Amyloid Precursor Protein (APP) Affects Global Protein Synthesis in Dividing Human Cells

Abstract

Hypoxic non‐small cell lung cancer (NSCLC) is dependent on Notch‐1 signaling for survival. Targeting Notch‐1 by means of γ‐secretase inhibitors (GSI) proved effective in killing hypoxic NSCLC. Post‐mortem analysis of GSI‐treated, NSCLC‐burdened mice suggested enhanced phosphorylation of 4E‐BP1 at threonines 37/46 in hypoxic tumor tissues. In vitro dissection of this phenomenon revealed that Amyloid Precursor Protein (APP) inhibition was responsible for a non‐canonical 4E‐BP1 phosphorylation pattern rearrangement—a process, in part, mediated by APP regulation of the pseudophosphatase Styx. Upon APP depletion we observed modifications of eIF‐4F composition indicating increased recruitment of eIF‐4A to the mRNA cap. This phenomenon was supported by the observation that cells with depleted APP were partially resistant to silvestrol, an antibiotic that interferes with eIF‐4A assembly into eIF‐4F complexes. APP downregulation in dividing human cells increased the rate of global protein synthesis, both cap‐ and IRES‐dependent. Such an increase seemed independent of mTOR inhibition. After administration of Torin‐1, APP downregulation and Mechanistic Target of Rapamycin Complex 1 (mTORC‐1) inhibition affected 4E‐BP1 phosphorylation and global protein synthesis in opposite fashions. Additional investigations indicated that APP operates independently of mTORC‐1. Key phenomena described in this study were reversed by overexpression of the APP C‐terminal domain. The presented data suggest that APP may be a novel regulator of protein synthesis in dividing human cells, both cancerous and primary. Furthermore, APP appears to affect translation initiation using mechanisms seemingly dissimilar to mTORC‐1 regulation of cap‐dependent protein synthesis. J. Cell. Physiol. 230: 1064–1074, 2015. © 2014 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

­­Depletion of Amyloid Precursor Protein (APP) Causes G0 Arrest in Non‐Small Cell Lung Cancer (NSCLC) Cells

“…Paradoxically, cells arrested in G0 display a substantially increased protein synthesis rate (Fig. and Sobol et al, ). There is evidence that cell division can be uncoupled with cytoplasmic cell growth and protein synthesis by blocking CDK activity.…”

Deubiquitinase OTUD6B Isoforms Are Important Regulators of Growth and Proliferation

“…Depletion of amyloid precursor protein (APP) in NSCLC cells causes a complex phenotype, including increased global protein synthesis (20,21). To determine the critical mediators of APP depletion, we used siRNA to silence mRNAs which were downregulated upon APP depletion in NSCLC.…”

“…Cap binding assay was performed after transfection with control siRNA or siRNA against OTUD6B as previously described (20) with one modification: initiation complexes were formed using 2’/3’-O-(2-Aminoethyl-carbamoyl)-N7-methyl-guanosine-5’-triphosphate-Biotin, Triethylammonium salt (Jena Bioscience) and captured on streptavidin magnetic beads (Pierce). Complexes were washed and eluted with an excess of m 7 GTP.…”

Evidence For and Against a Pathogenic Role of Reduced γ-Secretase Activity in Familial Alzheimer’s Disease

“…A␤PP influences Fe ion homeostasis via its interaction with Ferroportin (SLC40A1, [125]) and A␤PP affects embryo development, including vascular development, possibly via secretion of its extracellular/luminal domain [126,127] and A␤ [128]. A␤PP also influences the rate of protein synthesis [129], neurite outgrowth [130], and axonal pruning [131] as well as LPSmediated innate immune responses [132]. Signaling via AICD regulates genes including MEMBRANE METALLOENDOPEPTIDASE (MME, also known as neprilysin) [133] and TRANSTHYRETIN, TTR [134] that encode proteins involved in degradation and clearance of A␤ from the CNS, respectively.…”