Essential requirement for two-pore channel 1 in NAADP-mediated calcium signaling

Abstract

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a widespread and potent calcium-mobilizing messenger that is highly unusual in activating calcium channels located on acidic stores. However, the molecular identity of the target protein is unclear. In this study, we show that the previously uncharacterized human two-pore channels (TPC1 and TPC2) are endolysosomal proteins, that NAADP-mediated calcium signals are enhanced by overexpression of TPC1 and attenuated after knockdown of TPC1, and that mutation of a single highly conserved residue within a putative pore region abrogated calcium release by NAADP. Thus, TPC1 is critical for NAADP action and is likely the long sought after target channel for NAADP.

Organelle-specific Subunit Interactions of the Vertebrate Two-pore Channel Family

“…It therefore seems reasonable to conclude that the capacity for ER coupling is conferred not by a specific TPC, but by the ability of lysosome-targeted TPCs to support Ca 2ϩ release from these organelles, at least in HEK293 cells. In this respect, our findings in relation to hTPC1 are entirely inconsistent with previous proposals that hTPC1 and sea urchin TPC1 couple to the ER by CICR when transiently overexpressed in HEK293 cells or SKBR3 cells (4,6). The only obvious explanation for these contrary data is that transient expression of TPC1, from whatever species, in a human cell line provides for erroneous targeting of TPC1 to lysosomes, which would appear to be supported by the associated colocalization data.…”

“…That there are multiple TPCs and that each may be targeted to different intracellular organelles imply that each TPC subtype may underpin spatially segregated and thus compartmentalized signaling via endosomes and lysosomes, respectively. That this may be the case is also open to question, given that more widespread distribution of hTPC1 (6) and sea urchin TPC1 (4) across endosomes, lysosomes, and even the endoplasmic reticulum (ER) has been reported. Then again, such promiscuity could increase the complexity of signal modulation through, for example, the formation of homo-and heterodimers by TPC1 and TPC2 interaction on the same membrane.…”

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

“…2,3 TPCs are encoded by 3 genes in most deuterostomes, including sea urchins, whereas only 2 isoforms, TPC1 and TPC2, are present in rats, mice and humans. [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.…”

P2X receptor homologs in basal fungi

“…P2X receptors appear to be present in all vertebrate and many invertebrate genomes but are absent in some invertebrates such as Caenorhabditis elegans and Drosophila melanogaster [4,7,8]. It should be noted that C. elegans and D. melanogaster are also known to lack two other Ca 2+ -permeable channelsthe voltage-gated CatSper Ca 2+ channels at the plasma membrane [9] and the two-pore channels underlying NAADP-sensitive Ca 2+ release from acidic Ca 2+ stores [10].ATP is widely utilized as an energy source in many organisms, and so, ATP could serve as an evolutionarily conserved means to mediate cell-cell communications or intracellular signaling through P2X receptors. The emergence of purinergic signaling by P2X receptors is believed to have occurred in early evolution of eukaryotes [4,8], which is supported by the identification and characterization of P2X receptor homologs in non-metazoan organisms such as the dictyostelid social amoeba Dictyostelium discoideum [11], the green alga Ostreococcus tauri [12], and the choanoflagellate Monosiga brevicollis, one of the closet unicellular relatives of animals [12,13].…”

“…P2X receptors appear to be present in all vertebrate and many invertebrate genomes but are absent in some invertebrates such as Caenorhabditis elegans and Drosophila melanogaster [4,7,8]. It should be noted that C. elegans and D. melanogaster are also known to lack two other Ca 2+ -permeable channelsthe voltage-gated CatSper Ca 2+ channels at the plasma membrane [9] and the two-pore channels underlying NAADP-sensitive Ca 2+ release from acidic Ca 2+ stores [10].…”