The two-pore channel TPCN2 mediates NAADP-dependent Ca2+-release from lysosomal stores

Abstract

Second messenger-induced Ca 2+ -release from intracellular stores plays a key role in a multitude of physiological processes. In addition to 1,4,5-inositol trisphosphate (IP 3 ), Ca 2+ , and cyclic ADP ribose (cADPR) that trigger Ca 2+ -release from the endoplasmatic reticulum (ER), nicotinic acid adenine dinucleotide phosphate (NAADP) has been identified as a cellular metabolite that mediates Ca 2+ -release from lysosomal stores. While NAADP-induced Ca 2+ -release has been found in many tissues and cell types, the molecular identity of the channel (s) conferring this release remained elusive so far. Here, we show that TPCN2, a novel member of the two-pore cation channel family, displays the basic properties of native NAADP-dependent Ca 2+ -release channels. TPCN2 transcripts are widely expressed in the body and encode a lysosomal protein forming homomers. TPCN2 mediates intracellular Ca 2+ -release after activation with lownanomolar concentrations of NAADP while it is desensitized by micromolar concentrations of this second messenger and is insensitive to the NAADP analog nicotinamide adenine dinucleotide phosphate (NADP). Furthermore, TPCN2-mediated Ca 2+ -release is almost completely abolished when the capacity of lysosomes for storing Ca 2+ is pharmacologically blocked. By contrast, TPCN2-specific Ca 2+ -release is unaffected by emptying ER-based Ca 2+ stores. In conclusion, these findings indicate that TPCN2 is a major component of the long-sought lysosomal NAADP-dependent Ca 2+ -release channel.

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

“…NAADP-dependent currents in WT lysosomes displayed a bell-shaped dose-response relationship (Fig. 1d) as reported previously 25,26 .…”

“…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. Patch-clamp 21,22,24 , lipid bilayer and calcium imaging experiments 18,25,26 indicate that TPCs are Ca 2 þ permeable channels and, hence, may directly confer Ca 2 þ release from endosomes/lysosomes.…”

Nicotinic acid adenine dinucleotide phosphate regulates skeletal muscle differentiation via action at two-pore channels

“…InsP 3 and cADPR act at the endoplasmic and sarcoplasmic reticulum via InsP 3 and ryanodine receptors (RyRs), respectively. In contrast, the NAADP signaling cascade is more controversial, with action reported at both RyRs on the endo-or sarcoplasmic reticulum (5)(6)(7)(8), and two-pore channels (TPCs) on acidic stores having been described (9)(10)(11).…”

Two-pore channel 1 interacts with citron kinase, regulating completion of cytokinesis

“…[3][4][5] TPC transcripts are found in most human and mouse tissues, suggesting a ubiquitous function. 3,6 All TPC isoforms localize to acidic organelles, with TPC2 expression predominantly lysosomal, and TPC1 with a wider distribution within the endolysosomal system, found in lysosomes, early and recycling endosomes. 3,4,7 In plants, studies of Ca 2C release in Arabidopsis identified AtTPC1 as a channel 8 that mediates the slow vacuolar current, 9 regulating germination and stomatal movement.…”

“…10 TPCs have been shown to regulate differentiation, 11 smooth muscle contraction 12 and endothelial cell activation, 13 consistent with previous studies implicating nicotinic acid adenine dinucleotide phosphate (NAADP)-induced Ca 2C release in these events, [14][15][16] and supported by several overexpression, knockdown and knockout models. 3,4,6,17 Regulation and affinity of TPC ion channels is a contentious issue. Literature suggest proton-permeable ion channels activated by NAADP or Ca 2C ; 18 although photoaffinity labeling studies suggest that NAADP does not directly bind TPCs.…”