title: Calcium-dependent clustering of inositol 1,4,5-trisphosphate receptors.
abstract: Rat basophilic leukemia (RBL-2H3) cells predominantly express the type II receptor for inositol 1,4,5-trisphosphate (InsP3), which operates as an InsP3-gated calcium channel. In these cells, cross-linking the high-affinity immunoglobulin E receptor (FcepsilonR1) leads to activation of phospholipase C gamma isoforms via tyrosine kinase- and phosphatidylinositol 3-kinase-dependent pathways, release of InsP3-sensitive intracellular Ca2+ stores, and a sustained phase of Ca2+ influx. These events are accompanied by a redistribution of type II InsP3 receptors within the endoplasmic reticulum and nuclear envelope, from a diffuse pattern with a few small aggregates in resting cells to large isolated clusters after antigen stimulation. Redistribution of type II InsP3 receptors is also seen after treatment of RBL-2H3 cells with ionomycin or thapsigargin. InsP3 receptor clustering occurs within 5-10 min of stimulus and persists for up to 1 h in the presence of antigen. Receptor clustering is independent of endoplasmic reticulum vesiculation, which occurs only at ionomycin concentrations >1 microM, and maximal clustering responses are dependent on the presence of extracellular calcium. InsP3 receptor aggregation may be a characteristic cellular response to Ca2+-mobilizing ligands, because similar results are seen after activation of phospholipase C-linked G-protein-coupled receptors; cholecystokinin causes type II receptor redistribution in rat pancreatoma AR4-2J cells, and carbachol causes type III receptor redistribution in muscarinic receptor-expressing hamster lung fibroblast E36(M3R) cells. Stimulation of these three cell types leads to a reduction in InsP3 receptor levels only in AR4-2J cells, indicating that receptor clustering does not correlate with receptor down-regulation. The calcium-dependent aggregation of InsP3 receptors may contribute to the previously observed changes in affinity for InsP3 in the presence of elevated Ca2+ and/or may establish discrete regions within refilled stores with varying capacity to release Ca2+ when a subsequent stimulus results in production of InsP3.
authors.affiliation: Department of Pathology and Cancer Research and Treatment Center, University of New Mexico, Albuquerque, New Mexico 87131, USA. bwilson@rapunzel.unm.edu
authors.forename: B S
authors.initials: BS
authors.lastname: Wilson
authors.forename: J R
authors.initials: JR
authors.lastname: Pfeiffer
authors.forename: A J
authors.initials: AJ
authors.lastname: Smith
authors.forename: J M
authors.initials: JM
authors.lastname: Oliver
authors.forename: J A
authors.initials: JA
authors.lastname: Oberdorf
authors.forename: R J
authors.initials: RJ
authors.lastname: Wojcikiewicz
mesh_terms: D000818:Animals; D000906:Antibodies / Q000378:metabolism; D000941:Antigens / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002458:Cell Fractionation; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D006224:Cricetinae; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D015759:Ionomycin / Q000494:pharmacology; D007536:Isomerism; D009685:Nuclear Envelope; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D013395:Sucrose; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000906:Antibodies; D000941:Antigens; D015220:Calcium Channels; D018840:HSP70 Heat-Shock Proteins; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D015759:Ionomycin; D013395:Sucrose; D019284:Thapsigargin; D002118:Calcium