p73β inhibits transcriptional activities of enhancer I and X promoter in hepatitis B virus more efficiently than p73α

The effects of HBx gene on the expression of DNA repair enzymes hOGG1 and hMYHalpha mRNA in HepG2 cells

To observe the alteration in the expression of DNA repair enzymes hOGG1 and hMYHalpha and the change in 8-OHdG levels in the HBx gene-transfected cells HepG2/HBx and to explore the mechanisms of the HBV-associated hepatocellular carcinoma, the gene-transfected cells HepG2/HBx which stably expressed HBx was established, and the effect of HBx on the cell cycle and proliferation of HepG2 was examined. By using the beta-actin as the interior control, real-time polymerase chain reaction (Real-time qPCR) was employed to quantitatively detect the expression of DNA repair enzymes hOGG1 and hMYHalpha in the HepG2/HBx, the control cells HepG2 and HepG2 transfected with pcDNA3.1 vector (HepG2/pDNA3.1). The 8-OHdG levels were determined by HPLC/ECD in the established gene-transfected cells HepG2/HBx and the control cells HepG2 and HepG2/pcDNA3.1. Our results showed that the expression of DNA repair enzyme hMYHalpha in the HepG2/HBx (0.021+/-0.007) was significantly lower than that of HepG2 (0.099+/-0.041) (P<0.05) and HepG2/pDNA3.1 (0.121+/-0.005) (P<0.05). However, the no significant differences existed in the expression of DNA repair enzyme hOGG1 among the three cell strains (P>0.05). The 8-OHdG level in the HepG2/HBx was significantly higher than that in HepG2 and HepG2/pcDNA3.1 (P<0.05). It is concluded that HBx gene may inhibit the expression of DNA repair enzyme hMYHalpha mRNA to impair the ability to repair the intracellular DNA oxidative damage, to increase the oxidative DNA-adduct 8-OHdG and to affect the nucleotide excision repair function, thus participate in the occurrence and development of hepatocellular carcinoma.

Hepatitis B virus X protein sensitizes cells to starvation-induced autophagy via up-regulation of beclin 1 expression

Human beclin 1 is the first identified mammalian gene to induce autophagy. It is commonly expressed at reduced levels in breast tumors; however, it is overexpressed in hepatitis B virus (HBV)-infected cancerous liver tissues. To expose the possible mechanism and biological significance of this up-regulation of beclin 1, we investigated the regulation of beclin 1 expression by HBV x protein (HBx) in hepatic or hepatoma cell lines. Here, we showed that enforced expression of HBx by transfection technology results in the up-regulation of the endogenous messenger RNA (mRNA) and protein levels of Beclin 1 in the tested cells. Using a luciferase- reporter assay, we demonstrated that HBx transactivates beclin 1 promoter activity in a dose-dependent manner. The promoter region of the beclin 1 gene identified in this study is located at nt -277/+197 and has the maximum transcriptional activity. HBx-mediated up-regulation of beclin 1 expression might be direct, that is, via its promoter. Furthermore, the cells that transiently or stably expressed HBx showed an enhanced accumulation of vacuoles carrying the autophagy marker LC3 as compared with the control cells, which was induced by nutrient starvation, indicating HBx-enhanced autophagy. Moreover, this enhanced autophagy occurred in HepG2.2.15 cells that replicate HBV and in cells transfected with HBV genomic DNA, suggesting that HBV infection also causes increased levels of autophagy under starvation conditions. Treatment of cells with beclin 1 small interfering RNA (siRNA) blocked HBx-enhanced autophagy, demonstrating that the function of HBx in influencing autophagy is Beclin 1 dependent.

CONCLUSION

Our findings suggest a novel function of HBx in increasing autophagy through the up-regulation of beclin1 expression, and this may provide an important mechanism in HBV-infected hepatocytes growing under nutrient-deficient conditions.

Molecular mechanism of p73-mediated regulation of hepatitis B virus core promoter/enhancer II: implications for hepatocarcinogenesis

Hepatitis B virus (HBV) is a causative agent of chronic hepatitis and hepatocellular carcinoma. Recent findings demonstrating p73 and specifically N-terminally truncated p73 (DeltaTAp73) accumulation in hepatocellular carcinoma suggest that p73 plays a role in the malignant phenotype. Here, we investigated the mechanism of HBV pregenomic core promoter/enhancer II (cp/EII) regulation by full-length TAp73 and its oncogenic counterpart DeltaTAp73. Ectopic and endogenous expression of TAp73 leads to a significant downregulation of cp/EII activity in p53-deficient hepatoma cell lines. In contrast, overexpression of DeltaTAp73 results in significant cp/EII activation and increased HBV core (HBc) expression. TAp73-mediated repression of HBV transcription was substantially abolished by DeltaTAp73. We show that both TAp73 and DeltaTAp73 proteins directly bind to the Sp1 transcription factor, a key stimulator of HBV gene expression. However, only TAp73 abolishes Sp1 binding to cp/EII, whereas the DeltaTAp73-Sp1 complex further persists on the DNA. The inhibitory effect of p53/p73 on HBc expression is associated with the inhibition of viral replication, while DeltaTAp73 is not. These data strongly support the fact that the p73-isoform-related interaction with Sp1 is the underlying mechanism of the diverse outcome on HBc expression, suggesting a new mechanism by which oncogenic DeltaTAp73 could enhance the carcinogenic process in liver cells.

Construction of hepatitis B virus X gene expression vector in eucaryotic cells and its transfection in HL-7702 cells

AIM: To establish a human hepatocyte cell line which can express hepatitis B virus (HBV) X gene.

METHODS: HBV X gene was obtained through PCR techn-ology. After A-tailing added, X gene was connected into vector PUCmT. Vector PUCmT-X and PcDNA3 were digested with EcoRI and HindIII. The fragments of X and PcDNA3 were connected to establish reconstituted plasmid PcDNA3-X. Then PcDNA3-X and PcDNA3 were transfected into HL-7702 cells by lipid-mediated transfection. After selected with G418, HL-7702/HBx cells were analysed by the reverse transcription-PCR to confirm the steady expression of X gene in HL-7702.

RESULTS: Reconstituted plasmid PcDNA3-X included the anticipated fragment of HBV X gene was proved by auto-sequencing assay. RT-PCR analysis showed that reconstituted plasmid PcDNA3-X could express the X protein efficiently in HL-7702 cells.

CONCLUSION: Hepatocyte can express HBV X gene, which is an ideal model to study the effect of HBV X gene on the development of hepatitis and hepatocelular carcinoma.

Overexpression of HBxAg in hepatocellular carcinoma and its relationship with Fas/FasL system

AIM: To study the expression and serum level of HBxAg, Fas and FasL in tissues of HCC patients, and to assess the relationship between HBxAg and Fas/FasL system.

METHODS: Tissues from 50 patients with HCC were tested for the expression of HBxAg, Fas and FasL by S-P immunohistochemistry. Serum levels of sFas/sFasL and HBsAg/HBeAg were measured by ELISA assay. HBV X gene was detected by PCR in serum and confirmed by automatic sequencing. Fifty cases of liver cirrhosis and 30 normal controls were involved in serum analysis.

RESULTS: The expression of HBxAg, Fas and FasL in carcinoma tissues was 96%, 84% and 98%, respectively. Staining of HBxAg, Fas and FasL was observed predominately in cytoplasms, no significant difference was found in intensity between HBxAg, Fas and FasL (P > 0.05). HBxAg, Fas and FasL might express in the same area of carcinoma tissues and this co-expression could be found in most patients with HCC. The mean levels of sFas in serum from HCC, cirrhosis and normal controls were 762.29 ± 391.56 μg·L^-1, 835.36 ± 407.33 μg·L^-1 and 238.27 ± 135.29 μg·L^-1. The mean levels of sFasL in serum from HCC, cirrhosis and normal controls were 156.36 ± 9.61 μg·L^-1, 173.63 ± 18.74 μg·L^-1 and 121.96 ± 7.83 μg·L^-1. Statistical analysis showed that both sFas and sFasL in HCC and cirrhosis patients were significantly higher than those in normal controls (P < 0.01). Serum HBV X gene was found in 32% of HCC patients and 46% of cirrhotic patients. There was no significant relationship between serum level of sFas/sFasL and serum X gene detection (P > 0.05). Eight percent of HCC patients with negative HBsAg and HBeAg in serum might have X gene in serum and HBxAg expression in carcinoma tissues.

CONCLUSION: Our data suggest that HBxAg and Fas/FasL system plays an important role in the development of human HCC. Expression of HBxAg can leads to expression of Fas/ FasL system which and reverse apoptosis of hepatocellular carcinoma induced by FasL.

Study on X gene mutation of hepatitis B virus from patients with hepatocellular carcinoma

AIM

To study the association of mutations of hepatitis B virus(HBV) X gene with hepatocellular carcinoma(HCC).

METHODS

The complete X region of HBV from the serum of 5 patients with HCC and 12 patients with chronic hepatitis B (CH) was amplified by PCR and then the purified PCR products were sequenced.

RESULTS

A comparison of 492bp nucleotide sequence of the HBV X gene from 5 HCC patients with that of the several previously reported isolates of different serotype in Genebank showed that the nucleotide homology was 89-96 % and most of the strains were similar to serotype adw. The number of nucleotide changes in the X gene of HBV from HCC group (19.4±12.1) was significantly greater than that from the CH group (4.4±2.4, P =0.00 093).There were 4 models of substitutions in X gene and 6 hot spots found in HCC group and 12 hot spots found in HCC group.

CONCLUSION

The mutations of HBV X gene may be closely associated with the development of HCC.

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