title: Inositol pyrophosphates inhibit synaptotagmin-dependent exocytosis.
abstract: Inositol pyrophosphates such as 5-diphosphoinositol pentakisphosphate (5-IP7) are highly energetic inositol metabolites containing phosphoanhydride bonds. Although inositol pyrophosphates are known to regulate various biological events, including growth, survival, and metabolism, the molecular sites of 5-IP7 action in vesicle trafficking have remained largely elusive. We report here that elevated 5-IP7 levels, caused by overexpression of inositol hexakisphosphate (IP6) kinase 1 (IP6K1), suppressed depolarization-induced neurotransmitter release from PC12 cells. Conversely, IP6K1 depletion decreased intracellular 5-IP7 concentrations, leading to increased neurotransmitter release. Consistently, knockdown of IP6K1 in cultured hippocampal neurons augmented action potential-driven synaptic vesicle exocytosis at synapses. Using a FRET-based in vitro vesicle fusion assay, we found that 5-IP7, but not 1-IP7, exhibited significantly higher inhibitory activity toward synaptic vesicle exocytosis than IP6 Synaptotagmin 1 (Syt1), a Ca(2+) sensor essential for synaptic membrane fusion, was identified as a molecular target of 5-IP7 Notably, 5-IP7 showed a 45-fold higher binding affinity for Syt1 compared with IP6 In addition, 5-IP7-dependent inhibition of synaptic vesicle fusion was abolished by increasing Ca(2+) levels. Thus, 5-IP7 appears to act through Syt1 binding to interfere with the fusogenic activity of Ca(2+) These findings reveal a role of 5-IP7 as a potent inhibitor of Syt1 in controlling the synaptic exocytotic pathway and expand our understanding of the signaling mechanisms of inositol pyrophosphates.
authors.affiliation: Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea; Center for Nanomedicine, Institute for Basic Science (IBS), Yonsei University, Seoul 30722, Korea; Yonsei-IBS Institute, Yonsei University, Seoul 30722, Korea;
authors.forename: Tae-Sun
authors.initials: TS
authors.lastname: Lee
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea;
authors.forename: Joo-Young
authors.initials: JY
authors.lastname: Lee
authors.affiliation: Department of Biomedical Science, Graduate School, Kyung Hee University, Seoul 02447, Korea;
authors.forename: Jae Won
authors.initials: JW
authors.lastname: Kyung
authors.affiliation: Biomedical Research Institute, Korea Institute of Science and Technology, Seoul 02792, Korea;
authors.forename: Yoosoo
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea;
authors.forename: Seung Ju
authors.initials: SJ
authors.lastname: Park
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea;
authors.forename: Seulgi
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Chemistry, University of Zurich, 8057 Zurich, Switzerland;
authors.forename: Igor
authors.initials: I
authors.lastname: Pavlovic
authors.affiliation: Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea;
authors.forename: Byoungjae
authors.initials: B
authors.lastname: Kong
authors.affiliation: Asia-Pacific Center for Theoretical Physics, Pohang, Gyeongbuk 37673, Korea;
authors.forename: Yong Seok
authors.initials: YS
authors.lastname: Jho
authors.affiliation: Institute of Organic Chemistry, Albert-Ludwigs-University Freiburg, Freiburg 79104, Germany;
authors.forename: Henning J
authors.initials: HJ
authors.lastname: Jessen
authors.affiliation: Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 16419, Korea;
authors.forename: Dae-Hyuk
authors.initials: DH
authors.lastname: Kweon
authors.affiliation: Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011;
authors.forename: Yeon-Kyun
authors.initials: YK
authors.lastname: Shin
authors.affiliation: Department of Biomedical Science, Graduate School, Kyung Hee University, Seoul 02447, Korea; Department of Physiology, School of Medicine, Neurodegeneration Control Research Center, Kyung Hee University, Seoul 02447, Korea; sunghyunkim@khu.ac.kr tyyoon@yonsei.ac.kr seyunkim@kaist.ac.kr.
authors.forename: Sung Hyun
authors.initials: SH
authors.lastname: Kim
authors.affiliation: Center for Nanomedicine, Institute for Basic Science (IBS), Yonsei University, Seoul 30722, Korea; Yonsei-IBS Institute, Yonsei University, Seoul 30722, Korea; sunghyunkim@khu.ac.kr tyyoon@yonsei.ac.kr seyunkim@kaist.ac.kr.
authors.forename: Tae-Young
authors.initials: TY
authors.lastname: Yoon
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea; Korea Advanced Institute of Science and Technology Institute for the BioCentury, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea sunghyunkim@khu.ac.kr tyyoon@yonsei.ac.kr seyunkim@kaist.ac.kr.
authors.forename: Seyun
authors.initials: S
authors.lastname: Kim
mesh_terms: D000818:Animals; D005089:Exocytosis / Q000187:drug effects*; D006624:Hippocampus / Q000166:cytology; D007295:Inositol Phosphates / Q000494:pharmacology*; D009474:Neurons / Q000502:physiology; D016716:PC12 Cells; D017856:Phosphotransferases (Phosphate Group Acceptor) / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D050863:Synaptotagmin I / Q000502:physiology*
chemical_list: D007295:Inositol Phosphates; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; C079849:1-diphosphoinositol pentakisphosphate; D017856:Phosphotransferases (Phosphate Group Acceptor)
keywords: inositol pyrophosphate; synaptic vesicle exocytosis; synaptotagmin