C‐terminal fragments of amyloid precursor protein exert neurotoxicity by inducing glycogen synthase kinase‐3β expression

Abstract

The AICD (amyloid precursor protein [APP] intracellular domain) and C31, the caspase-cleaved C-terminal fragment of APP, have been found in the brains of patients with Alzheimer's disease (AD). Here, we demonstrate for the first time that the C-terminal fragments of APP (AICD [C57, C59] and C31) exert neurotoxicity on differentiated PC 12 cells and rat primary cortical neurons by inducing the expression of glycogen synthase kinase 3beta, forming a ternary complex with Fe65 and CP2/LSF/LBP1 in the nucleus, whereas deletion mutants and a point mutant with Y682G of the YENPTY domain, a Fe65 binding domain, do not. Moreover, expression of APP770 and Swedish mutant form of APP increased the levels of C-terminal fragments of APP (APP-CTs) in neuronal cells and also induced the up-regulation of glycogen synthase kinase-3beta at both the mRNA and the protein levels. In addition, we show that CP2/LSF/LBP1 binding site (nt +0 to approximately +10) in human glycogen synthase kinase 3beta promoter region is essential for the induction of the gene transcription by APP-CTs. The neurotoxicities induced by APP-CTs (AICD and C31) were accompanied by an increase in the active form of glycogen synthase kinase-3beta, and by the induction of tau phosphorylation and a reduction in nuclear beta-catenin levels, and led to apoptosis.

Modulation of Gene Expression and Cytoskeletal Dynamics by the Amyloid Precursor Protein Intracellular Domain (AICD)

“…AICD-EGFP-transfected cells showed predominantly nuclear staining, whereas enhanced green fluorescent protein (EGFP) control vector-transfected cells were stained through the whole cell (see Supplemental Figure). Interestingly, transfection rates were low, and just low-level-expressing AICD-EGFP-transfected cells survived 24 h. This supports the discussed toxicity of AICD (Bertrand et al, 2001;Kim et al, 2003), which might be increased as a result of higher stability when expressed as fusion protein. FE65 immunostaining in iFA clones revealed nuclear staining of FE65 (data not shown).…”

“…Indeed, there is evidence that binding of FE65 to AICD is necessary for the nuclear translocation (Kimberly et al, 2001;Muresan and Muresan, 2004;von Rotz et al, 2004). Two different AICD transcriptionally active complexes based on the binding of AICD-FE65 to TIP60 and to CP2/ LSF/LBP1 have been suggested (Cao and Sudhof, 2001;Kim et al, 2003). TIP60 is part of a large nuclear complex with DNA binding, ATPase and DNA helicase activity (Ikura et al, 2000).…”

“…This hypothesis is not in contrast to our findings, because elevated cytosolic levels of AICD might be sufficient to cause a change in the conformation of FE65. This second ternary complex (AICD-FE65-CP2/LSF/LBP1) was suggested to modulate expression of glycogen synthase kinase-3␤ (Kim et al, 2003). Therefore, different AICD transcriptional complexes might explain different regulation patterns.…”

“…Several recent studies have reported putative target genes differentially regulated by an AICD-containing complex. Candidate genes include the prostate cancer antimetastasis gene KAI1 (Baek et al, 2002), glycogen synthase kinase 3␤ (GSK3␤) (Kim et al, 2003), ␤-APP cleaving enzyme (BACE) (von Rotz et al, 2004), APP (von Rotz et al, 2004), and neprilysin (MME) (Pardossi-Piquard et al, 2005). However, regulation of some of these genes is controversial (Ryan and Pimplikar, 2005;Hebert et al, 2006).…”

Stress in the brain: novel cellular mechanisms of injury linked to Alzheimer's disease

“…The generation of the C-terminal fragment C31 results from the cleavage of APP at the caspase site D720 of the C-terminus by caspase 3 [165]. Once generated, C31 enhances glycogen synthase kinase-3β expression and tau protein phosphorylation [107].…”