A novel function of FAF1, which induces dopaminergic neuronal death through cell-to-cell transmission
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(2020) 18:133
RESEARCH
Open Access
A novel function of FAF1, which induces dopaminergic neuronal death through cellto-cell transmission Gyeongrin Park†, Bok-Seok Kim† and Eunhee Kim*
Abstract Background: Fas-associated factor 1 (FAF1) has been implicated in Parkinson’s disease (PD) and activates the cell death machinery in the cytosol. However, the presence of extracellular FAF1 has not been studied. Methods: Serum-free conditioned medium (CM) from FAF1-transfected SH-SY5Y cells was concentrated and analyzed by western blotting. Exosomes were isolated from CM by ultracentrifugation and analyzed by western blotting, electron microscopy and nanoparticle tracking analysis. Soluble FAF1 from CM was immunodepleted using anti-FAF1 antibody. Transmission of secreted FAF1 was examined by transwell assay under a confocal microscope. CM-induced cell death was determined by measuring propidium iodide (PI) uptake using a flow cytometer. Results: FAF1 was secreted from SH-SY5Y cells via exocytosis and brefeldin A (BFA)-resistant secretory pathways. Furthermore, FAF1 was secreted as a vesicle-free form and a genuine exosome cargo in the lumen of exosomes. In addition, FAF1 increased the number of exosomes, suggesting a regulatory role in exosome biogenesis. Extracellular FAF1 was transmitted via endocytosis to neighboring cells, where it induced cell death through apoptotic and necrotic pathways. Conclusions: This study presents a novel route by which FAF1 induces neuronal death through cell-to-cell transmission. Keywords: FAF1, Secretion, Exosome, Vesicle-free form, Cell-to-cell transmission, Cell death
Background Cells secrete proteins harboring signal peptides through the classical secretory pathway via the endoplasmic reticulum (ER)-Golgi complex, from which vesicles with cargo proteins move toward and fuse with the plasma membrane and subsequently export cargos to the extracellular space [1]. However, proteins lacking signal peptides are secreted via alternative, nonclassical secretory pathways [2]. These pathways are classified as vesicular and nonvesicular secretory pathways [3]. Some proteins * Correspondence: [email protected] † Gyeongrin Park and Bok-Seok Kim are considered co-first authors. Department of Biological Sciences, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, South Korea
are secreted via extracellular vesicles including exosomes and other vesicles of various sizes [4, 5]. Alternatively, other proteins are secreted through membrane pores and ATP-binding cassette (ABC) transporters, although the exact mechanisms of nonvesicular secretory pathways are elusive [6, 7]. Exosomes, which are nanosized membrane vesicles (50– 150 nm in diameter) secreted into the extracellular environment by various cell types, are associated with intercellular communication with neighboring cells and play a role in a myriad of pathological functions in diseases including cancer, cardiovascular, and neurodegenerative diseases [8–13]. In particular, exosomes remodel the extracellular matrix and promote me
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