β-Catenin is closely associated with carcinoma invasion/metastasis and poor survival. Recent studies have demonstrated that abnormal expression of β-catenin, especially its nuclear accumulation, also plays an important role in wingless/Wnt signaling pathway. In this study, we evaluated immunohistochemically the nuclear localization of β-catenin in a total of 93 human-endocrine-related tumors including 1 medullary carcinoma (thyroid gland), 12 parathyroid tumors, 22 carcinoid tumors (digestive tract and liver), 7 islet cell tumors, 26 adrenocortical tumors, 13 neuroblastoma (adrenal gland), and 12 pheochromocytoma (adrenal gland), and also studied genetic alterations of the β-catenin gene. Nuclear accumulation of β-catenin was frequently detected in 8 of 22 (36%) carcinoid tumors and 2 of 7 (29%) islet cell tumors. No genetic alteration in exon 3 of the β-catenin gene encoding serine/threonine rich domain, which was phosphorylated by GSK-3β, was detected in any groups of the endocrine tumors. However, nuclear accumulation of β-catenin in carcinoid tumors was significantly correlated with the proliferative marker Ki-67 (MIB-1) labeling index (p < 0.001). Our findings suggest that nuclear transfer and accumulation of the β-catenin may contribute in the tumorigenesis of carcinoid tumor as an oncoprotein.
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