title: Cluster formation of inositol 1,4,5-trisphosphate receptor requires its transition to open state.
abstract: The inositol 1,4,5-trisphosphate (IP(3)) receptor (IP(3)R) Ca(2+) channel plays pivotal roles in many aspects of physiological and pathological events. It was previously reported that IP(3)R forms clusters on the endoplasmic reticulum when cytosolic Ca(2+) concentration ([Ca(2+)](C)) is elevated. However, the molecular mechanism of IP(3)R clustering remains largely unknown, and thus its physiological significance is far from clear. In this study we found that the time course of clustering of green fluorescent protein-tagged IP(3)R type 1 (GFP-IP(3)R1), evoked by IP(3)-generating agonists, did not correlate with [Ca(2+)](C) but seemed compatible with cytoplasmic IP(3) concentration. IP(3) production alone induced GFP-IP(3)R1 clustering in the absence of a significant increase in [Ca(2+)](C) but elevated [Ca(2+)](C) without IP(3) production did not. Moreover IP(3)R1 mutants that do not undergo an IP(3)-induced conformational change failed to form clusters. Thus, IP(3)R clustering is induced by its IP(3)-induced conformational change to the open state. We also found that GFP-IP(3)R1 clusters colocalized with ERp44, a luminal protein of endoplasmic reticulum that inhibits its channel activity. This is the first example of ligand-induced clustering of a ligand-gated channel protein.
authors.affiliation: Division of Molecular Neurobiology, Institute of Medical Science and Division of Neural Signal Information, NTT-IMSUT, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Tateishi
authors.forename: Mitsuharu
authors.initials: M
authors.lastname: Hattori
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Nakayama
authors.forename: Miwako
authors.initials: M
authors.lastname: Iwai
authors.forename: Hiroko
authors.initials: H
authors.lastname: Bannai
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nakamura
authors.forename: Takayuki
authors.initials: T
authors.lastname: Michikawa
authors.forename: Takafumi
authors.initials: T
authors.lastname: Inoue
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mikoshiba
mesh_terms: D000818:Animals; D019556:COS Cells; D002118:Calcium / Q000032:analysis; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D002522:Chlorocebus aethiops; D003600:Cytosol / Q000737:chemistry; D049452:Green Fluorescent Proteins; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D008856:Microscopy, Fluorescence; D011487:Protein Conformation; D011940:Receptor Aggregation; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D014162:Transfection
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D049452:Green Fluorescent Proteins; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium