The purpose of this study was to identify and validate novel serological
protein biomarkers of human
colorectal cancer (CRC).
Proteins from matched CRC and adjacent normal tissue samples were resolved by two-dimensional gel electrophoresis. From each gel all spots were excised, and enveloped
proteins were identified by MS. By comparison of the resulting
protein profiles, dysregulated
proteins can be identified. A list of all identified
proteins and validation of five exemplarily selected
proteins, elevated in CRC was reported previously (Roessler, M., Rollinger, W., Palme, S., Hagmann, M. L., Berndt, P., Engel, A. M., Schneidinger, B., Pfeffer, M., Andres, H., Karl, J., Bodenmuller, H., Ruschoff, J., Henkel, T., Rohr, G., Rossol, S., Rosch, W., Langen, H., Zolg, W., and Tacke, M. (2005) Identification of
nicotinamide N-methyltransferase as a novel serum
tumor marker for
colorectal cancer. Clin.
Cancer Res. 11, 6550-6557). Here we describe identification and initial validation of another potential marker
protein for CRC. Comparison of tissue
protein profiles revealed strong elevation of
proteasome activator complex subunit 3 (PSME3) expression in CRC tissue. This dysregulation was not detectable based on the spot pattern. The PSME3-containing spot on
tumor gels showed no visible difference to the corresponding spot on matched control
gels. MS analysis revealed the presence of two
proteins, PSME3 and
annexin 4 (ANXA4) in one and the same spot on
tumor gels, whereas the matched spot contained only one
protein, ANXA4, on control
gels. Therefore, dysregulation of PSME3 was masked by ANXA4 and could only be recognized by MS-based analysis but not by image analysis. To validate this finding, antibody to PSME3 was developed, and up-regulation in CRC was confirmed by Western blot analysis and immunohistochemistry. Finally by developing a highly sensitive immunoassay, PSME3 could be detected in human sera and was significantly elevated in CRC patients compared with healthy donors and patients with benign bowel disease. We propose that PSME3 be considered a novel serum
tumor marker for CRC that may have significance in the detection and in the management of patients with this disease. Further studies are needed to fully assess the potential clinical value of this marker candidate.