title: Tubulin polymerization-promoting protein (TPPP/p25α) promotes unconventional secretion of α-synuclein through exophagy by impairing autophagosome-lysosome fusion.
abstract: Aggregation of α-synuclein can be promoted by the tubulin polymerization-promoting protein/p25α, which we have used here as a tool to study the role of autophagy in the clearance of α-synuclein. In NGF-differentiated PC12 catecholaminergic nerve cells, we show that de novo expressed p25α co-localizes with α-synuclein and causes its aggregation and distribution into autophagosomes. However, p25α also lowered the mobility of autophagosomes and hindered the final maturation of autophagosomes by preventing their fusion with lysosomes for the final degradation of α-synuclein. Instead, p25α caused a 4-fold increase in the basal level of α-synuclein secreted into the medium. Secretion was strictly dependent on autophagy and could be up-regulated (trehalose and Rab1A) or down-regulated (3-methyladenine and ATG5 shRNA) by enhancers or inhibitors of autophagy or by modulating minus-end-directed (HDAC6 shRNA) or plus-end-directed (Rab8) trafficking of autophagosomes along microtubules. Finally, we show in the absence of tubulin polymerization-promoting protein/p25α that α-synuclein release was modulated by dominant mutants of Rab27A, known to regulate exocytosis of late endosomal (and amphisomal) elements, and that both lysosomal fusion block and secretion of α-synuclein could be replicated by knockdown of the p25α target, HDAC6, the predominant cytosolic deacetylase in neurons. Our data indicate that unconventional secretion of α-synuclein can be mediated through exophagy and that factors, which increase the pool of autophagosomes/amphisomes (e.g. lysosomal disturbance) or alter the polarity of vesicular transport of autophagosomes on microtubules, can result in an increased release of α-synuclein monomer and aggregates to the surroundings.
authors: Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, 2200 Copenhagen N, Denmark.
authors: Patrick
authors: P
authors: Ejlerskov
authors: Izabela
authors: I
authors: Rasmussen
authors: Troels Tolstrup
authors: TT
authors: Nielsen
authors: Ann-Louise
authors: AL
authors: Bergström
authors: Yumi
authors: Y
authors: Tohyama
authors: Poul Henning
authors: PH
authors: Jensen
authors: Frederik
authors: F
authors: Vilhardt
mesh_terms: D000818:Animals; D001343:Autophagy; D002352:Carrier Proteins / Q000502:physiology*; D002454:Cell Differentiation; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D055785:Gene Knockdown Techniques; D000073864:Histone Deacetylase 6; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D002479:Inclusion Bodies / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008561:Membrane Fusion; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D020932:Nerve Growth Factor / Q000502:physiology; D016501:Neurites / Q000502:physiology; D016716:PC12 Cells; D010588:Phagosomes / Q000378:metabolism*; D021381:Protein Transport; D059748:Proteolysis; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D055571:Secretory Pathway; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014199:Trehalose / Q000494:pharmacology; D051844:alpha-Synuclein / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D008869:Microtubule-Associated Proteins; D034741:RNA, Small Interfering; C539090:TPPP protein, rat; D051844:alpha-Synuclein; D020932:Nerve Growth Factor; D014199:Trehalose; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases; C545556:HDAC6 protein, rat; D000073864:Histone Deacetylase 6; D006655:Histone Deacetylases; C530052:Rab8a protein, rat; D020691:rab GTP-Binding Proteins; D020123:Sirolimus
keywords: Autophagosomes; Exophagy; HDAC6; Parkinson Disease; Protein Degradation; Protein Secretion; Trafficking; p25α; α-Synuclein
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