Orai1 and STIM Reconstitute Store-operated Calcium Channel Function

• Published in: The Journal of biological chemistry 2006-07, Vol.281 (30), p.20661-20665
• Main Authors: Soboloff, Jonathan, Spassova, Maria A., Tang, Xiang D., Hewavitharana, Thamara, Xu, Wen, Gill, Donald L.
• Format: Article
• Language: English
• Subjects: Animals; Boron Compounds - pharmacology; Calcium - metabolism; Calcium Channels; Cell Adhesion Molecules; Cell Line; Cell Line, Tumor; Cell Membrane - metabolism; Electrophysiology; Endoplasmic Reticulum - metabolism; Humans; Membrane Proteins - biosynthesis; Membrane Proteins - physiology; Models, Biological; Neoplasm Proteins - biosynthesis; Neoplasm Proteins - physiology; ORAI1 Protein; Rats; Stromal Interaction Molecule 1; Stromal Interaction Molecule 2
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.C600126200

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 Ca2+ entry (SOCE) in human embryonic kidney 293 cells and the Ca2+ release-activated Ca2+ current (ICRAC) 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 Ca2+entry by up to 103-fold. This entry is entirely store-dependent since the same coexpression causes no measurable store-independent Ca2+ 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) Ca2+ entry. STIM proteins are known to mediate Ca2+ 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 Ca2+ entry. The suppression of SOC function by Orai1 overexpression likely reflects a required stoichiometry between STIM1 and Orai1.