Micropreparative immobilized pH gradient two‐dimensional electrophoresis in combination with protein microsequencing for the analysis of human liver proteins

Abstract

Simplified methodology has been developed for the direct N-terminal amino acid microsequencing of human liver and hepatoma derived polypeptides, following micropreparative two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). Utilization of immobilized pH gradient (IPG) gel strips in the first dimension permitted protein loading of 0.5-2.0 mg with negligible diminution of polypeptide resolution. Following 2-D separation and electrotransfer to polyvinylidene difluoride (PVDF) membranes nearly 100 well resolved Ponceau S stained polypeptides were readily visualized, from which, 32 adult liver S-9 and 72 HepG2 nuclear cytosolic polypeptides were subjected to N-terminal microsequencing. Twenty normal adult liver and 54 HepG2 polypeptides yielded N-terminal sequence information, of which 17 and 19 polypeptides, respectively, exhibited high sequence homology to previously identified proteins. The initial yields of the proteins sequenced ranged from 2-14 pmols and yielded sequences of 14-26 amino acid residues. Many of the adult liver and HepG2 proteins contained inferred leader sequences since the first sequenced residue was several (20-30) residues from the methionine initiation site predicted by the cDNA of the adult liver. Quantitative comparison of 60 well characterized hepatic proteins between normal adult liver and two nontransformed, Chang and WRL-68, and four human hepatoma derived cell lines, HepG2, Huh-7, FOCUS, and SK-Hep, revealed a high homogeneity of protein expression both qualitatively and quantitatively in both whole cell lysate and purified nuclear preparations. Most notable differences include the previously characterized polypeptides: carbamoyl phosphate synthase, MER5 homologous protein, cytidylate kinase, phosphatidylethanolamine-binding protein and mitochondrial enoyl-CoA hydratase as well as three N-terminally blocked polypeptides: 11 (63 kDa/pI 7.00), 56 (26/6.45) and 59 (22/6.00) all of which were expressed at similar levels in normal adult liver tissue and each of the nontransformed, Chang and WRL-68, cell lines but not expressed or expressed at greatly decreased levels in each of tumor derived liver cell lines. Pyruvate carboxylase, superoxide dismutase, serotransferrin, liver fatty acid binding protein, 1-hydroxyprostaglandin dehydrogenase, NADH dehydrogenase (ubiquinone) as well as three N-terminally blocked polypeptides: 9 (57/6.00), 53 (24/4.90) and 63 (16/4.70) were detected only in whole adult liver tissue and not in any of the cultured cell lines. Two additional polypeptides: U35, (27/6.05) and 58 (22/5.70) yielded N-terminal partial amino acid sequences but were not identified in established protein databases. We have shown that micropreparative IPG 2-D PAGE In combination with protein microsequencing provides a convenient one step procedure to rapidly obtain partial amino acid sequence information for nearly 100 individual polypeptides directly from a single 2-D PAGE gel with numerous applications to a wide variety of biological model systems.

Detection and identification of tumor-associated protein variants in human hepatocellular carcinomas

“…2,13,14 Numerous so-called tumor-associated or cancer-related proteins were identified; these provide valuable information for the establishment of HCC protein databases. 2,[11][12][13][14] Comparative analysis of liver tissue and hepatocellular carcinomas might give additional insights into the induction or repression of tumor-associ- …”

“…These protein alterations might represent tumor markers that are useful in the diagnosis of human tumors and may also help the understanding of mechanisms of tumor induction and development. Proteome analysis of liver proteins and HCC were predominantly performed using either chemically induced hepatomas in animals (predominantly the rat [5][6][7][8][9][10] ) or human HCC cell lines, such as HepG2 and Huh7 cells, 11 BEL-7404 cells, 12 or HCC-M cells. 2,13,14 Numerous so-called tumor-associated or cancer-related proteins were identified; these provide valuable information for the establishment of HCC protein databases.…”

Proteomic Profiling of Differentially Expressed Proteins from Bax inhibitor-1 Knockout and Wild Type Mice

“…This protein can sequester inactive Raf-1 and MEK1 (Yeung et al, 2000) and is expressed at greatly reduced levels in tumorderived liver cell lines (Wirth et al, 1995). Rats subjected to chronic corticosterone treatment showed a decrease in hippocampal PEBP-1 expression and impaired cognition (Feldmann et al, 2008).…”

Proteomics for the early detection and treatment of hepatocellular carcinoma

“…This approach was partially validated by comparing the protein expression profiles of normal liver tissue, untransformed liver cell lines and HCC cell lines using 2D-PAGE-MS (Wirth et al, 1995). In a more recent study using a 2D-DIGE-MS approach, the protein expression profiles of primary cultured hepatocytes and of HCC cell lines were compared (Fujii et al, 2005); in this study, 44 out of 1238 protein spots detected were differentially expressed in HCC cell lines.…”