title: Functional analysis of rare variants found in schizophrenia implicates a critical role for GIT1-PAK3 signaling in neuroplasticity.
abstract: Although the pathogenesis of schizophrenia (SCZ) is proposed to involve alterations of neural circuits via synaptic dysfunction, the underlying molecular mechanisms remain poorly understood. Recent exome sequencing studies of SCZ have uncovered numerous single-nucleotide variants (SNVs); however, the majority of these SNVs have unknown functional consequences, leaving their disease relevance uncertain. Filling this knowledge gap requires systematic application of quantitative and scalable assays to assess known and novel biological functions of genes. Here we demonstrate loss-of-function effects of multiple rare coding SNVs found in SCZ subjects in the GIT1 (G protein-coupled receptor kinase interacting ArfGAP 1) gene using functional cell-based assays involving coexpression of GIT1 and PAK3 (p21 protein (Cdc42/Rac)-activated kinase 3). Most notably, a GIT1-R283W variant reported in four independent SCZ cases was defective in activating PAK3 as well as MAPK (mitogen-activated protein kinase). Similar functional deficits were found for a de novo SCZ variant GIT1-S601N. Additional assays revealed deficits in the capacity of GIT1-R283W to stimulate PAK phosphorylation in cultured hippocampal neurons. In addition, GIT1-R283W showed deficits in the induction of GAD1 (glutamate decarboxylase 1) protein expression. Extending these functional assays to 10 additional rare GIT1 variants revealed the existence of an allelic series with the majority of the SCZ case variants exhibiting loss of function toward MAPK activation in a manner correlated with loss of PAK3 activation. Taken together, we propose that rare variants in GIT1, along with other genetic and environmental factors, cause dysregulation of PAK3 leading to synaptic deficits in SCZ.
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Kim
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.
authors.forename: J
authors.identifier: 0000-0003-0891-9567
authors.initials: J
authors.lastname: Biag
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.|Chemical Neurobiology Laboratory, Departments of Neurology and Psychiatry, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.|Center for Human Genetic Research, Massachusetts General Hospital, Boston, MA, USA.|Psychiatric and Neurodevelopmental Genetics Unit, Massachusetts General Hospital, Boston, MA, USA.|Molecular Neurogenetics Unit, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Fass
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Lewis
authors.affiliation: McGovern Institute for Brain Research, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.|McGovern Institute for Brain Research, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Fleishman
authors.affiliation: Department of Pharmacology and Toxicology, Sealy Center for Structural Biology and Biophysics, University of Texas Medical Branch, Galveston TX, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: Gangwar
authors.affiliation: Department of Pharmacology and Toxicology, Sealy Center for Structural Biology and Biophysics, University of Texas Medical Branch, Galveston TX, USA.
authors.forename: M
authors.initials: M
authors.lastname: Machius
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.|Division of Psychiatric Genomics, Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
authors.forename: M
authors.initials: M
authors.lastname: Fromer
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.|Center for Human Genetic Research, Massachusetts General Hospital, Boston, MA, USA.|Psychiatric and Neurodevelopmental Genetics Unit, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Purcell
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: McCarroll
authors.affiliation: Department of Pharmacology and Toxicology, Sealy Center for Structural Biology and Biophysics, University of Texas Medical Branch, Galveston TX, USA.
authors.forename: G
authors.initials: G
authors.lastname: Rudenko
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC, USA.
authors.forename: R T
authors.initials: RT
authors.lastname: Premont
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.
authors.forename: E M
authors.initials: EM
authors.lastname: Scolnick
authors.affiliation: Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA.|Chemical Neurobiology Laboratory, Departments of Neurology and Psychiatry, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.|Center for Human Genetic Research, Massachusetts General Hospital, Boston, MA, USA.|Psychiatric and Neurodevelopmental Genetics Unit, Massachusetts General Hospital, Boston, MA, USA.|Molecular Neurogenetics Unit, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Haggarty
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D018929:Cell Culture Techniques / Q000379:methods; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D057809:HEK293 Cells / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009473:Neuronal Plasticity / Q000235:genetics / Q000502:physiology; D009474:Neurons / Q000378:metabolism; D010750:Phosphoproteins; D010766:Phosphorylation; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012559:Schizophrenia / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D054462:p21-Activated Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C485647:GIT1 protein, human; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020928:Mitogen-Activated Protein Kinases