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

Abstract

The proteomic approach is a valuable tool to detect and identify proteins that are associated with cancer. In previous investigations on experimentally induced rat hepatomas, we detected aldose reductase‐like protein (ARLP) as a highly significant marker protein. Our present study was intended to look for the presence of similar tumor‐associated marker proteins on human hepatocellular carcinomas (HCC). We found several novel tumor‐associated protein variants that represent members of the aldo‐keto reductase (AKR) superfamily. Human aldose reductase‐like protein‐1 (hARLP‐1) was the most prominent tumor‐associated AKR member detected in HCC by 2‐dimensional electrophoresis (2‐DE) and identified by mass spectrometric fingerprinting. The enzyme was found in 4 distinct forms (hARLP‐1, 36/7.4 (kd/pI); hARLP‐2, 36/7.2; hARLP‐3, 36/6.4; and hARLP‐4, 33/7.35). In addition, a human aldose reductase‐like protein (hARLP‐5, 36/7.6) was identified that differed from hARLP‐1 by 1 amino acid (D313N), indicating 2 allelic forms of the human aldose reductase‐like gene. A novel antibody directed against common parts of the hARLPs revealed hARLP reactivity in human HCC by immunohistochemistry. Furthermore, aldose reductase (AR) was identified and characterized as a tumor‐associated variant. In conclusion, in all investigated human HCCs at least one of the various types of the described tumor‐associated proteins of the AKR superfamily was clearly present. Of these HCC samples, 95% were positive for hARLPs as proven by 2‐DE analysis and/or by use of the antibody directed against hARLP. Thus, hARLP is a strong candidate for use as an immunohistochemical diagnostic marker of human HCC. (HEPATOLOGY 2004;39:540–549.)