title: Rescuable folding defective NaV1.1 (SCN1A) mutants in epilepsy: properties, occurrence, and novel rescuing strategy with peptides targeted to the endoplasmic reticulum.
abstract: Mutations of the voltage gated Na(+) channel Na(V)1.1 (SCN1A) are important causes of different genetic epilepsies and can also cause familial hemiplegic migraine (FHM-III). In previous studies, some rescuable epileptogenic folding defective mutants located in domain IV of Na(V)1.1 have been identified, showing partial loss of function also with maximal rescue. Variable rescue may be one of the causes of phenotypic variability, and rescue might be exploited for therapeutic approaches. Recently, we have identified a folding defective FHM-III Na(V)1.1 mutant that showed overall gain of function when rescued, consistent with a differential pathomechanism. Here, we have evaluated functional properties and cell surface expression of six Na(V)1.1 epileptogenic missense mutations in different rescuing conditions, including a novel one that we have developed expressing a selective sodium channel toxin (CsEI) targeted to the endoplasmic reticulum (ER). All the mutants showed loss of function and reduced cell surface expression, consistently with possibility of rescue. Four of them were rescuable by incubation at low temperature and interactions with different co-expressed proteins or a pharmacological chaperone (phenytoin). Notably, CsEI was able to rescue four mutants. Thus, Na(V)1.1 folding defective mutants can be relatively common and mutations inducing rescuable folding defects are spread in all Na(V)1.1 domains. Importantly, epileptogenic mutants showed overall loss of function even upon rescue, differently than FHM-III ones. The effectiveness of CsEI demonstrates that interactions in the ER are sufficient for inducing rescue, and provides a proof of concept for developing possible therapeutic approaches that may overcome some limitations of pharmacological chaperones.
authors.affiliation: Department of Neurophysiopathology, Epilepsy Center, C. Besta Foundation Neurological Institute, 20133 Milano, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Bechi
authors.affiliation: Institute of Molecular and Cellular Pharmacology (IPMC), LabEx ICST, CNRS UMR7275 and University of Nice-Sophia Antipolis, 06560 Valbonne, France.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Rusconi
authors.affiliation: Institute of Molecular and Cellular Pharmacology (IPMC), LabEx ICST, CNRS UMR7275 and University of Nice-Sophia Antipolis, 06560 Valbonne, France.
authors.forename: Sandrine
authors.initials: S
authors.lastname: Cestèle
authors.affiliation: Pediatric Neurology and Neuromuscular Diseases Unit, Department of Neurosciences, Institute G. Gaslini, University of Genova, Genova, Italy.
authors.forename: Pasquale
authors.initials: P
authors.lastname: Striano
authors.affiliation: Department of Neurophysiopathology, Epilepsy Center, C. Besta Foundation Neurological Institute, 20133 Milano, Italy.
authors.forename: Silvana
authors.initials: S
authors.lastname: Franceschetti
authors.affiliation: Institute of Molecular and Cellular Pharmacology (IPMC), LabEx ICST, CNRS UMR7275 and University of Nice-Sophia Antipolis, 06560 Valbonne, France. Electronic address: mantegazza@ipmc.cnrs.fr.
authors.forename: Massimo
authors.initials: M
authors.lastname: Mantegazza
mesh_terms: D015153:Blotting, Western; D002461:Cell Line, Transformed; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D004827:Epilepsy / Q000235:genetics* / Q000378:metabolism*; D004926:Escherichia coli; D006801:Humans; D007150:Immunohistochemistry; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D049990:Membrane Transport Modulators / Q000494:pharmacology; D008959:Models, Neurological; D020125:Mutation, Missense; D062550:NAV1.1 Voltage-Gated Sodium Channel / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D017510:Protein Folding; D012604:Scorpion Venoms / Q000494:pharmacology; D014162:Transfection
chemical_list: D049990:Membrane Transport Modulators; D062550:NAV1.1 Voltage-Gated Sodium Channel; C568242:SCN1A protein, human; D012604:Scorpion Venoms; C053969:scorpion toxin II, Androctonus
keywords: Dravet syndrome; Epileptic encephalopathy; Folding; GEFS+; Rescue; Sodium channel; Toxin