title: Mitochondrial Ca2+ uptake and not mitochondrial motility is required for STIM1-Orai1-dependent store-operated Ca2+ entry.
abstract: Store-operated Ca(2+) entry (SOCE) is established by formation of subplasmalemmal clusters of the endoplasmic reticulum (ER) protein, stromal interacting molecule 1 (STIM1) upon ER Ca(2+) depletion. Thereby, STIM1 couples to plasma membrane channels such as Orai1. Thus, a close proximity of ER domains to the plasma membrane is a prerequisite for SOCE activation, challenging the concept of local Ca(2+) buffering by mitochondria as being essential for SOCE. This study assesses the impact of mitochondrial Ca(2+) handling and motility on STIM1-Orai1-dependent SOCE. High-resolution microscopy showed only 10% of subplasmalemmal STIM1 clusters to be colocalized with mitochondria. Impairments of mitochondrial Ca(2+) handling by inhibition of mitochondrial Na(+)-Ca(2+) exchanger (NCX(mito)) or depolarization only partially suppressed Ca(2+) entry in cells overexpressing STIM1-Orai1. However, SOCE was completely abolished when both NCX(mito) was inhibited and the inner mitochondrial membrane was depolarized, in STIM1- and Orai1-overexpressing cells. Immobilization of mitochondria by expression of mAKAP-RFP-CAAX, a construct that physically links mitochondria to the plasma membrane, affected the Ca(2+) handling of the organelles but not the activity of SOCE. Our observations indicate that mitochondrial Ca(2+) uptake, including reversal of NCX(mito), is fundamental for STIM1-Orai1-dependent SOCE, whereas the proximity of mitochondria to STIM1-Orai1 SOCE units and their motility is not required.
authors.affiliation: Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, 8010 Graz, Austria.
authors.forename: Shamim
authors.initials: S
authors.lastname: Naghdi
authors.forename: Markus
authors.initials: M
authors.lastname: Waldeck-Weiermair
authors.forename: Ismene
authors.initials: I
authors.lastname: Fertschai
authors.forename: Michael
authors.initials: M
authors.lastname: Poteser
authors.forename: Wolfgang F
authors.initials: WF
authors.lastname: Graier
authors.forename: Roland
authors.initials: R
authors.lastname: Malli
mesh_terms: D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D000071740:ORAI1 Protein; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000071737:Stromal Interaction Molecule 1
chemical_list: D015220:Calcium Channels; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; D002118:Calcium