Store-dependent and -independent Modes Regulating Ca super(2+) Release-activated Ca super(2+) Channel Activity of Human Orai1 and Orai3

• Published in: The Journal of biological chemistry 2008-06, Vol.283 (25), p.17662-17671
• Main Authors: Zhang, Shenyuan L, Kozak, JAshot, Jiang, Weihua, Yeromin, Andriy V, Chen, Jing, Yu, Ying, Penna, Aubin, Shen, Wei, Chi, Victor, Cahalan, Michael D
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X

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 super(2+)-selective current with Ca super(2+)-induced slow inactivation. A point mutation of Orai1 (E106D) altered the ion selectivity of the induced Ca super(2+) release-activated Ca super(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 super(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 super(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.