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

Peace Atakpa,Nagendra Babu Thillaiappan,Stefania Mataragka,David L Prole,Colin W Taylor

doi:10.1016/j.celrep.2018.11.064

Peace Atakpa, Nagendra Babu Thillaiappan + Show 3 more

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https://doi.org/10.1016/j.celrep.2018.11.064

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Journal: Cell Reports	Publication Date: Dec 1, 2018
Citations: 130	License type: cc-by

Affiliation: University of Cambridge

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.

Highlights

Increases in cytosolic free Ca2+ concentration ([Ca2+]c) regulate the activities of all cells, allowing them to respond to internal and extracellular signals
Lysosomes Selectively Sequester Ca2+ Released by IP3 receptors (IP3Rs) The vacuolar H+-ATPase (V-ATPase) maintains the luminal pH of lysosomes at about 4.5
SiRNA to ATP6V0C increased the amplitude of the CCh-evoked Ca2+ signals to the same extent as concanamycin A (CcA), and there was no further effect of CcA on the CCh-evoked increase in [Ca2+]c after knockdown of the V-ATPase (Figure 1H)

Summary

Introduction

Increases in cytosolic free Ca2+ concentration ([Ca2+]c) regulate the activities of all cells, allowing them to respond to internal and extracellular signals. In non-excitable cells, extracellular stimuli typically evoke Ca2+ signals by stimulating phospholipase C (PLC), which catalyzes formation of inositol 1,4,5-trisphosphate (IP3). Binding of both IP3 and Ca2+ to IP3 receptors (IP3Rs) causes them to open and release Ca2+ from the ER (Foskett et al, 2007; Taylor and Tovey, 2010). The spatial organization of Ca2+ signals allows Ca2+ entering the cytosol through different channels to evoke different responses (Giorgi et al, 2018).

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