Phosphorylation of Amyloid Precursor Protein (APP) at Thr668 Regulates the Nuclear Translocation of the APP Intracellular Domain and Induces Neurodegeneration

Abstract

Amyloid precursor protein (APP) has eight potential phosphorylation sites in its cytoplasmic domain.Recently, it has demonstrated that the constitutive phosphorylation of APP at T668 (APP695 isoform numbering) was observed specifically in the brain. Neuron-specific phosphorylation of APP at T668 is thought to be important for neuronal functions of APP, although its exact physiological significance remains to be clarified. In this study, we show that the phosphorylation of the APP intracellular domain (AICD) at T668 is essential for its binding to Fe65 and its nuclear translocation and affects the resultant neurotoxicity, possibly mediated through the induction of glycogen synthase kinase 3␤ and tau phosphorylation by enhancing the formation of a ternary complex with Fe65 and CP2 transcription factor. Taken together, these results suggest that the phosphorylation of AICD at T668 contributes to the neuronal degeneration in Alzheimer's disease (AD) by regulating its translocation into the nucleus and then affects neurodegeneration; therefore, the specific inhibitor of T668 phosphorylation might be the target of AD therapy.Amyloid beta peptide (A␤) generated from amyloid precursor protein (APP) is the main component of neuritic plaques in the brains of Alzheimer's disease (AD) patients, and its aggregation is hypothesized to be central to the pathogenesis of AD (28). APP, which is a type I transmembrane protein, is cleaved consecutively, first at the extracellular juxtamembrane region by ␣-or ␤-secretase and then at the intramembrane region by ␥-secretase. Following the first cleavage, a soluble APP fragment (sAPP␣ or sAPP␤) is secreted, and then, following the second cleavage, p3 or A␤ peptides and the AICD (APP intracellular domain) are generated, together with release of the cytoplasmic fragment into the cytoplasm (7,29,31,37,39).APP contains eight potential phosphorylation sites within its cytoplasmic domain (21). Seven of these potential phosphorylation sites were recently shown to be phosphorylated in AD brains, i.e., Y653, S655, T668, S675, Y682, T686, and Y687 (APP695 isoform numbering) (21). The constitutive phosphorylation of APP at T668 is observed specifically in the brain (14).

Protein Phosphatase 2A Methyltransferase Links Homocysteine Metabolism with Tau and Amyloid Precursor Protein Regulation

“…It is of particular significance that APP can be phosphorylated on Thr-668 by cdk5 and glycogen-synthase kinase 3, two tau protein kinases that have been implicated in the neurofibrillary degeneration in AD (Stoothoff and Johnson, 2005). Notably, phosphorylation at Thr-668 has been linked to increased amyloidogenic processing of APP (Ando et al, 2001;Liu et al, 2003;Phiel et al, 2003;Vingtdeux et al, 2005;Chang et al, 2006;Pierrot et al, 2006). Accordingly, enhanced APP phosphorylation at the Thr-668 site correlated with increased A␤ production in our experiments.…”

Amyloid precursor protein regulates neurogenesis by antagonizing miR-574-5p in the developing cerebral cortex

“…NATURE COMMUNICATIONS | DOI: 10.1038/ncomms4330 ARTICLE the exact molecular mechanism of how APP-mediated regulation of miR-574-5p transcription is unclear, we speculate that APP may directly bind to the genomic regions surrounding miR-574-5p through intracellular C-terminal Domain (AICD) of APP, given that AICD can translocate to nucleus upon phosphorylation of APP and mediate some nuclear signalling events [26][27][28] . Next, what is the molecular target of miR-574-5p in regulating the proliferation and differentiation of NPCs?…”

The Loss of c-Jun N-Terminal Protein Kinase Activity Prevents the Amyloidogenic Cleavage of Amyloid Precursor Protein and the Formation of Amyloid PlaquesIn Vivo

“…Active JNK phophorylates AP1 transcription factors to regulate gene expression (i), and APP at T668 to enhance the amyloidogenic cleavage of APP (ii). CTF␤ generated by ␤-secretase is processed by ␥-secretase to produce a phosphorylated form of AICD, which can translocate to the nucleus (Chang et al, 2006), and more A␤, which further stimulates JNK activity. Sustained high-level JNK activity in the brain induces caspase activation (iii) causing synaptic dysfunction (D'Amelio et al, 2011) and/or neuronal death.…”