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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.

SUBMITTER: Sobol A

PROVIDER: S-EPMC4445069 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The Î²-amyloid precursor protein APP and the related APLPs, undergo complex proteolytic processing giving rise to several fragments. Whereas it is well established that AÎ² accumulation is a central trigger for Alzheimer disease (AD), the physiological role of APP family members and their diverse proteolytic products is still largely unknown. The secreted APPsÎ± ectodomain has been shown to be involved in neuroprotection and synaptic plasticity. The Î³-secretase generated APP intracellular domain AICD, functions as a transciptional regulator in heterologous reporter assays, although its role for endogenous gene regulation has remained controversial. To gain further insight into the molecular changes associated with knockout phenotypes and to elucidate the physiological functions of APP family members including their proposed role as transcriptional regulators we performed a DNA microarray transcriptome profiling of the frontal cortex of adult wild type, APP-/-, APLP2-/- and APPsÎ± knockin (KI) mice, APPÎ±/Î±, expressing solely the secreted APPsÎ± ectodomain. Biological pathways affected by the lack of APP family members included regulation of neurogenesis, regulation of transcription and regulation of neuron projection development. Comparative analysis of transcriptome changes and qPCR validation identified co-regulated gene sets. Interestingly, these included heat shock proteins and plasticity related genes that were down-regulated in knock-out cortices. In contrast, we failed to detect significant differences in expression of previously proposed AICD target genes including Bace1, Kai1, Gsk3b, p53, Tip60 and Vglut2. Only Egfr was slightly up-regulated in APLP2-/- mice. Comparison of APP-/- and APPÎ±/Î± with wild-type mice revealed a high proportion of co-regulated genes indicating an important role of the C-terminus for cellular signaling. Finally, comparison of APLP2-/- on different genetic backgrounds revealed that background related transcriptome changes may dominate over changes due to the knockout of a single gene. Shared transcriptome profiles corroborated closely related physiological functions of APP family members in the adult central nervous system. As expression of proposed AICD target genes was not altered in adult cortex, this may indicate that these genes are not affected by lack of APP under resting conditions or only in a small subset of cells. Prefrontal cortices of adult male mice (24 - 28 weeks) of the following genotypes were analyzed: WT (n=3), APP-/- (n=3), APPÎ±/Î± (n=3), APLP2-/- (n=3), APLP2(R1)-/- (n=3). WT, APP-/-, APPÎ±/Î±, APLP2-/- had been backcrossed for six generations to C57BL/6 mice. APLP2(R1)-/- harbors the identical knockout allele as APLP2-/- but was back-crossed only once.

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Amyloid precursor protein (APP) affects global protein synthesis in dividing human cells.

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