Epigenetic modulation of insulin-like growth factor-II overexpression by hepatitis B virus X protein in hepatocellular carcinoma.

Hepatitis B virus X protein (HBx) is involved in the pathogenesis of hepatocellular carcinoma (HCC). Overexpression of the transcripts from the P3 and P4 promoters of the insulin-like growth factor-II (IGF-II) gene is observed in HCC. The present study investigated the involvement of HBx in IGF-II overexpression and its epigenetic regulation. Firstly, the effects of HBx on P3 and P4 mRNA expression, the methylation status of the P3 and P4 promoters, and MBD2 expression were analyzed in human HCC cells and HCC samples. Next, interaction between HBx and MBD2 or CBP/p300 was assessed by co-immunoprecipitation, and HBx-mediated binding of MBD2 and CBP/p300 to the P3 and P4 promoters and the acetylation of the corresponding histones H3 and H4 were evaluated by quantitative chromatin immunoprecipitation. Finally, using siRNA knockdown, we investigated the roles of MBD2 and CBP/p300 in IGF-II overexpression and its epigenetic regulation. Our results showed that HBx promotes IGF-II expression via inducing the hypomethylation of the P3 and P4 promoters, and that HBx increases MBD2 expression, directly interacts with MBD2 and CBP/p300, and elevates their recruitment to the hypomethylated P3 and P4 promoters with increased acetylation levels of the corresponding histones H3 and H4. Further results showed that endogenous MBD2 and CBP/p300 are necessary for HBx-induced IGF-II overexpression and that CBP/p300 presence and CBP/p300-mediated acetylation of histones H3 and H4 are partially required for MBD2 binding and its demethylase activity. These data suggest that HBx induces MBD2-HBx-CBP/p300 complex formation via interaction with MBD2 and CBP/p300, which contributes to the hypomethylation and transcriptional activation of the IGF-II-P3 and P4 promoters and that CBP/p300-mediated acetylation of histones H3 and H4 may be a rate-limiting step for the hypomethylation and activation of these two promoters. This study provides an alternative mechanism for understanding the pathogenesis of HBx-mediated HCC.

[The construction of IGF-II P4 promoter-driven tk expression vector].

OBJECTIVE: To investigate the selective killing effect of herpes simplex virus-thymidine kinase/ganciclovir (HSV-tk/GCV) suicide gene system controlled by human IGF-II P4 promoter on HCC cells in vitro. METHODS: Recombinant shuttle plasmid vectors driven by IGF-II P4 promoter and driven by CMV promoter were constructed by techniques of gene recombination. The recombinant shuttle plasmids were then transfected into HepG2 and HeLa cells by techniques of lipidosome transfection. EGFP expression was detected by fluoroscopy. Tk and EGFP mRNA expression were detected by RT-PCR. The selective killing effect after GCV application was determined with MTT method. Statistical analysis was performed with ANOVA analysis. RESULTS: Identification of pDC316-tkEGFP-P4 by enzyme digestion and sequencing analysis showed that the construction of the recombinant shuttle plasmid was correct. It was found that green fluorescence protein could only be seen in HepG2 cells, not in HeLa cells. The results of RT-PCR showed only two bands could be seen in the samples of pDC316-tkEGFP-P4 transfected HepG2 cells. The growth of HepG2 cells transfected with pDC316-tkEGFP-CMV and pDC316-tkEGFP-P4 were inhibited remarkably, the growth inhibition rates were 6.95% +/- 0.67%, 24.99% +/- 1.53%, 49.68% +/- 1.68%, 71.85% +/- 3.28% and 4.83% +/- 0.35% vs 17.34% +/- 1.15%, 30.17% +/- 1.30%, 40.39% +/- 0.82% (F = 24.055, P < 0.05), respectively. The growth of HeLa cells transfected with pDC316-tkEGFP-CMV were also inhibited, the growth inhibition rates were 6.36% +/- 0.83%, 23.95% +/- 1.72%, 45.13% +/- 1.64% and 69.38% +/- 3.17%, respectively. The growth of HeLa cells transfected with pDC316-tkEGFP-P4 was not inhibited. The growth inhibition rates were 0.91 +/- 0.04, 1.18 +/- 1.32, 1.19 +/- 0.10 and 1.32 +/- 0.05 (F = 26.469, P < 0.01) , respectively. CONCLUSION: The shuttle plasmid vector carrying the tkEGFP fusion protein gene driven by IGF-II P4 promoter has been constructed successfully and its specific expression in HepG2 cells provided the basis for targeted gene therapy for HCC.

Hypomethylated P4 promoter induces expression of the insulin-like growth factor-II gene in hepatocellular carcinoma in a Chinese population.

PURPOSE: The expression of human insulin-like growth factor-II (IGF-II) is regulated by the activation of four promoters (P1-P4) acting in a development-dependent, tissue-specific manner. IGF-II overexpression associated with P3 and P4 activation is observed in animal and human hepatocarcinogenesis. We correlated P4 epigenetic alteration with P4 transcript activation and clinicopathologic features. EXPERIMENTAL DESIGN: We analyzed P4 epigenetic alteration using methylation-specific PCR in 34 hepatocellular carcinoma (HCC) specimens, 34 matched adjacent nontumor specimens, and 8 normal adult liver specimens. The data were correlated with activation of P4 transcription by using reverse transcription-PCR. Epigenetic alteration was compared with patients' clinicopathologic features. RESULTS: Compared with normal liver tissue, hypomethylation of P4 CpG islands was significantly more frequent in HCC (P = 0.03) and matched tissues (P = 0.047). P4 mRNA levels in HCC with unmethylated alleles were significantly higher than in HCC without unmethylated alleles (P = 0.001); P4 mRNA levels in matched nontumor tissues with unmethylated alleles were significantly higher than in matched nontumor tissues without unmethylated alleles (P = 0.005). P4 hypomethylation in HCC was associated with portal vein tumor embolus (P = 0.017) and poorer tumor differentiation (P = 0.025). CONCLUSIONS: These findings suggest that IGF-II P4 hypomethylation may be an early and frequent event and that it may contribute to P4 transcription expression activation during the transformation of a premalignant liver lesion to HCC. Furthermore, aberrant hypomethylation of P4 CpG islands not only may play an important role during hepatocarcinogenesis but might also be a useful biomarker for poor prognosis of patients with HCC.

Differential promoter usage for insulin-like growth factor-II gene in Chinese hepatocellular carcinoma with hepatitis B virus infection.

BACKGROUND: Human insulin-like growth factor-II (IGF-II) gene contains nine exons and four different promoters (P1-P4). Expression of the gene is elevated in the preneoplastic hepatic foci and hepatocellular carcinoma (HCC) of experimental animals and humans. To gain insight into transcriptional regulation of the gene in HCC, we analyzed the relative usage of the P1-P4 promoters and its correlation with the clinical and pathological characteristics in Chinese hepatocellular carcinoma with hepatitis B virus (HBV) infection. METHODS: P1-P4 usage levels of the gene in tumorous and matched adjacent nontumorous tissues from 23 HCC patients and 7 normal liver tissues were evaluated using a semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) assay. The mutation status of p53 gene in HCC tissues was analyzed by PCR and sequencing. RESULTS: Transcripts from P1 were not detectable in 65.2% HCC tissues, and were expressed at low levels or not expressed in all nontumorous tissues compared with normals, but P2 usage levels showed no differences. P3 and P4 expression was significantly increased in most of HCC and almost all adjacent nontumorous tissues. There was a positive association of expression levels of both P3 and P4 transcripts in HCC tissues with the p53 mutation and presence of tumor embolus of portal vein, and expression of P3 were negatively related to differentiation of HCC. However, expression of both P3 and P4 was not associated with other parameters. CONCLUSIONS: Loss of P1 activity and reactivation of P3 and P4 are important characteristics in most of Chinese HCC with HBV infection, and increased IGF-II expression from P3 and P4 may play an active role in early proliferation of precancerous liver cells and hepatocarcinogenesis of these cases. Significant increase in fetal transcripts is associated with the p53 mutation and poor prognosis of the HCC patients and might serve as one of identification parameters of poor HCC prognosis.

[Construction of a plasmid vector of fused protein genes driven by human insulin-like growth factor II P3 promoter].

OBJECTIVE: To construct a shuttle plasmid vector of fused herpes simplex virus thymidine kinase (HSV-tk) gene and enhanced green fluorescent protein (EGFP) gene driven by human insulin-like growth factor II (IGF-II) P3 promoter, and investigate the special killing effect of the HSV-tk/ganciclovir (GCV) system on hepatocellular carcinoma (HCC) cells. METHODS: An adenovirus shuttle plasmid, pDC316-tkEGFP-CMV containing fused genes tkEGFP and an adenovirus shuttle plasmid pDC316-tkEGFP-P3 driven by IGF-II P3 promoter were constructed by techniques of gene recombination and screening, and identified by restriction digestion and sequencing analysis. Human hepatocellular carcinoma cells HepG2 and human cervical carcinoma cells HeLa were cultured and transfected with these 2 recombinant shuttle plasmids. RT-PCR was used to detect the mRNA expression of EGFP and HSV/tk. GCV of the final concentrations of 0, 1, 10, and 100 microg/ml respectively was added into the culture fluid of the HepG2 cells transfected with pDC316-tkEGFP-CMV or pDC316-tkEGFP-P3, and MTT method was used to detect the cell inhibition rate. RESULTS: Digestion and sequencing analysis showed that the recombinant plasmid pDC316-tkEGFP-P3 accorded with the design. Fluorescent microscopy showed that EGFP was expressed only in the HepG2 cells, but not in the HeLa cells. RT-PCR showed that mRNA expression of EGFP and HSV/tk could be seen in both HepG2 and HeLa cells transfected with pDC316-tkEGFP-CMV or pDC316-tkEGFP-P3, however, only in the pDC316-tkEGFP-P3 transfected HepG2 cells, but not in the HeLa cells transfected with pDC316-tkEGFP-P3. MTT assay showed that GCV dose-dependently inhibited the 2 cancer cells, the inhibition rates of GCV of the final concentrations of 1, 10, and 100 microg/ml were 24.1% +/- 1.9%, 45.1% +/- 1.7%, and 69.4% +/- 3.6% in the HepG2 cells, and 25.1% +/- 1.6%, 49.3% +/- 1.1%, and 72.2% +/- 2.9% in the HeLa cells. However, the inhibition rates of the pDC316-tkEGFP-P3-transfected HepG2 cells by GCV of the final concentrations of 1, 10, and 100 microg/ml wee 19.8% +/- 1.3%, 36.2% +/- 2.0% and 48.7% +/- 1.9% respectively, all significantly lower than those of the pDC316-tkEGFP-CMV-transfected HepG2 cells (all P < 0.01), and no significant cell inhibition was found in the HeLa cells transfected with pDC316-tkEGFP-CMV. CONCLUSION: A shuttle plasmid vector containing the tkEGFP fusion protein gene driven by IGF-II P3 promoter has been constructed successfully and its specific expression in HepG2 cells provides a sound basis for targeted gene therapy for HCC.