S100A6 and CacyBP/SIP – Two Proteins Discovered in Ehrlich Ascites Tumor Cells That Are Potentially Involved in the Degradation of β-Catenin

S100A6 is a low-molecular-weight calcium-binding protein belonging to the S100 family. Originally, S100A6 was purified from Ehrlich ascites tumor cells, but later, it was found in fibroblasts, epithelial cells and in tumor cells with high metastatic activity. When Ca(2+)-dependent interaction of S100A6 with target proteins was studied in Ehrlich ascites tumor cells, a novel protein, now called CacyBP/SIP, was discovered. Later, it was found that CacyBP/SIP interacted with Siah-1 and Skp1 and that it was involved in the ubiquitination and degradation of an oncogen, namely beta-catenin. Thus, this review describes the discovery and characterization of S100A6 and Cacy BP/SIP, the function of these two proteins in ubiquitination and degradation processes and their possible role in tumorigenesis.