title: A STIM1-dependent 'trafficking trap' mechanism regulates Orai1 plasma membrane residence and Ca²⁺ influx levels.
abstract: The key proteins mediating store-operated Ca(2+) entry (SOCE) are the endoplasmic reticulum (ER) Ca(2+) sensor STIM1 and the plasma membrane Ca(2+)-selective channel Orai1. Here, we quantitatively dissect Orai1 trafficking dynamics and show that Orai1 recycles rapidly at the plasma membrane (Kex≃0.1 min(-1)), with ∼40% of the total Orai1 pool localizing to the plasma membrane at steady state. A subset of intracellular Orai1 localizes to a sub-plasmalemal compartment. Store depletion is coupled to Orai1 plasma membrane enrichment in a STIM1-dependent fashion. This is due to trapping of Orai1 into cortical ER STIM1 clusters, leading to its removal from the recycling pool and enrichment at the plasma membrane. Interestingly, upon high STIM1 expression, Orai1 is trapped into STIM1 clusters intracellularly, thus preventing its plasma membrane enrichment following store depletion. Consistent with this, STIM1 knockdown prevents trapping of excess Orai1 into limiting STIM1 clusters in the cortical ER. SOCE-dependent Ca(2+) influx shows a similar biphasic dependence on the Orai1:STIM1 ratio. Therefore, a STIM1-dependent Orai1 'trafficking trap' mechanism controls Orai1 plasma membrane enrichment and SOCE levels, thus modulating the SOCE 'bandwidth' for downstream signaling.
authors.affiliation: Department of Physiology & Biophysics, Weill Cornell Medical College in Qatar, PO Box 24144, Qatar.
authors.forename: Rawad
authors.initials: R
authors.lastname: Hodeify
authors.affiliation: Department of Physiology & Biophysics, Weill Cornell Medical College in Qatar, PO Box 24144, Qatar.
authors.forename: Senthil
authors.initials: S
authors.lastname: Selvaraj
authors.affiliation: Department of Biochemistry, Weill Cornell Medical College, New York, 10021 USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wen
authors.affiliation: Department of Physiology & Biophysics, Weill Cornell Medical College in Qatar, PO Box 24144, Qatar.
authors.forename: Abdelilah
authors.initials: A
authors.lastname: Arredouani
authors.affiliation: Department of Physiology & Biophysics, Weill Cornell Medical College in Qatar, PO Box 24144, Qatar.
authors.forename: Satanay
authors.initials: S
authors.lastname: Hubrack
authors.affiliation: Department of Physiology & Biophysics, Weill Cornell Medical College in Qatar, PO Box 24144, Qatar.
authors.forename: Maya
authors.initials: M
authors.lastname: Dib
authors.affiliation: Department of Physiology & Biophysics, Weill Cornell Medical College in Qatar, PO Box 24144, Qatar.
authors.forename: Sara N
authors.initials: SN
authors.lastname: Al-Thani
authors.affiliation: Department of Biochemistry, Weill Cornell Medical College, New York, 10021 USA.
authors.forename: Timothy
authors.initials: T
authors.lastname: McGraw
authors.affiliation: Department of Physiology & Biophysics, Weill Cornell Medical College in Qatar, PO Box 24144, Qatar Khm2002@qatar-med.cornell.edu.
authors.forename: Khaled
authors.initials: K
authors.lastname: Machaca
mesh_terms: D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000096:biosynthesis / Q000235:genetics*; D020013:Calcium Signaling / Q000235:genetics*; D002462:Cell Membrane / Q000378:metabolism; D003412:Cricetulus; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics*; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics*; D000071740:ORAI1 Protein; D021381:Protein Transport / Q000235:genetics; D034741:RNA, Small Interfering; D015398:Signal Transduction; D000071737:Stromal Interaction Molecule 1
chemical_list: D015220:Calcium Channels; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; D034741:RNA, Small Interfering; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; D002118:Calcium
keywords: Orai1; STIM1; Store-operated Ca2+ entry; Trafficking