Received:
07 October 2015
Accepted:
30 March 2016
Published online:
14 April 2016
Abstract
Hepatitis B virus X protein (HBx) plays an important role in HBV-related hepatocarcinogenesis; however, mechanisms underlying HBx-mediated carcinogenesis remain unclear. In this study, an NMR-based metabolomics approach was applied to systematically investigate the effects of HBx on cell metabolism. EdU incorporation assay was conducted to examine the effects of HBx on DNA synthesis, an important feature of nucleic acid metabolism. The results revealed that HBx disrupted metabolism of glucose, lipids, and amino acids, especially nucleic acids. To understand the potential mechanism of HBx-induced abnormalities of nucleic acid metabolism, gene expression profiles of HepG2 cells expressing HBx were investigated. The results showed that 29 genes involved in DNA damage and DNA repair were differentially expressed in HBx-expressing HepG2 cells. HBx-induced DNA damage was further demonstrated by karyotyping, comet assay, Western blotting, immunofluorescence and immunohistochemistry analyses. Many studies have previously reported that DNA damage can induce abnormalities of nucleic acid metabolism. Thus, our results implied that HBx initially induces DNA damage, and then disrupts nucleic acid metabolism, which in turn blocks DNA repair and induces the occurrence of hepatocellular carcinoma (HCC). These findings further contribute to our understanding of the occurrence of HCC.
Introduction
With a high degree of malignancy, rapid progression, and high mortality rate, hepatocellular carcinoma (HCC) is the third most frequent cause of cancer-related death worldwide1. Hepatitis B virus (HBV) infection is a major risk factor for HCC2. In recent years, ~2 billion individuals have been found to be infected with HBV, of which, more than 350 million are chronically infected3,4. Thus, HBV has become one of the most important pathogens threatening human health.
As is well known, the main function of the liver is metabolism, thus plays a central role in metabolism of glucose, lipids, amino acids and nucleic acids. HBV infection leads to liver dysfunction, which in turn induces alterations of metabolism. Several recent studies have shown that HBV-related liver disease resulted in many metabolic abnormalities. One study showed that metabolite components of HCC markedly differed from those of adjacent non-tumor tissues, and low-grade HCC had clear metabolomics differences from high-grade HCC5. Another study reported that HBV-related HCC exhibited glucose and lipid metabolic abnormalities6. The levels of many indicators associated with lipid metabolism are altered in patients with chronic HBV infection7,8. Additionally, HBV infection can induce other abnormalities of metabolism such as amino acids, cholesterol, and choline9,10,11.
Hepatitis B virus X protein (HBx) is a multifunctional regulator, which is involved in viral replication, transcriptional regulation, cell cycle progression, DNA repair, apoptosis, and genetic stability12. Recently, several studies have also shown that HBx can disturb cell metabolism. HBx can interact with peroxisome proliferator-activated receptor-γ (PPAR-γ) and sterol regulatory element binding protein 1, increase their respective mRNA and protein expression, and lead to lipid accumulation in hepatocytes7. HBx can induce activation of lipogenic genes and fatty acid accumulation, which contributes to disease progression by promoting steatosis and liver inflammation in transgenic mice13. However, no systematic investigations about the effects of HBx on cell metabolism have been reported thus far.
Metabonomics is a systematic approach in studying low-molecular-weight compounds in cells, tissues and biofluids, which directly reflects the phenotypic features of an organism and provides important information on disease processes, biochemical functions, and drug toxicity14,15. Here, an NMR-based metabolomics approach was applied to study the mechanisms of HBx-mediated carcinogenesis. Studying the HBx-related mechanisms contributes to understanding of the occurrence of HCC. 作者: StephenW 时间: 2016-4-21 22:00