The Alzheimer's disease (AD) brain pathology is characterized by extracellular deposits of amyloid-beta (Abeta) peptides and intraneuronal fibrillar structures. These pathological features may be functionally linked, but the mechanism by which Abeta accumulation relates to neuronal degeneration is still poorly understood. Abeta peptides are fragments cleaved from the amyloid precursor protein (APP), a transmembrane protein ubiquitously expressed in the nervous system. Although the proteolytic processing of APP has been implicated in AD, the physiological function of APP and the subcellular site of APP cleavages remain unknown. The overall structure of the protein and its fast anterograde transport along the axon support the idea that APP functions as a vesicular receptor for cytoskeletal motor proteins. In the current study, we test the hypothesis that myosin II, important contributor to the cytoskeleton of neuronal cells, may influence the trafficking and/or the processing of APP. Our results demonstrate that downregulation of myosin II-B, the major myosin isoform in neurons, is able to increase Abeta deposition, concomitantly altering the subcellular localization of APP. These new insights might be important for the understanding of the function of APP and provide a novel conceptual framework in which to analyze its pathological role.
"Equal amounts of protein were incubated with NeutrAvidinTM Protein immobilized onto 6% cross-linked beaded agarose (Thermo Fisher Scientific Inc). After washing in NP-40 buffer, the beads were boiled in sample-buffer, fractionated in sodium dodecyl sulfate–polyacrylamide gel electrophoresis and immunoblotted according to Massone et al. (2007) with the rabbit anti-P2X7 extracellular antibody (1 : 400). Analysis software KODAK 1D 3.6 (Eastman Kodak Co., Rochester, NY, USA) was used for standardization and band quantification; surface expression of rP2X7tr was normalized for full-length rP2X7 expression. "
"The improper production of APP isoforms or aberrant APP trafficking during AD pathogenesis is believed to favor the amyloidogenic pathway23. In addition, recent reports have shown that Aβ production is influenced more by the location of APP cleavage than the total amount of secretase present within the cell24. However, in our study, neither the total amount of APP nor the amount of membrane-associated APP (Figure 2A) was altered in response to PIMT siRNA treatment. "
[Show abstract][Hide abstract] ABSTRACT: To examine the role of protein L-isoaspartyl O-methyltransferase (PIMT; EC 22.214.171.124) on the secretion of Aβ peptides.
HEK293 APPsw cells were treated with PIMT siRNA or adenosine dialdehyde (AdOX), a broad-spectrum methyltransferase inhibitor. Under the conditions, the level of Aβ secretion and regulatory mechanism by PIMT were examined.
Knock-down of PIMT and treatment with AdOX significantly increased Aβ(40) secretion. Reductions in levels of PIMT decreased the secretion of soluble amyloid precursor protein alpha (sAPPα) without altering the total expression of APP or its membrane-bound C83 fragment. However, the levels of the C99 fragment generated by β-secretase were enhanced. Moreover, the decreased secretion of sAPPα resulting from PIMT knock-down seemed to be linked with the suppression of the expression of α-secretase gene products, α-disintegrin and metalloprotease 10 (ADAM10) and ADAM17, as indicated by Western blot analysis. In contrast, ADAM10 was not down-regulated in response to treatment with the protein arginine methyltransferase (PRMT) inhibitor, AMI-1.
This study demonstrates a novel role for PIMT, but not PRMT, as a negative regulator of Aβ peptide formation and a potential protective factor in the pathogenesis of AD.
[Show abstract][Hide abstract] ABSTRACT: A substantial body of evidence indicates that protein kinase C (PKC) is involved in the alpha-secretory processing of the amyloid precursor protein (APP), an event that reduces the formation of the pathogenic amyloid-beta peptide. Recently, we have shown that trafficking and processing of APP are both impaired by knockdown of myosin II-B, one of the major neuronal motor proteins. Here, we provide evidence that the alpha-secretory processing of APP is mediated by PKC-dependent phosphorylation of myosin II-B. This signaling pathway provides an important link between APP and the neuronal cytoskeleton and might be crucial for the understanding of the biological and pathological roles of APP.
The FASEB Journal 04/2009; 23(4):1246-51. DOI:10.1096/fj.08-119263 · 5.04 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.