title: Inherited genetic variants in autism-related CNTNAP2 show perturbed trafficking and ATF6 activation.
abstract: Although genetic variations in several genes encoding for synaptic adhesion proteins have been found to be associated with autism spectrum disorders, one of the most consistently replicated genes has been CNTNAP2, encoding for contactin-associated protein-like 2 (CASPR2), a multidomain transmembrane protein of the neurexin superfamily. Using immunofluorescence confocal microscopy and complementary biochemical techniques, we compared wild-type CASPR2 to 12 point mutations identified in individuals with autism. In contrast to the wild-type protein, localized to the cell surface, some of the mutants show altered cellular disposition. In particular, CASPR2-D1129H is largely retained in the endoplasmic reticulum (ER) in HEK-293 cells and in hippocampal neurons. BiP/Grp78, Calnexin and ERp57, key ER chaperones, appear to be responsible for retention of this mutant and activation of one signaling pathway of the unfolded protein response (UPR). The presence of this mutation also lowers expression and activates proteosomal degradation. A frame-shift mutation that causes a form of syndromic epilepsy (CASPR2-1253*), results in a secreted protein with seemingly normal folding and oligomerization. Taken together, these data indicate that CASPR2-D1129H has severe trafficking abnormalities and CASPR2-1253* is a secreted soluble protein, suggesting that the structural or signaling functions of the membrane tethered form are lost. Our data support a complex genetic architecture in which multiple distinct risk factors interact with others to shape autism risk and presentation.
authors.affiliation: Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, CA 92093, USA.
authors.forename: Giulia
authors.initials: G
authors.lastname: Falivelli
authors.forename: Antonella
authors.initials: A
authors.lastname: De Jaco
authors.forename: Flores Lietta
authors.initials: FL
authors.lastname: Favaloro
authors.forename: Hyuck
authors.initials: H
authors.lastname: Kim
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wilson
authors.forename: Noga
authors.initials: N
authors.lastname: Dubi
authors.forename: Mark H
authors.initials: MH
authors.lastname: Ellisman
authors.forename: Brett S
authors.initials: BS
authors.lastname: Abrahams
authors.forename: Palmer
authors.initials: P
authors.lastname: Taylor
authors.forename: Davide
authors.initials: D
authors.lastname: Comoletti
mesh_terms: D051702:Activating Transcription Factor 6 / Q000235:genetics / Q000378:metabolism; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000235:genetics* / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006624:Hippocampus / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D017354:Point Mutation; D017510:Protein Folding; D021381:Protein Transport / Q000235:genetics; D015398:Signal Transduction; D056811:Unfolded Protein Response / Q000235:genetics
chemical_list: C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; C403049:CNTNAP2 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins