title: Competitive modulation of Ca2+ release-activated Ca2+ channel gating by STIM1 and 2-aminoethyldiphenyl borate.
abstract: Activation of Ca(2+) release-activated Ca(2+) channels by depletion of intracellular Ca(2+) stores involves physical interactions between the endoplasmic reticulum Ca(2+) sensor, STIM1, and the channels composed of Orai subunits. Recent studies indicate that the Orai3 subtype, in addition to being store-operated, is also activated in a store-independent manner by 2-aminoethyldiphenyl borate (2-APB), a small molecule with complex pharmacology. However, it is unknown whether the store-dependent and -independent activation modes of Orai3 channels operate independently or whether there is cross-talk between these activation states. Here we report that in addition to causing direct activation, 2-APB also regulates store-operated gating of Orai3 channels, causing potentiation at low doses and inhibition at high doses. Inhibition of store-operated gating by 2-APB was accompanied by the suppression of several modes of Orai3 channel regulation that depend on STIM1, suggesting that high doses of 2-APB interrupt STIM1-Orai3 coupling. Conversely, STIM1-bound Orai3 (and Orai1) channels resisted direct gating by high doses of 2-APB. The rate of direct 2-APB activation of Orai3 channels increased linearly with the degree of STIM1-Orai3 uncoupling, suggesting that 2-APB has to first disengage STIM1 before it can directly gate Orai3 channels. Collectively, our results indicate that the store-dependent and -independent modes of Ca(2+) release-activated Ca(2+) channel activation are mutually exclusive: channels bound to STIM1 resist 2-APB gating, whereas 2-APB antagonizes STIM1 gating.
authors.affiliation: Department of Molecular Pharmacology and Biological Chemistry, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
authors.forename: Megumi
authors.initials: M
authors.lastname: Yamashita
authors.forename: Agila
authors.initials: A
authors.lastname: Somasundaram
authors.forename: Murali
authors.initials: M
authors.lastname: Prakriya
mesh_terms: D001896:Boron Compounds / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism*; D000071740:ORAI1 Protein; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D000071737:Stromal Interaction Molecule 1
chemical_list: D001896:Boron Compounds; D015220:Calcium Channels; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; C522867:Orai3 protein, human; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium