The aim of the study was to detect proteomic markers usable to distinguish colorectal carcinoma from colon adenoma for a better understanding of the molecular mechanisms in the process of tumourigenesis. Therefore, we microdissected colon carcinoma tissue, epithelial colon adenoma tissue as well as normal adjacent colon epithelium and determined protein profiles by SELDI-TOF MS. A multitude of significantly different signals was detected. For their identification colon biopsis were lysed and subjected to a two-dimensional gel electrophoresis for separation. Subsequently, we identified nearly 100 proteins by tryptic digestion, peptide fingerprint mapping and database search. Calgizzarin (S100A11; S100C) identified by peptide fingerprint mapping correlated very well with a significantly differentially expressed signal found in prior protein profiling. Using an immunodepletion assay we confirmed the identity of this signal as calgizzarin. To localise calgizzarin in tissues we performed immunohistochemistry. For further confirmation of the identity of calgizzarin we re-analysed IHC-positive as well as IHC-negative tissue sections on ProteinChip arrays. This work demonstrates that biomarkers in colorectal cancer can be detected, identified and assessed by a proteomic approach comprising tissue-microdissection, protein profiling and immunological techniques.

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