• Lily Paemka, Vinit B Mahajan, Salleh N Ehaideb, Jessica M Skeie, Men Chee Tan, Shu Wu, Allison J Cox, Levi P Sowers, Jozef Gecz, Lachlan Jolly, Polly J Ferguson, Benjamin Darbro, Amy Schneider, Ingrid E Scheffer, Gemma L Carvill, Heather C Mefford, Hatem El-Shanti, Stephen A Wood, J Robert Manak, and Alexander G Bassuk.
• Department of Pediatrics, The University of Iowa, Iowa City, Iowa, United States of America; Interdisciplinary Program in Genetics, The University of Iowa, Iowa City, Iowa, United States of America.
• PLoS Genet. 2015 Mar 1; 11 (3): e1005022.

AbstractEpilepsy is a common disabling disease with complex, multifactorial genetic and environmental etiology. The small fraction of epilepsies subject to Mendelian inheritance offers key insight into epilepsy disease mechanisms; and pathologies brought on by mutations in a single gene can point the way to generalizable therapeutic strategies. Mutations in the PRICKLE genes can cause seizures in humans, zebrafish, mice, and flies, suggesting the seizure-suppression pathway is evolutionarily conserved. This pathway has never been targeted for novel anti-seizure treatments. Here, the mammalian PRICKLE-interactome was defined, identifying prickle-interacting proteins that localize to synapses and a novel interacting partner, USP9X, a substrate-specific de-ubiquitinase. PRICKLE and USP9X interact through their carboxy-termini; and USP9X de-ubiquitinates PRICKLE, protecting it from proteasomal degradation. In forebrain neurons of mice, USP9X deficiency reduced levels of Prickle2 protein. Genetic analysis suggests the same pathway regulates Prickle-mediated seizures. The seizure phenotype was suppressed in prickle mutant flies by the small-molecule USP9X inhibitor, Degrasyn/WP1130, or by reducing the dose of fat facets a USP9X orthologue. USP9X mutations were identified by resequencing a cohort of patients with epileptic encephalopathy, one patient harbored a de novo missense mutation and another a novel coding mutation. Both USP9X variants were outside the PRICKLE-interacting domain. These findings demonstrate that USP9X inhibition can suppress prickle-mediated seizure activity, and that USP9X variants may predispose to seizures. These studies point to a new target for anti-seizure therapy and illustrate the translational power of studying diseases in species across the evolutionary spectrum.

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