title: AP-1/σ1B-Dependent SV Protein Recycling Is Regulated in Early Endosomes and Is Coupled to AP-2 Endocytosis.
abstract: Adaptor protein (AP)-1/σ1B(-/-) mice have reduced synaptic-vesicle (SV) recycling and increased endosomes. Mutant mice have impaired spatial memory, and σ1B-deficient humans have a severe mental retardation. In order to define these σ1B(-/-) 'bulk' endosomes and to determine their functions in SV recycling, we developed a protocol to separate them from the majority of the neuronal endosomes. The σ1B(-/-) 'bulk' endosomes proved to be classic early endosomes with an increase in the phospholipid phosphatidylinositol 3-phosphate (PI-3-P), which recruits proteins mediating protein sorting out of early endosomes into different routes. σ1B deficiency induced alterations in the endosomal proteome reveals two major functions: SV protein storage and sorting into endolysosomes. Alternative endosomal recycling pathways are not up-regulated, but certain SV proteins are misrouted. Tetraspanins are enriched in σ1B(-/-) synaptosomes, but not in their endosomes or in their clathrin-coated-vesicles (CCVs), indicating AP-1/σ1B-dependent sorting. Synapses contain also more AP-2 CCV, although it is expected that they contain less due to reduced SV recycling. Coat composition of these AP-2 CCVs is altered, and thus, they represent a subpopulation of AP-2 CCVs. Association of calmodulin-dependent protein kinase (CaMK)-IIα, -δ and casein kinase (CK)-IIα with the endosome/SV pool is altered, as well as 14-3-3η, indicating changes in specific signalling pathways regulating synaptic plasticity. The accumulation of early endosomes and endocytotic AP-2 CCV indicates the regulation of SV recycling via early endosomes by the interdependent regulation of AP-2-mediated endocytosis and AP-1/σ1B-mediated SV reformation.
authors.affiliation: Center for Biochemistry and Molecular Cell Biology, Department for Cellular Biochemistry, Georg-August University Göttingen, Humboldtallee 23, 37073, Göttingen, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Kratzke
authors.forename: Ermes
authors.initials: E
authors.lastname: Candiello
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schmidt
authors.forename: Olaf
authors.initials: O
authors.lastname: Jahn
authors.forename: Peter
authors.initials: P
authors.lastname: Schu
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D000818:Animals; D002498:Centrifugation; D022163:Clathrin-Coated Vesicles / Q000378:metabolism; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D007553:Isotope Labeling; D008247:Lysosomes / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000378:metabolism; D059748:Proteolysis; D013572:Synaptic Vesicles / Q000378:metabolism*; D013574:Synaptosomes / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D050656:Transcription Factor AP-2 / Q000378:metabolism*
chemical_list: D048948:14-3-3 Proteins; D018808:Transcription Factor AP-1; D050656:Transcription Factor AP-2