Abstract
ABSTRACTMitochondria contribute to cell signaling by controlling store-operated Ca2+ entry (SOCE). SOCE is activated by Ca2+ release from the endoplasmic reticulum (ER), whereupon stromal interacting molecule 1 (STIM1) forms oligomers, redistributes to ER–plasma-membrane junctions and opens plasma membrane Ca2+ channels. The mechanisms by which mitochondria interfere with the complex process of SOCE are insufficiently clarified. In this study, we used an shRNA approach to investigate the direct involvement of mitochondrial Ca2+ buffering in SOCE. We demonstrate that knockdown of either of two proteins that are essential for mitochondrial Ca2+ uptake, the mitochondrial calcium uniporter (MCU) or uncoupling protein 2 (UCP2), results in decelerated STIM1 oligomerization and impaired SOCE following cell stimulation with an inositol-1,4,5-trisphosphate (IP3)-generating agonist. Upon artificially augmented cytosolic Ca2+ buffering or ER Ca2+ depletion by sarcoplasmic or endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitors, STIM1 oligomerization did not rely on intact mitochondrial Ca2+ uptake. However, MCU-dependent mitochondrial sequestration of Ca2+ entering through the SOCE pathway was essential to prevent slow deactivation of SOCE. Our findings show a stimulus-specific contribution of mitochondrial Ca2+ uptake to the SOCE machinery, likely through a role in shaping cytosolic Ca2+ micro-domains.
Highlights
Store-operated Ca2+ entry (SOCE) is a common form of Ca2+ influx that is linked to important physiological functions of different cell types (Parekh and Putney, 2005)
MCUKD and UCP2KD cells can serve as suitable models to investigate the role of mitochondrial Ca2+ sequestration in SOCE regulation
We took advantage of recent findings showing that uncoupling protein 2 (UCP2) is involved in mitochondrial Ca2+ sequestration upon intracellular Ca2+ release, but not in the buffering of entering Ca2+ (WaldeckWeiermair et al, 2010b; Waldeck-Weiermair et al, 2011), whereas mitochondrial calcium uniporter (MCU) is generally involved in mitochondrial Ca2+ uptake regardless the source of Ca2+ (Waldeck-Weiermair et al, 2013; De Stefani et al, 2011)
Summary
Store-operated Ca2+ entry (SOCE) is a common form of Ca2+ influx that is linked to important physiological functions of different cell types (Parekh and Putney, 2005). With the identification of the key molecular constituents of SOCE – the stromal interacting molecule 1 (STIM1) (Zhang et al, 2005; Liou et al, 2005) and the plasma membrane Ca2+-pore-forming Orai (Vig et al, 2006; Zhang et al, 2006) – the clarification of the. In this form, STIM1 couples with and activates Orai (Park et al, 2009) and other storeoperated channels (Cheng et al, 2013), resulting in Ca2+ entry
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