title: The Proteome of BLOC-1 Genetic Defects Identifies the Arp2/3 Actin Polymerization Complex to Function Downstream of the Schizophrenia Susceptibility Factor Dysbindin at the Synapse.
abstract: Proteome modifications downstream of monogenic or polygenic disorders have the potential to uncover novel molecular mechanisms participating in pathogenesis and/or extragenic modification of phenotypic expression. We tested this idea by determining the proteome sensitive to genetic defects in a locus encoding dysbindin, a protein required for synapse biology and implicated in schizophrenia risk. We applied quantitative mass spectrometry to identify proteins expressed in neuronal cells the abundance of which was altered after downregulation of the schizophrenia susceptibility factor dysbindin (Bloc1s8) or two other dysbindin-interacting polypeptides, which assemble into the octameric biogenesis of lysosome-related organelles complex 1 (BLOC-1). We found 491 proteins sensitive to dysbindin and BLOC-1 loss of function. Gene ontology of these 491 proteins singled out the actin cytoskeleton and the actin polymerization factor, the Arp2/3 complex, as top statistical molecular pathways contained within the BLOC-1-sensitive proteome. Subunits of the Arp2/3 complex were downregulated by BLOC-1 loss of function, thus affecting actin dynamics in early endosomes of BLOC-1-deficient cells. Furthermore, we demonstrated that Arp2/3, dysbindin, and subunits of the BLOC-1 complex biochemically and genetically interact, modulating Drosophila melanogaster synapse morphology and homeostatic synaptic plasticity. Our results indicate that ontologically prioritized proteomics identifies novel pathways that modify synaptic phenotypes associated with neurodevelopmental disorder gene defects.
  
  
  
  The mechanisms associated with schizophrenia are mostly unknown despite the increasing number of genetic loci identified that increase disease risk. We present an experimental strategy that impartially and comprehensively interrogates the proteome of neurons to identify effects of genetic mutations in a schizophrenia risk factor, dysbindin. We find that the expression of the actin polymerization complex Arp2/3 is reduced in dysbindin-deficient cells, thus affecting actin-dependent phenotypes in two cellular compartments where dysbindin resides, endosomes and presynapses. Our studies indicate that a central cellular structure affected by schizophrenia susceptibility loci is the actin cytoskeleton, an organelle necessary for synaptic function in the presynaptic and postsynaptic compartment.
authors.affiliation: Department of Cell Biology and agokhal@emory.edu vfaunde@emory.edu.
authors.forename: Avanti
authors.identifier: 0000-0001-7432-8541
authors.initials: A
authors.lastname: Gokhale
authors.affiliation: Kennesaw State University, Atlanta, Georgia 30144.|Department of Chemistry, Agnes Scott College, Decatur, Georgia 30030.
authors.forename: Cortnie
authors.identifier: 0000-0002-6612-0780
authors.initials: C
authors.lastname: Hartwig
authors.affiliation: Department of Cell Biology and.|Center for the Study of Human Health, Emory University, Atlanta, Georgia 30322.
authors.forename: Amanda H
authors.identifier: 0000-0003-0084-7618
authors.initials: AH
authors.lastname: Freeman
authors.affiliation: Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, Georgia 30302.
authors.forename: Ravi
authors.identifier: 0000-0003-3725-9115
authors.initials: R
authors.lastname: Das
authors.affiliation: Department of Cell Biology and.
authors.forename: Stephanie A
authors.identifier: 0000-0003-0758-9500
authors.initials: SA
authors.lastname: Zlatic
authors.affiliation: Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, and.
authors.forename: Rachel
authors.identifier: 0000-0002-2172-9947
authors.initials: R
authors.lastname: Vistein
authors.affiliation: Department of Cell Biology and.
authors.forename: Amelia
authors.identifier: 0000-0001-8533-4293
authors.initials: A
authors.lastname: Burch
authors.affiliation: Department of Chemistry, Agnes Scott College, Decatur, Georgia 30030.
authors.forename: Guillemette
authors.identifier: 0000-0002-2979-1200
authors.initials: G
authors.lastname: Carrot
authors.affiliation: Department of Cell Biology and.
authors.forename: Arielle F
authors.identifier: 0000-0001-5291-4283
authors.initials: AF
authors.lastname: Lewis
authors.affiliation: Kennesaw State University, Atlanta, Georgia 30144.
authors.forename: Sheldon
authors.identifier: 0000-0002-1682-8633
authors.initials: S
authors.lastname: Nelms
authors.affiliation: Department of Biology, Neurobiology Section, University of Southern California, Los Angeles, California 90089.
authors.forename: Dion K
authors.identifier: 0000-0003-1884-284X
authors.initials: DK
authors.lastname: Dickman
authors.affiliation: Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, and.
authors.forename: Manojkumar A
authors.identifier: 0000-0002-3177-4231
authors.initials: MA
authors.lastname: Puthenveedu
authors.affiliation: Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, Georgia 30302.
authors.forename: Daniel N
authors.identifier: 0000-0001-9191-9212
authors.initials: DN
authors.lastname: Cox
authors.affiliation: Department of Cell Biology and agokhal@emory.edu vfaunde@emory.edu.
authors.forename: Victor
authors.identifier: 0000-0002-2114-5271
authors.initials: V
authors.lastname: Faundez
mesh_terms: D051378:Actin-Related Protein 3 / Q000235:genetics*; D000199:Actins / Q000235:genetics; D000091302:Angiopoietin-Like Protein 2; D000075802:Angiopoietin-like Proteins; D042682:Angiopoietins / Q000235:genetics*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000235:genetics; D004331:Drosophila melanogaster; D000074765:Dysbindin; D049029:Dystrophin-Associated Proteins / Q000235:genetics*; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D037102:Lectins / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D058105:Polymerization; D020543:Proteome; D012559:Schizophrenia / Q000235:genetics*; D013569:Synapses
chemical_list: D051378:Actin-Related Protein 3; D000199:Actins; C495929:Actr3 protein, mouse; D000091302:Angiopoietin-Like Protein 2; D000075802:Angiopoietin-like Proteins; D042682:Angiopoietins; C485793:Angptl2 protein, mouse; C513476:Bloc1s6 protein, mouse; D002352:Carrier Proteins; C498992:Dtnbp1 protein, mouse; D000074765:Dysbindin; D049029:Dystrophin-Associated Proteins; D047908:Intracellular Signaling Peptides and Proteins; D037102:Lectins; D020543:Proteome
keywords: Arp2/3; BLOC-1; dysbindin; proteomics; schizophrenia; synapse