Store-dependent and -independent modes regulating Ca2+ release-activated Ca2+ channel activity of human Orai1 and Orai3.
We evaluated currents induced by expression of human homologs of Orai together with STIM1 in human embryonic kidney cells. When co-expressed with STIM1, Orai1 induced a large inwardly rectifying Ca(2+)-selective current with Ca(2+)-induced slow inactivation. A point mutation of Orai1 (E106D) altered the ion selectivity of the induced Ca(2+) release-activated Ca(2+) (CRAC)-like current while retaining an inwardly rectifying I-V characteristic. Expression of the C-terminal portion of STIM1 with Orai1 was sufficient to generate CRAC current without store depletion. 2-APB activated a large relatively nonselective current in STIM1 and Orai3 co-expressing cells. 2-APB also induced Ca(2+) influx in Orai3-expressing cells without store depletion or co-expression of STIM1. The Orai3 current induced by 2-APB exhibited outward rectification and an inward component representing a mixed calcium and monovalent current. A pore mutant of Orai3 inhibited store-operated Ca(2+) entry and did not carry significant current in response to either store depletion or addition of 2-APB. Analysis of a series of Orai1-3 chimeras revealed the structural determinant responsible for 2-APB-induced current within the sequence from the second to third transmembrane segment of Orai3. The Orai3 current induced by 2-APB may reflect a store-independent mode of CRAC channel activation that opens a relatively nonselective cation pore.
Zhang
Shenyuan L
SL
Department of Physiology and Biophysics, University of California, Irvine, California 92697, USA.
Kozak
J Ashot
JA
Jiang
Weihua
W
Yeromin
Andriy V
AV
Chen
Jing
J
Yu
Ying
Y
Penna
Aubin
A
Shen
Wei
W
Chi
Victor
V
Cahalan
Michael D
MD
D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D003001:Cloning, Molecular; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D009363:Neoplasm Proteins / Q000378:metabolism; D000071740:ORAI1 Protein; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D000071737:Stromal Interaction Molecule 1
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