A possible link between KCNQ2‐ and STXBP1‐related encephalopathies: STXBP1 reduces the inhibitory impact of syntaxin‐1A on M current

• DOI: 10.1111/epi.13927
• Publication Date: 2017-10-25T05:46:38Z
• Authors: Jérôme Devaux; Sandra Dhifallah; Michela De Maria; Geoffrey Stuart‐L...; Hélène Becq; Mathieu Milh; Florence Molinari; Laurent Aniksztejn
• Keywords: Syntaxin 1A; Potassium Channels; [SDV]Life Sciences [q-bio]; [SDV.NEU.NB]Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]/Neurobiology; Early onset epileptic encephalopathies; Syntaxin 1; CHO Cells; KCNQ3 Potassium Channel; 03 medical and health sciences; Cricetulus; Munc18 Proteins; Cricetinae; [SDV.BC.IC]Life Sciences [q-bio]/Cellular Biology/Cell Behavior [q-bio.CB]; Potassium Channel Blockers; Animals; Humans; KCNQ2 Potassium Channel; Biotinylation; 0303 health sciences; Dose-Response Relationship, Drug; M current; Electroencephalography; Kv7 channels; [SDV.IMM.IA]Life Sciences [q-bio]/Immunology/Adaptive immunology; KCNQ1 Potassium Channel; STXBP1; [SDV.NEU]Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC]; Spasms, Infantile

SummaryObjectiveKv7 channels mediate the voltage‐gated M‐type potassium current. Reduction of M current due to KCNQ2 mutations causes early onset epileptic encephalopathies (EOEEs). Mutations in STXBP1 encoding the syntaxin binding protein 1 can produce a phenotype similar to that of KCNQ2 mutations, suggesting a possible link between STXBP1 and Kv7 channels. These channels are known to be modulated by syntaxin‐1A (Syn‐1A) that binds to the C‐terminal domain of the Kv7.2 subunit and strongly inhibits M current. Here, we investigated whether STXBP1could prevent this inhibitory effect of Syn‐1A and analyzed the consequences of two mutations in STXBP1 associated with EOEEs.MethodsElectrophysiologic analysis of M currents mediated by homomeric Kv7.2 or heteromeric Kv7.2/Kv7.3 channels in Chinese hamster ovary (CHO) cells coexpressing Syn‐1A and/or STXBP1 or mutants STXBP1 p.W28* and p.P480L. Expression and interaction of these different proteins have been investigated using biochemical and co‐immunoprecipitation experiments.ResultsSyn‐1A decreased M currents mediated by Kv7.2 or Kv7.2/Kv7.3 channels. STXBP1 had no direct effects on M current but dampened the inhibition produced by Syn‐1A by abrogating Syn‐1A binding to Kv7 channels. The mutation p.W28*, but not p.P480L, failed to rescue M current from Syn‐1A inhibition. Biochemical analysis showed that unlike the mutation p.W28*, the mutation p.P480L did not affect STXBP1 expression and reduced the interaction of Syn‐1A with Kv7 channels.SignificanceThese data indicate that there is a functional link between STXBP1 and Kv7 channels via Syn‐1A, which may be important for regulating M‐channel activity and neuronal excitability. They suggest also that a defect in Kv7 channel activity or regulation could be one of the consequences of some STXBP1 mutations associated with EOEEs. Furthermore, our data reveal that STXBP1 mutations associated with the Ohtahara syndrome do not necessarily result in protein haploinsufficiency.