NAADP mobilizes calcium from acidic organelles through two-pore channels

Abstract

Ca2+ mobilization from intracellular stores represents an important cell signaling process 1 which is regulated, in mammalian cells, by inositol 1,4,5-trisphosphate (InsP3), cyclic ADP ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP). InsP3 and cADPR release Ca2+ from sarco / endoplasmic reticulum (S/ER) stores through activation of InsP3 and ryanodine receptors (InsP3Rs and RyRs). By contrast, the nature of the intracellular stores targeted by NAADP and molecular identity of the NAADP receptors remain controversial 1,2, although evidence indicates that NAADP mobilizes Ca2+ from lysosome-related acidic compartments 3,4. Here we show that two-pore channels (TPCs) comprise a family of NAADP receptors, with TPC1 and TPC3 being expressed on endosomal and TPC2 on lysosomal membranes. Membranes enriched with TPC2 exhibit high affinity NAADP binding and TPC2 underpins NAADP-induced Ca2+ release from lysosome-related stores that is subsequently amplified by Ca2+-induced Ca2+ release via InsP3Rs. Responses to NAADP were abolished by disrupting the lysosomal proton gradient and by ablating TPC2 expression, but only attenuated by depleting ER Ca2+ stores or blocking InsP3Rs. Thus, TPCs form NAADP receptors that release Ca2+ from acidic organelles, which can trigger additional Ca2+ signals via S/ER. TPCs therefore provide new insights into the regulation and organization of Ca2+ signals in animal cells and will advance our understanding of the physiological role of NAADP.

Intracellular localization and physiological function of a rice Ca2+-permeable channel OsTPC1

“…5 Human TPCs mediate nicotinic acid adenine dinucleotide phosphate-induced Ca 2+ release from acidic organelles in HEK293 cells. 6 Arabidopsis AtTPC1 shows a slow-activating vacuolar cation channel activity 7,8 and be involved in the sucrose-induced Ca 2+ rise, 9 abscisic acid-induced repression of germination 10 and the stomatal response to extracellular Ca 2+ changes. 7,10 Tobacco NtTPC1s have roles in increasing Ca 2+ concentrations, defense-related gene expression, and regulation of hypersensitive cell death triggered by cryptogein, an elicitor from an oomycete, in tobacco BY-2 cells.…”

High susceptibility to fatty liver disease in two-pore channel 2-deficient mice

“…There is evidence that TPC1 is mainly present in the proximal endosomal system, and TPC2 is predominantly expressed on late endosomes and lysosomes 16,18,19 . The activation mechanism of TPCs is complex and has been suggested to involve the second messenger nicotinic acid adenine dinucleotide phosphate (NAADP) and the endolysosomal membrane lipidphosphatidylinositol (3,5)bisphosphate (PI(3,5)P 2 ) 17,18,[20][21][22][23][24] . Independent of what the nature of the endogenous ligand of these channels might be, there is substantial evidence that on activation TPCs mediate the release of Ca 2 þ from lysosomal stores.…”

Differential effects of two-pore channel protein 1 and 2 silencing in MDA-MB-468 breast cancer cells

“…Likewise, alterations in TPC1 and TPC2 mRNA were not a feature of a particular breast cancer cell molecular subtype. The similar levels of TPC1 and TPC2 among breast cell lines may be reflective of the diverse tissue distribution of these channels [23,24] and of important roles in epithelial cells.…”