HBx induces the proliferation of hepatocellular carcinoma cells via AP1 over-expressed as a result of ER stress.

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide and chronic hepatitis B virus (HBV) infection is the most common risk factor for HCC. The HBV proteins can induce oncogenic or synergy effects with a hyperproliferative response on transformation into HCC. CREBH (cAMP-responsive, element-binding protein H), activated by stress in the endoplasmic reticulum (ER), is an ER-resident transmembrane bZIP (basic leucine zipper) transcription factor that is specifically expressed in the liver. In the present study, we address the role played by CREBH activated by ER stress in HBV-induced hepatic cell proliferation. We confirmed CREBH activation by ER stress and showed that it occurred as a result of/via hepatitis B virus X (HBx)-induced ER stress. CREBH activated by HBx increased the expression of AP-1 target genes through c-Jun induction. Under pathological conditions such as liver damage or liver regeneration, activated CREBH may have an important role to play in hepatic inflammation and cell proliferation, as an insulin receptor with dual functions under these conditions. We showed that CREBH activated by HBx interacted with HBx protein, leading to a synergistic effect on the expression of AP-1 target genes and the proliferation of HCC cells and mouse primary hepatocytes. In conclusion, in HBV-infected hepatic cells or patients with chronic HBV, CREBH may induce proliferation of hepatic cells in co-operation with HBx, resulting in HCC.

Bile acid increases expression of the histamine-producing enzyme, histidine decarboxylase, in gastric cells.

AIM: To investigate the effect of bile acid on the expression of histidine decarboxylase (HDC), which is a major enzyme involved in histamine production, and gene expression of gastric transcription factors upon cooperative activation. METHODS: HDC expression was examined by immunohistochemistry, reverse transcriptase polymerase chain reaction, and promoter assay in human gastric precancerous tissues, normal stomach tissue, and gastric cancer cell lines. The relationship between gastric precancerous state and HDC expression induced by bile acid was determined. The association between the expression of HDC and various specific transcription factors in gastric cells was also evaluated. MKN45 and AGS human gastric carcinoma cell lines were transfected with farnesoid X receptor (FXR), small heterodimer partner (SHP), and caudal-type homeodomain transcription factor (CDX)1 expression plasmids. The effects of various transcription factors on HDC expression were monitored by luciferase-reporter promoter assay. RESULTS: Histamine production and secretion in the stomach play critical roles in gastric acid secretion and in the pathogenesis of gastric diseases. Here, we show that bile acid increased the expression of HDC, which is a rate-limiting enzyme of the histamine production pathway. FXR was found to be a primary regulatory transcription factor for bile acid-induced HDC expression. In addition, the transcription factors CDX1 and SHP synergistically enhanced bile acid-induced elevation of HDC gene expression. We confirmed similar expression patterns for HDC, CDX1, and SHP in patient tissues. CONCLUSION: HDC production in the stomach is associated with bile acid exposure and its related transcriptional regulation network of FXR, SHP, and CDX1.

Tumor suppressor protein VHL inhibits Hedgehog-Gli activation through suppression of Gli1 nuclear localization.

The transcription factor Gli1 acts in the last known step of the Hedgehog signaling, and deregulation of Gli1 is implicated in human cancers. VHL protein is widely expressed in both fetal and adult tissues and acts as a tumor suppressor. Here, we demonstrate the molecular mechanism through which VHL inhibits the Hedgehog-Gli pathway. VHL decreased Gli1-mediated promoter transactivation as well as the expression of Hedgehog/Gli pathway target genes. Nuclear translocation of cytosolic Gli1 protein was inhibited by VHL via protein-protein interaction. These results indicate that overexpression of VHL may antagonize Hedgehog-Gli activation at the post-translational level in Hedgehog pathway-induced cancers.

Hypoxia induces expression of COX-2 through the homeodomain transcription factor CDX1 and orphan nuclear receptor SHP in human endometrial cells.

Endometriosis, the presence of ectopic endometrial tissue outside the uterine cavity, is a common disease affecting women during their reproductive years. The aim of this study was to identify the molecular mechanism of transcriptional regulation of inflammatory cyclooxygenase-2 (COX-2) gene during endometriosis by hypoxia. Hypoxia induced COX-2 expression in endometrial cells together with the induction of the orphan nuclear receptor SHP and intestinal-specific transcription factor Caudal-related transcription factor 1 (CDX1). Hypoxia-inducible factor (HIF)-1α was responsible for SHP induction mediated by a hypoxia. In addition, we observed that ectopic expression of CDX1 enhanced COX-2 gene expression in hypoxia-dependent fashion. Additionally, we evaluated that induction of CDX1 by hypoxia was mediated by SHP. Expression of COX-2, CDX1, SHP and HIF-1α mRNA in hypoxia-treated human endometrial cells were significantly higher than normal control cells. These results suggest that the SHP and CDX1 expression increased by hypoxia play an active role in inducing inflammatory COX-2 expression in the pathogenesis of endometriosis.

Oxygenated derivatives of cholesterol promote hepatitis B virus gene expression through nuclear receptor LXRα activation.

Hepatitis B virus (HBV) gene expression and replication are regulated by the activation of a number of liver-enriched transcription factors dependent on intracellular and extracellular stimuli. However, the association between the metabolic events and HBV gene expression remains unclear. In this study, we assessed the effects of cholesterol metabolism on HBV viral replication and gene expression. Exposure of oxygenated derivatives of cholesterol (oxysterols) increased HBV gene expression and viral promoter activity. This increase in HBV transcription and replication was directed by nuclear receptor LXRα induction in the presence of oxysterols. In addition, HBV viral expression by oxysterol was inhibited through small heterodimer partner and sterol regulatory element-binding protein 2, key regulators of cholesterol synthesis. When IFNα and oxysterols were co-incubated, oxysterols and LXRα significantly reduced the anti-HBV effects of IFNα. These results point to a novel mechanism of oxysterol-mediated gene regulation in HBV replication and a potent mechanism underlying the failure of IFNα-based treatment.

SHP (small heterodimer partner) suppresses the transcriptional activity and nuclear localization of Hedgehog signalling protein Gli1.

Gli (glioma-associated oncogene homologue) proteins act as terminal effectors of the Hedgehog signalling pathway, which is implicated in the development of many human malignancies. Gli activation is important for cell proliferation and anti-apoptosis in various cancers. Several studies have suggested that nuclear receptors have anti-cancer effects by inhibiting the activation of various oncoproteins. However, the involvement of nuclear receptors on the Hedgehog/Gli signalling pathway is poorly defined. In the present study we identified SHP (small heterodimer partner) as a nuclear receptor that decreased the expression of Gli target genes by repressing the transcriptional activity of Gli1. The inhibitory effect of SHP was associated with the inhibition of Gli1 nuclear localization via protein-protein interaction. Finally, SHP overexpression decreased the expression of Gli target genes and SHP knockdown increased the expression of these genes. Taken together, these results suggest that SHP can play a negative role in Hedgehog/Gli1 signalling.

The orphan nuclear receptor SHP inhibits apoptosis during the monocytic differentiation by inducing p21WAF1.

Small heterodimer partner (SHP) is an atypical member of nuclear receptor superfamily that lacks a DNA-binding domain. In previous study, we showed that SHP, c-jun, p65 of NF-gammaB subunits, and p21WAF1 expression was increased during monocytic differentiaton with the exposure of human leukemia cells to a differentiation agent, PMA. In this study, c-Jun and p65 were shown to mediate the transcriptional activation of the SHP promoter. In addition, SHP induced the cell cycle regulatory protein levels and cooperatively increased an induction of p21WAF1 expression with p65. Furthermore, SHP protected differentiated cells from etoposide-induced cellular apoptosis through the induction and cytoplasmic sequestration of p21WAF1. Complex formation between SHP and p21WAF1 was demonstrated by means of coimmunoprecipitation. These results suggest that SHP prolongs a cellular survival of differentiating monocytes through the transcriptional regulation of target genes of cell survival and differentiation.

Hepatitis B virus X protein induces lipogenic transcription factor SREBP1 and fatty acid synthase through the activation of nuclear receptor LXRalpha.

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.

Chemokine stromal cell-derived factor-1 induction by C/EBPbeta activation is associated with all-trans-retinoic acid-induced leukemic cell differentiation.

Stromal cell-derived factor-1 (SDF-1/CXCL12) is one of the essential chemokines, which mediates hematopoietic differentiations. However, the mechanism by which SDF-1 expression is regulated in granulocyte differentiation is poorly understood. Here, we suggest a novel mechanism by which all-trans-retinoic acid (ATRA) induces the expression of SDF-1 during the differentiation of promyelomonocytic leukemic U937 cells. Moreover, we also demonstrate that activation of transcription factor C/EBPbeta by ATRA regulates SDF-1 expression in U937 cells. In addition, we show that the cyclin-dependent kinase inhibitors p21(WAF1/CIP1) and Pyk2 are up-regulated by SDF-1 and increased markedly by the costimulation of ATRA and SDF-1. Furthermore, ATRA and SDF-1alpha additively induce U937 cell differentiation. Indeed, silencing the expression of SDF-1 inhibits ATRA-induced granulocyte differentiation significantly. Taken together, these results indicate that SDF-1alpha is involved in granulocyte differentiation in response to ATRA, mediated by the activation of the transcription factor C/EBPbeta.

Hepatitis B virus X protein induces hepatic steatosis via transcriptional activation of SREBP1 and PPARgamma.

BACKGROUND & AIMS: 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. METHODS: Lipid accumulation and the expression of various lipid metabolic genes were investigated in HBx-transfected Chang liver cells, HepG2-HBx stable cells, and HBx-transgenic mice. RESULTS: Overexpression of HBx induced hepatic lipid accumulation in HepG2-HBx stable cells and HBx-transgenic mice. It also up-regulated the messenger RNA and protein levels of sterol regulatory element binding protein 1, but not peroxisome proliferator-activated receptor alpha (PPARalpha). Moreover, we also determined that the expression of HBx increases PPARgamma gene expression as well as its transcriptional activity in hepatic cells, mediated by CCAAT enhancer binding protein alpha activation. Finally, we showed that HBx expression is able to up-regulate the gene expressions of various lipogenic and adipogenic enzymes in hepatic cells. CONCLUSIONS: We showed that the increased HBx expression causes lipid accumulation in hepatic cells mediated by sterol regulatory element binding protein 1 and PPARgamma, which could be a putative molecular mechanism mediating the pathophysiology of HBV infection.

Transcriptional repression of the gluconeogenic gene PEPCK by the orphan nuclear receptor SHP through inhibitory interaction with C/EBPalpha.

SHP (short heterodimer partner) is an orphan nuclear receptor that plays an important role in regulating glucose and lipid metabolism. A variety of transcription factors are known to regulate transcription of the PEPCK (phosphoenolpyruvate carboxykinase) gene, which encodes a rate-determining enzyme in hepatic gluconeogenesis. Previous reports identified glucocorticoid receptor and Foxo1 as novel downstream targets regulating SHP inhibition [Borgius, Steffensen, Gustafsson and Treuter (2002) J. Biol. Chem. 277, 49761-49796; Yamagata, Daitoku, Shimamoto, Matsuzaki, Hirota, Ishida and Fukamizu (2004) J. Biol. Chem. 279, 23158-23165]. In the present paper, we show a new molecular mechanism of SHP-mediated inhibition of PEPCK transcription. We also show that the CRE1 (cAMP regulatory element 1; -99 to -76 bp relative to the transcription start site) of the PEPCK promoter is also required for the inhibitory regulation by SHP. SHP repressed C/EBPalpha (CCAAT/enhancer-binding protein alpha)-driven transcription of PEPCK through direct interaction with C/EBPalpha protein both in vitro and in vivo. The formation of an active transcriptional complex of C/EBPalpha and its binding to DNA was inhibited by SHP, resulting in the inhibition of PEPCK gene transcription. Taken together, these results suggest that SHP might regulate a level of hepatic gluconeogenesis driven by C/EBPalpha activation.

Chemokine stromal cell-derived factor-1 induction by C/EBPß activation is associated with all-trans-retinoic acid-induced leukemic cell differentiation.

Stromal cell-derived factor-1 (SDF-1/CXCL12) is one of the essential chemokines, which mediates hematopoietic differentiations. However, the mechanism by which SDF-1 expression is regulated in granulocyte differentiation is poorly understood. Here, we suggest a novel mechanism by which all-trans-retinoic acid (ATRA) induces the expression of SDF-1 during the differentiation of promyelomonocytic leukemic U937 cells. Moreover, we also demonstrate that activation of transcription factor C/EBPß by ATRA regulates SDF-1 expression in U937 cells. In addition, we show that the cyclin-dependent kinase inhibitors p21WAF1/CIP1 and Pyk2 are up-regulated by SDF-1 and increased markedly by the costimulation of ATRA and SDF-1. Furthermore, ATRA and SDF-1α additively induce U937 cell differentiation. Indeed, silencing the expression of SDF-1 inhibits ATRA-induced granulocyte differentiation significantly. Taken together, these results indicate that SDF-1α is involved in granulocyte differentiation in response to ATRA, mediated by the activation of the transcription factor C/EBPß.