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A possible link between KCNQ 2 ‐ and STXBP 1 ‐related encephalopathies: STXBP 1 reduces the inhibitory impact of syntaxin‐1A on M current
Author(s) -
Devaux Jérôme,
Dhifallah Sandra,
De Maria Michela,
StuartLopez Geoffrey,
Becq Hélène,
Milh Mathieu,
Molinari Florence,
Aniksztejn Laurent
Publication year - 2017
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/epi.13927
Subject(s) - chinese hamster ovary cell , homomeric , mutation , microbiology and biotechnology , syntaxin , biology , mutant , protein subunit , chemistry , genetics , cell culture , membrane protein , gene , membrane
Summary Objective Kv7 channels mediate the voltage‐gated M‐type potassium current. Reduction of M current due to KCNQ 2 mutations causes early onset epileptic encephalopathies ( EOEEs ). Mutations in STXBP 1 encoding the syntaxin binding protein 1 can produce a phenotype similar to that of KCNQ 2 mutations, suggesting a possible link between STXBP 1 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 STXBP 1could prevent this inhibitory effect of Syn‐1A and analyzed the consequences of two mutations in STXBP 1 associated with EOEEs . Methods Electrophysiologic 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 STXBP 1 or mutants STXBP 1 p.W28* and p.P480L. Expression and interaction of these different proteins have been investigated using biochemical and co‐immunoprecipitation experiments. Results Syn‐1A decreased M currents mediated by Kv7.2 or Kv7.2/Kv7.3 channels. STXBP 1 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 STXBP 1 expression and reduced the interaction of Syn‐1A with Kv7 channels. Significance These data indicate that there is a functional link between STXBP 1 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 STXBP 1 mutations associated with EOEE s. Furthermore, our data reveal that STXBP 1 mutations associated with the Ohtahara syndrome do not necessarily result in protein haploinsufficiency.