IP3 Receptors Preferentially Associate with ER-Lysosome Contact Sites and Selectively Deliver Ca2+ to Lysosomes

Abstract

SummaryInositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) allow extracellular stimuli to redistribute Ca2+ from the ER to cytosol or other organelles. We show, using small interfering RNA (siRNA) and vacuolar H+-ATPase (V-ATPase) inhibitors, that lysosomes sequester Ca2+ released by all IP3R subtypes, but not Ca2+ entering cells through store-operated Ca2+ entry (SOCE). A low-affinity Ca2+ sensor targeted to lysosomal membranes reports large, local increases in cytosolic [Ca2+] during IP3-evoked Ca2+ release, but not during SOCE. Most lysosomes associate with endoplasmic reticulum (ER) and dwell at regions populated by IP3R clusters, but IP3Rs do not assemble ER-lysosome contacts. Increasing lysosomal pH does not immediately prevent Ca2+ uptake, but it causes lysosomes to slowly redistribute and enlarge, reduces their association with IP3Rs, and disrupts Ca2+ exchange with ER. In a “piston-like” fashion, ER concentrates cytosolic Ca2+ and delivers it, through large-conductance IP3Rs, to a low-affinity lysosomal uptake system. The involvement of IP3Rs allows extracellular stimuli to regulate Ca2+ exchange between the ER and lysosomes.

Quercetin depletes intracellular Ca2+ stores and blunts ATP‐triggered Ca2+ signaling in bEnd.3 endothelial cells

“…Lysosomes have been demonstrated to be physiologically active Ca 2+ stores . Our results ( Figure ) show that quercetin mobilized Ca 2+ from both endoplasmic reticulum and lysosomes without emptying these organelles.…”

“…The reason why quercetin-discharged Ca 2+ release had a very sustained phase could be that quercetin also inhibits the plasma membrane Ca 2+ pump [20], so that Ca 2+ clearance was much retarded. Lysosomes have been demonstrated to be physiologically active Ca 2+ stores [12,21,22]. Our results ( Figure 3) show that quercetin mobilized Ca 2+ from both endoplasmic reticulum and lysosomes without emptying these organelles.…”

A genetically-encoded toolkit of functionalized nanobodies against fluorescent proteins for visualizing and manipulating intracellular signalling

“…4 ). The affinities of these sensors for Ca 2+ ( of 1.2 µM for G-GECO1.2 and R-GECO1.2, and 10 µM for LAR-GECO1.2) are low relative to global changes in the cytosolic free Ca 2+ concentration ([Ca 2+ ] c ) after receptor stimulation (typically ∼300 nM) [34]. This facilitates selective detection of the large, local rises in [Ca 2+ ] that are important for intracellular signalling, at the contacts between active inositol 1,4,5-trisphosphate receptors (IP 3 Rs) and mitochondria, for example [27].…”

“…In some cells, the targeted Nab-Ca 2+ sensors revealed local changes in [Ca 2+ ] c after receptor stimulation with histamine, which stimulates IP 3 formation and Ca 2+ release from the ER in HeLa cells [34]. Imperfect targeting of the RNab-GGECO1.2 to the OMM allowed Ca 2+ signals at the surface of individual mitochondria to be distinguished from those in nearby cytosol in some cells ( Fig.…”

Revisiting the role of calcium in phagosome formation and maturation

“…). Atakpa et al . suggests that in the vicinity of the Ins(1,4,5)P 3 receptor, ER‐resident VapA proteins form a novel lysosome–ER contact site, although the lysosomal tether that interacts with VapA is unknown.…”