title: The Protein Complex of Neurodegeneration-related Phosphoinositide Phosphatase Sac3 and ArPIKfyve Binds the Lewy Body-associated Synphilin-1, Preventing Its Aggregation.
abstract: The 5-phosphoinositide phosphatase Sac3, in which loss-of-function mutations are linked to neurodegenerative disorders, forms a stable cytosolic complex with the scaffolding protein ArPIKfyve. The ArPIKfyve-Sac3 heterodimer interacts with the phosphoinositide 5-kinase PIKfyve in a ubiquitous ternary complex that couples PtdIns(3,5)P2 synthesis with turnover at endosomal membranes, thereby regulating the housekeeping endocytic transport in eukaryotes. Neuron-specific associations of the ArPIKfyve-Sac3 heterodimer, which may shed light on the neuropathological mechanisms triggered by Sac3 dysfunction, are unknown. Here we conducted mass spectrometry analysis for brain-derived interactors of ArPIKfyve-Sac3 and unraveled the α-synuclein-interacting protein Synphilin-1 (Sph1) as a new component of the ArPIKfyve-Sac3 complex. Sph1, a predominantly neuronal protein that facilitates aggregation of α-synuclein, is a major component of Lewy body inclusions in neurodegenerative α-synucleinopathies. Modulations in ArPIKfyve/Sac3 protein levels by RNA silencing or overexpression in several mammalian cell lines, including human neuronal SH-SY5Y or primary mouse cortical neurons, revealed that the ArPIKfyve-Sac3 complex specifically altered the aggregation properties of Sph1-GFP. This effect required an active Sac3 phosphatase and proceeded through mechanisms that involved increased Sph1-GFP partitioning into the cytosol and removal of Sph1-GFP aggregates by basal autophagy but not by the proteasomal system. If uncoupled from ArPIKfyve elevation, overexpressed Sac3 readily aggregated, markedly enhancing the aggregation potential of Sph1-GFP. These data identify a novel role of the ArPIKfyve-Sac3 complex in the mechanisms controlling aggregate formation of Sph1 and suggest that Sac3 protein deficiency or overproduction may facilitate aggregation of aggregation-prone proteins, thereby precipitating the onset of multiple neuronal disorders.
authors.affiliation: Departments of Physiology, Wayne State School of Medicine, Detroit, Michigan 48201.
authors.forename: Ognian C
authors.initials: OC
authors.lastname: Ikonomov
authors.affiliation: Departments of Physiology, Wayne State School of Medicine, Detroit, Michigan 48201.
authors.forename: Diego
authors.initials: D
authors.lastname: Sbrissa
authors.affiliation: Departments of Physiology, Wayne State School of Medicine, Detroit, Michigan 48201.
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Compton
authors.affiliation: Departments of Physiology, Wayne State School of Medicine, Detroit, Michigan 48201; Departments of Emergency Medicine, Wayne State School of Medicine, Detroit, Michigan 48201.
authors.forename: Rita
authors.initials: R
authors.lastname: Kumar
authors.affiliation: Departments of Pharmacology, Wayne State School of Medicine, Detroit, Michigan 48201.
authors.forename: Ellen J
authors.initials: EJ
authors.lastname: Tisdale
authors.affiliation: Departments of Physiology, Wayne State School of Medicine, Detroit, Michigan 48201.
authors.forename: Xuequn
authors.initials: X
authors.lastname: Chen
authors.affiliation: Departments of Physiology, Wayne State School of Medicine, Detroit, Michigan 48201. Electronic address: ashishev@med.wayne.edu.
authors.forename: Assia
authors.initials: A
authors.lastname: Shisheva
mesh_terms: D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism*; D002522:Chlorocebus aethiops; D005420:Flavoproteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D016631:Lewy Bodies / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D019636:Neurodegenerative Diseases / Q000201:enzymology / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D002352:Carrier Proteins; D005420:Flavoproteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C118958:SNCAIP protein, human; C494631:VAC14 protein, human; D049452:Green Fluorescent Proteins; C522215:FIG4 protein, human; D010744:Phosphoric Monoester Hydrolases
keywords: ArPIKfyve-Sac3 complex; Parkinson disease; Synphilin-1; aggregation; aggresome; neurodegenerative disease; neuron; phosphatidylinositol phosphatase; phospholipid; proteasome