Orai1 and STIM reconstitute store-operated calcium channel function.
The two membrane proteins, STIM1 and Orai1, have each been shown to be essential for the activation of store-operated channels (SOC). Yet, how these proteins functionally interact is not known. Here, we reveal that STIM1 and Orai1 expressed together reconstitute functional SOCs. Expressed alone, Orai1 strongly reduces store-operated Ca(2+) entry (SOCE) in human embryonic kidney 293 cells and the Ca(2+) release-activated Ca(2+) current (I(CRAC)) in rat basophilic leukemia cells. However, expressed along with the store-sensing STIM1 protein, Orai1 causes a massive increase in SOCE, enhancing the rate of Ca(2+)entry by up to 103-fold. This entry is entirely store-dependent since the same coexpression causes no measurable store-independent Ca(2+) entry. The entry is completely blocked by the SOC blocker, 2-aminoethoxydiphenylborate. Orai1 and STIM1 coexpression also caused a large gain in CRAC channel function in rat basophilic leukemia cells. The close STIM1 homologue, STIM2, inhibited SOCE when expressed alone but coexpressed with Orai1 caused substantial constitutive (store-independent) Ca(2+) entry. STIM proteins are known to mediate Ca(2+) store-sensing and endoplasmic reticulum-plasma membrane coupling with no intrinsic channel properties. Our results revealing a powerful gain in SOC function dependent on the presence of both Orai1 and STIM1 strongly suggest that Orai1 contributes the PM channel component responsible for Ca(2+) entry. The suppression of SOC function by Orai1 overexpression likely reflects a required stoichiometry between STIM1 and Orai1.
Soboloff
Jonathan
J
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201. Electronic address: jsobo001@umaryland.edu.
Spassova
Maria A
MA
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201.
Tang
Xiang D
XD
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201.
Hewavitharana
Thamara
T
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201.
Xu
Wen
W
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201.
Gill
Donald L
DL
Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201. Electronic address: dgill@umaryland.edu.
D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels; D015815:Cell Adhesion Molecules; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D004594:Electrophysiology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis / Q000502:physiology*; D008954:Models, Biological; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000502:physiology*; D000071740:ORAI1 Protein; D051381:Rats; D000071737:Stromal Interaction Molecule 1; D000071738:Stromal Interaction Molecule 2
D001896:Boron Compounds; D015220:Calcium Channels; D015815:Cell Adhesion Molecules; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; C103530:STIM1 protein, human; C513279:STIM2 protein, human; D000071737:Stromal Interaction Molecule 1; D000071738:Stromal Interaction Molecule 2; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium