title: Targeting of inositol 1,4,5-trisphosphate receptors to the endoplasmic reticulum by multiple signals within their transmembrane domains.
abstract: Most inositol 1,4,5-trisphosphate receptors (IP3R) are expressed in the endoplasmic reticulum (ER), where their precise distribution underlies the spatially complex Ca2+ signals evoked by extracellular stimuli. The signals that target IP3R to the ER or, less commonly, to other membranes are unknown. We expressed yellow fluorescent protein-tagged fragments of type 1 IP3R alone or fused with a plasma membrane protein to establish the determinants of ER targeting in COS-7 cells. By using a combination of confocal imaging and glycoprotein analyses, we demonstrated that any pair of the six transmembrane domains (TMD) linked by a luminal loop retains the protein within the ER, and when attached to a plasma membrane protein (ICAM-1), prevents it from reaching the medial Golgi. TMD1 or TMD2 alone were accumulated in mitochondria, whereas TMD5 and TMD6 were retained in ER, but were unable to prevent ICAM from reaching the plasma membrane. We conclude that IP3R are targeted to the ER membrane only after synthesis of TMDs 1 and 2, and that after co-translational insertion of the remaining TMDs, redundant retention signals present in any pair of TMD retain IP3R in the ER.
authors.affiliation: Department of Pharmacology and Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Cambridge CB2 1PD, United Kingdom.
authors.forename: Andrew K T
authors.initials: AK
authors.lastname: Parker
authors.forename: Fanni V
authors.initials: FV
authors.lastname: Gergely
authors.forename: Colin W
authors.initials: CW
authors.lastname: Taylor
mesh_terms: D000818:Animals; D001692:Biological Transport; D015220:Calcium Channels; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear; D015398:Signal Transduction
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; C488910:Itpr1 protein, rat; D008562:Membrane Glycoproteins; D018160:Receptors, Cytoplasmic and Nuclear; D018799:Intercellular Adhesion Molecule-1