Yoshihiro Taura: Department of Pediatrics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Takenori Tozawa: Department of Pediatrics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan. Electronic address: takenori@koto.kpu-m.ac.jp.
Takahiro Fujimoto: Department of Pathology and Applied Neurobiology, Kyoto Prefectural University of Medicine, Graduate School of Medical Science, Kyoto, Japan.
Eisuke Ichise: Department of Pediatrics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Tomohiro Chiyonobu: Department of Pediatrics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan; Department of Molecular Diagnostics and Therapeutics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Kyoko Itoh: Department of Pathology and Applied Neurobiology, Kyoto Prefectural University of Medicine, Graduate School of Medical Science, Kyoto, Japan.
Tomoko Iehara: Department of Pediatrics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Syntaxin-binding protein 1 (STXBP1, also known as Munc18-1) regulates exocytosis as a chaperone protein of Syntaxin1A. The haploinsufficiency of STXBP1 causes early infantile-onset developmental and epileptic encephalopathy, known as STXBP1encephalopathy. Previously, we reported impaired cellular localization of Syntaxin1A.in induced pluripotent stem cell-derived neurons from an STXBP1encephalopathypatient harboring a nonsense mutation. However, the molecular mechanism of abnormal Syntaxin1A.localization in the haploinsufficiency of STXBP1 remains unknown. This study aimed to identify the novel interacting partner of STXBP1 involved in transporting Syntaxin1A.to the plasma membrane. Affinity purification coupled with mass spectrometry analysis identified a motor protein Myosin Va.as a potential binding partner of STXBP1. Co-immunoprecipitation analysis of the synaptosomal fraction from the mouse and tag-fused recombinant proteins revealed that the STXBP1 short splice variant (STXBP1S) interacted with Myosin Va.in addition to Syntaxin1A. These proteins colocalized at the tip of the growth cone and axons in primary cultured hippocampal neurons. Furthermore, RNAi-mediated gene silencing in Neuro2a cells showed that STXBP1 and Myosin Va.were required for membrane trafficking of Syntaxin1A. In conclusion, this study proposes a potential role of STXBP1 in the trafficking of the presynaptic protein Syntaxin1A.to the plasma membrane in conjunction with Myosin Va.
