title: STIM2 is an inhibitor of STIM1-mediated store-operated Ca2+ Entry.
abstract: The coupling mechanism between endoplasmic reticulum (ER) Ca(2+) stores and plasma membrane (PM) store-operated channels (SOCs) remains elusive [1-3]. STIM1 was shown to play a crucial role in this coupling process [4-7]; however, the role of the closely related STIM2 protein remains undetermined. We reveal that STIM2 is a powerful SOC inhibitor when expressed in HEK293, PC12, A7r5, and Jurkat T cells. This contrasts with gain of SOC function in STIM1-expressing cells. While STIM1 is expressed in both the ER and plasma membrane, STIM2 is expressed only intracellularly. Store depletion induces redistribution of STIM1 into distinct "puncta." STIM2 translocates into puncta upon store depletion only when coexpressed with STIM1. Double labeling shows coincidence of STIM1 and STIM2 within puncta, and immunoprecipitation reveals direct interactions between STIM1 and STIM2. Independent of store depletion, STIM2 colocalizes with and blocks the function of a STIM1 EF-hand mutant that preexists in puncta and is constitutively coupled to activate SOCs. Thus, whereas STIM1 is a required mediator of SOC activation, STIM2 is a powerful inhibitor of this process, interfering with STIM1-mediated SOC activation at a point downstream of puncta formation. The opposing functions of STIM1 and STIM2 suggest they may play a coordinated role in controlling SOC-mediated Ca(2+) entry signals.
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Medicine, University of Maryland, Baltimore, 21201, USA. jsobo001@umaryland.edu
authors.forename: Jonathan
authors.initials: J
authors.lastname: Soboloff
authors.forename: Maria A
authors.initials: MA
authors.lastname: Spassova
authors.forename: Thamara
authors.initials: T
authors.lastname: Hewavitharana
authors.forename: Li-Ping
authors.initials: LP
authors.lastname: He
authors.forename: Wen
authors.initials: W
authors.lastname: Xu
authors.forename: Lorna S
authors.initials: LS
authors.lastname: Johnstone
authors.forename: Marie A
authors.initials: MA
authors.lastname: Dziadek
authors.forename: Donald L
authors.initials: DL
authors.lastname: Gill
mesh_terms: D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D015815:Cell Adhesion Molecules; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D008565:Membrane Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000071737:Stromal Interaction Molecule 1; D000071738:Stromal Interaction Molecule 2
chemical_list: D015220:Calcium Channels; D015815:Cell Adhesion Molecules; D008565:Membrane Proteins; D009363:Neoplasm Proteins; C103530:STIM1 protein, human; C513279:STIM2 protein, human; D000071737:Stromal Interaction Molecule 1; D000071738:Stromal Interaction Molecule 2; D002118:Calcium