Abstract 2283: β-catenin silencing induces both apoptotic and autophagic cell death through LKB1/AMPK signal in head and neck cancer cells

Abstract

Abstract β-Catenin, a multifunctional protein involved in key molecule of Wnt signaling transduction, has been well known to regulate cell proliferation, differentiation, cell-cell adhesion, survival, and apoptosis as well as plays an important role in human tumorigenesis. Our previous report showed that Wnt/β-catenin pathway controls radiosensitivity of head and neck caner (HNC) cell via cyclooxygenase-2-mediated Ku expression. However, the specific molecular mechanisms of β-catenin in tumor cell survival and death are still not fully understood, so in the present study we attempted to elucidate the mechanism of cell death in HNC cell by studying how β-catenin silencing regulates cell death through KB1/AMPK signaling. We performed β-catenin knockdown in HNC cell by using small interfering RNA. Its effect on the cell viability was confirmed by observation of cell morphologic change, electron microscopy, MTT and FACS analysis. Also, we confirmed the expression of several proteins corresponding signal pathway by western blot analysis. β-catenin silencing significantly induced G1 cell-cycle arrest and also increased the expression of Bax and the active form of caspase-3, and decreased the expression of Bcl-2, demonstrating the sequential activation of apoptotic cascades following treatment with β-catenin siRNA in HNC cell. Interestingly, β-catenin silencing induced autophagy as well as apoptosis. We confirmed that the numbers of autophagic vacuoles and the expression of LC3-II increased in cells treated with β-catenin siRNA. This is probably because LKB1-dependent AMPK is activated by β-catenin silencing in HNC cell. Activated AMPK, in β-catenin silenced AMC-HN-3 cells, causes a G1 cell cycle arrest by phosphorylated p53 as well as inhibited protein synthesis by suppressing mTOR activity. Also, Treatment with LKB1 siRNA or compound C in AMC-HN-3 cells preserved cell viability against β-catenin silencing-induced cytotoxicity. Taken together, our data show that β-catenin silencing induces cell death through LKB1/AMPK signal, and as a result, apoptosis and autophagy are induced together in HNC cell, suggesting that a novel interaction between β-catenin and LKB1/AMPK signaling pathway occurs. Our study provides new insights into understanding the cellular and molecular mechanisms involving β-catenin silencing-induced cell death. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2283. doi:1538-7445.AM2012-2283