpha. These studies place LXRalpha in a key position within the HBx-induced lipogenic pathways, and suggest a molecular mechanism through which HBV infection can stimulate the SREBP1-mediated control of hepatic lipid accumulation.

Hepatic steatosis occurs frequently in patients with chronic hepatitis B virus (HBV) or chronic hepatitis C virus (HCV) infection. Recently, several studies suggested that steatosis plays an important role as a cofactor in other liver diseases such as hepatic fibrosis, hepatitis, and liver cancer. In contrast to HCV, however, the molecular mechanism by which HBV mediates hepatic steatosis has not been clearly studied. Here, we show the molecular mechanism by which hepatitis B virus X protein (HBx) induces hepatic steatosis.

BACKGROUND/AIMS: Transgenic mice overexpressing hepatitis B x protein (HBx) show an increased susceptibility to mutations if exposed to mutagens. Also involved in HBx signalling, reactive oxygen intermediates (ROI) can induce DNA adducts such as 8-hydroxy-2'-deoxyguanosine that can in turn lead to G/T transversion mutations. Therefore, we investigated whether HBx expression increases the level of the mutational precursor 8-hydroxy-2'-deoxyguanosine in hepatocellular DNA. METHODS: 8-hydroxy-2'-deoxyguanosine concentrations of DNA hydrolysates of HBx protein expressing HepG2 cells and livers of HBx transgenic mouse lines were determined electrochemically after HPLC fractionation. RESULTS: 8-hydroxy-2'-deoxyguanosine concentrations in genomic DNA of HBx protein expressing cell lines correlated with the factor of transactivation. The 8-hydroxy-2'-deoxyguanosine levels were reduced after incubation of HBx recombinant cell lines with 0.1 or 1 mM of the antioxidant N-acetylcysteine. Hepatic 8-hydroxy-2'-deoxyguanosine concentrations in DNA of old transgenic mice were significantly, i.e. twofold, (p 0.01) increased as compared to those of old nontransgenic or young transgenic controls and of control mice expressing a second HBV transactivator (MHBs(t76)). Conclusion: HBx expression results in elevated DNA adduct levels. This could reflect a direct inhibitory interaction of HBx with cellular repair mechanisms. Alternatively, this may be an effect of an increased generation of reactive oxygen intermediates through HBx.

Transgenic mice, which selectively express the WAP-HBX transgene in mammary gland epithelial cells (ME-cells), were established in order to elucidate the consequences of HBX gene expression on organ differentiation, cell death program and tumor development. Transgene expression was demonstrable by RT-PCR, Northern and Western blot analysis during pregnancy, lactation and after weaning. HBX synthesis neither affect mammary gland differentiation nor apoptosis in ME-cells. Although breast cancer formation was rare in WAP-HBX animals (less than 1%), WAP-HBX*p53+/- hybrid animals developed breast tumors at an increased rate (12/85) after a latency period of 8-18 months. We also show here for the first time that HBX can immortalize ME-cells generated from mammary gland tissue segments in a p53-independent fashion. HBX causes cyclin D1 gene overexpression during early pregnancy, and this is maintained in ME-cells isolated either from mammary gland or from breast tumors. Intranuclear cyclin D1 accumulation also occurs in the absence of external growth factors and the BrdU incorporation rate remains high under serum starvation conditions. Finally, both cyclin D1 induction and HBX mitotic activity are dependent on p38 and c-Jun N-terminal kinase, but not on MEK-1 kinase activity.