Sun Jung Myung

Wnt signaling enhances the activation and survival of human hepatic stellate cells

Wnt signaling was implicated in pulmonary and renal fibrosis. Since Wnt activity is enhanced in liver cirrhosis, Wnt signaling may also participate in hepatic fibrogenesis. Thus, we determined if Wnt signaling modulates hepatic stellate cell (HSC) activation and survival. Wnt3A treatment significantly activated human HSCs, while this was inhibited in secreted frizzled‐related protein 1 (sFRP1) overexpressing cells. Wnt3A treatment significantly suppressed TRAIL‐induced apoptosis in control HSCs versus sFRP1 over‐expressing cells. Particularly, caspase 3 was more activated in sFRP1 over‐expressing cells following TRAIL and Wnt3A treatment. These observations imply that Wnt signaling promotes hepatic fibrosis by enhancing HSC activation and survival.

Heat Shock Protein 90 Inhibitor Induces Apoptosis and Attenuates Activation of Hepatic Stellate Cells

Activated hepatic stellate cells (HSCs) are major participants in hepatic fibrosis; thus, the induction of HSC apoptosis has been proposed as an antifibrotic treatment strategy. Heat shock protein (Hsp) 90 is a molecular chaperone that stabilizes major signal transduction proteins, and its inhibitors have antitumor activity. In this study, the susceptibility of HSCs to an Hsp90 inhibitor was evaluated. LX-2 cells, an immortalized human HSC line, 17-(allylamino)-17-demethoxygeldanamycin (17AAG), an Hsp90 inhibitor, and monensin, an acidic sphingomyelinase inhibitor, were used in this study. Cellular apoptosis was quantified by 4′,6-diamidino-2-phenylindole dihydrochloride staining, and signaling cascades were explored using immunoblotting and immunoprecipitation techniques. Nuclear factor (NF) κB activities were evaluated by immunofluorescent microscopy and enzyme-linked immunosorbent assay. Collagen α1 and α-smooth muscle actin expressions were determined by real-time reverse transcription-polymerase chain reaction and immunoblotting, respectively. It was found that 17AAG induced HSC apoptosis and that caspase 8 cleavage preceded the downstream activation of apoptotic signaling cascades. Furthermore, this caspase 8 activation was dependent on ceramide generation by acidic sphingomyelinase. In addition, 17AAG prevented NFκB nuclear translocation and activation, specifically by inducing complex formation between NFκB and the glucocorticoid receptor. In accordance, NFκB-dependent cellular FLICE-like inhibitory protein expression level was found to be reduced by 17AAG. Finally, 17AAG down-regulated collagen α1 and α-smooth muscle actin expression levels in HSCs before inducing apoptosis. These results demonstrate that the Hsp90 inhibitor induces HSC apoptosis via a sphingomyelinase- and NFκB-dependent mechanism. Because this inhibitor also reduces HSC activation before apoptosis, Hsp90 inhibitor treatment might be therapeutically useful as an antifibrotic strategy in a variety of liver diseases.

Hypoxia and retinoic acid-inducible NDRG1 expression is responsible for doxorubicin and retinoic acid resistance in hepatocellular carcinoma cells.

Hypoxia may activate survival signals in cancer cells. Moreover, hypoxic cells are less sensitive than normoxic cells to doxorubicin cytotoxicity, a potent activator of the p53 tumor suppressor gene. N-myc downstream-regulated gene-1 (NDRG1) is a hypoxia- and retinoic acid-inducible protein, and has been previously implicated in carcinogenesis. As this protein is also a downstream target of p53 and hepatocellular carcinoma (HCC) cells frequently evidence resistance to retinoic acid (RA) cytotoxicity, we attempted to determine whether the suppression of NDRG1 expression may sensitize HCC cells to doxorubicin and/or RA cytotoxicity. HCC cells expressed NDRG1 protein, and the expression of this protein was hypoxia- and RA-inducible. Doxorubicin treatment induced HCC cell cytotoxicity via the activation of mitochondrial apoptotic signals, including caspase-9 activation. Hypoxic HCC cells are less sensitive to doxorubicin-induced apoptosis. The suppression of NDRG1 expression either by siRNA or flavopiridol sensitized hypoxic HCC cells to doxorubicin cytotoxicity, and this was attributed to more profound augmentation of JNK and caspase-9 activation. The suppression of NDRG1 expression also sensitized RA-resistant HCC cells to RA-induced apoptosis, and this sensitization was more apparent in hypoxic HCC cells than in normoxic cells. Glutaredoxin2 expression was down-regulated in NDRG1-suppressed HCC cells. These results show that hypoxia- and RA-inducible NDRG1 expression is responsible for doxorubicin and RA resistance in HCC cells. Thus, the selective interruption of NDRG1 signaling may prove to be therapeutically useful in HCCs, particularly in the advanced infiltrative type of tumors exposed to hypoxic environments.

Inhibition of hypoxia-inducible carbonic anhydrase-IX enhances hexokinase II inhibitor-induced hepatocellular carcinoma cell apoptosis

Aim:The hypoxic condition within large or infiltrative hypovascular tumors produces intracellular acidification, which could activate many signaling pathways and augment cancer cell growth and invasion. Carbonic anhydrase-IX (CA-IX) is an enzyme lowering pH. This study is to examine whether hypoxia induces CA-IX in hepatocellular carcinoma (HCC) cells, and to evaluate its clinical implication in HCC patients.Methods:Human HCC cell lines (Huh-7 and HepG2 cells) were used, and cell growth was assessed using MTS assay. CA-IX expression and apoptotic/kinase signaling were evaluated using immunoblotting. The cells were transfected with CA-IX-specific siRNA, or treated with its inhibitor 4-(2-aminoethyl) benzenesulfonamide (CAI#1), and/or the hexokinase II inhibitor, 3-bromopyruvate (3-BP). A clinic pathological analysis of 69 patients who underwent an HCC resection was performed using a tissue array.Results:Incubation of HCC cells under hypoxia (1% O2, 5% CO2, 94% N2) for 36 h significantly increased CA-IX expression level. CAI#1 (400 μmol/L) or CA-IX siRNA (100 μmol/L) did not influence HCC cell growth and induce apoptosis. However, CAI#1 or CA-IX siRNA at these concentrations enhanced the apoptosis induced by 3-BP (100 μmol/L). This enhancement was attributed to increased ER stress and JNK activation, as compared with 3-BP alone. Furthermore, a clinic pathological analysis of 69 HCC patients revealed that tumor CA-IX intensity was inversely related to E-cadherin intensity.Conclusion:Inhibition of hypoxia-induced CA-IX enhances hexokinase II inhibitor-induced HCC apoptosis. Furthermore, CA-IX expression profiles may have prognostic implications in HCC patients. Thus, the inhibition of CA-IX, in combination with a hexokinase II inhibitor, may be therapeutically useful in patients with HCCs that are aggressively growing in a hypoxic environment.

Hypoxia-inducible adrenomedullin accelerates hepatocellular carcinoma cell growth

Adrenomedullin is implicated in tumor progression and induced by hypoxia. We evaluated if adrenomedullin signaling is active in hepatocellular carcinoma (HCC), especially under hypoxic conditions, and to analyze its prognostic implication in HCC patients. HCC cells expressed adrenomedullin and its receptor, and hypoxia induced adrenomedullin expression. Adrenomedullin stimulated HCC cell growth via Akt activation, which was prevented by adrenomedullin peptide inhibitor. Clinico-pathological analysis revealed adrenomedullin extent was related to vascular invasion and N-cadherin intensity, which were reported to indicate a poor prognosis. In conclusion, adrenomedullin signaling is hypoxia-inducible and functionally active in HCCs, and its expression may be a prognostic factor.

Ursodeoxycholic acid-induced inhibition of DLC1 protein degradation leads to suppression of hepatocellular carcinoma cell growth

Ursodeoxycholic acid (UDCA), a hydrophilic bile acid, has been shown to inhibit mitogenic signaling and suppressing cell proliferation in colonic tumorigenesis. The transcription of DLC1 (deleted in liver cancer), a tumor suppressor gene, is frequently silenced in various types of human cancer. In this study, we postulated that UDCA may inhibit DLC1 protein degradation in hepatocellular carcinoma (HCC) cells, and increased DLC1 expression may suppress HCC cell growth. Human HCC cell lines were used in this study. The methylation status was measured by methylation-specific PCR following sodium bisulfite treatment. Cell proliferation was assessed using an MTS assay. Kinase signaling cascades were evaluated by immunoblot analysis. For assessing ubiquitination, immunoprecipitation analysis was used. To inhibit cellular protein, specific small interfering RNAs (siRNAs) were transfected into cells. DLC1 protein levels increased over time following UDCA treatment. Specifically, UDCA increased the half-life of the DLC1 protein by inhibiting proteasomal degradation of DLC1 without affecting ubiquitination of the DLC1 protein. In addition, HCC cell growth was suppressed following UDCA treatment and this growth suppression was significantly reversed following transfection with DLC1-siRNA. Inhibition of DLC1 increased cellular proliferation; this was reduced after Rho-inhibitor treatment. Finally, RhoA activity was reduced following UDCA treatment; this result was reversed and thus increased following DLC1-siRNA transfection. In conclusion, these results demonstrate that UDCA induces DLC1 protein expression by inhibiting proteasomal DLC1 degradation in a ubiquitin-independent manner, and that DLC1 induction participates in UDCA-induced suppression of HCC cell growth. These observations implicate UDCA as an anti-proliferative agent in HCC.

STAT3 & Cytochrome P450 2C9: A novel signaling pathway in liver cancer stem cells

Although cancer stem cells (CSCs) are believed to be the key drivers in tumor growth and resistance to therapy, the specific signaling of CSCs is largely unknown. In this study, we evaluated the roles of hypoxia and STAT3 signaling on the treatment resistance of CSCs. Side population (SP) cell analysis and sorting were used to detect subpopulations that function as CSCs. Huh-7 cells, doxorubicin, sulfaphenazole (a CYP2C9 inhibitor), and AG490 (a STAT3 inhibitor) were used in this study. Cell growth and apoptosis were assessed using MTS assays, and apoptotic and kinase signaling pathways were explored by immunoblotting. Treatment with IL-6 induced STAT3 activation more significantly in SP than non-SP cells. Hypoxia induced SP cell proliferation, and microarray analysis showed that the expression of CYP2C9 was significantly increased in hypoxic than normoxic SP cells. Although hypoxic SP cells were less sensitive to doxorubicin-induced apoptosis, pretreatment with sulfaphenazole sensitized hypoxic SP cells to doxorubicin cytotoxicity. These results indicate that STAT3 is critical for CSC survival and hypoxia-inducible CYP2C9 expression is responsible the doxorubicin resistance of CSCs under hypoxic conditions. Thus, the selective inhibition of CYP2C9 and STAT3 may be implicated in the sensitization of CSCs to anti-cancer treatment, particularly in advanced cases.

Serum HBsAg levels during peginterferon α-2a treatment with or without thymosin α-1 in HBeAg-positive chronic hepatitis B patients.

The importance of serum hepatitis B surface antigen (HBsAg) level as a surrogate marker for viral load and a predictor of treatment response remains unclear. The aim of this study was to investigate whether serum HBsAg correlates with serum hepatitis B virus (HBV) DNA during peginterferon (PEG‐IFN) α‐2a treatment (with or without thymosin α‐1) in hepatitis B e antigen (HBeAg)‐positive chronic hepatitis B patients and whether it can predict treatment response. Sera from 37 HBeAg‐positive chronic hepatitis B patients receiving 48‐weeks PEG‐IFN α‐2a with (n = 20) or without (n = 17) an initial 12‐weeks thymosin α‐1 were obtained at baseline and at weeks 12, 24, 36, 48 (end of treatment), 56, 72, 84, and 96 (end of follow‐up). Taqman HBV DNA tests (Roche) and Architect HBsAg QT (Abbott) were performed. There was a moderate correlation between the HBsAg and HBV DNA levels (r = 0.452, P < 0.001). Median HBsAg levels at baseline and at week 96 were 6,218 IU/ml and 4,038 IU/ml, respectively. The mean HBV DNA and alanine aminotransferase (ALT) levels were 7.48 log10 IU/ml and 173 IU/L at baseline and 5.37 log10 IU/ml and 102 IU/L at week 96, respectively. A decrease to <60% of baseline levels of HBsAg at week 12 was identified as an independent predictive factor for HBeAg seroconversion (OR = 45.7, P < 0.05) at week 96. Serum HBsAg levels may be helpful for predicting the response to PEG‐IFN therapy in HBeAg‐positive chronic hepatitis B patients. J. Med. Virol. 83:88–94, 2011.

Guggulsterone attenuates activation and survival of hepatic stellate cell by inhibiting nuclear factor kappa B activation and inducing apoptosis

Liver fibrosis is associated with the deposition of the extracellular matrix, and hepatic stellate cells (HSCs) are the major source of these matrix proteins. Guggulsterone has recently been shown to induce apoptosis in several cell lines. Thus, the aim of this study was to evaluate whether guggulsterone has antifibrotic activities by reducing the activation and survival of HSCs.

Retinoic acid and its binding protein modulate apoptotic signals in hypoxic hepatocellular carcinoma cells

Hypoxia induces survival signals in hepatocellular carcinoma (HCC). We attempted to find a hypoxia-induced signal that could be used for modulating HCC cell death. Cellular retinoic acid binding protein-II (CRABP-II) expression was significantly increased in hypoxic HCC cells. Treatment with retinoic acid (RA), a ligand for CRABP-II, induced HCC cell apoptosis more effectively in hypoxia than in normoxia, whereas hypoxia-induced CRABP-II expression attenuated RA-induced apoptosis. Inhibition of CRABP-II enhanced RA-induced apoptosis and sensitized RA-resistant HCC cells to RA cytotoxicity by attenuating p42/44 MAPK and Akt activation. Therefore, RA/CRABP-II signal modulation is therapeutically implicated in infiltrative HCCs exposed to hypoxia.