Identification of differentially expressed proteins between human hepatoma and normal liver cell lines by two-dimensional electrophoresis and liquid chromatography-ion trap mass spectrometry.

In the previous study, the proteomes of the human hepatoma cell line BEL-7404 and the normal human liver cell line L-02 were separated by high resolution two-dimensional electrophoresis (2-DE). Image analysis revealed that 99 protein spots showed quantitative and qualitative variations that were significant (P < 0.01) and reproducible. Here we report the identification results of some of these protein spots. Protein spots excised from 2-D gels were subjected to in-gel digestion with trypsin, and the resulting peptides were measured by microbore high performance liquid chromatography - ion trap - mass spectrometry (LC-IT-MS) to obtain the tandem mass (MS/MS) spectra. Twelve protein spots were identified with high confidence using SEQUEST with uninterpreted MS/MS raw data. Besides inosine-5'-monophosphate dehydrogenase 2, heat shock 27 kDa protein, calreticulin and calmodulin, whose expression was elevated in hepatoma cells, glutathione-S-transferase P was identified from hepatoma cells in which its level was 18-fold higher compared to human liver cells. Two spots were identified as the homologs of reticulocalbin for the first time in hepatoma cells and their expression increased compared to liver cells. However, tubulin beta-1 chain and natural killer cell enhancing factor B were downregulated in hepatoma cells. A tumor suppressing serpin, maspin precursor, was identified from one spot whose quantity was much higher in the normal liver cell line. More interestingly, epidermal fatty acid-binding protein (E-FABP) and fatty acid-binding protein, adipocyte-type (A-FABP), were detected in liver cells but not in hepatoma cells. The functional implication of the identified proteins was discussed.