Investigation of the role of β-catenin n-terminal alterations in neoplastic processes

β-catenin is a multifunctional protein and located at the center of Wnt pathway. Intracellular localization and level of β-catenin are strictly controlled by special amino acid residues located at its N-terminal domain. These amino acid residues are encoded by the third exon (exon 3) of CTNNB1 (β-catenin encoding gene) and the mutations altering this region lead to neoplastic transformation by changing the amino acid sequence of the N-terminal domain. Our research group has recently defined an immunohistochemistry-based approach that can detect CTNNB1 exon 3 mutations. The primary purpose of this study is to evaluate the CTNNB1 exon 3 alterations in neoplastic diseases of unknown pathogenesis by using this immunohistochemistry-based approach. For this purpose, β-catenin N-terminal domain alterations were evaluated with this method in the cases of sclerosing angiomatoid nodular transformation (SANT) of the spleen, a rare vascular lesion of the spleen. As a result of immunohistochemical staining, findings suggesting the presence of exon 3 mutations were obtained. These findings were confirmed with polymerase chain reaction and Sanger sequencing. The secondary purpose of this study is to evaluate the post-translational modifications of the β-catenin N-terminal domain by using the immunohistochemical staining method that we have described. For this purpose, the intracellular localization of β-catenin phosphorylated at the amino acids S33, S37 and T41 (phospho-S33/S37/T41-β-catenin) was investigated using immunohistochemical and immunofluorescent staining methods, and it was shown that this protein could accumulate in the nucleus of the colon cancer cells. By evaluating protein lysates of colorectal cancer patients with Western Blot method, it was also suggested that low molecular weight β-catenin forms might be formed after proteolytic cleavage of N-terminal and C-terminal regions of β-catenin.