Abstract C40: Amyloid precursor protein (APP) synchronizes cell cycle progression and the rate of global protein synthesis in dividing cells

Abstract

Abstract In previous studies we targeted hypoxic Non-Small Cell Lung Cancer (NSCLC) tumor tissue using gamma-secretase inhibitors (GSI) in a preclinical model of advanced NSCLC. GSI treatment of mice suggested reactivation of mTORC-1 in otherwise quiescent hypoxic NSCLC tissue. Methods included immunohistochemistry and cytochemistry, immunoblotting, immunoprecipitation, siRNA-mediated gene knockdown, nucleotide and amino acid analogs incorporation, FACS analysis, various imaging techniques, Q-PCR, gene transfection, cap binding assays, RNA and antibodies arrays. GSI treatment of mice showed a re-induced phosphorylation of 4E-BP1 at T37/46 in hypoxic tumor masses. In vitro studies indicated a role for APP in this phenomenon. APP downregulation caused a rearrangement in 4E-BP1's phosphorylation pattern at residues T37/46, S65 and T70, reversed by overexpression of the APP C-terminal domain. Increased recruitment of eIF4A on the mRNA cap was observed. These events coincided with a drastic increase in the rate of global protein synthesis, an event that appeared to be mTOR-independent. Meanwhile, NSCLC cells with depleted APP were arrested in G0/G1 through a cyclin C-mediated mechanism. Cells arrested in G0/G1 with augmented rate of global protein synthesis (both cap- and IRES-dependent) increased their size and underwent a substantial necrotic cell death due to cell membrane permeabilization. These results indicate a novel role for APP in synchronizing the rate of protein synthesis and cell cycle progression, raising questions on how these processes interact in malignant transformation. The data presented here suggest that cells of different origin, including NSCLC cells, have developed some mechanisms to couple cell growth with cell cycle progression independent of overlapping signals which derive, among others, from the PI3-K pathway. APP seems to play a central role in this synchronization, and its loss of function causes cell size abnormalities and death. Citation Format: Anna Sobol, Paola Galluzzo, Shuang Liang, Brittany Rambo, Sylvia Skucha, Megan Weber, Maurizio Bocchetta. Amyloid precursor protein (APP) synchronizes cell cycle progression and the rate of global protein synthesis in dividing cells. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr C40.