Beck Andreas, Fleig Andrea, Penner Reinhold, Peinelt Christine
Queen's Center for Biomedical Research, Laboratory of Cell and Molecular Signaling, The Queen's Medical Center, Honolulu, HI 96813, United States; John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96813, United States; Department of Pharmacology and Toxicology, ZHMB, Saarland University, D-66421 Homburg, Germany.
Queen's Center for Biomedical Research, Laboratory of Cell and Molecular Signaling, The Queen's Medical Center, Honolulu, HI 96813, United States; John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96813, United States.
Cell Calcium. 2014 Sep;56(3):235-43. doi: 10.1016/j.ceca.2014.07.011. Epub 2014 Aug 2.
Deviations from physiological pH (∼pH 7.2) as well as altered Ca(2+) signaling play important roles in immune disease and cancer. One of the most ubiquitous pathways for cellular Ca(2+) influx is the store-operated Ca(2+) entry (SOCE) or Ca(2+) release-activated Ca(2+) current (ICRAC), which is activated upon depletion of intracellular Ca(2+) stores. We here show that extracellular and intracellular changes in pH regulate both endogenous ICRAC in Jurkat T lymphocytes and RBL2H3 cells, and heterologous ICRAC in HEK293 cells expressing the molecular components STIM1/2 and Orai1/2/3 (CRACM1/2/3). We find that external acidification suppresses, and alkalization facilitates IP3-induced ICRAC. In the absence of IP3, external alkalization did not elicit endogenous ICRAC but was able to activate heterologous ICRAC in HEK293 cells expressing Orai1/2/3 and STIM1 or STIM2. Similarly, internal acidification reduced IP3-induced activation of endogenous and heterologous ICRAC, while alkalization accelerated its activation kinetics without affecting overall current amplitudes. Mutation of two aspartate residues to uncharged alanine amino acids (D110/112A) in the first extracellular loop of Orai1 significantly attenuated both the inhibition of ICRAC by external acidic pH as well as its facilitation by alkaline conditions. We conclude that intra- and extracellular pH differentially regulates ICRAC. While intracellular pH might affect aggregation and/or binding of STIM to Orai, external pH seems to modulate ICRAC through its channel pore, which in Orai1 is partially mediated by residues D110 and D112.
生理pH值（约pH 7.2）的偏离以及钙（Ca(2+)）信号的改变在免疫疾病和癌症中起着重要作用。细胞钙（Ca(2+)）内流最普遍的途径之一是储存式钙（Ca(2+)）内流（SOCE）或钙（Ca(2+)）释放激活钙（Ca(2+)）电流（ICRAC），它在细胞内钙（Ca(2+)）储存耗尽时被激活。我们在此表明，细胞外和细胞内pH值的变化调节了Jurkat T淋巴细胞和RBL2H3细胞中的内源性ICRAC，以及表达分子成分STIM1/2和Orai1/2/3（CRACM1/2/3）的HEK293细胞中的异源性ICRAC。我们发现，外部酸化会抑制，而碱化会促进IP3诱导的ICRAC。在没有IP3的情况下，外部碱化不会引发内源性ICRAC，但能够激活表达Orai1/2/3和STIM1或STIM2的HEK293细胞中的异源性ICRAC。同样，内部酸化会降低IP3诱导的内源性和异源性ICRAC的激活，而碱化则加速其激活动力学，而不影响总体电流幅度。将Orai1第一个细胞外环中的两个天冬氨酸残基突变为不带电荷的丙氨酸氨基酸（D110/112A），显著减弱了外部酸性pH对ICRAC的抑制以及碱性条件对其的促进作用。我们得出结论，细胞内和细胞外pH值对ICRAC的调节存在差异。虽然细胞内pH值可能影响STIM与Orai的聚集和/或结合，但外部pH值似乎通过其通道孔调节ICRAC，在Orai1中，这部分是由残基D110和D112介导的。
