期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 109, 期 51, 页码 E3539-E3548出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1218247109
关键词
SERCA; cameleon; FRET; purinergic; IP3
资金
- National Institutes of Health (NIH) [GM083913, NS08174, F32 DC068982, K01 MH08611, RR025429]
- National Science Foundation of China [30871225, 81222020]
- National Key Technology RD Program [SQ2011SF11B01041]
Secretory granules (SGs) sequester significant calcium. Understanding roles for this calcium and potential mechanisms of release is hampered by the difficulty of measuring SG calcium directly in living cells. We adapted the Forster resonance energy transfer-based D1-endoplasmic reticulum (ER) probe to develop a unique probe (D1-SG) to measure calcium and pH in secretory granules. It significantly localizes to SGs and reports resting free Ca2+ of 69 +/- 15 mu M and a pH of 5.8. Application of extracellular ATP to activate P2Y receptors resulted in a slow monotonic decrease in SG Ca2+ temporally correlated with the occurrence of store-operated calcium entry (SOCE). Further investigation revealed a unique receptor-mediated mechanism of calcium release from SGs that involves SG store-operated Orai channels activated by their regulator stromal interaction molecule 1 (STIM1) on the ER. SG Ca2+ release is completely antagonized by a SOCE antagonist, by switching to Ca2+-free medium, and by overexpression of a dominant-negative Orai1(E106A). Overexpression of the CRAC activation domain (CAD) of STIM1 resulted in a decrease of resting SG Ca2+ by similar to 75% and completely abolished the ATP-mediated release of Ca2+ from SGs. Overexpression of a dominant-negative CAD construct (CAD-A376K) induced no significant changes in SG Ca2+. Colocalization analysis suggests that, like the plasma membrane, SG membranes also possess Orai1 channels and that during SG Ca2+ release, colocalization between SGs and STIM1 increases. We propose Orai channel opening on SG membranes as a potential mode of calcium release from SGs that may serve to raise local cytoplasmic calcium concentrations and aid in refilling intracellular calcium stores of the ER and exocytosis.
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