Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA 90095, USA.
J Immunol. 2011 Oct 1;187(7):3620-30. doi: 10.4049/jimmunol.1100847. Epub 2011 Aug 26.
ORAI1 is a pore subunit of Ca(2+) release-activated Ca(2+) channels that mediate TCR stimulation-induced Ca(2+) entry. A point mutation in ORAI1 (ORAI1(R91W)) causes SCID in human patients that is recapitulated in Orai1(-/-) mice, emphasizing its important role in the immune cells. In this study, we have characterized a novel function of ORAI1 in T cell death. CD4(+) T cells from Orai1(-/-) mice showed robust proliferation with repetitive stimulations and strong resistance to stimulation-induced cell death due to reduced mitochondrial Ca(2+) uptake and altered gene expression of proapoptotic and antiapoptotic molecules (e.g., Fas ligand, Noxa, and Mcl-1). Nuclear accumulation of NFAT was severely reduced in ORAI1-deficient T cells, and expression of ORAI1 and a constitutively active mutant of NFAT recovered cell death. These results indicate NFAT-mediated cell death pathway as one of the major downstream targets of ORAI1-induced Ca(2+) entry. By expressing various mutants of ORAI1 in wild-type and Orai1(-/-) T cells to generate different levels of intracellular Ca(2+), we have shown that activation-induced cell death is directly proportional to the intracellular Ca(2+) concentration levels. Consistent with the in vitro results, Orai1(-/-) mice showed strong resistance to T cell depletion induced by injection of anti-CD3 Ab. Furthermore, ORAI1-deficient T cells showed enhanced survival after adoptive transfer into immunocompromised hosts. Thus, our results demonstrate a crucial role of the ORAI1-NFAT pathway in T cell death and highlight the important role of ORAI1 as a major route of Ca(2+) entry during activated T cell death.
ORAI1 是钙释放激活钙通道的孔亚基，介导 TCR 刺激诱导的钙内流。ORAI1 中的一个点突变（ORAI1[R91W]）导致人类患者的 SCID，在 Orai1(-/-) 小鼠中得到了重现，这强调了它在免疫细胞中的重要作用。在这项研究中，我们描述了 ORAI1 在 T 细胞死亡中的一个新功能。来自 Orai1(-/-) 小鼠的 CD4(+) T 细胞在重复刺激下表现出强烈的增殖，并且由于线粒体钙摄取减少和促凋亡和抗凋亡分子（例如 Fas 配体、Noxa 和 Mcl-1）的基因表达改变，对刺激诱导的细胞死亡具有很强的抗性。NFAT 的核积累在 ORAI1 缺陷型 T 细胞中严重减少，而 ORAI1 和 NFAT 的组成活性突变体的表达恢复了细胞死亡。这些结果表明 NFAT 介导的细胞死亡途径是 ORAI1 诱导的钙内流的主要下游靶标之一。通过在野生型和 Orai1(-/-) T 细胞中表达各种 ORAI1 突变体以产生不同水平的细胞内 Ca(2+)，我们表明激活诱导的细胞死亡与细胞内 Ca(2+)浓度水平直接成正比。与体外结果一致，Orai1(-/-) 小鼠对注射抗 CD3 Ab 诱导的 T 细胞耗竭表现出强烈的抗性。此外，在免疫缺陷宿主中过继转移后，ORAI1 缺陷型 T 细胞表现出更强的存活能力。因此，我们的结果表明 ORAI1-NFAT 途径在 T 细胞死亡中起着关键作用，并强调了 ORAI1 作为激活的 T 细胞死亡过程中钙内流的主要途径的重要作用。
