Store-dependent and -independent modes regulating CRAC channel activity of human Orai1 and Orai3
Zhang SL, Kozak JA, Jiang W, Yeromin AV, Chen J, Yu Y, Penna A, Shen W, Chi V, Cahalan MD
J Biol Chem
Cancer Research/Cell Biology
Cells used in publication:
Tissue Origin: kidney
Tissue Origin: blood
We evaluated currents induced by expression of human homologs of Orai together with STIM1 in HEK cells. When coexpressed with STIM1, Orai1 induced a large inwardly rectifying Ca2+ selective current with Ca2+-induced slow inactivation. A point mutation of Orai1 (E106D) altered the ion selectivity of the induced 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 Ca2+ 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 Ca2+ 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.
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