Identification of human hepatocellular carcinoma-related biomarkers by two-dimensional difference gel electrophoresis and mass spectrometry

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death throughout the world. Although hepatitis B or C viral infections are main risk factors for HCC, the molecular mechanisms leading to HCC formation have not been clarified. To reduce the mortality and improve the effectiveness of therapy, it is important to search for changes in tumor-specific biomarkers whose function may involve in disease progression and which may be useful as potential therapeutic targets. In this study, we employed two-dimensional difference gel electrophoresis (2D-DIGE) combined with nano flow liquid chromatography tandem mass spectrometry (nanoLC-MS/MS) to investigate differentially expressed proteins in HCC. For each of eight HCC patients, Cy3-labeled proteins isolated from tumor tissue were combined with Cy5-labeled proteins isolated from the surrounding nontumor tissue and separated by 2D gel electrophoresis along with a Cy2-labeled mixture of all tumor and nontumor samples as an internal standard. Thirty-four protein spots corresponding to 30 different proteins were identified by nanoLC-MS/MS as showing significant change (paired t-test, p < 0.05) in the level of expression between tumor and nontumor tissues. Sixteen proteins were up-regulated and 14 were down-regulated in HCC; they seem to play important roles in a variety of pathways including glycolysis, fatty acid transport and trafficking, amino acid metabolism, iron and xenobiotic metabolism, ethanol metabolism, cell cycle regulation, cytoskeleton, and stress. A remarkable finding is the up-regulation of 14-3-3gamma protein in HCC. 14-3-3 isoforms had been linked to carcinogenesis because they are involved in various cellular processes such as cell cycle regulation, apoptosis, proliferation, and differentiation. In conclusion, 2D-DIGE is an efficient strategy that enables us to identify differentially expressed proteins in HCC. Identification of potential biomarkers, such as the pinpointing of 14-3-3gamma in our findings, may provide further useful insights into the pathogenesis of HCC.