A mutation in Orai1 causes immune deficiency by abrogating CRAC channel function

Abstract

Antigen stimulation of immune cells triggers Ca²⁺ entry through Ca²⁺ release-activated Ca²⁺ (CRAC) channels, promoting the immune response to pathogens by activating the transcription factor NFAT. We have previously shown that cells from patients with one form of hereditary severe combined immune deficiency (SCID) syndrome are defective in store-operated Ca²⁺ entry and CRAC channel function. Here we identify the genetic defect in these patients, using a combination of two unbiased genome-wide approaches: a modified linkage analysis with single-nucleotide polymorphism arrays, and a Drosophila RNA interference screen designed to identify regulators of store-operated Ca²⁺ entry and NFAT nuclear import. Both approaches converged on a novel protein that we call Orai1, which contains four putative transmembrane segments. The SCID patients are homozygous for a single missense mutation in ORAI1, and expression of wild-type Orai1 in SCID T cells restores store-operated Ca²⁺ influx and the CRAC current (I_CRAC). We propose that Orai1 is an essential component or regulator of the CRAC channel complex.