Characterization and over-expression of chaperonin t-complex proteins in colorectal cancer.

The chaperonins are key molecular complexes, which are essential in the folding of proteins to produce stable and functionally competent protein conformations. One member of the chaperonin group of proteins is TCP1 (chaperonin containing t-complex polypeptide 1, or CCT), but little is known about this protein in tumours. In this study, we used comparative proteomic analysis to show that t-complex protein subunits TCP1 beta and TCP1 epsilon are over-expressed in colorectal adenocarcinomas. Monoclonal antibodies to these proteins were developed and the expression and cellular localization of these two proteins in colorectal cancer were analysed by immunohistochemistry on a colorectal cancer tissue microarray. In colorectal cancer, TCP1 beta cellular localization was exclusively cytoplasmic, whereas TCP1 epsilon staining was seen in both the nucleus and the cytoplasm. Both cytoplasmic TCP1 beta and cytoplasmic TCP1 epsilon were significantly over-expressed (p < 0.001 for each protein) in primary colorectal cancer and also showed increased expression with advancing Dukes' stage (p = 0.018 for TCP1 beta and p = 0.045 for TCP1 epsilon). A trend was also identified between over-expression of cytoplasmic TCP1 beta and reduced patient survival (p = 0.05). These results show that both TCP1 beta and TCP1 epsilon are over-expressed in colorectal cancer and indicate a role for TCP1 beta and TCP1 epsilon in colorectal cancer progression.

Heterogeneous nuclear ribonucleoprotein K is over expressed, aberrantly localised and is associated with poor prognosis in colorectal cancer.

Heterogeneous ribonucleoprotein K (hnRNP K) is a member of the hnRNP family which has several different cellular roles including transcription, mRNA shuttling, RNA editing and translation. Several reports implicate hnRNP K having a role in tumorigenesis, for instance hnRNP K increases transcription of the oncogene c-myc and hnRNP K expression is regulated by the p53/MDM 2 pathway. In this study comparing normal colon to colorectal cancer by proteomics, hnRNP K was identified as being overexpressed in this type of cancer. Immunohistochemistry with a monoclonal antibody to hnRNP K (which we developed) on colorectal cancer tissue microarray, confirmed that hnRNP K was overexpressed in colorectal cancer (P<0.001) and also showed that hnRNP K had an aberrant subcellular localisation in cancer cells. In normal colon hnRNP K was exclusively nuclear whereas in colorectal cancer the protein localised both in the cytoplasm and the nucleus. There were significant increases in both nuclear (P=0.007) and cytoplasmic (P=0.001) expression of hnRNP K in Dukes C tumours compared with early stage tumours. In Dukes C patient's good survival was associated with increased hnRNP K nuclear expression (P=0.0093). To elaborate on the recent observation that hnRNP K is regulated by p53, the expression profiles of these two proteins were also analysed. There was no correlation between hnRNP K and p53 expression, however, patients who presented tumours that were positive for hnRNP K and p53 had a poorer survival outcome (P=0.045).

Liver fatty acid binding protein expression in colorectal neoplasia.

Liver fatty acid binding protein is a member of the fatty acid binding group of proteins that are involved in the intracellular transport of bioactive fatty acids and participate in intracellular signalling pathways, cell growth and differentiation. In this study we have used proteomics and immunohistochemistry to determine the changes in liver fatty acid binding protein in colorectal neoplasia. Comparative proteome analysis of paired samples colorectal cancer and normal colon identified consistent loss of liver fatty acid binding protein (L-FABP) in colorectal cancer compared with normal colon. To identify the changes in liver fatty acid binding protein expression during colorectal cancer development and progression the cell-specific expression of L-FABP was determined by immunohistochemistry in a series of colorectal cancers and colorectal adenomas. Decreased L-FABP immunoreactivity was significantly associated with poorly differentiated cancers (P<0.001). In colorectal adenomas there was a significant trend towards decreased staining of L-FABP in the larger adenomas (P<0.001). There was consistent L-FABP immunostaining of normal surface colonocytes. This study demonstrates that loss of L-FABP occurs at the adenoma stage of colorectal tumour development and also indicates that L-FABP is a marker of colorectal cancer differentiation.

Application of laser capture microdissection and proteomics in colon cancer.

AIMS: Laser capture microdissection is a recent development that enables the isolation of specific cell types for subsequent molecular analysis. This study describes a method for obtaining proteome information from laser capture microdissected tissue using colon cancer as a model. METHODS: Laser capture microdissection was performed on toluidine blue stained frozen sections of colon cancer. Tumour cells were selectively microdissected. Conditions were established for solubilising proteins from laser microdissected samples and these proteins were separated by two dimensional gel electrophoresis. Individual protein spots were cut from the gel, characterised by mass spectrometry, and identified by database searching. These results were compared with protein expression patterns and mass spectroscopic data obtained from bulk tumour samples run in parallel. RESULTS: Proteins could be recovered from laser capture microdissected tissue in a form suitable for two dimensional gel electrophoresis. The solubilised proteins retained their expected electrophoretic mobility in two dimensional gels as compared with bulk samples, and mass spectrometric analysis was also unaffected. CONCLUSION: A method for performing two dimensional gel electrophoresis and mass spectrometry using laser capture microdissected tissue has been developed.

Characterization of crosslinking sites in fibrinogen for plasminogen activator inhibitor 2 (PAI-2).

PAI-2 is a serpin that can be crosslinked to fibrin(ogen) via the Gln-Gln-Ile-Gln sequence (residues 83-86). We have characterized the lysine residues in fibrinogen to which PAI-2 is crosslinked by tissue transglutaminase and factor XIIIa. There was no competition with the crosslinking of alpha 2-antiplasmin, another inhibitor of fibrinolysis, which was specific for Lys 303 in the A alpha chain. PAI-2 was crosslinked to several lysine residues, all in the A alpha chain, 148, 176, 183, 230, 413, and 457, but not to Lys 303. The contrast with alpha 2-antiplasmin was clear from studies with truncated fibrinogens and competition by peptides. This was confirmed and extended by mass spectrometry of peptides after protease digestion of crosslinked products, which identified the lysine residues to which the inhibitors were crosslinked. PAI-2 remained active after cross-linking and inhibited fibrin breakdown, even by two-chain t-PA. Thus, a second inhibitor of fibrinolysis, in addition to alpha 2-antiplasmin, is crosslinked to fibrin and protects it from lysis.

Spot the differences: proteomics in cancer research.

Separation of thousands of cellular proteins by two-dimensional electrophoresis allows the detailed comparison of proteins from normal and diseased tissue. Mass spectrometry provides a fast and reliable way of characterising proteins of interest, particularly when the gene sequence of the source organism is known. The availability of the human genome sequence has opened up the possibility of identifying protein differences between normal and diseased tissue, thus providing the opportunity to search for tumour markers or for therapeutic targets. This new technology will give much-needed insight into the molecular mechanisms of tumour development and progression.

Cross-linking of plasminogen activator inhibitor 2 and alpha 2-antiplasmin to fibrin(ogen).

In this study, we identified lysine residues in the fibrinogen Aalpha chain that serve as substrates during transglutaminase (TG)-mediated cross-linking of plasminogen activator inhibitor 2 (PAI-2). Comparisons were made with alpha(2)-antiplasmin (alpha(2)-AP), which is known to cross-link to lysine 303 of the Aalpha chain. A 30-residue peptide containing Lys-303 specifically competed with fibrinogen for cross-linking to alpha(2)-AP but not for cross-linking to PAI-2. Further evidence that PAI-2 did not cross-link via Lys-303 was the cross-linking of PAI-2 to I-9 and des-alphaC fibrinogens, which lack 100 and 390 amino acids from the C terminus of the Aalpha chain, respectively. PAI-2 or alpha(2)-AP was cross-linked to fibrinogen and digested with trypsin or endopeptidase Glu-C, and the resulting peptides analyzed by mass spectrometry. Peptides detected were consistent with tissue TG (tTG)-mediated cross-linking of PAI-2 to lysines 148, 176, 183, 457 and factor XIIIa-mediated cross-linking of PAI-2 to lysines 148, 230, and 413 in the Aalpha chain. alpha(2)-AP was cross-linked only to lysine 303. Cross-linking of PAI-2 to fibrinogen did not compete with alpha(2)-AP, and the two proteins utilized different lysines in the Aalpha chain. Therefore, PAI-2 and alpha(2)-AP can cross-link simultaneously to the alpha polymers of a fibrin clot and promote resistance to lysis.