Hepatitis B virus X induces cell proliferation in the hepatocarcinogenesis via up-regulation of cytoplasmic p21 expression.

BACKGROUND: Hepatitis B virus X protein (HBx) has been shown to induce hepatocarcinogenesis by disrupting the functions of intracellular molecules. Cyclin-dependent kinase inhibitor p21 (Cip1/WAF1), known as a tumour-suppressor gene, has been reported to have paradoxical function, that is, acting as an oncogene, particularly when expressed in the cytoplasm. The effects of HBx on the expression and function of p21 also remain controversial. AIMS: We attempted to investigate the role of HBx in the hepatocarcinogenic process, focusing on the association with this paradoxical function of p21. The results obtained were further verified with experiments using the antihepatocarcinogenic action of interferon (IFN)-ß. METHODS: HBx transgenic mice (Xg) and HBx-transfected hepatoma cell lines were used. Intracellular localization of p21 was determined by Western blot analysis and immunofluorescence. RESULTS: Xg and HBx-transfected cells exhibited increased expression of p21. Up-regulation of p21 was positively correlated with the expression of cyclin D1 and inactive phosphorylation of retinoblastoma protein (pRb). These HBx-induced cell proliferative responses were cancelled by knockdown of p21, which resulted in growth reduction in HBx-expressing cells, suggesting the oncogenic properties of HBx-induced p21. HBx induced accumulation of p21 in the cytoplasm, and activation of PKCα was involved. Finally, IFN-ß-treated Xg liver, as well as hepatoma cells, showed a shift of cytoplasmic p21 to the nucleus, accompanied by the abrogation of HBx-induced oncogenic modulation. CONCLUSIONS: Our results suggest that HBx induces hepatocarcinogenesis via PKCα-mediated overexpression of cytoplasmic p21 and IFN-ß suppressed these molecular events by shifting p21 to the nucleus.

P21-activated kinase-2 is a critical mediator of transforming growth factor-ß-induced hepatoma cell migration.

BACKGROUND AND AIM: Transforming growth factor-ß (TGF-ß) has been shown to play a central role in the promotion of cell motility, but its functional mechanism has remained unclear. With the aim of investigating the diagnostic and treatment modalities for patients with hepatocellular carcinoma (HCC), the signaling pathway that may contribute to TGF-ß-mediated cell invasion in hepatoma cells was evaluated. METHODS: Three hepatoma cell lines, HepG2, PLC/PRF/5, and HLF, were treated with TGF-ß, and the involvement of the non-canonical TGF-ß pathway was analyzed by cell migration assays. HepG2 cells were treated with a p21-activated kinase-2 (PAK2)-targeting small interfering RNA and analyzed for their cell motility. The relationships between the PAK2 status and the clinicopathological characteristics of 62 HCC patients were also analyzed. RESULTS: The cell migration assays showed that Akt is a critical regulator of TGF-ß-mediated cell migration. Western blotting analyses showed that TGF-ß stimulated Akt and PAK2 in all three hepatoma cell lines, and phosphorylated PAK2 was blocked by Akt inhibitor. Suppression of PAK2 expression by small interfering RNA resulted in increased focal adhesions with significantly repressed cell migration in the presence of TGF-ß. Clinicopathological analyses showed that the phosphorylation level of PAK2 was closely associated with tumor progression, metastasis, and early recurrence of HCC. CONCLUSIONS: PAK2 may be a critical mediator of TGF-ß-mediated hepatoma cell migration, and may represent a potential target for the treatment of HCC.

DNA damage sensor γ -H2AX is increased in preneoplastic lesions of hepatocellular carcinoma.

BACKGROUND: Phosphorylated histone H2AX ( γ -H2AX) is a potential regulator of DNA repair and is a useful tool for detecting DNA damage. To evaluate the clinical usefulness of γ -H2AX in hepatocellular carcinoma (HCC), we measured the level of γ -H2AX in HCC, dysplastic nodule, and nontumorous liver diseases. METHODS: The level of γ -H2AX was measured by immunohistochemistry in fifty-eight HCC, 18 chronic hepatitis, 22 liver cirrhosis, and 19 dysplastic nodules. Appropriate cases were also examined by fluorescence analysis and western blotting. results: All cases with chronic liver disease showed increased levels of γ -H2AX expression. In 40 (69.9%) of 58 cases with HCC, the labeling index (LI) of γ -H2AX was above 50% and was inversely correlated with the histological grade. Mean γ -H2AX LI was the highest in dysplastic nodule (74.1 ± 22.1%), which was significantly higher than HCC (P < 0.005). Moreover, γ -H2AX was significantly increased in nontumorous tissues of HCC as compared with liver cirrhosis without HCC (62.5 ± 24.7%, from 5.1 to 96.0%, P < 0.005). CONCLUSIONS: γ -H2AX was increased in the preneoplastic lesions of HCC and might be a useful biomarker for predicting the risk of HCC.

Clinical significance of cell cycle inhibitors in hepatocellular carcinoma.

It is well accepted that cell cycle regulators are strongly implicated in the progression of cancer development. p16 and p27 are potent cyclin-dependent kinase (CDK) inhibitors involved in G1 phase progression, and are regarded as adverse prognostic biomarkers for various types of cancers. It has been reported that the main mechanism for p16 inactivation is aberrant DNA methylation, while p27 is exclusively inactivated by proteasome-mediated protein degradation. We have found that p27 is decreased in around half of hepatocellular carcinomas (HCCs), and in some cases p27 is inactivated by inappropriate interaction with cyclin D1/CDK4 complexes. In such cases, p16 is concomitantly inactivated through DNA methylation. Taking into consideration the complex interaction between p16 and p27, a comprehensive analysis including p16 and p27 would be useful for predicting the prognosis of HCC patients.

Hepatitis B virus X stimulates redox signaling through activation of ataxia telangiectasia mutated kinase.

Hepatitis B virus X (HBX) protein plays a crucial role in carcinogenesis, but its mechanism is unclear. The involvement of ataxia telangiectasia mutated (ATM) kinase in the enhanced redox system was investigated by examining the phosphorylation level of ATM in HBX gene-transfected cells and in transgenic mice following redox system manipulation by treatment with hydrogen peroxide (H2O2) or antioxidant. Western blotting and immunostaining showed that phospho-ATM was significantly increased by HBX both in vitro (3.2-fold; p<0.05) and in vivo (4-fold; p<0.05), and this effect was abrogated by antioxidant treatment. The level of PKC-δ in HBX-expressing cells was increased 3.5-fold compared to controls. Nuclear localized NF-E2-related factor 2 (Nrf2) was increased in HBX-expressing cells exposed to H2O2, but remained at lower levels after the treatment with rottlerin, KU55933, or caffeine. The levels of anti-oxidant molecules were increased in HBX expressing cells and in transgenic mice, indicating that HBX stimulates the Nrf2-mediated redox system. The levels of intracellular reactive oxygen species (ROS) were significantly increased in HBX-expressing cells treated with hydrogen peroxide in the presence of ATM inhibitor KU55933 or caffeine. Treatment of HBX-expressing cells with KU55933 or caffeine before the exposure to H2O2 increased the ratio of cell apoptosis to 33±4% (p<0.05) and 22±4% (p<0.05), respectively. Collectively, HBX stimulates the ATM-mediated PKC-δ/Nrf2 pathway, and maintains the enhanced activity of the redox system. Therefore, manipulating ATM kinase activity might be a useful strategy for treating HBX-induced carcinogenesis.

Mycotoxins are conventional and novel risk biomarkers for hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a common malignant disease with poor prognosis. To improve the clinical outcome, early diagnosis of HCC arising from nonviral agents and hepatitis virus is important. Among several etiological factors, mycotoxins defined as carcinogens by the International Agency for Research in Cancer (IARC) might be one of the critical risk factors for nonviral HCC. Aflatoxin B1 is the most well-known carcinogenic mycotoxin for HCC, but the role of the other types of mycotoxin remains unclear. Several studies have reported that a chromatographic separation technique based on high-performance liquid chromatography can successfully detect the concentration of mycotoxins in plasma. Recently, serum level of ochratoxin A (OTA), a widely distributed mycotoxin classified as Group 2B by IARC, was evaluated in HCC patients in Egypt. The results suggested that serum OTA levels might be a good biomarker for HCC. In this article, we review recent studies of OTA, and discuss its possible significance as a biomarker of HCC.

Blockade of ataxia telangiectasia mutated sensitizes hepatoma cell lines to sorafenib by interfering with Akt signaling.

Sorafenib is a multi-kinase inhibitor applicable to hepatocellular carcinoma (HCC), but its limited therapeutic effects are a major problem to be solved. Here, we show that blockade of ataxia telangiectasia mutated (ATM) improves the antitumor effects of sorafenib. When hepatoma cell lines HepG2 and PLC/PRF/5 were treated with sorafenib plus ATM small inhibitory RNAs, ATM inhibitor KU55933 or caffeine, Akt signaling was suppressed and the cytotoxic effects were significantly potentiated. Moreover, ATM inhibition effectively suppressed the sorafenib-induced cell migration. Taken together, manipulation of ATM activity might be a useful strategy for improving sorafenib treatment of HCC.

Multidrug resistance-associated protein 2 determines the efficacy of cisplatin in patients with hepatocellular carcinoma.

We hypothesized that expression of multidrug resistance-associated protein 2 (MRP2), a major cisplatin transporter, may determine the efficacy of cisplatin as a treatment for patients with hepatocellular carcinoma (HCC). A prospective analysis was conducted of 49 consecutive patients who underwent resection for HCC (16 patients treated with cisplatin-based neoadjuvant chemotherapy and 33 patients treated without neoadjuvant chemotherapy). Expression of MRP2 in resected specimens was assessed by immunohistochemical and Western blot analyses. The extent of tumor necrosis was assessed histologically in the greatest dimension of the tumor specimen from each patient. The median percentage of tumor necrosis was 81% (range: 0-100%) and complete tumor necrosis was found in 3 patients. Overexpression of MRP2 was detected in 24/46 (52%) tumor specimens. In 16 patients treated with cisplatin, tumor size and dose of cisplatin did not correlate with tumor necrosis of the resected specimens (P=0.706 and P=0.555, respectively). Of 13 tumor specimens containing vivid tumor from 16 patients treated with cisplatin, 8 had overexpression of MRP2. Tumor specimens with overexpression of MRP2 showed a lower percentage of tumor necrosis than those with non-overexpression (median percentage of tumor necrosis, 19% vs. 99%, P=0.003). In conclusion, overexpression of MRP2 correlates with a lower percentage of tumor necrosis in patients treated with cisplatin-based neoadjuvant chemotherapy for HCC, whereas either tumor size or dose of cisplatin does not. Expression of MRP2 determines the efficacy of cisplatin-based chemotherapy in patients with HCC.