Hepatitis B virus X protein induces p16 gene promoter methylation through upregulation of DNA methylation transferases DNMT1 and DNMT3A.

BACKGROUND: As a tumor suppressor, p16 can competitively block the cyclin D1-CDK4/6 complex to arrest the cell cycle in the G1 phase. Lack of p16 gene expression can lead to infinite cell proliferation and malignant transformation. OBJECTIVES: To determine whether the hepatitis B virus X protein (HBx) regulates the methylation and expression of the p16 gene. MATERIAL AND METHODS: We constructed a eukaryotic expression vector carrying the HBx gene and green fluorescent protein (GFP), and transfected it into HepG2 cells to build cell lines stably expressing GFP and GFP-HBx. The p16 protein level and p16 gene methylation were measured in these cell lines. We further detected the mRNA expression of DNA methyltransferases (DNMTs) 1, 3A and 3B. The DNMT1, DNMT3A and DNMT3B gene promoter sequences were inserted into a reporter vector (pGL3-Basic) to build recombinant vectors, which were then transiently transfected into different cell lines. After 48 h, the luciferase activity was measured. RESULTS: The level of p16 protein in GFP-HBx/HepG2 cells was significantly lower than in HepG2 and GFP/HepG2 cells. The CpG methylation was present in the p16 gene promoter region of GFP-HBx/HepG2 cells. The DNMT1 and DNMT3A mRNA levels in GFP-HBx/HepG2 cells were significantly elevated compared to that in the HepG2 cells (p = 0.0495). The luciferase activity in GFP-HBx/HepG2 cells transfected with the pGL3-DNMT1/3A pro plasmid was significantly higher than in HepG2 and GFP/HepG2 cells (both p < 0.05). CONCLUSIONS: The HBx can induce p16 gene promoter methylation and inhibit the expression of p16 in HepG2 cells. This occurs due to HBx activation of DNMT1 and DNMT3A promoters and the induction of p16 promoter methylation, which downregulates the expression of p16 protein.

Effect of hepatitis B virus X in inhibiting the apoptosis of trophoblastic cells and its potential mechanism / 西安交通大学学报(医学版)

【Objective】 To investigate the relationship between hepatitis B virus X （HBx） protein and EGFR promoter， and the role of HBx protein in activating EGFR/PI3K/p-Akt signaling pathway and inhibiting apoptosis. 【Methods】 EGFR promoter plasmids were constructed and the relationship between HBx and EGFR promoters was characterized using a luciferase reporter assay. EGFR-overexpressing trophoblast cells were constructed， and EGFR expression in the overexpressing cells was knocked down using EGFR shRNA. The expression and localization of EGFR/PI3K/p-Akt were detected by Western blotting and confocal laser microscopy. Cell apoptosis was analyzed using flow cytometry. HBV plasmids carrying either full-length HBx or HBx with a deletion mutation （ΔHBx） and HBx plasmids were transfected into two types of trophoblast cells； HBx and PI3K/p-Akt protein expressions were detected by Western blotting. Cell apoptosis was analyzed using flow cytometry. 【Results】 Co-transfection of HBx and EGFR promoter plasmids in JEG-3 and HTR-8/Svneo cells significantly elevated the expression of EGFR promoter driven luciferase compared with the control group （P<0.01）. In EGFR-overexpressing cells， the expression of PI3K/p-Akt was significantly increased （P<0.01）， whereas the apoptosis rate was significantly decreased for JEG-3 cells and HTR-8/Svneo cells （both P<0.01）. These results were reversed in the EGFR-knock down group. When the intracellular HBx protein was expressed in JEG-3 and HTR-8 cells， PI3K/p-Akt protein expression was significantly increased （both P<0.05）， and the proportion of apoptosis was significantly decreased （both P<0.05）. 【Conclusion】 In placental trophoblast cells， HBx protein activates the expression of EGFR by acting on the EGFR promoter， and inhibits the apoptosis of trophoblast cells via the downstream EGFR/PI3K/p-Akt signaling pathway.

Detection of hyper-conserved regions in hepatitis B virus X gene potentially useful for gene therapy.

AIM: To detect hyper-conserved regions in the hepatitis B virus (HBV) X gene (HBX) 5' region that could be candidates for gene therapy. METHODS: The study included 27 chronic hepatitis B treatment-naive patients in various clinical stages (from chronic infection to cirrhosis and hepatocellular carcinoma, both HBeAg-negative and HBeAg-positive), and infected with HBV genotypes A-F and H. In a serum sample from each patient with viremia > 3.5 log IU/mL, the HBX 5' end region [nucleotide (nt) 1255-1611] was PCR-amplified and submitted to next-generation sequencing (NGS). We assessed genotype variants by phylogenetic analysis, and evaluated conservation of this region by calculating the information content of each nucleotide position in a multiple alignment of all unique sequences (haplotypes) obtained by NGS. Conservation at the HBx protein amino acid (aa) level was also analyzed. RESULTS: NGS yielded 1333069 sequences from the 27 samples, with a median of 4578 sequences/sample (2487-9279, IQR 2817). In 14/27 patients (51.8%), phylogenetic analysis of viral nucleotide haplotypes showed a complex mixture of genotypic variants. Analysis of the information content in the haplotype multiple alignments detected 2 hyper-conserved nucleotide regions, one in the HBX upstream non-coding region (nt 1255-1286) and the other in the 5' end coding region (nt 1519-1603). This last region coded for a conserved amino acid region (aa 63-76) that partially overlaps a Kunitz-like domain. CONCLUSION: Two hyper-conserved regions detected in the HBX 5' end may be of value for targeted gene therapy, regardless of the patients' clinical stage or HBV genotype.

Nuclear Expression of Hepatitis B Virus X Protein Is Associated with Recurrence of Early-Stage Hepatocellular Carcinomas: Role of Viral Protein in Tumor Recurrence.

BACKGROUND: Hepatitis B virus (HBV) plays well-known roles in tumorigenesis of hepatocellular carcinoma (HCC) in infected patients. However, HBV-associated protein status in tumor tissues and the relevance to tumor behavior has not been reported. Our study aimed to examine the expression of HBV-associated proteins in HCC and adjacent nontumorous tissue and their clinicopathologic implication in HCC patients. METHODS: HBV surface antigen (HBsAg), HBV core antigen (HBcAg), and HBV X protein (HBx) were assessed in 328 HBV-associated HCCs and in 155 matched nontumorous tissues by immunohistochemistry staining. RESULTS: The positive rates of HBsAg and cytoplasmic HBx staining in tumor tissue were lower than those in nontumorous tissue (7.3% vs. 57.4%, p < .001; 43.4% vs. 81.3%, p < .001). Conversely, nuclear HBx was detected more frequently in tumors than in nontumorous tissue (52.1% vs. 30.3%, p < .001). HCCs expressing HBsAg, HBcAg, or cytoplasmic HBx had smaller size; lower Edmondson-Steiner (ES) nuclear grade, pT stage, and serum alpha-fetoprotein, and less angioinvasion than HCCs not expressing HBV-associated proteins. Exceptionally, nuclear HBx-positive HCCs showed higher ES nuclear grade and more frequent large-vessel invasion than did nuclear HBx-negative HCCs. In survival analysis, only nuclear HBx-positive HCCs had shorter disease-free survival than nuclear HBx-negative HCCs in pT1 and ES nuclear grade 1-2 HCC subgroup (median, 126 months vs. 35 months; p = .015). CONCLUSIONS: Our data confirmed that expression of normal HBV-associated proteins generally decreases in tumor cells in comparison to nontumorous hepatocytes, with the exception of nuclear HBx, which suggests that nuclear HBx plays a role in recurrence of well-differentiated and early-stage HCCs.

Nuclear Expression of Hepatitis B Virus X Protein Is Associated with Recurrence of Early-Stage Hepatocellular Carcinomas: Role of Viral Protein in Tumor Recurrence

BACKGROUND: Hepatitis B virus (HBV) plays well-known roles in tumorigenesis of hepatocellular carcinoma (HCC) in infected patients. However, HBV-associated protein status in tumor tissues and the relevance to tumor behavior has not been reported. Our study aimed to examine the expression of HBV-associated proteins in HCC and adjacent nontumorous tissue and their clinicopathologic implication in HCC patients. METHODS: HBV surface antigen (HBsAg), HBV core antigen (HBcAg), and HBV X protein (HBx) were assessed in 328 HBV-associated HCCs and in 155 matched nontumorous tissues by immunohistochemistry staining. RESULTS: The positive rates of HBsAg and cytoplasmic HBx staining in tumor tissue were lower than those in nontumorous tissue (7.3% vs. 57.4%, p < .001; 43.4% vs. 81.3%, p < .001). Conversely, nuclear HBx was detected more frequently in tumors than in nontumorous tissue (52.1% vs. 30.3%, p < .001). HCCs expressing HBsAg, HBcAg, or cytoplasmic HBx had smaller size; lower Edmondson-Steiner (ES) nuclear grade, pT stage, and serum alpha-fetoprotein, and less angioinvasion than HCCs not expressing HBV-associated proteins. Exceptionally, nuclear HBx-positive HCCs showed higher ES nuclear grade and more frequent large-vessel invasion than did nuclear HBx-negative HCCs. In survival analysis, only nuclear HBx-positive HCCs had shorter disease-free survival than nuclear HBx-negative HCCs in pT1 and ES nuclear grade 1-2 HCC subgroup (median, 126 months vs. 35 months; p = .015). CONCLUSIONS: Our data confirmed that expression of normal HBV-associated proteins generally decreases in tumor cells in comparison to nontumorous hepatocytes, with the exception of nuclear HBx, which suggests that nuclear HBx plays a role in recurrence of well-differentiated and early-stage HCCs.

Autophagy and apoptosis in liver injury.

Apoptosis is a primary characteristic in the pathogenesis of liver disease. Hepatic apoptosis is regulated by autophagic activity. However, mechanisms mediating their interaction remain to be determined. Basal level of autophagy ensures the physiological turnover of old and damaged organelles. Autophagy also is an adaptive response under stressful conditions. Autophagy can control cell fate through different cross-talk signals. A complex interplay between hepatic autophagy and apoptosis determines the degree of hepatic apoptosis and the progression of liver disease as demonstrated by pre-clinical models and clinical trials. This review summarizes recent advances on roles of autophagy that plays in pathophysiology of liver. The autophagic pathway can be a novel therapeutic target for liver disease.

Hepatitis B virus X protein promotes hepatocellular carcinoma transformation through interleukin-6 activation of microRNA-21 expression.

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and chronic hepatitis B virus (HBV) infection is the major risk factor of HCC. The virus encodes HBV X (HBx) protein that plays a critical role in the development of HCC. Studies have revealed numerous HBx-altered genes and signalling pathways that heavily contribute to tumourigenesis of non-tumour hepatocytes. However, the role of HBx in regulating other critical gene regulators such as microRNAs is poorly understood, which impedes the exploration of a complete HBx-associated carcinogenic network. Besides, critical microRNAs that drive the transformation of non-tumour hepatocytes are yet to be identified. Here, we overexpressed C-terminal truncated HBx protein in a non-tumour hepatocyte cell line MIHA, and measured a panel of cancer-associated miRNAs. We observed that oncogenic miR-21 was upregulated upon ectopic expression of this viral protein variant. HBx-miR-21 pathway was prevalent in HCC cells as inhibition of HBx in Hep3B and PLC/PRF/5 cells significantly suppressed miR-21 expression. Subsequently, we showed that the upregulation of miR-21 was mediated by HBx-induced interleukin-6 pathway followed by activation of STAT3 transcriptional factor. The high dependency of miR-21 expression to HBx protein suggested a unique viral oncogenic pathway that could aberrantly affect a network of gene expression. Importantly, miR-21 was essential in the HBx-induced transformation of non-tumour hepatocytes. Inhibition of miR-21 effectively attenuated anchorage-independent colony formation and subcutaneous tumour growth of MIHA cells. Our study suggested that overexpression of miR-21 was critical to promote early carcinogenesis of hepatocytes upon HBV infection.

Unraveling the complexity of hepatitis B virus: from molecular understanding to therapeutic strategy in 50 years.

Hepatitis B virus (HBV) is a well-known hepadnavirus with a double-stranded circular DNA genome. Although HBV was first described approximately 50 years ago, the precise mechanisms of HBV infection and effective therapeutic strategies remain unclear. Here, we focus on summarizing the complicated mechanisms of HBV replication and infection, as well as genomic factors and epigenetic regulation. Additionally, we discuss in vivo models of HBV, as well as diagnosis, prevention and therapeutic drugs for HBV. Together, the data in this 50-year review may provide new clues to elucidate molecular mechanisms of HBV pathogenesis and shed new light on the future HBV therapies.

Molecular Pathogenesis of Hepatitis-B-virus-associated Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is one of the most frequent and malignant diseases worldwide. Epidemiological studies have clearly demonstrated that chronic hepatitis B virus (HBV) infection is a major etiological factor in the development of HCC. The pathogenesis of HBV-associated HCC has been studied extensively, and the molecular changes associated with malignant transformation have been identified. The predominant carcinogenic mechanisms of HBV-associated HCC are chronic inflammation and the effects of cytokines in the development of fibrosis and liver cell proliferation. An important role is also played by the integration of HBV DNA into host cellular DNA, which disrupts or promotes the expression of cellular genes that are important in cell growth and differentiation. Especially, HBx protein is a transactivating protein that promotes cell growth, survival, and the development of HCC. Continued investigation of the mechanisms underlying hepatocarcinogenesis will refine our current understanding of the molecular and cellular basis for neoplastic transformation in the liver. Prevention of HBV infections and effective treatments for chronic hepatitis B are still needed for the global control of HBV-associated HCC. This review summarizes the current knowledge on the mechanisms involved in HBV-associated hepatocarcinogenesis.

Molecular Pathogenesis of Hepatitis-B-virus-associated Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent and malignant diseases worldwide. Epidemiological studies have clearly demonstrated that chronic hepatitis B virus (HBV) infection is a major etiological factor in the development of HCC. The pathogenesis of HBV-associated HCC has been studied extensively, and the molecular changes associated with malignant transformation have been identified. The predominant carcinogenic mechanisms of HBV-associated HCC are chronic inflammation and the effects of cytokines in the development of fibrosis and liver cell proliferation. An important role is also played by the integration of HBV DNA into host cellular DNA, which disrupts or promotes the expression of cellular genes that are important in cell growth and differentiation. Especially, HBx protein is a transactivating protein that promotes cell growth, survival, and the development of HCC. Continued investigation of the mechanisms underlying hepatocarcinogenesis will refine our current understanding of the molecular and cellular basis for neoplastic transformation in the liver. Prevention of HBV infections and effective treatments for chronic hepatitis B are still needed for the global control of HBV-associated HCC. This review summarizes the current knowledge on the mechanisms involved in HBV-associated hepatocarcinogenesis.

Molecular Mechanisms of Hepatitis B Virus-associated Hepatocellular Carcinoma / 대한간학회지

Hepatocellular carcinoma (HCC) is one of the most common malignant diseases in the world. The hepatitis B virus (HBV) replicates non-cytopathically in hepatocytes, and most of the liver injury associated with this infection reflects the immune response. Epidemiological studies have clearly demonstrated that a chronic HBV infection is a major etiological factor in the development of HCC. The pathogenesis of HBV-associated HCC has been studied extensively, and the molecular changes during the malignant transformation have been identified. The main carcinogenic mechanism of HBV-associated HCC is related to the long term-inflammatory changes caused by a chronic hepatitis B infection, which might involve the integration of the HBV. Integration of the HBV DNA into the host genome occurs at the early steps of clonal tumorous expansion. The hepatitis B x protein (HBx) is a multifunctional regulatory protein that communicates directly or indirectly with a variety of host targets, and mediates many opposing cellular functions, including its function in cell cycle regulation, transcriptional regulation, signaling, encoding of the cytoskeleton and cell adhesion molecules, as well as oncogenes and tumor suppressor genes. Continued study of the mechanisms of hepatocarcinogenesis will refine our current understanding of the molecular and cellular basis for neoplastic transformations in the liver. This review summarizes the current knowledge of the mechanisms involved in HBV-associated hepatocarcinogenesis.