Gleevec Increases Levels of the Amyloid Precursor Protein Intracellular Domain and of the Amyloid-β–degrading Enzyme Neprilysin

Abstract

Amyloid-␤ (A␤) deposition is a major pathological hallmark of Alzheimer's disease. Gleevec, a known tyrosine kinase inhibitor, has been shown to lower A␤ secretion, and it is considered a potential basis for novel therapies for Alzheimer's disease. Here, we show that Gleevec decreases A␤ levels without the inhibition of Notch cleavage by a mechanism distinct from ␥-secretase inhibition. Gleevec does not influence ␥-secretase activity in vitro; however, treatment of cell lines leads to a dose-dependent increase in the amyloid precursor protein intracellular domain (AICD), whereas secreted A␤ is decreased. This effect is observed even in presence of a potent ␥-secretase inhibitor, suggesting that Gleevec does not activate AICD generation but instead may slow down AICD turnover. Concomitant with the increase in AICD, Gleevec leads to elevated mRNA and protein levels of the A␤-degrading enzyme neprilysin, a potential target gene of AICDregulated transcription. Thus, the Gleevec mediated-increase in neprilysin expression may involve enhanced AICD signaling. The finding that Gleevec elevates neprilysin levels suggests that its A␤-lowering effect may be caused by increased A␤-degradation. INTRODUCTIONThe main neuropathological features of Alzheimer's disease (AD) are the extracellular deposition of amyloid-␤ (A␤) peptides and the formation of intracellular neurofibrillary tangles, accompanied by neuron loss and dementia (Selkoe, 2001). A␤ is generated by sequential proteolytic cleavages of the amyloid precursor protein (APP) by ␤-secretase (BACE) and ␥-secretase. The ␥-secretase cleavage occurs within the membrane, releasing the APP intracellular domain (AICD) into the cytosol. AICD, together with its binding partners Fe65 and Tip60, is considered to be involved in transcriptional regulation (Cao and Sudhof, 2001). Putative target genes of AICD signaling have been suggested (Baek et al., 2002;Kim et al., 2003;von Rotz et al., 2004;Pardossi-Piquard et al., 2005;Ryan and Pimplikar, 2005;Muller et al., 2007), although results for some of these genes are controversial (Hass and Yankner, 2005;Hebert et al., 2006;Chen and Selkoe, 2007;Pardossi-Piquard et al., 2007). One potential AICD target gene is the A␤-degrading enzyme neprilysin (Pardossi-Piquard et al., 2005, a metalloprotease that is one of the main A␤-degrading enzymes in the brain (Carson and Turner, 2002).␥-Secretase is a multiprotein complex, processing several type I integral membrane proteins, including APP and the Notch receptor (Kopan and Ilagan, 2004). Therapeutic strategies aimed at lowering A␤ include the development of selective ␥-secretase inhibitors (Evin et al., 2006). However, long-term treatment with ␥-secretase inhibitors has shown severe side effects in preclinical animal studies due to inhibition of Notch processing and signaling (Searfoss et al., 2003;Wong et al., 2004).Recently, Gleevec (signal transduction inhibitor 571, STI571, imantinib mesylate), a tyrosine kinase inhibitor, has been described to lower A␤ in a cell-free system, in N2A cells e...

The Role of γ-Secretase Activating Protein (GSAP) and Imatinib in the Regulation of γ-Secretase Activity and Amyloid-β Generation

“…However, our findings do give rise to the possibility that imatinib can decrease A␤ levels by some alternative mechanism independent of GSAP. For instance, it has been shown that imatinib can regulate A␤ and AICD levels in cells by a mechanism involving increased neprilysin expression (26,27).…”

Neprilysin and Amyloid Beta Peptide Degradation

“…Although the differences between the original study of Pardossi-Piquard et al [74] and those of Chen and Selkoe [79] have been discussed [80], these studies need to be verified independently. Indirect support for the regulation of the NEP gene by AICD was recently published by Eisele et al [81]. They showed that Gleevac caused an increase in AICD levels by an unknown mechanism, possibly by decreasing the rate of AICD catabolism.…”

BRI2 Protein Regulates β-Amyloid Degradation by Increasing Levels of Secreted Insulin-degrading Enzyme (IDE)

“…To detect total A␤, equal amounts of conditioned cell media were analyzed on 12% NuPAGE gels using MES running buffer (Invitrogen). For analysis of APP C-terminal fragments, separation of A␤40/A␤42 and Western blot detection of proteins was carried out as described previously (29). Representative blots from at least three independent experiments are shown.…”