Identification of differentially expressed proteins between human hepatomaand 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-74 04 and the normal human liver cell line L-02 were separated by high resolut ion two-dimensional electrophoresis (2-DE). image analysis revealed that 99 protein spots showed quantitative and qualitative variations that were sig nificant (P < 0.01) and reproducible. Here we report the identification res ults of some of these protein spots. Protein spots excised from 2-D gels we re subjected to in-gel digestion with trypsin, and the resulting peptides w ere 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 wit h uninterpreted MS/MS raw data. Besides inosine-5'-monophosphate dehydrogen ase 2, heat shock 27 kDa protein, calreticulin and calmodulin, whose expres sion was elevated in hepatoma cells, glutathione-S-transferse P was identif ied from hepatoma cells in which its level was 18-fold higher compared to h uman liver cells. Two spots were identified as the homologs of reticulocalb in for the first time in hepatoma cells and their expression increased comp ared to liver cells. However, tubulin beta-1 chain and natural killer cell enhancing factor B were downregulated in hepatoma cells. A tumor suppressin g serpin, maspin precursor, was identified from one spot whose quantity was much higher in the normal liver cell line. More interestingly, epidermal f atty acid-binding protein (E-FABP) and fatty acid-binding protein, adipocyt e-type (A-FABP), were detected in liver cells but not in hepatoma cells. Th e functional implication of the identified proteins was discussed.