Downregulation of myosin II-B by siRNA alters the subcellular localization of the amyloid precursor protein and increases amyloid-b deposition in N2a cells Sara Massone a , Francesca Argellati a , Mario Passalacqua a , Andrea Armirotti a , Luca Melone a , Cristina d’Abramo a,b , Umberto M. Marinari a , Cinzia Domenicotti a , Maria A. Pronzato a , Roberta Ricciarelli a, * a Department of Experimental Medicine, University of Genoa, Via L.B. Alberti 2, 16132 Genoa, Italy b Department of Pathology, Albert Einstein College of Medicine, Bronx, NY, USA Received 30 July 2007 Available online 21 August 2007 Abstract The Alzheimer’s disease (AD) brain pathology is characterized by extracellular deposits of amyloid-b (Ab) peptides and intraneuronal fibrillar structures. These pathological features may be functionally linked, but the mechanism by which Ab accumulation relates to neu- ronal degeneration is still poorly understood. Ab peptides are fragments cleaved from the amyloid precursor protein (APP), a transmem- brane 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 Ab deposition, concomitantly altering the subcellular localization of APP. These new insights might be impor- tant for the understanding of the function of APP and provide a novel conceptual framework in which to analyze its pathological role. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Alzheimer’s disease; Amyloid precursor protein (APP); Amyloid-b; Myosin II Alzheimer’s disease (AD) is the most common neurode- generative disorder of the elderly and is characterized clin- ically by a progressive memory loss, as well as other cognitive impairments. The neuropathological hallmarks of AD include abundant deposits of amyloid-b (Ab) pep- tides organized in senile plaques, accumulation of abnor- mal tau protein in neurofibrillary tangles (NFTs), and extensive neuronal degeneration and loss. The pathogenic role of Ab deposition is underscored by the evidence that each of the disease-causing mutations in familial AD results in enhanced production of amyloidogenic Ab pep- tides. However, the numbers of NFTs are more closely cor- related with neuronal loss and dementia than are the numbers of senile plaques, and the issue of whether Ab deposits are neurotoxic, protective, or simply incidental markers of disease has remained controversial. The Ab peptides found in senile plaques derive by the proteolytic cleavage of the b-amyloid precursor protein (APP), which is cleaved sequentially by enzymes termed b- and c-secre- tase. The b-site APP cleavage enzyme (BACE) has been identified recently as a membrane-bound aspartyl-protease [1]. Cleavage of APP by BACE, at the N-terminus of the Ab sequence, is the first prerequisite for generation of Ab peptides. An additional cleavage in the transmembrane domain of APP by c-secretase generates the C-terminal 0006-291X/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2007.08.061 * Corresponding author. Fax: +39 010 3538836. E-mail address: ricciarelli@medicina.unige.it (R. Ricciarelli). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 362 (2007) 633–638