Hepatitis B virus-related hepatocellular carcinoma: paradigms for viral-related human carcinogenesis

Metallothionein expression is suppressed in primary human hepatocellular carcinomas and is mediated through inactivation of CCAAT/enhancer binding protein alpha by phosphatidylinositol 3-kinase signaling cascade

Reactive oxygen species (ROS) resulting from chronic inflammation cause liver injury leading to transformation of regenerating hepatocytes. Metallothioneins (MT), induced at high levels by oxidative stress, are potent scavengers of ROS. Here, we report that the levels of MT-1 and MT-2A are drastically reduced in primary human hepatocellular carcinomas (HCCs) and in diethylnitrosamine-induced liver tumors in mice, which is primarily due to transcriptional repression. Expression of the transcription factor, MTF-1, essential for MT expression, and its target gene Zn-T1 that encodes the zinc transporter-1 was not significantly altered in HCCs. Inhibitors of both phosphatidylinositol 3-kinase (PI3K) and its downstream target AKT increased expression of MT genes in HCC cells but not in liver epithelial cells. Suppression of MT-1 and MT-2A by ectopic expression of the constitutively active PI3K or AKT and their up-regulation by dominant-negative PI3K or AKT mutant confirmed negative regulation of MT expression by PI3K/AKT signaling pathway. Further, treatment of cells with a specific inhibitor of glycogen synthase kinase-3 (GSK-3), a downstream effector of PI3K/AKT, inhibited MT expression specifically in HCC cells. Short interfering RNA-mediated depletion of CCAAT/enhancer binding protein alpha (C/EBPalpha), a target of GSK-3, impeded MT expression, which could not be reversed by PI3K inhibitors. DNA binding activity of C/EBPalpha and its phosphorylation at T222 and T226 by GSK-3 are required for MT expression. MTF-1 and C/EBPalpha act in concert to increase MT-2A expression, which probably explains the high level of MT expression in the liver. This study shows the role of PI3K/AKT signaling pathway and C/EBPalpha in regulation of MT expression in hepatocarcinogenesis.

Hepatitis B virus splice-generated protein induces T-cell responses in HLA-transgenic mice and hepatitis B virus-infected patients

Hepatitis B virus splice-generated protein (HBSP), encoded by a spliced hepatitis B virus RNA, was recently identified in liver biopsy specimens from patients with chronic active hepatitis B. We investigated the possible generation of immunogenic peptides by the processing of this protein in vivo. We identified a panel of potential epitopes in HBSP by using predictive computational algorithms for peptide binding to HLA molecules. We used transgenic mice devoid of murine major histocompatibility complex (MHC) class I molecules and positive for human MHC class I molecules to characterize immune responses specific for HBSP. Two HLA-A2-restricted peptides and one immunodominant HLA-B7-restricted epitope were identified following the immunization of mice with DNA vectors encoding HBSP. Most importantly, a set of overlapping peptides covering the HBSP sequence induced significant HBSP-specific T-cell responses in peripheral blood mononuclear cells from patients with chronic hepatitis B. The response was multispecific, as several epitopes were recognized by CD8(+) and CD4(+) human T cells. This study provides the first evidence that this protein generated in vivo from an alternative reading frame of the hepatitis B virus genome activates T-cell responses in hepatitis B virus-infected patients. Given that hepatitis B is an immune response-mediated disease, the detection of T-cell responses directed against HBSP in patients with chronic hepatitis B suggests a potential role for this protein in liver disease progression.

Hepatitis B virus infection and replication in primarily cultured human fetal hepatocytes

AIM: To investigate the infection and replication of hepatitis B virus (HBV) in primarily cultured human fetal hepatocytes (HFHs).

METHODS: The human fetal hepatocytes were cultured in serum-free medium, HBV-positive serum was added into the medium to study the susceptibility of hepatocytes to HBV infection. The supernatant was collected for ELISA assay of HBsAg and HBeAg, and quantitative fluorescence PCR for HBV-DNA assay daily. Albumin and HBcAg, CK8 and CK18 expressions were detected by immunohistochemistry in cultured hepatocytes. Content of lactate dehydrogenate (LDH) was measured to find out the integrity of the cell membrane.

RESULTS: A stable hepatocyte culture system was established. HBV could infect the hepatocytes and replicate, and HBcAg expression could be detected by immunohistochemistry in hepatocyte-like cells. HBV-DNA in the supernatant could be detected from d 2 to d 18 and HBsAg and HBeAg were positive on d 3-d 18 after HBV infection. HBV in medium increased from d 0 to d 6 and subsequently decreased as the cells were progressively loosing their hepatocyte phenotypes.

CONCLUSION: HBV could infect human fetal hepato-cytes and replicate. This in vitro model allowed a detailed study on early events associated with human HBV entry into cells and subsequent replication.

Fasting Serum Glucose and Subsequent Liver Cancer Risk in a Korean Prospective Cohort

OBJECTIVES

Chronic infections with hepatitis B or C and alcoholic cirrhosis are three well-known major risk factors for liver cancer. Diabetes has also been suggested as a potential risk factor. However, the findings of previous studies have been controversial in terms of the causal association. Therefore, the aim of this study was to evaluate the association between serum glucose levels and liver cancer development in a Korean cohort.

METHODS

Thirty-six liver cancer cases were identified in the Korean Multi-Center Cancer Cohort (KMCC). Baseline information on lifestyle characteristics was obtained via questionnaire. Serum glucose levels were measured at the study's enrollment. Relative risks (RRs) were estimated using a Cox proportional hazard regression model. The adjusting variables included age, gender, smoking history, alcohol consumption, body mass index, and hepatitis B surface antigen (HBsAg) seropositivity.

RESULTS

The RRs of serum glucose for liver cancer were 1.20 (95% CI = 0.48-2.99) for the category of 100 to 125 mg/dL of serum glucose and 2.77 (95% CI = 1.24-6.18) for the > 126 mg/dL serum glucose category (both compared to the < 100 mg/dL category). In a subgroup analysis, the RR of serum glucose among those who were both HBsAg seronegative and non-drinkers was 4.46 (95% CL = 1.09-18.28) for those with glucose levels > 100 mg/dL.

CONCLUSIONS

The results of this study suggest that a high level of serum glucose can increase liver cancer risk independently of hepatitis infection and drinking history in Koreans. This study implies that glucose intolerance may be an independent risk factor for liver cancer.

Cytobiological consequences of calcium-signaling alterations induced by human viral proteins

Since calcium-signaling regulates specific and fundamental cellular processes, it represents the ideal target of viral proteins, in order for the virus to control cellular functions and favour its persistence, multiplication and spread. A detailed analysis of reports focused on the impact of viral proteins on calcium-signaling has shown that virus-related elevations of cytosolic calcium levels allow increased viral protein expression (HIV-1, HSV-1/2), viral replication (HBx, enterovirus 2B, HTLV-1 p12(I), HHV-8, EBV), viral maturation (rotavirus), viral release (enterovirus 2B) and cell immortalization (EBV). Interestingly, virus-induced decreased cytosolic calcium levels have been found to be associated with inhibition of immune cells functions (HIV-1 Tat, HHV-8 K15, EBV LMP2A). Finally, several viral proteins are able to modulate intracellular calcium-signaling to control cell viability (HIV-1 Tat, HTLV-1 p13(II), HCV core, HBx, enterovirus 2B, HHV-8 K7). These data point out calcium-signaling as a key cellular target for viral infection and should stimulate further studies exploring new calcium-related therapeutic strategies.